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Why finding the right thickness of filter is important.
Ensuring that your filter fits properly in your HVAC system means making sure that you have not only the right length and width, but also thickness of your filter. Most standard air filters are 1 - 2 inches in thickness. Whereas media filters are typically 3 to 5 inches in thickness. The best way to measure your air filter size is to get out the measuring tape and measure it directly.
Regularly replacing your air filter will help improve the efficiency and longevity of your furnace.
A dirty filter in your HVAC system will raise your energy bills. A dirty filter restricts the air flow into your HVAC systems air handler, causing it to work harder to cool or heat your home.
A dirty clogged filter can restrict HVAC airflow and potentially cause problems with the system. They also cease to filter allergens and other particulates out of your air.
Dirty, unchanged filters can make your HVAC system fail completely. Repairing a broken HVAC system can end up costing you a pretty penny.
This is only a preview of the April 1997 issue of Silicon Chip. You can view 25 of the 96 pages in the full issue and the advertisments. For full access, purchase the issue for $8.20 or subscribe for access to the latest issues. Items relevant to 'Build A TV Picture-In-Picture (PIP) Unit':
Articles in this series:
Items relevant to 'A Digital Voltmeter For Your Car':
Articles in this series:
Items relevant to 'Loudspeaker Protector For Stereo Amplifiers':
Items relevant to 'Train Controller For Model Railway Layouts':
Articles in this series:
Purchase a printed copy of this issue for $9.05-9.95. | Motherboard Upgrades: Avoiding Win95 HasslesSILICONCHIPAPRIL1997$4.95*NZ $6.50INCLGSTCIMANYD'SAILAAUSTRENIZAGAMSCIELECTRONSERVICING - VINTAGE RADIO - COMPUTERS - SATELLITE TV - PROJECTS TO BUILDYou can havePictureinPicturePRINT POST APPROVED - PP255003/01272on your TVUniversaLoudspe lakerProtectorDigital Voltmeter For CarsSimple Model Train ControllerISSN 1030-266204April 1997 19 771030 266001SILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auContentsVol.10, No.4; April 1997FEATURES 4 Automotive Design By NumbersBoeing entirely designed its 777 jetliner on computer screens & Mazda plansto be the first with cars – by Julian Edgar 7 Motherboard Upgrades: How To Avoid Win95 HasslesYou don’t have to reinstall Windows 95 when you upgrade the motherboard inyour computer. Here’s the path to a hassle-free upgrade – by Jason Cole86 Cathode Ray Oscilloscopes; Pt.8Digital storage scopes excel when it comes to displaying multiple inputs orslow signals. Find out how these functions work – by Bryan MaherTV Picture-In-Picture Unit –Page 10PROJECTS TO BUILD10 Build A TV Picture-In-Picture (PIP) UnitWatch two TV channels on the screen at once with this easy-to-build unit. It’sfully remote controlled & is based on a prebuilt module – by John Clarke24 The Teeny Timer: A Low-Tech Timer With No ICsThis unit uses just a handful of low-tech parts to provide time delays up toseveral minutes. Use it as a light timer or cool-down timer – by Leo Simpson26 A Digital Voltmeter For Your CarKeep tabs on your car’s battery & charging system with this accurate digitalvoltmeter. It reads from 0-39.9V & has a 3-digit LED display – by John ClarkeA Digital Voltmeter For Your Car– Page 2654 Loudspeaker Protector For Stereo AmplifiersProtect your loudspeakers from damage due to amplifier faults with this simple circuit. There are three versions to choose from – by Leo Simpson66 Train Controller For Model Railway LayoutsOne knob provides full reverse to full forward speed control. There’s also simulated inertia, a brake switch & overload protection – by Rick WaltersSPECIAL COLUMNS22 Computer BitsInstalling A PC-compatible floppy drive in an Amiga 500 – by Franc ZabkarLoudspeaker Protector ForStereo Amplifiers – Page 5442 Serviceman’s LogA mixed bag of trouble & strife – by the TV Serviceman53 Satellite WatchThe latest news on satellite TV – by Garry Cratt76 Vintage RadioA look at signal tracing, Pt.1 – by John HillDEPARTMENTS 2 Publisher’s Letter 38 Bookshelf 40 Circuit Notebook 75 Order Form 80 Product Showcase 84 Back Issues91 Ask Silicon Chip93 Notes & Errata94 Market Centre96 Advertising IndexTrain Controller For ModelRailway Layouts – Page 66April 1997 1Publisher & Editor-in-ChiefLeo Simpson, B.Bus., FAICDEditorGreg Swain, B.Sc.(Hons.)Technical StaffJohn Clarke, B.E.(Elec.)Robert FlynnRick WaltersReader ServicesAnn JenkinsonAdvertising ManagerBrendon SheridanPhone (03) 9720 9198Mobile 0416 009 217Regular ContributorsBrendan AkhurstGarry Cratt, VK2YBXJulian Edgar, Dip.T.(Sec.), B.EdJohn HillMike Sheriff, B.Sc, VK2YFKRoss TesterPhilip Watson, MIREE, VK2ZPWBob YoungPhotographyGlenn A. KeepSILICON CHIP is published 12 timesa year by Silicon Chip PublicationsPty Ltd. A.C.N. 003 205 490. Allmaterial copyright ©. No part ofthis publication may be reproducedwithout the written consent of thepublisher.Printing: Macquarie Print, Dubbo,NSW.Distribution: Network DistributionCompany.Subscription rates: $54 per yearin Australia. For overseas rates, seethe subscription page in this issue.Editorial & advertising offices:Unit 34, 1-3 Jubilee Avenue, Warriewood, NSW 2102. Postal address:PO Box 139, Collaroy Beach, NSW2097. Phone (02) 9979 5644. Fax(02) 9979 6503.PUBLISHER'S LETTERMarketing hypedoesn’t sell anythingOne of the disadvantages of the all the newso-called high technology devices which areswamping the market is the high level of marketing nonsense which accompanies theseproducts. In fact, there is so much “hype”in today’s marketplace that it must build upthe suspicion, at least in the minds of cynicalbuyers, that most of these new products aren’twhat they’re cracked up to be.It affects us here at SILICON CHIP too. Every day, lots of press releases comeover the desk and when we read some of them we wonder why the companiesconcerned ever bothered producing the product; if they need that much hype,they must be garbage!As you might expect, a lot of these press releases never see the light of day,or at least they don’t appear in SILICON CHIP. Others we attempt to make somesense of, filtering out the real information from the bull. You’d be amazed at howoften a two or three page press release comes down to just a couple of paragraphs.Just to give you some idea of the level of this nonsense, I’ll give you a fewexamples. One of the common claims is that a product is “ergonomically designed”. As far as I can determine, such a product has knobs or buttons on itwhich have some function. At least, I don’t think any manufacturer would admitto producing a device that was “not ergonomically designed”.Then there are products, often software, which offer “full functionality” ona PC, Mac or whatever. I think this means that they will work on a PC, Mac orwhatever. I really don’t think that these products would be on sale if they didn’toffer this “full functionality” but then again, you never know.Of course, all software that runs under Windows 95 or NT is “interactive andeasy to use” which is, as anyone who has used some of this software knows,a load of old cobblers. Of course, many CAD programs are intuitive as well,which I think means that you can use them before you’ve opened the manual.We know that’s not true either.And the reason they’re “intuitive” is to “increase the design throughput,minimising commissioning times and speeding up the product time-to-marketcycle”. Heaven forbid that any product or software would actually slow downthe product time-to-market cycle. That wouldn’t do at all, would it?For me, much of this hype appears to be written by public relations people whoreally don’t have a clue what they are writing about, or perhaps, the productsconcerned really don’t have any features worth talking about anyway.More than ever, the warning “Caveat Emptor” or “Let the Buyer Beware” is asrelevant today as it ever was. So look out. If you see meaningless hype accompanying a product, watch out. And if you are the person who actually writesthis stuff, please don’t.Leo SimpsonISSN 1030-2662WARNING!SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects shouldbe considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to theinstructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact withmains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages,you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killedor injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICONCHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling ofany such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant governmentregulations and by-laws.Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act1974 or as subsequently amended and to any governmental regulations which are applicable.2 Silicon ChipSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Macservice Pty LtdBy JULIAN EDGARDESIGN BYNUMBERS4 Silicon ChipThe recently-released Mazda 121Metro trialled Mazda’s new digitaldesign scheme. Here’s how it looksin the metal . . .. . . and here’s how it appearedon the computer screen.The “paperless aeroplane” is soon to befollowed by the “paperless car”. Just asBoeing entirely designed their 777 airlineron computer screens, so Mazda expects tofollow with automotive design.Long recognised as one of theworld’s most innovative car manufacturers, Mazda is to invest more than$A200 million in a process that willsee new cars designed completely oncomputer screens. The new process,The interior of the Metro was modelled in digital 3-dimensional form prior toconstruction. As well as providing a broad overview, this approach also allowsthe design to be examined for errors and ease of assembly.known as the Mazda Digital Innovation (MDI) scheme, will cover alldesign stages from R&D through toactual component production.Mazda says that MDI is being developed so that the company can quicklyrespond to changes in demand andproduce profits from even relativelysmall-scale production runs. Of the$A200 million to be invested, $A111million will be spent on computerhardware and software and a further$A88 million on machines and equipment. Around 4000 new computersare to be bought, while a further 1000existing machines are to be upgraded.In the MDI system, product designand production engineering will bedeveloped 3-dimensionally. All product data will be digitally processedto create digital mock-ups. This willallow the simulation of:(1) layouts of the engine bay, cabin,etc;(2) interference and gaps betweenadjoining parts;(3) ease of maintenance and access toparts; and(4) ease of assembly.In addition to the shape of theobject, product data such as quality,performance and cost will be digitised.Advanced machining and assemblyApril 1997 5The body structure ofthe Metro as seen on theMDI system.A digital machine in a digital factory conducts a trial component assembly.Design changes can be made with ease at this stage, reducing costs and modeldevelopment time and potentially improving build quality.facilities will be introduced and thesystem will also contribute to factorymanagement, keeping track of suchthings as process control, labour hoursand quality control.Trials of the new system began asearly as mid-1995, the recently-introduced Mazda Metro being one of thevehicles used to “prove” the process.The company plans to fully apply MDI6 Silicon Chipon all vehicles whose design is frozenafter the spring of this year.With most of the component parts ofa car produced and often developed byexternal suppliers, this type of designprocess cannot be undertaken in isolation. Mazda is therefore encouragingits component suppliers to also makeuse of the new system, so that it isSCfully effective.Motherboard upgradesfor your computerHow to avoid reinstallingWindows 95You don’t have to reinstall Windows 95when you upgrade the motherboard inyour computer. Here’s how to save timeand avoid the hassles of reinstallation.By JASON COLEIn the article, “*!#$*&<at>* Computers” in the February 1997 issue,the author referred to the need toreinstall Windows after replacing themotherboard in his system. However,provided your old motherboard hasn’tfailed and you are simply upgrading,you don’t have to do this.The trick is to remove all the device drivers for your hardware beforeremoving the old board. Here is theprocedure I use and it does work as Ihave done it numerous times:(1) Either boot into SAFE MODE orexit into DOS and type WIN/D:M (ie,start Windows in SAFE MODE withno network).(2) When Windows has loaded insafe mode, click on the START buttonthen select SETTINGS and CONTROLPANEL. In the Control Panel, doubleclick on SYSTEM. This brings up theSystem Properties box.(3) Click on the DEVICE MANAGERtab and systematically remove all devices. This deletes that portion of theregistry that contains the hardwareprofiles. A couple of things to note:(a) Occasionally, after deleting thekeyboard, mouse or Com Port 1 (usually the Mouse port), you may losecontrol of the keyboard or mouse. So,if possible, removethese last otherwisecontinue using thekeyboard or restartFig.1: the trick is to delete all the device driversagain straight intobefore removing the old motherboard. You do that bySAFE MODE . Thisselecting each device in turn and clicking Remove.can be done by pressing F8 when the“Booting Windows 95” message ap- if you had installed Windows 95 frompears and selecting SAFE MODE from scratch or if you reinstalled it.the list of options. Keyboard control(6) When it starts for the first timeshould return.after replacing the motherboard, Win(b) When removing the Standard dows 95 will detect that it has no videoIDE/ESDI Hard Disk Controller, readapter setting and offers to detect itmember that these are the parent deautomatically. At this point, click onvices and that the Primary/SecondaryYES and allow it to do an auto detectIDE Controller cannot be removed onfor hardware components (otherwiseits own.known as the “Add New HardwareWizard”).(4) When all the devices have beenremoved click the START button, then(7) Once it has finished detectingselect SHUT DOWN and SHUT DOWNthe video card, you may be asked toTHE COMPUTER.restart the computer to implement thechanges. Upon restarting, the new Plug(5) When the computer has shutdown, switch off the power and install and Play (PnP) BIOS will continue tothe new motherboard and any new detect components and update thecards. When Windows 95 starts up registry.again with the new motherboard, itAny non-PnP cards that are not deinitially does not know what it has to tected should be installed manually inSCwork with. This is exactly the same as the usual way (see Feb. 1997).April 1997 7SILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:dicksmith.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:dicksmith.com.auBy JOHN CLARKEWatch two TV channels at once!If you want to watch two TV channels at once, thisPicture-in-Picture unit will come in handy. It willenable you to check on the golf, cricket or yoursecond favourite show while also watching anotherchannel. It’s easy to build and all functions areinfrared remote controlled.TV Picture-in10 Silicon ChipHOW MANY times have youwanted to see what is happening on a second TV channelwhile watching another program?It may be that the program that youwant to watch next starts before thepresent one is finished or there aretwo programs that you want to seebut they are showing at the same time.You may also want to watch anotherchannel while the advertisementsare on but not want to miss the showwhen it comes back on. With thisPicture-in-Picture unit you can do allthose things and more.Picture-in-picture or PIP on a television screen means that there is a second small picture of another channelsuperimposed on the main picture. Itis usually about 1/6th the size of thescreen and so it does not normallydetract too seriously from the mainprogram. If it does cause problems, itcan either quickly be switched off or“flicked” (using the ROTATE button)to another corner of the screen.You can also quickly swap thePIP with the main picture,just by pressing the SWAPbutton on the remotecontrol. When this isdone, the original PIP isviewed full size, whilethe original full-sizedprogram is shrunk to thesmaller PIP area. The soundis automatically swapped withthe picture.Note that you can also swap thesound from one channel to the other,so that either the main or PIP channelcan be heard.Another very useful feature is asound muting facility. This is particularly handy for advertisements whichare usually at a louder volume thannormal program material.As shown in the photos, the TVPicture-In-Picture Unit is housed ina slimline plastic case with terminalsat the rear for the audio and videoconnections. On the front is the powerswitch, a power indicator LED anda window for the infrared remotecontrol sensor. The handheld remotecontrol takes care of all functions,except for power on/off switching.To make the construction easy,the PIP unit is based on a pre-builtmodule which performs all the video functions. We have added in theaudio and remote control facilities tocomplete the unit.What you needTwo video sources are required forthe PIP unit to operate and this wouldnormally be provided by two videoplayers. Just about every householdhas at least one VCR and many havetwo, although often the tape transportmechanism in the older unit has failed.Main Features• Adds a small picture (PIP)• • • • • • • • of another channel to onecorner of the TV screenPIP can be displayed in anycorner of the screenMain picture & PIP can beswapped at the press of abuttonAudio automatically swapswith picture swapAudio signal can be eitherfor the main picture or forthe PIPAudio mute facilityStereo or mono audioRemote control functions forall featuresDirect video or RF modulatoroutput (channel 0 or 1)This handpiece remotely selects all thefunctions of the Picture-In-Picture Unit. Itlets you move the PIP to any corner of thescreen, swap between the PIP and the mainpicture, and swap and mute the audio.-Picture UnitApril 1997 11Don’t do this unless you are experienced with TV/video circuits andknow exactly what you are doing.Be aware also that some older TVsets may have a live chassis and thatany modifications will invalidate theset’s warranty. Add in any technicaldifficulties that you may encounter(signal levels, etc) and you can seewhy we recommend the two-VCRapproach.Fig.1 shows a typical installationfor the PIP Unit. The two VCRs receivethe incoming RF from the antenna viaa splitter and their audio and videooutputs are fed to the PIP Unit. TheRF modulated output from the PIPunit (channel 0 or 1) is then fed tothe antenna input (RF IN) of the TVreceiver.Alternatively, the audio and videooutputs from the PIP Unit can be fedto the TV receiver, provided the sethas provision for these inputs. Theleft and right (L & R) audio outputscan also be fed to a stereo amplifier.Note that although Fig.1 depictsstereo VCRs, mono VCRs can alsobe used – just use mono cables andconnect to either the left or right audiochannel of the PIP unit.Block diagramBy default, the PIP appears in the bottom righthand corner of the screen whenit is turned on. It can be moved to any of the other corners of the screen at thepress of a button. Note that the PIP quality is not as good as the main picture.That doesn’t matter – it’s the tuner section of the older unit that we’re reallyafter and provided that still works, itcan be pressed into service.If you don’t have a second VCR,you can probably obtain a junkedunit quite cheaply from a video repairshop. Don’t worry too much about thetape transport mechanism – just makesure that the tuner/RF section works.An old Beta player could probably bepicked up for a few dollars (or even12 Silicon Chipgiven away), for example.Although using two VCRs to provide the two channels is the obviousway to go, it may be possible to modifythe TV set in some cases so that it canfunction as a signal source. That way,only one VCR would be necessary toprovide the second channel. Modifying the TV set would involve breakingthe audio and video signal paths at theappropriate points so that the PIP unitcan be interposed.Fig.2 shows the block diagram ofthe TV PIP Unit which can be dividedinto audio and video sections. Theaudio section (IC5, IC6a, IC6b & IC6d)accepts the stereo inputs from theVCRs and produces a single output(AUDIO OUT) which may be switchedbetween either VCR or muted. Inaddition, the left and right channelsof the selected source are mixed toproduce a mono signal which is fedto the video modulator audio input.The video outputs from the VCRsare fed to the video inputs of the PIPboard. The output from this boardis either video 1, video 2 or a picture-in-picture signal. This output isthen split two ways. First, it is buffered by driver stage Q4 to provide thevideo output signal. And second, it isfed to the video modulator which produces the alternative RF output signal.As mentioned before, the remotetransmitter controls all the functionsof the PIP unit. The PIP button switches the picture-in-picture display onor off, while the SWAP button belowit switches the PIP and full-screenchannels (the audio automaticallyswaps as well). You can also use theadjacent audio SWAP button to switchthe sound from the main picture to thePIP, or vice versa.The ROTATE button selects whichcorner of the screen plays host to thePIP. This button sequentially movesthe PIP display anticlockwise to thenext corner of the screen each time itis pressed.Finally, as its name implies, theMUTE button kills the audio.The signals from the remote controlunit are picked up by a remote controlreceiver circuit which is based on IC1.Its output is then fed to the controllogic block (IC2-IC4) and this in turncontrols the audio switching and thePIP board.Fig.1: the PIP Unit acceptsvideo and audio signalsfrom two VCRs. Theprocessed output from thePIP Unit is then fed to theTV set, either via theantenna socket or via videoand audio inputs (if fitted).Circuit details – transmitterFig.3 shows the circuit for the IRTransmitter. IC1 is an SM5021B encoder which outputs a unique code foreach switch. This code gates a 38kHzcarrier on and off and the output atpin 15 then drives Darlington transistor pair Q1 & Q2. These in turn driveIRLED1 via a 4.7Ω current limitingresistor. The 38kHz carrier is derivedby dividing the 455kHz oscillator frequency at pins 12 & 13 by 12.LK1 and LK2 are included to alterthe coding for each switch. This willFig.2: block diagram of the PIPUnit. The PIP board (bottom,centre) processes the videosignals from the two VCRs andproduces a single PIP signal. Italso controls the logiccircuitry which switches theaudio signals from the twoVCRs.April 1997 13Fig.3 the circuit forthe IR Transmitter.IC1 is an SM5021Bencoder whichoutputs a unique codefor each switch. Thiscode gates a 38kHzcarrier on and offand the output at pin15 drives Darlingtontransistor pair Q1& Q2. These in turndrive IRLED1.avoid conflict with another remotecontrol which uses the same device.Normally, these can both be left openfor the default coding. Connectingeither or both pins 1 & 2 of IC1 toground will change the code.Circuit details – PIP unitRefer now to Fig.4 for the circuitdetails of the PIP Unit. It’s designedaround the PIP board which, as mentioned above, comes as a pre-builtmodule.Starting at the top lefthand corner,IRD1 picks up the signals from thehandheld transmitter. This 3-terminaldevice is actually a bit more complicated than it looks. It contains an IRreceiver diode, an amplifier tuned to38kHz, a 38kHz bandpass filter, anautomatic gain control (AGC) sectionSpecificationsVideoPicture-in-picture size .............................Less than 1/6th full screenVideo output ...........................................1Vp-p (adjustable)Modulator output ....................................Channel 0 or 1 mono audioAudio (wrt 100mV in or out)Frequency response ...............................-0.25dB at 10Hz & -1dB at 60kHzand a detector. Its output is a digitalpulse train identical to that generatedby the transmitter but inverted.Q1 is used to re-invert the signal,after which it is fed to pin 2 of decoderIC1 (SM5032B). The decoding linksLK1 and LK2 must match those in thetransmitter, to ensure compatibility.IC1 has eight outputs (A-H) andthese match the switches in the transmitter. In this circuit, however, weonly use the A, B, C, E & F outputswhich are all momentary action.Pressing the ROTATE (A) switch onthe transmitter will produce a highoutput on the ‘A’ output of decoderIC1. Similarly, pressing the otherbuttons on the transmitter produceshighs on the other decoder outputs.The ‘C’ output (PIP) of IC1 drivesthe clock input of flipflop IC2a. Eachtime ‘C’ goes high, IC2a’s Q output(pin 1) toggles (low to high or highto low). When this output goes high,the output of Schmitt NAND gateIC3d goes low. This selects the picture-in-picture function for the PIPboard.The ‘A’ output (ROTATE) of IC1 isbuffered by gates IC3a & IC3b. Whenthe ‘A’ output goes high, the inputs toIC3c are pulled high via the .012µFcapacitor and IC3c’s output goes low.After about 120µs, the capacitor charges via its associated 10kΩ resistor andso IC3c’s output goes high again.As a result, IC3d delivers a 120µshigh-going pulse to the PIP inputof the PIP board (assuming that pin8 of IC3d is high). This short pulseinstructs the PIP board to rotate thepicture-in-picture display to the nextposition on the screen. The pulseduration is not critical by the wayand can be anywhere between 1µs to10ms for the rotate function to workcorrectly.The ‘B’ output of IC1 drives a second flipflop designated here as IC2b.This also toggles its Q output (pin13) at each positive going pulse toTotal harmonic distortion ........................< 0.01% from 20Hz to 20kHzSignal-to-noise ratio ������������������������������78dB wrt 100mV & 20Hz to 20kHzfilter with input unloaded; 88dB wrt100mV & 20Hz-20kHz filter withinput loaded by 1kΩ resistorCrosstalk between any two channels .....-56db worst case at 10kHzMaximum signal handling .......................3V RMSSignal gain .............................................0dB (x1)14 Silicon ChipFig.4 (right): the signals from thehandpiece are picked up by IRD1and decoded by IC1. The decodedoutputs then drive the PIP module vialogic circuitry. CMOS analog switchIC5 switches the audio signals and iscontrolled by IC1 via flipflops IC4a& IC4b and transistors Q1 & Q2. Themodulator produces an RF outputsignal on either CH0 or CH1.Mute level ...............................................-63dBApril 1997 15Fig.5: install the parts on the PC board as shown in this wiringdiagram. Note that the two links shown dotted are mounted onthe main board beneath the PIP module.TABLE 1:RESISTOR COLOUR CODES No. 2 1 14 1 2 3 7 1 2 1 1 16 Silicon ChipValue 100kΩ 39kΩ 10kΩ 5.6kΩ 4.7kΩ 2.2kΩ 1kΩ 180Ω 100Ω 75Ω 4.7Ω 4-Band Code (1%) brown black yellow brown orange white orange brown brown black orange brown green blue red brown yellow violet red brown red red red brown brown black red brown brown grey brown brown brown black brown brown violet green black brown yellow violet gold brown 5-Band Code (1%)brown black black orange brownorange white black red brownbrown black black red browngreen blue black brown brownyellow violet black brown brownred red black brown brownbrown black black brown brownbrown grey black black brownbrown black black black brownviolet green black gold brownyellow violet black silver brownUse the shielded cable and the connectors supplied with the PIP module tomake the connections to the main board. A small round piece of red Perspex isfitted to the front panel to provide a window for the infrared receiver (IRD1).the clock input. In this case, the Qoutput drives the SWAP input of thePIP board. This instructs the PIP boardto swap the main picture with the PIP.When power is first applied to IC2aand IC2b, their reset inputs (pins 4 &10) are pulled high via a 10µF capacitor. This resets their Q outputs low.The 10µF capacitor then charges viaits associated 100kΩ resistor, so thatthe resets are released after about onesecond. The low Q outputs ensurethat the power on default settings forthe PIP board are: (1) PIP off; and (2)Video Input 1 selected.The ‘B’ output of IC1 also drives theclock input of flipflop IC4a, via diodeD1. This swaps the audio channelwhenever the video swap functionis enabled. Similarly, the ‘E’ outputof IC1 also drives IC4a’s clock input,this time via diode D2, to perform theaudio swap function. Let’s see howthis all works.As shown, the output of IC4a drivestransistor Q2 via a 10kΩ resistor. Thistransistor effectively inverts and levelshifts the 5V signal from IC4a to a12V signal which is then applied topin 10 of IC5.IC4b and Q3 function in exactly thesame fashion. In this case, however,the clock (CK) input of IC4b is drivenby the ‘F’ output of decoder IC1. Thelevel shifted output appears at Q3’scollector and is fed to pin 9 of IC5.Audio switchingIC5 is a 4052 CMOS analog switch.It is basically a 2-pole 4-way switchwhich is controlled by the signals onits A & B inputs (pins 9 & 10).When A & B are both low, the X0and Y0 inputs are selected and fedThe switches on the PIP module mustbe set exactly as shown here; ie, twoswitches down, the rest up.through to the X and Y outputs (pins13 & 3). Similarly, if A is high andB is low, the X1 and Y1 inputs areselected. And if B is high, eitherX2 or X3 and either Y2 or Y3 areselected, while X0, X1, Y0 and Y1are all open.Note, however, that inputs X2, X3,Y2 & Y3 are all connected togetherand biased to half supply (V/2). Theyare also AC-coupled to ground via a10µF capacitor. If B is high, X2 & X3are connected to the X output, whileY2 & Y3 are connected to the Y output.The left and right audio signals fromVCR 1 are fed to the X0 & Y0 inputsof IC5, while those from VCR 2 arefed to the X1 & Y1 inputs. Each inputis AC-coupled via a 10µF capacitorand biased to half supply via a 10kΩresistor. In addition, a 1kΩ resistor isincluded in series with each input toprovide current limiting.If A & B are both low, it followsthat the signals from VCR 1 are fedthrough to the X & Y outputs of IC5.Similarly, if A is pulled high (ie, Q2switches off), the signals from VCR 2are fed through instead. And finally,if B is pulled high, no input signalsare selected and the X and Y outputsare shunted to ground via the 10µFcapacitor connected to X2, X3, Y2 &Y3; ie, the audio is muted.When power is first applied, flipApril 1997 17The various inputs and outputs are all run via RCA sockets at the rear of theunit. Note that the power supply socket must be insulated from the rear panelif a metal label is used.flops IC4a & IC4b are set via the 10µFcapacitor connected between theirSet inputs (pins 8 & 6) and the +12Vsupply rail. This sets the Q outputshigh and the collectors of Q2 andQ3 low. Thus at power up, the audiosignals from VCR 1 are selected andthe muting is off.The left & right audio signalsfrom IC5 are buffered using op ampsIC6a and IC6b. The outputs fromthese stages appear at pins 7 & 14respectively and are fed to the outputsockets via 100Ω resistors and 10µFcapacitors.In addition, the left and right channels are mixed via 10kΩ resistors andfed to amplifier stage IC6d. Its pin14 output in turn drives the audioinput of the modulator via a 10µFcapacitor. VR1 provides a level settingadjustment.PIP boardWhile we do not propose to describein detail how the PIP board works, wecan give a precis of its operation. Avideo signal consists of luminance(brightness) and chrominance (colour)information, mixed with colour burstand line and frame sync pulses.The line sync pulses indicate thebeginning and end of each line inthe picture; ie, from the far left to thefar right of the TV screen. The videoluminance and colour signals arepresent between these sync pulsesand produce the picture informationin each line. The frame sync pulsesindicate the beginning and end of aWhere To Buy The PartsThe major parts for this design are available as follows:(1) PIP module plus main PC board: Av-Comm Pty Ltd, PO Box 225,Balgowlah, NSW 2093. Phone (02) 9949 7417; Fax (02) 9949 7095. Price– $209 plus $10 p&p. Please quote Cat. K1400 (available end of May 1997).(2) Complete IR transmitter kit plus all IR receiver parts (please specifyno PC board for receiver when ordering): Oatley Electronics, PO Box 89,Oatley, NSW 2223. Phone (02) 9584 3563; Fax (02) 9584 3561. Price $30plus $3.50 p&p.(3) Astec UM1285AUS 0/1 video modulator: Dick Smith Electronics (Cat.K-6043).18 Silicon Chipcomplete picture.In order to shrink the full-sizedpicture into a PIP size, the line syncinformation must be altered so thatthe picture is positioned on a differentpart of the screen. This is done in twoways. First, the line length for the PIPis reduced by discarding some of thevideo information so that it fits into asmaller space. And second, the number of lines is reduced to decrease thepicture height.The way in which this is done israther complicated. First, the requiredinformation for each video frame issampled using a fast A-D converterand stored in a dual-port RAM. Theterm “dual-port” simply means thatwe can simultaneously store information in memory and retrieve it, without halting either process. The storedvideo information is then retrievedfrom the memory at the appropriaterate, reconverted to analog format andinserted into the main (full-screen)video signal.Basically, all we are doing is substituting PIP video information overpart of each line for the main picture,until the PIP is complete. Because ofthis, the information retrieved fromthe RAM does not contain vertical orhorizontal sync pulses, since thesewould upset the operation of themain picture.The video output from the PIPboard goes to two separate circuits:(1) a buffer stage based on transistorQ4; and (2) to the modulator.VR2 sets the video level into thebase of Q4. This transistor is wired asan emitter follower and the resultingsignal is coupled to the video outputsocket via a 470µF capacitor. The75Ω emitter resistor sets the outputimpedance.VR3 sets the input level for thevideo modulator. This modulator provides an RF output on either channel 0or 1, depending on the channel selectlinking option. Power to the modulator is derived from the +12V rail via a180Ω current limiting resistor.Power supplyPower for the circuit is derived froma 12VAC plugpack. It’s output is fedto bridge rectifier D3-D6 and filteredwith a 2200µF capacitor to derive a16VDC (nom.) supply. This is thenapplied to 3-terminal regulator REG1which provides a 12V supply rail forthe PIP board and ICs 5 & 6.A 3-terminal regulator on the PIPboard provides a separate +5V railand this is used to power IRD1 andICs 1-4. It also drives a LED powerindicator via a 560Ω resistor.Finally, a half-supply voltage is derived from a voltage divider consistingof two 10kΩ resistors. This is bufferedby unity gain amplifier stage IC6c andthe resulting V/2 output used to biasthe audio input signals to IC5.ConstructionThe parts for the PIP Unit are mounted on a PC board coded 02302971 andmeasuring 197 x 154mm. This boardaccommodates the preassembled PIPmodule, the modulator and all thesupport circuitry. You can buy thePIP module and the PC board fromAv-Comm Pty Ltd, while the handheld transmitter and receiver partsare available from Oatley Electronics.Dick Smith Electronics stocks thespecified video modulator.Fig.5 shows the parts layout on thePC board. Before mounting any ofthe parts, check the board carefullyfor shorts between the tracks and forbreaks in the copper pattern. Youshould also check that the mountingholes for the PIP board and for REG1are drilled to 3mm and that the mounting holes for the modulator earth lugsare correct.Begin the assembly by installingthe links and the resistors. Note thattwo of the links are shown dotted, toindicate that they go under the PIPmodule – don’t forget these. Table 1PARTS LIST1 PC board, code 02302971, 197x 154mm2 self-adhesive labels for front &rear panels, 215 x 34mm1 remote control transmitter label,31 x 63mm1 plastic case, 225 x 165 x 40mm(Jaycar Cat. HB5972)1 PIP board (from Av-Comm)1 video modulator, AstecUM1285AUS 0/1 (DSE Cat.K-6043)1 12VAC 500mA plugpack2 2 x 2-way PC-mount RCAsockets (Altronics P-0211)1 RCA panel-mount socket1 DC panel socket to suitplugpack1 SPDT toggle switch (S1)1 TO220 heatsink, 19 x 19 x6mm1 50kΩ horizontal trimpot (VR1)2 1kΩ horizontal trimpots(VR2,VR3)1 400mm length of 0.8mm tinnedcopper wire1 500mm length of hook-up wire4 self-tapping screws to secureboard to case4 3mm dia. x 9mm screws & nuts4 5mm spacers1 3mm dia. x 6mm screw and nut1 8mm ID grommet (to insulateDC socket)15 PC stakes1 10mm dia. x 3mm red Perspexfor IR sensor windowSemiconductors2 4013 dual-D flipflops (IC2,IC4)1 4093 quad Schmitt NAND gate(IC3)1 4052 dual 1-to-4 analogmultiplexer/demultiplexer(IC5)1 TL074, LF354 quad op amp(IC6)1 7812 12V 3-terminal regulator(REG1)3 BC548 NPN transistors (Q2,Q3, Q4)2 IN914, 1N4148 signal diodes(D1,D2)4 1N4004 1A diodes (D3-D6)1 3mm LED (LED1)Capacitors1 2200µF 16VW PC electrolytic1 470µF 16VW PC electrolytic1 47µF 16VW PC electrolytic1 22µF 16VW PC electrolytic14 10µF 16VW PC electrolytic1 .012µF (12n or 123) MKTpolyesterResistors (0.25W 1%)2 100kΩ 5 1kΩ13 10kΩ 1 180Ω1 5.6kΩ 2 100Ω1 4.7kΩ 1 75Ω3 2.2kΩ8-Channel IR Transmitter1 Magnavox remote controlhandpiece (includes IRLEDand battery clips)1 455kHz resonator (X1)1 PC board2 AAA cells2 PC stakesSemiconductors1 SM5021B encoder (IC1)1 BC548 NPN transistor (Q1)1 C8050 NPN transistor (Q2)Capacitors1 10µF 16VW PC electrolytic2 100pF (100p or 101) ceramicResistors2 1kΩ 1 4.7Ω8-Channel IR Receiver1 SM5023B remote controlreceiver (IC1)1 BC338 NPN transistor (Q1)1 PIC12043 infrared receiver(IRD1)Capacitors1 10µF 16VW PC electrolytic1 .001µF (1n0, 102 or 1000p)ceramicResistors1 39kΩ 1 10kΩ1 4.7kΩApril 1997 19RF OUT++MUTE+AUDIO+ROTATE+VIDEOPICTUREIN-PICTUREREMOTECONTROLSWAPSWAP+PIPFig.7: the full-size artwork for the rear panel. It can be photocopied and affixed to the rear panel using double-sided adhesive tape.AUDIO OUTIN2IN112VACIN+R+VIDEOIN 2+R++L+VIDEOIN 1+VIDEOOUTFig.6: this full-size artwork can be used as a drilling template for the front panel.POWER++++L++TV PICTURE-IN-PICTUREFig.8: this is the full-size front panelartwork for the hand-held transmitter.lists the resistor colour codes but it is also a goodidea to check each value using a digital multimeter,just to make sure.The diodes can be mounted next, taking care toensure that they are oriented correctly. Note thattwo types are used on the main PC board: (1) the1A 1N4004s which have a black body; and (2) thesmaller 1N914s which are usually orange in colour.The 14 PC stakes can now be installed on the PCboard, followed by the ICs. Take care with the orientation of each IC and check that the correct type hasbeen installed at each location before soldering. Noteparticularly that IC1 & IC6 are oriented differentlyto the other ICs.The LK1 and LK2 linking options for IC1 can beleft open circuit, unless you already have an identicalIR remote control with the same coding.The four transistors are all BC548 types and thesemust be oriented exactly as shown. REG1 is mountedhorizontally, with its leads bent at rightangles so thatthey pass through the PC board. It is fitted with asmall heatsink and bolted to the PC board using a3mm screw and nut.The capacitors can now be installed, along withIRD1, LED1 and the trimpots. Be sure to orient IRD1with its bubble-shaped lens towards the front. LED1should be mounted at full lead length, so that it canlater be bent over and pushed through its mountinghole in the front panel hole.The two RCA socket sets must have their plasticlocating pins removed before they are mounted.Remove these using sidecutters, then solder the RCAsockets in position, taking care to ensure that theirbottom surfaces sit flush with the board.The video modulator is mounted in the toprighthand corner of the board. As shown, the unit iswired for channel 0. If you want channel 1, simplytransfer the lead from the CH0 position to the CH1position.The PC board assembly can now be completed bymounting the PIP module. This board is mountedon 5mm spacers and secured using 3mm screws andnuts. Wire up the board using the supplied shieldedleads and the red/black power lead. Don’t forget tosolder a length of hookup wire from the onboard 5Vregulator output to the +5V PC stake on the mainPC board.Final assemblyThe completed assembly is housed in a standardplastic instrument case measuring 225 x 165 x 40mm.20 Silicon ChipThe infrared transmitter should only take a few minutes to assemble. Noticehow the two transistors are bent over, so that they sit flat against the board. Theboard simply clips into position in the case.Begin the case assembly by affixingthe labels to the front and rear panels.This done, drill out the holes on therear panel for the RCA sockets, thepower socket and the RF OUT socket.The best way to go about this is to firstdrill small pilot holes and then carefully enlarge each hole to the correctsize using a tapered reamer.Moving now to the front panel, drillthe holes for the power switch and itsadjacent indicator LED. You will alsohave to drill a 10mm hole in the frontpanel in line with IRD1. We fitted a10mm-dia. red Perspex window to thishole, rather than simply leave it open.The various items can now all bemounted in position and the wiringcompleted as shown in Fig.5. Notethat the PC board assembly is securedusing self-tapping screws which gointo integral pillars in the base of thecase. Two small self-tapping screwsare also used to secure the stereo RCAsockets to the rear panel.Important: if a metal label is usedon the rear panel (eg, Dynamark),be sure to insulate the power socketfrom the panel. This can be done bystripping back the label from aroundthe mounting hole and then fittinga large insulating washer under themounting nut. If this is not done, themetal label will short one side of the12VAC power supply to ground.Transmitter assemblyVery little work is required to assemble the IR transmitter, as Fig.9shows. It’s mainly a matter of soldering a few parts to the transmitterboard. Take care to ensure that theinfrared LED is installed with thecorrect polarity and note that Q1 is aBC548 while Q2 is a C8050.After that, all you have to do is attach the label to the transmitter caseand cut out the holes for the switchpads, as marked. You will also haveto cut off the switch pads on the rubber membrane that were originallyintended for the volume and CDselections.The two halves of the case are simply clipped together after installingthe two 1.5V AAA cells.TestingNow for the smoke test but first goback over your work carefully andcheck for possible wiring errors. Inparticular, check that all componentsare correctly oriented and that thecorrect part has been used at eachlocation.This done, apply power and checkthat there is +12V at the output ofREG1 and +5V at the output of theregulator on the PIP board. If thesevoltages are OK, switch off and set twoof the DIP switches on the PIP moduleto the down position, as shown onFig.5. These select the video sourcesfor the main and PIP display.It’s now simply a matter of connecting the unit as shown in Fig.1and testing it for correct operation.Remember to tune the TV set to theappropriate channel (either CH0 orCH1), if you are using the RF outputfrom the PIP Unit. Of course, this stepwill not be necessary if you are feedingthe audio/video outputs from the PIPUnit to the TV set.Now apply power and check thatthe signal applied to INPUT 1 appearson the screen as the main picture. Atthis stage, there should be no PIP. Ifthis is correct, adjust VR3 to obtain thecorrect contrast range and to preventFig.9: take care with the orientationof the infrared LED and don’t confusetransistors Q1 & Q2 when installingthe parts on the transmitter board.The two transistors are installed flatagainst the board as shown in thephoto at the top of the page.overmodulation (assuming the RFoutput is being used). If the directvideo output is being used, adjustVR2 for correct contrast instead. VR1is adjusted for a normal sound level.You can now check the remotecontrol. Select PIP and check that asmall picture corresponding to thesecond video input appears in thelower righthand corner of the screen.If it does, check that the ROTATE andvideo SWAP functions work – thesound should follow the main picture.Finally, check that the audio SWAPSCand MUTING functions work.April 1997 21COMPUTER BITSBY FRANC ZABKARInstalling a PC-compatible floppydisc drive in an Amiga 500This simple circuit allows a PC-compatible1.44Mb floppy disc drive to be used in anAmiga 500 computer. The new drive can takethe place of the original Commodore unitwhich was very expensive.Replacing or upgrading the floppy disc drive in an Amiga 500 hastraditionally been something of aheadache. Unfortunately, a PC-compatible 1.44Mb drive is not a plug-inreplacement, while the original Commodore unit is costly and no longereasy to obtain.The good news is that only a fewsimple modifications are required tomake the PC-compatible unit workin the Amiga 500. A PC-compatible1.44Mb drive can now be picked up for$50 or less, whereas the Commodoredrive costs about $150. If the floppydrive in your Amiga 500 has died, youcan save about $100 by substituting aPC-compatible unit.Note, however, that you will not beable to use the greater capacity of thePC-compatible drive, unless a specialsoftware driver is installed. Instead,discs will still be formatted to the880Kb Amiga standard (does anyoneknow where to obtain a suitable driverso that the full 1.44Mb capacity canbe used?).CHANGE output; on the Amiga, it isthe READY output.(2). Pin 2 on the PC is the LOW/HIGHDENSITY input; on the Amiga it is theDISKCHANGE output.Drive differencesThe 34-way interface cable is madeas follows:(1). At the drive end of the cable,separate leads 10, 11 & 12 as a threelead wide strip and twist this strip,PC fashion, through 180°. This stepeffectively transposes leads 10 & 12The main interfacing differencesbetween the PC and Amiga floppydisc drives (FDDs) involve pins 34and 2. These differences are as follows:(1). Pin 34 on the PC is the DISK22 Silicon ChipIn addition, the PC’s outputs areopen collector and the correspondinginputs to the drive are pulled high atthe drive itself. Furthermore, PC-compatible FDDs are set up as Drive 1rather than Drive 0 as on the Amiga.Basically, all we have to do to getthe PC-compatible floppy drive towork in the Amiga is make an appropriate 34-way interface cable andadd a simple logic circuit. This logiccircuit is based on a 7438 TTL quadNAND gate (only two gates used) andis shown, along with the interface cable, in Fig.1.The logic circuit is needed to simulate the READY signal that Amigarequires but which the PC floppy drivedoes not provide. Several pull-upresistors (2.2kΩ) are also required forthe open collector outputs (see Fig.1).Making the cablewhen the headers are attached andserves to designate the FDD as Drive0; ie, pin 10 on the Amiga header goesto pin 12 on the drive header and viceversa (note: the pin 11 connections areunaffected). Note that lead 1 of the cable is designated by a red colour stripe.(2). Install a 34-way female IDCheader at the drive end (pin 1 to thelead with the red stripe).(3). At the Amiga 500 end, snap on asimilar IDC header about 50mm fromthe end of the cable. This 50mm-longfree end is used to make the connections to the logic circuitry.(4). At the drive end, carefully separate and cut lead 2 and peel it backuntil its end is just over half-way downthe cable. Similarly, at the Amiga endbut working from the drive side of theheader (important), separate and cutlead 34 and peel it back until it reachesthe end of lead 2.(5). Strip the two lead ends, slipsome heatshrink tubing over one ofthem, and solder the two leads together (ie, solder lead 2 to lead 34). Pushthe heatshrink tubing over the joinand carefully shrink it down with ahot-air gun.(6). Assemble the logic circuit on asmall piece of Veroboard or similar andconnect this to the 50mm of trailingcable at the Amiga end. You only needto connect leads 2, 8, 10, 26, 28, 30 &34 to the logic circuit – the remainingleads can be cut off flush with the endof the header.(7). Connect a power cable consisting of two leads (+5V, GND) to the logicboard. Terminate the other end of thiscable in a 3-pin header (+5V, GND, key)somewhere on the Amiga PC board(choose your own spot).Fig.1: theinterface circuitconsists of acouple of NANDgates plus amodified driveconnector cable.Alternatively, you can hardwirethe supply leads to the appropriateterminals inside the Amiga.Mechanical arrangementThe mechanical arrangement is reasonably straightforward. Note that youwill have to remove the plastic faciafrom the front of the drive and thatyou may need to pack the standoffswith washers to raise the drive to thecorrect height.Depending on the arrangement, itmay also be necessary to cut a hole inthe side of the Amiga’s cover to gain access to the FDD’s disc eject lever. Thislever may also have to be extended bysome suitable means.$7.95+ $3 p&pFinally, note that some FDDs keepspinning for a second or two after theAmiga’s disc activity LED has extinguished. For this reason, don’t changediscs until you hear the disc motorcome to a stop.Alternatively, re-route the FDD’sown disc activity LED to a visibleSCposition on the front panel.Especially For ModelRailway EnthusiastsTHE PROJECTS: LED Flasher; Railpower Walkaround Throttle;SteamSound Simulator; Diesel Sound Generator; Fluorescent LightSimulator; IR Remote Controlled Throttle; Track Tester; Single ChipSound Recorder; Three Simple Projects (Train Controller, TrafficLights Simulator & Points Controller); Level Crossing Detector;Sound & Lights For Level Crossings; Diesel Sound Simulator. Order direct from “Silicon Chip”PRICE: $7.95 (plus $3 for postage). Order by phoning (02) 9979 5644 "ing your credit card number; or fax the details to (02) 9979 6503; ormail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097.April 1997 23Teeny Timer: a low-techtimer for your carThere are plenty of applications in a car wherea simple timer is required. This one doesn’t useany ICs or even a PC board. It just uses atransistor, a capacitor, a relay and very littleelse. You could wire it up in almost no time atall and get delays of up to 30 seconds.By LEO SIMPSONThis simple circuit came aboutbecause one of our readers wanteda timer for his water-cooled turbointercooler. The timer was to be usedto control an electric water pump andwas to operate for a set time (seven seconds) each time after it was switchedoff. No doubt you can come up witha dozen other uses.Now we could have come up witha fancier design using an IC suchas a 555 timer. But that would haverequired a PC board and this reader24 Silicon Chipjust doesn’t feel at home with ICs andPC boards. He also wanted the timerto operate in the engine bay and thatruled out consumer versions of the555 or other timer ICs since their maximum operating temperature is only70°C.OK, we thought, “how do we comeup with a simple timer, not using an ICand the absolute minimum of parts?”Oh, that was the other requirement: hedidn’t want a lot of parts in it becausehe gets confused when soldering themup! He’s a pretty demanding customer,this one.Anyway, we put the feet up on thedesk, thought of faraway places, anything but timers really and finally thisidea popped into the vacuum: “use atransistor”. The result you can see inthe circuit of Fig.1.How it worksThe heart of the Teeny Timer is aDarlington NPN transistor, Q1. Whencurrent is fed to its base via the 10kΩresistor, the transistor is turned onand the relay is actuated to operatewhatever you want. The diode acrossTop of page: the Teeny Timer usesone Darlington transistor, a 1000µFcapacitor and not a lot else to providedelays of about 38 seconds. A biggercapacitor would give a longer delay.Note that the circuit is wired on lowtech tagboard.Fig.1: when switch S1is closed, the +12V railis applied to the 1000µFcapacitor and the 10kΩbase resistor of thetransistor, to turn therelay on. When switchS1 is opened, the 1000µFcapacitor discharges viathe 10kΩ base resistorto provide a fixed timedelay.the relay is there to absorb the backEMF generated by the relay when itturns off.The circuit operates as follows.When switch S1 is closed, it feeds+12V to the 1000µF capacitor and the10kΩ resistor. This turns on the transistor and operates the relay. When theswitch opens, the 1000µF capacitorcontinues to feed bias current to thetransistor and so the relay stays onuntil the capacitor is substantiallydischarged.There’s not much more to it thanthat. The +12V supply is fed via anin-line fuse.Varying the delayThe time delay can be varied byvarying the size of the capacitor. Onour version, the 1000µF capacitor gavea delay of about 38 seconds. 470µFwould give about 17 seconds; 220µFabout seven seconds; 100µF wouldgive about four seconds and anythingsmaller you wouldn’t bother about.Longer delays could be obtained byusing bigger capacitors. For example,2200µF should give about one minutePARTS LIST1 12V automotive relay (seetext)1 SPST toggle switch (S1)1 inline 3AG fuseholder1 5A 3AG fuse1 plastic utility case, 130 x 68 x42mm1 BD679 or BD682 NPN Darlington transistor (Q1)1 1N4004 silicon diode (D1)1 1000µF 16VW electrolytic capacitor (see text for value)1 10kΩ 0.25W resistor1 5-way tagstrip1 grommet1 screw and nut to suit relayMiscellaneousSpade lug connectors, hook-upwire, solder.10 seconds while 4700µF should giveabout three minutes.The actual delays will depend onthe capacitor tolerance, the gain of thetransistor, the ambient temperatureand the supply voltage and whetheryou’ve had too much to drink lately.Not precise enough for you? Hey, thisis a low-tech, low-cost design.Building itNo PC board! Whoa! Whaddya wedo now?In a throwback to the dim distantpast, we built the circuit on a 5-waytagstrip. Fig.2 shows the wiring details. The relay is a standard automotive type with SPST contacts and ratedat 20-30A. They can be purchasedfrom any automotive parts outlet forabout $11 or from Jaycar Electronicsat $6.95. The relay is mounted witha single screw and nut, to the base ofthe plastic case.You can either solder the connections directly to the relay or fit thewires with spade lug connectors, aswe did.Testing itThis is the easy part. Connect thecircuit up to a battery or 12V supplyand operate the switch. The relayshould operate immediately. Thenturn the switch off. The relay shouldstay closed for your desired delay timeand then give a click to show that ithas opened.We mounted the whole lot in a plastic case and the leads all came in via agrommeted hole at one end. If you aregoing to mount the Teeny Timer in theengine bay of your car, keep it as faraway from the hot spots as possible.Mount the case so that the wire entryhole is at the bottom, so that watersplashes don’t become a problem. SCFig.2: the wiring diagram shows all thedetails. Note the polarity of the diode andelectrolytic capacitor and make sure youwire the transistor correctly otherwise itwon’t go.April 1997 25A digital voltmeterfor your carMain FeatHave you ever experienced that sinkingfeeling when your car won’t start on thosecold winter mornings? This digital voltmeterwill let you keep tabs on the condition ofyour car’s battery & the charging system.By JOHN CLARKEPerhaps the most unreliable component in a modern vehicle is its battery.This is not surprising consideringthe work it has to do, often underquite arduous conditions. On a coldwinter’s morning, for example, it isexpected to deliver enormous cranking currents to the starter motor, thisat a time when the battery is at itsworst.A car battery will only last well andperform at its best when it is properlymaintained. This means keeping an26 Silicon Chipeye on the electrolyte level and keeping the charging voltage within strictlimits. For a 12V battery, the chargingvoltage should be kept between 13.8Vand 14.4V, while for a 24V battery, thecharging voltage should be between27.6V and 28.8V.If the charging voltage is too low, thebattery will never fully charge and itwill be unable to deliver the necessarycurrent during cold starting. Conversely, if the battery is overcharged,the electrolyte will gas excessively,ures• Compactsize• 3-digit LED readout• 0.1V resolution• Suitablefor 12V andbatteries24V• Leading “0”• Display d blankingimming at night• High accuracy• Negligibledrift withtemperature• Can be used as a0-39.9Vmeterthereby reducing the electrolyte leveland shortening the life of the battery.On some vehicles, the charging system is only marginal, particularly inwet weather, with the lights on and inheavy traffic. In these circumstances,the battery is often required to deliverpower to all the electrical accessories.This is because the alternator is onlyFig.1: block diagram of theDigital Car Voltmeter. Most ofthe work is performed in IC1which is an ICL7107 analog-todigital (A-D) converter. This ICdirectly drives the 3-digit LEDdisplay and produces a readingthat corresponds to the voltageat its input. The accuracy of thisreading relies on the stability ofvoltage reference REF1.driven by an idling engine and cannotadequately top up the battery.Similarly, if you make lots of shorttrips, the battery might not have achance to adequately charge betweenstarts. The result – a flat battery andyou’re left stranded.By fitting this digital voltmeter toyour car, you can easily keep tabs onthe condition of the battery and thecharging circuit. If the battery voltageconsistently reads low, for example,then either the battery is on the wayout or the charging system is not working correctly. Either way, it’s time totake action.Conversely, if the battery voltage isalways high, then the battery is beingovercharged, as can easily happen ifthe regulator fails. This can not onlydamage the battery but, in severe cases,could also damage various electronicsystems in the vehicle.So there are good reasons for carefully monitoring the battery voltagein a car and this unit is ideal for thejob. It boasts high accuracy, negligibledrift with temperature and a 3-digitLED display that reads to the nearest0.1V. It also features automatic displaydimming when the lights are turnedon, to prevent the readout from beingexcessively bright at night.Fig.2(a) shows the basic method bywhich IC1 converts the analog inputvoltage to a digital display value. Thetwo inputs, Vin and Vref, are fed to anintegrator via switch S1 which selectsbetween them.To measure the voltage at Vin, S1 isswitched to position 1. The integratorinitially charges capacitor Cx at a rateset by Vin for a fixed period of time.The higher the voltage at Vin the higher the voltage at Vx at the end of thistime period – see Fig.2(b). Note thatslope ‘A’ in Fig.2(b) reaches a higherVx voltage than slope ‘B’ because Vinis higher for ‘A’.At the end of the fixed time period,switch S1 selects the Vref value (position 2) which is opposite in polarityto Vin. Thus, capacitor Cx dischargesat a fixed rate as set by Vref. Duringthis “de-integrate” period, a counter isclocked at a fixed rate until the capacitor is fully discharged. The comparatorthen switches and the number in thecounter is displayed.This number is directly related tothe voltage at Vin.How it worksFig.1 shows the block diagram forthe Digital Car Voltmeter. Most of thework is performed in IC1 which isan ICL7107 analog-to-digital (A-D)converter. This IC directly drives the3-digit LED display and produces areading that corresponds to the voltage at its input. The accuracy of thisreading relies on the stability of voltagereference REF1.Fig.2: how the A-D converter works. To measure the voltage at Vin, S1 is firstswitched to position 1. The integrator then charges capacitor Cx at a rate set byVin for a fixed period of time. At the end of this time, S1 is switched to Vref andthe capacitor discharges. During this time, a counter is clocked at a fixed rateuntil the capacitor is fully discharged.April 1997 27Fig.3: the reference voltage for A-D converter IC1 is derived using anLM336Z-2.5 (REF1). It's output is divided and applied to the REF HI and REFLO inputs. IC2 and its associated parts condition the signal input, while IC3provides the display dimming feature.This method of A-D conversion isoften used in digital voltmeters. Ithas the advantage that the accuracyis only dependent on the accuracy ofthe reference voltage. Although thetechnique uses a clock to set the fixedtime during the integrate period andthe count rate during the de-integratephase, the stability of the clock is notoverly important as far as conversionaccuracy is concerned. That’s because28 Silicon Chipthe resulting digital value is not dependent on the clock rate.To understand why, let’s considerwhat happens if the clock is slowerthan normal. In that case, the Vx valuewill be higher than expected after theintegrate stage and it will take longer todischarge Cx to 0V (ie, the de-integratestage will take longer). However, that’scompensated for because the counteris clocked at a slower rate over thislonger time period.As a result, the same value will berecorded, regardless of clock rate. Ofcourse, if the clock rate is far too slow,the integrator may saturate because itsoutput reaches the limit of the supplyvoltage.Conversely, if the clock is too fast,Vx will be lower but the counter willbe clocked at a faster rate during thedischarge period. Thus, any drift inthe clock rate over time is cancelled inthe conversion process, provided thatthe clock rate does not drift betweenconversions.PARTS LISTFig.4: this is the waveform at the output of the 555 timer (IC3) when the car’slights are on. Because the waveform is low for only 17% of the time, Q3 is onlyon for this time and so the displays are dimmed.Returning to Fig.1, the car batteryvoltage is applied to regulator REG1and to a signal conditioning circuitbased on IC2. The regulator providesa 5V supply rail, while the signalconditioning circuit converts the inputsignal to a voltage range suitable forfeeding to IC1 .The display is controlled usingdimming and leading “0” blankingcircuitry. Leading “0” blanking is acosmetic feature that blanks the firstdigit when the reading is below 10V.The leading zero blanking circuitworks by detecting when the “f” segment in the most significant display isdriven and then switching the wholedisplay digit off. The “f” segment isonly driven if 0, 4, 5, 6, 8 and 9 are tobe displayed. Since we are only interested in displaying values well below40.0, blanking the leading digit forvalues above “3” is of no consequence.The display is dimmed when thedimming input is pulled high. Thisactivates an oscillator which turnsthe displays on for only 17% of thetime, thereby effectively reducingthe average display brightness. Theswitching speed of the oscillator isset high enough so that the displaydoesn’t flicker.Circuit detailsRefer now to Fig.3 for the circuitdetails. At the heart of the designis an Intersil ICL7107CPL 31/2-DigitSingle Chip A-D Converter (IC1). Itdirectly drives the three 7-segmentLED displays and only requires a fewextra components to make it work.The clock components are at pins 38,39 & 40, while the RC network for theintegrator is at pins 27 & 28.To improve accuracy and removeany offsets in the internal op amps, anauto zero capacitor has been includedat pin 29. A reference capacitor atpins 33 & 34 is used to store the reference voltage during the de-integratestage of the dual-slope D-A conversion.The reference voltage is derivedusing an LM336Z-2.5 (REF1). Thisdevice is connected between the +5Vrail and the REFLO input of IC1. Thecurrent through REF1 is set to about1mA using a 2.2kΩ resistor, whilediodes D3 and D4 are used to compensate the reference for temperaturevariations. Trimpot VR1 is adjusted toset the reference to 2.490V, at whichpoint it has a minimum temperaturecoefficient.VR2 divides the 2.490V from REF1to provide a stable 1V reference voltagebetween REFLO and REFHI. This setsthe full scale input for IC1 to 1.999V.However, because we are only usingthree digits, the display can only show1 PC board, code 04304971,117 x 102mm1 PC board, code 04304972, 88x 30mm1 front panel label, 132 x 28mm1 ABS case, 140 x 110 x 35mm1 red transparent Perspex sheet,46 x 22 x 2-3mm1 small TO220 heatsink, 30 x 25x 13mm1 3mm x 6mm long screw plusnut4 9mm untapped standoffs4 3mm x 15mm screws9 PC stakes1 60mm length of 0.8mm tinnedcopper wire3 HDSP-5301 12.7mm highcommon anode LED displays2 10kΩ horizontal trimpots (VR1,VR3)1 50kΩ horizontal trimpot (VR2)Semiconductors1 ICL7107CPL 31/2 digit A-Dconverter (IC1)1 LF351, TL071 single op amp(IC2)1 555 timer (IC3)1 7805 5V regulator (REG1)1 BC548 NPN transistor (Q1)2 BC328 NPN transistors(Q2,Q3)1 LM334Z-2.5 reference (REF1)1 1N4752 33V 1W zener diode(ZD1)1 1N4732 4.7V 1W zener diode(ZD2)4 1N914, 1N4148 diodes (D1D4)Capacitors1 100µF 63VW PC electrolytic6 10µF 16VW PC electrolytic1 0.22µF MKT polyester2 0.1µF MKT polyester1 0.047µF MKT polyester1 100pF MKT polyester orceramicResistors (0.25W, 1%)1 470kΩ 2 2.2kΩ3 100kΩ 3 1kΩ1 39kΩ 1 390Ω3 10kΩ 1 47Ω2 4.7kΩ 1 150Ω 1W 5%MiscellaneousAutomotive wire, automotiveconnectors, solder, etc.April 1997 29CAPACITOR CODES Fig.5: the 7-segment displays must be installed with their decimal points at topleft, as shown here. Make sure that all polarised parts are correctly oriented.up to 999mV (ignoring the leading zeroblanking).The COM pin (pin 32) sits at a nominal 2.8V below the +5V supply rail;ie, at 2.2V. This means that INLO alsosits at 2.2V, since it is tied to COM.The 10kΩ resistor between the COMpin and the +5V rail ensures that the Value IEC Code EIA Code 0.22µF 220n 224 0.1µF 100n 104 0.047µF 47n 473 100pF 100p 101COM pin supply is biased correctly.With no input, INHI also nominallysits at 2.2V. That’s because the 2.2V onCOM is applied to pin 3 of op amp IC2via 1kΩ and 47Ω resistors. This stageoperates with a gain of 1.01 due to the1kΩ and 100kΩ feedback resistors andso its output is biased to 2.2V.IC2 and its associated input stageare also used to process and buffer thebattery voltage before it is applied toIC1. The battery voltage is monitoredvia the ignition switch and is dividedby 100 via a 100kΩ input resistor andthe 1kΩ resistor connected to COM.This divided voltage is effectivelyadded to the 2.2V bias voltage andthen fed to IC2.Let’s say, for example, that 10V isapplied to the input. This is divided to100 and added to the 2.2V bias to give2.3V on pin 3 of IC2. IC2 then buffersthis voltage and applies it to the INHIinput of IC2.As a result, the difference betweenthe INHI and INLO inputs is 2.3V - 2.2V= 100mV. This is then displayed as10.0 (ie, 10.0V) on the LED readouts.Diodes D1 & D2 are included tosuppress any voltage spikes whichcould otherwise go beyond the supplyrails and damage IC2. The associated10µF capacitor also damps any voltageTABLE 1: RESISTOR COLOUR CODES No. 1 3 1 3 2 2 3 1 1 1 30 Silicon ChipValue 470kΩ 100kΩ 39kΩ 10kΩ 4.7kΩ 2.2kΩ 1kΩ 390Ω 47Ω 150Ω 4-Band Code (1%) yellow violet yellow brown brown black yellow brown orange white orange brown brown black orange brown yellow violet red brown red red red brown brown black red brown orange white brown brown yellow violet black brown brown green black 5-Band Code (1%)yellow violet black orange brownbrown black black orange brownorange white black red brownbrown black black red brownyellow violet black brown brownred red black brown brownbrown black black brown brownorange white black black brownyellow violet black gold brownnot applicableThe display board is soldered at right angles to the main PC board, as shownhere (see text). Note the U-shaped heatsink fitted to REG1. This should besecurely fastened to the board so that it can’t short against other parts.spikes. Trimpot VR3 is used to adjustthe offset of IC2’s output so that thedisplay reads 0.0 when the input isconnected to ground.The LED displays are commonanode types and are all controlledby Q3. In addition, the leading digit(DISP1) is controlled by Q1 and Q2.Normally, the “f’ segment output fromIC1 is high and so Q1 & Q2 are on andDISP1 is turned on via Q3. However, ifthe “f” segment output for the DISP1digit goes low (eg, if a zero is to bedisplayed), Q1 turns off. This thenturns off Q2 and so DISP1 also turnsoff to provide the leading zero blanking feature.Display dimmingWhen the car’s lights are off, pin4 of 555 timer IC3 is pulled low andso its pin 3 output is also low. Thismeans that Q3 is on and so the displays run with a 100% duty cycle forfull brilliance.When the lights are turned on, pin4 of IC3 is pulled to 4.7V (as set byZD2) and so IC3 begins to oscillate.Its operating frequency is set to about244Hz while the duty cycle is about83%, as set by the RC timing components on pins 2, 6 & 7.This means that pin 3 is low for onlyabout 17% of the time. And since Q3is only on when pin 3 is low, it followsthat the displays only operate witha 17% duty cycle. This reduces thedisplay brightness, so that they don’tbecome intrusive at night.Power supplyPower for the circuit is derived fromthe car’s battery via the ignition switch.The 15Ω resistor and zener diode ZD1provide transient suppression, whilethe 100µF capacitor provides filtering.The filtered voltage is then fed to a3-terminal regulator which producesa 5V supply for IC1, IC2 and IC3.Normally, the supply voltage to theSPECIFICATIONS• • • • • • • Voltage range 8-33V (0-39.9V when separately powered)Resolution 0.1V (100mV)Accuracy within 0.1VTemperature drift less than 0.5% from 0-60°CQuiescent current 130mA <at>15V, 150mA <at> 30V (full brightness)Input impedance 100kΩInput current -27µA <at> 0V, 0µA at 2.2V, 122µA <at> 15VApril 1997 31Alternatively, if a separate powersupply is used to drive REG1, thecircuit can accurately measure inputvoltages down to 0V. As a result, the+12V supply and input terminals arenot connected on the PC board so thatthe unit can be used in applicationswhere low voltage measurements arerequired.ConstructionAnother view of the completed module, showing how the two boards aresoldered together. Note how the 10µF electrolytic capacitors are bent over sothat they clear the base of the case.The completed module is mounted upside down in the case, so that the displaydecimal points are at bottom right. The board is secured on 9mm spacers using12mm-long screws which go into integral standoffs on the base of the case.circuit is connected to the input so thatthe battery voltage can be measured.However, if the input voltage to theregulator drops below about 8V, thecircuit will give misleading resultsbecause of low voltage to the ICs.This is of no concern for a car batteryvoltmeter.DIGITAL CAR VOLTMETER32 Silicon ChipBuilding this unit is easy since mostof the parts are mounted on a main PCboard coded 04304971. The only partsnot on this board are the three 7-segment displays. These go on a separatedisplay PC board coded 04304972 andthis is then soldered to the main PCboard at right angles.Before mounting any of the parts,carefully check the PC boards forany shorts between tracks or brokensections. If necessary, cut out therectangular section at the front of themain board, where it meets the displayboard.Fig.5 shows the assembly details.Start by installing PC stakes at thefour external wiring points and at testpoints TP1-TP5. This done, install thewire links and the resistors. Table 1shows the resistor colour codes butit is also a good idea to check eachvalue using a digital multimeter, justto make sure.Next, install the ICs, followed bythe capacitors, diodes, zener diodesand the transistors. Make sure that allthese parts are correctly oriented andthat the correct type number is usedat each location. In particular, don’tconfuse transistors Q1 and Q2.The regulator (REG1) is mountedhorizontally on the PC board withits leads bent at rightangles. It isthen secured to both the board and aU-shaped heatsink using a screw, nutand lockwasher. A second heatsinkshould also be fitted to the copper sideof the board if the unit is to be usedwith a 24V battery. Make sure that thissecond heatsink doesn’t short out anyof the tracks.The display board can now beFig.6: this full-size frontpanel artwork can be usedas a template for cutting outthe display window.functioning correctly and you canproceed with the calibration.CalibrationFig.7: check your etched PC boards against these full-size artworks beforeinstalling any of the parts.quickly assembled by installing thethree LED displays. These must all beoriented with their decimal points attop left, as shown on Fig.5.Final assemblyThe unit is housed in a small ABScase measuring 140 x 110 x 35mm.This is fitted with a self-adhesivefront panel label, while a red Perspexwindow covers the display area.The main job in the final assemblyis to solder the two PC boards togetherat right angles. To do this, first mountthe main PC board upside down onthe base of the case and secure it on9mm spacers using 3mm x 12mmlong screws. This done, the displayboard is butted against the main boardand the two large end pads soldered.Make sure that the two boards are atrightangles and that the bottom edgeof the display board rests against thecase before making these connections.The PC board assembly shouldnow be removed from the case andthe remaining edge pads solderedtogether. Apply a generous fillet ofsolder to the two large end pad connections to ensure sufficient mechanicalstrength.Now for the smoke test but first goback over your work and carefullycheck for any errors. In particular,check that all parts are correctly oriented, that the correct part has beenused at each location and that thereare no missed solder joints.If everything is correct, apply powerand check that the display lights up(note: only the last two digits shouldlight). If it doesn’t, check transistor Q3.Now check for +5V at the output of theregulator (REG1), at pin 1 of IC1, at pin7 of IC2 and at pin 8 of IC3.Next, check that the display dimswhen +12V is applied to the LIGHTSinput. If it does, the unit is probablyThe calibration procedure is quitestraightforward – just follow this stepby-step guide:(1) Connect a multimeter betweenTP1 and TP2 and adjust VR1 for areading of 2.490V (this will give theminimum temperature drift for REF1).(2) Connect a multimeter betweenTP1 and TP3 and adjust VR2 for a 1Vreading. This calibrates the full scalereading for the A-D converter.(3) Connect the INPUT terminal onthe PC board to GND and adjust VR3for a 0.0V reading. This sets the offsetoutput of IC2.(4) Connect the INPUT and +12Vterminals together and connect themultimeter between these terminalsand GND. Check that the displayshows the same reading as the multimeter. If not, adjust VR2 slightly untilthe readings are the same.That completes the calibration.Connect suitable flying leads to thefour external wiring terminals anddrill a small hole in the rear panel toprovide an exit for these leads. Theboard assembly can now be finallysecured to the base of the case.Finally, complete the construction by fitting the front panel. Oneapproach is to substitute a piece ofred Perspex for the whole of the frontpanel, with the area outside the display panel suitably masked (eg, witha stick-on label). Alternatively, youcan cut a display window out of theexisting panel and fit this with a redPerspex window for the displays.InstallationThe Digital Car Voltmeter can beinstalled on the dashboard of the vehicle. It is wired to the ignition, lightsand ground connections on the fusedside of the fusebox. Use automotiveconnectors for all wiring.The ground connection can be madeto the chassis using an eyelet crimp-lugwhich is secured to the metal usinga self-tapping screw. The separateINPUT connection to the voltmetercan be made at the fusebox, at a pointwhich is switched via the ignitionswitch but which has a low currentdrain. This will ensure that the voltmeter is not measuring a low voltagedue to drops across the vehicle wirSCing.April 1997 33SILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:dicksmith.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:dicksmith.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:dicksmith.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:dicksmith.com.auBOOKSHELFHandy reference on microcomputerinterfacing & applicationsMicrocomputer Interfacing and Applications, M. A.Mustafa, published January 1995 by Newnes. Softcovers, 233 x 155mm, 456 pages. ISBN 0 7506 17527. Price $69.00.This is the second edition of thisbook which, in its 17 chapters, reasonably fully covers all aspects of theoperation and interfacing of micros tothe outside world.The first chapter is pitched at thebeginner who is assumed to havelittle or no knowledge of the subject.It covers processors, storage devices,input/output (I/O) devices, microprocessor operation, task execution andinterrupts.Chapter two explains why externaldevices may need to be connected toa microcomputer, the methods used tocommunicate with these devices andthe concept of input and output ports.The next chapter expands on thisby discussing the need for flexibilityin and optimisation of any add-onsthat you may use. The boards whichare described are mostly for the IBMstyle computer and its clones, mainlybecause of the diverse range of offthe-shelf boards which have becomeavailable for this type of computer.Mustafa then goes on to comparethe pros and cons of interrupt versusprogram controlled output. The chapter concludes with a few examplesof the decoding of external addressspaces.Chapter four, entitled Using DigitalInput and Output Ports, begins byshowing the methods used to detectexternal switch closures and includesa discussion on switch debounce usingboth hardware and software. It continues by explaining how comparators38 Silicon Chipcan be used to indicate out of tolerancevoltages.Hardware logic gates are coverednext, followed by an explanation ofhow the various gates can be implemented in software if there are sufficient processor input lines available.Most of the balance of the chapter istaken up with the solutions to variousproblems, using both hardware andsoftware approaches.The last 10 pages of this chapterdiscuss AC, inductive loads and powerfactor.Chapters five to eight cover, in greatdetail, Multiplexers, Sample and Holdcircuits, and Digital to Analog (D/A)and Analog to Digital (A/D) converters.This information will be familiar tothe experienced hobbyist or engineerbut should prove enlightening to thenovice.Chapter six explains how D/Aconverters can be interfaced to a microprocessor and chapter seven doesthe same for A/D converters. Chaptereight details the application of severalcommercial devices to the solutions ofsome hypothetical problems.The next chapter covers externalcounters and timers, although mostmodern micros now seem to includethese on the chip. Still it is often easierto implement counting or timing functions in hardware using an interrupt,than in software, as these functionscan occupy a large percentage of theprocessor’s time.Applications using several timers,including that old favourite the 555,are shown. Methods of measuringfrequency, time intervals and phaseshifts are examined, almost alwaysusing external hardware to processthe input signals.Chapter 10 diverges from micros todiscuss switching devices, althoughthe ultimate end is to control thesevia a computer. Diodes, zeners, transistors, FETs, MOSFETs, IGBTs, SCRs,thyristors, Triacs and relays are allincluded in this summary.The important subject of isolatingcontrol circuits from the mains supplyis adequately covered.The next chapter, titled OpticalDevices, is a continuation of theprevious one. It covers light sensingdevices such as photodiodes, phototransistors, light dependent resistorsand light emitting devices such asopto-couplers, light emitting diodes(LEDs) and 7-segment LED displays.Methods of interfacing these differentdevices to micros are shown and anexplanation is given of the way LEDdisplays are multiplexed.The chapter concludes with nearly nine pages which cover opticalencoders. The incremental encoderis widely used but suffers from theproblem that it can only count pulsesbut cannot give any absolute position.To increase their usefulness, modifications have been made such as anextra output providing one pulse perrevolution at a predetermined position.Absolute encoders overcome theprevious problems by representingeach position by a unique code butthis obviously will require more inputdata lines to a processor.Chapter 12 explains how to generatewaveforms, again by utilising eithersoftware or hardware under computercontrol. Mustafa begins this chapter bydiscussing the types of waveforms thatare usually generated by hardware,then compares the pros and cons ofreal time calculations versus look-uptables. He continues with examplesof the generation of different waveforms using both digital and analoginterfaces for frequency selection. Thechapter also shows how DC offsets canbe generated and added to the outputwaveform.The 13th chapter introduces us tomicrocomputer controlled roboticmechanisms. Both analog and digital,open and closed loop controls arecovered. While the chapter is quitecomprehensive, the robot designerswill know it all and the hobbyist isunlikely to begin designing robotsafter reading it.Temperature measurement andcontrol is the heading for chapter 14.The various types of sensors includingthermistors, thermocouples, RTDs(resistance temperature detectors) andsemiconductors are explained.The methods used to control thetemperature once it has been sensedare then described. These are on/off,pulse width, phase angle and zerocrossing switching. Some examples ofthese methods are then given.A chapter on motor control is next.Many industrial process control systems will, as part of their task, controlthe speed of a motor. As we knowthere are two types of motors, DC andPractical Guide to Satellite TVThe Practical Guide to SatelliteTV, by Garry Cratt. PublishedFebruary 1997. ISBN 0 646 306820. 296 x 210mm, soft covers, 116pages. R.R.P. $39.00.Published in February this year,this easy-to-read book has beencompiled by one of the most experienced satellite TV installers inAustralia, Garry Cratt. It is writtenin an informal style and is copiously illustrated.Topics covered include a historyof satellite development, principles of satellite operation, earthstation components, encryptionsystems, video standards, videocompression (MPEG, etc), systeminstallation and wiring.As you might expect, there is alot of information about satellitereceiver hardware such as dishes,feedhorns, polarisers, LNBs (lownoise block converter) and so on.There is a large glossary and 46pages of satellite orbital data, transponder loading and footprints.AC and they, unfortunately, requiredifferent methods of control.The author describes the varioustypes of DC motor speed control usingthe computer in a closed loop system,then other methods which use someexternal hardware but don’t take asmuch computer processing time.The speed of an AC motor can bevaried by altering either the appliedvoltage or the applied frequency.While the latter is harder to implement, it is the more efficient method,as the output torque is higher. Variousmethods using voltage, frequency andpulse width to vary the motor speedare then described.The penultimate chapter, headedMiscellaneous Applications, coverssuch things as interfacing a keypad toa micro, interrupt control, DMA (directmemory access) and handshaking. Itcontinues by discussing rudimentaryprocess control test procedures, theprovision of additional supplies topower the external add-ons and batterybackup of these add-ons.The final chapter talks about theIn summary, this book is downto earth and up to date. It is available at $39.00 plus $5 postage fromAv-Comm Pty Ltd, PO Box 225,Balgowlah, NSW 2093. Phone (02)9949 7417; fax (02) 9949 7095.possible limitations of an existingcomputer system and the upgradepaths available. It also describes thelimited storage of RAM and the probable need to transfer RAM data to ahard disc. Brief mention is then madeof operating systems, programminglanguages and emulators.An emulator is a collection of hardware which allows a software program(eg, for a microcontroller) to be loadedinto it and executed. The programsteps can be traced and intermediatevalues checked to confirm the correctoperation of the program before itis “burned” into the final device. If“bugs” are found, the program canbe altered then run again to verify itscorrect operation.To sum up, this book is a good reference for the hobbyist or student whowants to have a better understandingof the topics covered. It contains lotsof worked examples to illustrate eachchapter and is an ideal starting point.Our review copy came from ReedInternational Books Australia Pty Ltd.Phone (03) 9245 7168. (R.F.W.)SCApril 1997 39CIRCUIT NOTEBOOKInteresting circuit ideas which we have checked but not built and tested. Contributions fromreaders are welcome and will be paid for at standard rates.12V PA system has abalanced mic inputThis 12V PA system uses a TDA2004stereo amplifier IC in bridge mode todrive a 4Ω loudspeaker. Both amplifieroutputs at pins 8 & 10 have Zobel networks (1Ω & 0.1µF) to ensure stability,while the 100µF capacitors providebootstrapping to the driver stages. Thepower output is about 20W.IC1 is a low noise 5534 op ampand is connected as a balancedinput stage for the microphone. Theinput impedance is set by the two 1kΩresistors while the overall gain is setby the ratio of the two 470kΩ resistorsto the two 1kΩ resistors. Frequencycompensation is provided by a 33pFcapacitor between pins 5 & 8.The TDA2004 must be mounted onan adequate heatsink. The maximumcurrent drain is around 3.5A.S. Williamson,Hamilton, NZ. ($40)Switching circuit for theM65830P digital delayactivates the data send function ofthe remaining circuit. The six bits ofdelay information from the counterare latched in parallel into the shiftregister. The rest of the circuit transmits the data to the delay chip as inthe Stereo Simulator.Once this information has been sent,the binary counter with the delay timedata is cleared and the serial clockgoes back into reset mode until it istriggered by the edge detector again.With a 3kHz counting rate, theentire process takes about 20ms. Thecircuit updates the delay three timesevery second while ever switch S1 ispressed. At this rate, the user shouldnot notice any delay between adjustingthe control and hearing the effect.On the circuit, data is fed to IC3by IC8, a 4024 7-bit binary counterwhich is clocked by IC5b & IC5c. IC5is a quad NAND Schmitt trigger, setup to provide two oscillators. The firstis set to 3Hz and the second to 3kHz.This circuit is designed to generatethe delay time control data for theM65830P single chip digital delay. Itinterfaces to the serial transmitter section of the Stereo Simulator (SILICONCHIP, June 1996), providing a methodof varying the delay time without usinga microcontroller.Looking at the block diagram, the3Hz oscillator triggers a monostablemultivibrator with variable pulsewidth. This monostable switches ona second oscillator running at 3kHzwhich clocks the counter. The finaloutput consists of 3kHz bursts ofvarying length. Thus, the final countis determined by themonostable pulsewidth which is setby the delay control.When the binarycounter has reachedthe required valuefor the delay time(when the monostable output goes low),a falling edge detector40 Silicon ChipThe extra NAND gate following eachoscillator provides signal inversion.IC6 is a 555 timer configured inmonostable mode with its outputpulse width set by the 1µF capacitorand 20kΩ pot (VR1) at pins 6 & 7. The390Ω resistor in series with VR2 setsthe minimum pulse width. The monostable is triggered by the 3Hz clockand its output at pin 3 switches on the3kHz clock while it is high. The clockinput to IC8 consists of 3kHz bursts,three times a second. Thus, the countreached on IC8 is controlled by VR1,allowing the delay time to be continuously adjusted. It is updated each timethe monostable is triggered.Once the counter has reached thedesired value, the data must be sent.This is triggered by the negative edgedetector mentioned earlier. It is drivenby the monostable output. When themonostable is high, the 3kHz clock isactivated and so IC8 is counting. Whenthe monostable returns to the low state,the clock stops and the edge detectorgenerates a reset pulse to start the datasend sequence of IC1, 2 & 3. Once thedata has been sent, IC8 is cleared fromthe transition in the REQ line. Theentire cycle repeats three times everysecond, as set by the 3Hz clock.12V or 24Vlamp flasherThis circuit willhandle lamp loadsup to 3A with noheats ink requiredfor the Mosfet (Q3).Q1 & Q2 functiontogether as a breakdown device similarto a Diac. Up to adefined voltage, Q1& Q2 are both off, asdefined by the two 100kΩ and the1.5MΩ resistors at their bases. Whenpower is first applied, capacitor C1has no voltage across it and Q1 & Q2are both off. C1 is then charged viathe 220kΩ resistor R1 until the voltage across it is sufficient to allow Q1& Q2 to suddenly turn on. They thendischarge C1 to the point where Q1IC8 is a 7-bit counter but only six bitsare used. To prevent the counter goingover the 6-bit limit, IC7 (a 74HC308-input NAND gate) is used to reset themonostable when the first six bits are& Q2 turn off again. The cycle thenrepeats continuously and the pulsewaveform at the collector of Q1 isused to turn FET Q3 on and off.Capacitor C1 should be a plasticdielectric type. Resistor R1 determines the off time for Q3 whileresistor R2 determines the on time.G. La Rooy,Christchurch, NZ. ($30)high. The inputs are connected to theoutputs from IC8. The unused inputsmust be tied high.S. Eaton,Frankston, Vic. ($60)April 1997 41SERVICEMAN'S LOGA mixed bag of trouble & strifeI have rather a mixed bag this month. First,there was double-trouble with a tripler, thenI encountered a tricky Wyse monitor andfinally, an NEC TV wouldn’t stop whistlingat me.The day started badly when thekind and gracious gentleman of lastSaturday returned on Monday withhis ancient Philips TV set and castunkind aspersions on my technicalexpertise by groaning that it had onlylasted one hour. I put a brave face on itand told him to wait while I attendedto it immediately.This was a 13-year old KT3 Philipswhich had come in pulsating on Saturday morning and out of the generosity of my heart I had worked on itimmediately for him then, too.After I had removed the back andblown three centuries of dust fromwithin, I desoldered the tripler andswitched the set on. The sound forthcoming was indeed music to my ears,so I fitted a new (Philips-brand) triplerand checked the set out for dry joints,particularly around the vertical outputand east-west transistors and the flyback transformer.I also cleaned around the EHT ultorcap and applied silicone rubber toall the connections. On completion,I switched on and checked for anyarcing before looking at the focus,brightness and greyscale. All was inorder, and the client sallied out of theshop an hour later, content that hisbeloved Philips was again working.Unfortunately, the next Mondaywhen I went through theroutine again, it was the sametripler that had failed. Therewas nothing for it but to replace it again with as muchgrace as I could summon.These things happen – let’spray lightning doesn’t striketwice in the same place.Wising upThe next job that came inwas a Wyse WY-60 monitorand keyboard that belongedto a video franchise. Thecomplaint was that it was“dead and smoking”.These monitors are quiteinteresting but somewhatdated technologically nowadays. They are often referredto as “dumb terminals”, andare connected to a mainframethrough an RS-232 25-pinserial port, rather like amodem.42 Silicon ChipThe problem is that everythingabout them is expensive and they useonly Wyse dedicated technology. Thisterminal has a green phosphor CRT(some have orange) and is controlledfrom the mainframe using the XENIXSystem V operating system (circa1987).Unfortunately, most people usingthis system are now faced with a difficult decision. Do they dice a systemthat uses maybe five or more dumbterminals and put in a brand newnetwork costing tens of thousands ofdollars, or do they get their ancient(in computer terms) equipment fixed?The only bright spot is that Wyse partsare easily obtainable, even if they areexpensive.Access to the main board isn’t toobad once the back cover is removedand it didn’t take long to see that theset wasn’t quite dead. The switchmodepower supply was generating ±12Vand +5V rails but there was no EHTor secondary voltages on the flybacktransformer (T202). I reached for thevoltmeter and measured ±12V all theway to the collector of the line outputtransistor Q202 (BU405), as well as tothe collector of Q201 (2SC1213), thehorizontal driver.It was time to get technical and so Ipulled out the CRO and started lookingfor horizontal pulses. There were noneall the way back to U20, pin 7, the“Gate Array” IC. There was however+5V on the Vcc pin of this IC and soI checked the crystal clocks. X2 andX3 were OK, but there was nothing onX1, a 25.580MHz crystal, even thoughthere was voltage to it.This clock fed U21 (74LS00), whichin turn fed U20 as well as the CPU(V1). The only circuit I had was anextremely poor photocopy of a fax andI was reluctant to invest $88.90 plusfreight for a service manual. Whilstenquiring about this, I also asked aboutthe cost of U20 which was $50.30 plustax and freight.I was beginning to despair as toSILICON CHIP SOFTWARENow available: the complete index to allSILICON CHIP articles since the first issuein November 1987. The Floppy Indexcomes with a handy file viewer that letsyou look at the index line by line or pageby page for quick browsing, or you canuse the search function. All commandsare listed on the screen, so you’ll alwaysknow what to do next.Notes & Errata also now available:this file lets you quickly check out theNotes & Errata (if any) for all articles published in SILICON CHIP. Not an indexbut a complete copy of all Notes & Errata text (diagrams not included). The fileviewer is included in the price, so that you can quickly locate the item of interest.The Floppy Index and Notes & Errata files are supplied in ASCII format on a3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the FileViewer requires MSDOS 3.3 or above.ORDER FORMPRICE❏Floppy Index (incl. file viewer): $A7❏Notes & Errata (incl. file viewer): $A7❏Alphanumeric LCD Demo Board Software (May 1993): $A7❏Stepper Motor Controller Software (January 1994): $A7❏Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7❏Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7❏Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7❏Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7❏I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5Disc size required: ❏ 3.5-inch disc ❏ 5.25-inch discTOTAL $AEnclosed is my cheque/money order for $A__________ or please debit my❏ Bankcard ❏ Visa Card ❏ MasterCardCard No.Signature_______________________________ Card expiry date______/______Name ___________________________________________________________PLEASE PRINTStreet ___________________________________________________________Suburb/town ________________________________ Postcode______________Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax yourorder to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number(Bankcard, Visa Card or MasterCard).✂what to do when I had a stroke of realluck – another identical monitor camein but with a different fault. This wasintermittently displaying lines andcharacters on the screen. I decidedto fix this one first and then use it todonate parts to the other for checkingpurposes.By gently tapping the chassis, itdidn’t take me long to discover severaldry joints around IC U19, the “Fonts”character generator. After soldering itup, I reconnected the DB25M loopbackplug with pins 2 and 3 connected,in order to display the characters onthe screen as I entered them on thekeyboard.In short, I gave it a thorough workout and it passed all my tests withflying colours.Now that I had one working dumbterminal, I could resume work on thefirst. First, I swapped the crystal andICs U20 and U21 but to no avail. However, when I swapped the EEPROM(U6), I began to get a pulse on thehorizontal sync line but the problemwas now in the horizontal outputstage. The CRO reported severe ringing on the collector of the line outputtransistor and it was getting very hot.I removed the flyback transformerand checked the winding betweenpins 3 & 4 with a shorted turns tester (basically a 15.625kHz oscillatorwhich is damped by a short circuit orenhanced with an inductance, with theresult displayed on a meter). This testshowed that the winding was indeedshorted. Surprisingly, the cost of anew flyback transformer was only $25plus freight.Unfortunately, that wasn’t the endof the story because I then found thatdiode D203 was also shorted, whileC208 was literally bulging out of itsaluminium container.When I fired it up, it beeped happilyback at me: “Hi, I’m Hal. Thank you forfixing me. I’m your Wyse WY-60 Terminal”. Actually, I lie, it only beepedand flashed characters before settlingdown to a prompt. I then fitted theloopback plug and checked for screenecho with the keyboard. It all workedas expected.Last, but not least, I checked thesetup and selected the defaults. Ireminded myself to tell the customerthat the setup had changed – he wouldhave to compare it with other terminals for any changes. I also prayedthat the customer had enough moneyApril 1997 43to pay for all this, as it had taken quitesome time!The whistling NECThe phone rang and an elderlygentleman asked whether I wouldbe so good as to attend to his TV setwhich was on “the blink”. It took alittle coaxing to find out that it wasan NEC N-4830 with two problems.First, it was making a whistling noisewith associated patterning lines on thepicture. Second, it was making a ratherbizarre “bop-bop” noise on standby.Because the fellow was 85 years ofage and because I thought I knew allthere was to know about this DaewooC-500 chassis, I arranged to fix it inhis home.Despite his years, the customer wasvery sprightly and his fault descriptionwas fairly accurate. Unfortunately,access to the TV set was fairly poorand great care was required to avoid44 Silicon Chipknocking over the entire collection offamily photos and china ornaments.The serial number plus a visualexamination of the power supplyquickly established that this had beena Series 5 production. This meant thata few modifications were requiredto bring it up to the current Series 7specification, as briefly discussed inthe Serviceman’s Log for March 1996.To recap, this particular model hasan inherent weakness in the powersupply. It uses a 10-pin switching regulator IC (I801) and this can overheatand fail, taking a lot of componentswith it.The failure is not the fault of the ICitself but in the associated circuitryand a modification sheet has beenissued to cover this.In this case, the whistling noise wascoming from the vicinity of the powersupply but the regulator IC was stillOK. The set had never been repairedbefore and two small electros, C808and C810, were looking their age. Icarried out the recommended modifications, replaced these two electrosand soldered any suspicious dry joints.One of the electros had me puzzled,however. The circuit showed both asbeing 10µF and yet C808 was actuallymarked 0.47µF. Perhaps this was thereason the set was playing up but ifso surely it would have had thesesymptoms from new, which it hadn’t.In any event, I found I had fixed theloud motor-boating noise on standby,but the patterning and whistling werestill there.I was disappointed by this and so,with my ego suitably chastened, Idived in again and examined the entire chassis for possible problems. Butalthough I found and fixed many suspicious joints, the problem persisted.It was time to get serious.The B+ rails all measured correctlyand, apart from the whistle from thepower supply and the line patterning,everything else worked. The patternconsisted of lines and a succession ofhorizontal curves but it was the whistling noise that was the most alarming.It didn’t have a consistent pitch and itsounded as though the power supplywas running roughly and could perhaps fail at any moment.I was on the point of giving up andtelling my octogenarian friend that itwould have to go to the workshop,when inspiration struck me (it’samazing what the thought of havingto shift a TV set down three flights ofstairs can do). I put my brain into gearand measured the rectified B+ fromthe bridge rectifier to the main electroC807 (120µF 400VW). Although thisvoltage is not marked on the circuit, Iexpected a reading of about +340V butit actually measured +295V.I didn’t have a 120µF 400V electrowith me and so I connected an old100µF capacitor from the toolboxprecariously across C807 and switchedon. Hooray! It did the trick, the B+ railcame up, the patterning was gone andall was silent.I told the gentleman I would be backthe next day with the right part. Well,nearly. The nearest value I had wasa 220µF 105°C 400V unit which wasthe same physical size as the original.I installed it as promised the next day.Interestingly, the old electro lookedpristine even though it was definitelySCfaulty.SILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.jaycar.com.auSATELLITEWATCHCompiled by GARRY CRATT*Magnetic storm claims Telstar 401A violent magnetic storm on January 11th,believed to be caused by a coronal mass ejection(a magnetically charged cloud of hydrogen andhelium) from the Sun on January 6th, is the mostlikely cause of the failure of Telstar 401. Thiswas an AT&T television relay satellite located at97° W, serving continental USA.All control of the satellite was lost,although the spacecraft remains onstation, with no observable signalemissions and no response to groundcontrol.Telstar 401 was one of two primaryspacecraft in AT&T’s Skynet network.The spacecraft was insured for aboutUS$145 million. AT&T has applied tothe FCC for permission to move Telstar302, a 12-year old satellite used fortelephone traffic into the 97° W slot.In 1994, solar storms caused electrical failures in two Canadian Aniksatellites, as well as Intelsat K. Two ofthe three spacecraft recovered whilethe third suffered a permanent powerreduction.JCSAT 5, 150° E longitude:Japan Satellite Systems has announced a November launch for JCSAT5, a Hughes HS-601 that will be locatedat 150° E. The satellite will be used tocarry television, voice, data and internet services from Japan to the Pacific.Present information indicates thatthe satellite will carry 32 K-bandtransponders only. The effect (if any)of this new satellite on the operation ofPalapa C1, located at 150.5° E, remainsto be seen.JCSAT4, 124° E longitude:JCSAT4 was successfully launchedby an Atlas rocket on February 17thand will be located at 124° E. Thesatellite has 12 C-band transponders,28 K-band transponders and has a footprint covering Japan, India, Australiaand New Zealand.Late December saw the disappearance of two Chinese analog signals onAsiasat2, HN TV and Quandong TV.Replacing these two services are ninedigital services, including HN TV andGD TV, previously available as analogservices. CCTV4, RTPI, TVSN andthe Egyptian channel RTE remain inanalog format. RTE commenced transmission on Asiasat 2 in mid December.It requires a 3m dish for good receptionalong the east coast of Australia andNew Zealand.Asia Satellite Telecommunicationshas filed a claim for US$58 millionagainst the launch insurers of Asiasat 2for the loss of nine K-band transponders. The loss has been attributed toexcessive vibration during a “roughride” on the Long March launch vehicle in November 1995.Elsewhere, Laotian TV has appearedon Gorizont 30 (142.5° E) at an IF of1375MHz, LHCP and at good signalstrength across Australia. Curiously,re-broadcasts of Australian regionalsoccer matches have appeared on thischannel, bearing the Optus Vision logo,as well as that of Laos TV channel 3.This channel was previously locatedon the old Rimsat G1 satellite at 130°E. This brings the number of activetransponders to three, as EMTV andAsia Music/Zee education continueto operate on this satellite.Optus B3, 156° E longitude:Details of the new “Aurora” digitalsatellite platform utilising the OptusB3 satellite at 156° E were releasedby Optus at the Sydney Cable Showheld in February. The platform wouldseem ideal for a satellite-based pay TVservice, competing with Galaxy.It is also probable that this platformwill be used to carry ABC and SBSin digital format on a national beam,giving central and western Australianstheir first taste of SBS programming.Earliest projected operational start isgiven as September 1997.For readers equipped with internetfacilities, two new sites have appearedthis month. Star TV can be found athttp://www.startv.com while Asiasatis at http://www.asiasat.com.hk. SC* Garry Cratt is Managing Director of AvComm Pty Ltd, suppliers of satellite TVreception systems. Phone (02) 9949 7417.http://www.avcomm.com.auApril 1997 53This bare board version of the Universal Loudspeaker Protectorcan be built into a stereo amplifier to protect the loudspeakersand prevent switch-on and switch-off thumps.A universalloudspeaker protectorfor stereo amplifiersBy LEO SIMPSON & BOB FLYNNThis simple circuit is designed to mate withany stereo amplifier, music system or car soundsystem and will protect the loudspeakers fromdamage in the case of an amplifier failure. Itcould also prevent a fire. It has a turn-on delayand will eliminate switch-on thumps.Do you leave your stereo amplifieror home music system permanentlyswitched on in standby mode? Doyou realise they could be a fire hazard? If you haven’t thought about thisproblem in the past, then this articleis for you.Most power amplifiers these daysare direct-coupled to the loudspeakers.This means that there is no output54 Silicon Chipcoupling capacitor in series with eachloudspeaker terminal. This is truewhether you have a large stereo amplifier which delivers several hundredwatts per channel or a typical homemusic system which can be turnedon and controlled by a remote controlhandpiece.This means that if an output transistor goes short circuit or in the caseof smaller home music systems, ahybrid power amplifier fails, virtuallythe full supply rail to that part of thecircuit will be applied to the loudspeaker.The result is usually a burnt outloudspeaker voice coil or damagedsuspension system. That’s expensiveto fix but it may not be the end of thematter. In a worse case, the large DCcurrent in the voice coil does not burnit out immediately but allows it to getred hot so that it sets the speaker coneon fire. From there, the acetate fillingmaterial in the enclosure and the grillefabric also catch fire, generating hugequantities of choking black smoke.Ultimately, your house may catchfire too. This is not an imaginary scenario. Stereo systems do fail and theyFig.1: this is the self-contained version of the Universal Loudspeaker Protector,intended to be powered from a 9V or 12V DC plugpack. Q1, Q2 and Q3 monitorthe output of channel 1 of the amplifier while Q4, Q5 & Q6 monitor the secondchannel. If a high DC offset is detected, the base current to Q7 will be shunted todeck and this will cause Q8 and the relay to turn off.can cause house fires. That is whythey should not be left on for longperiods of time, especially if no-one ispresent to turn them off in the case ofa fault.Why does this sort of amplifier faultcause so much heat in the voice coilof a loudspeaker? Well, consider a100W per channel amplifier with ±50Vsupply rails and driving loudspeakerswith a voice coil resistance of 6Ω,a typical value for a speaker with anominal impedance of 8Ω.If one of the amplifier’s outputtransistors fails, it will apply almostthe full DC supply rail of 50V to theloudspeaker. The resulting heat dissipated by the voice coil will be 50V2/6= 416W! No wonder the voice coil getshot and burns out!Actually, the power dissipation isgenerally not as high as that becausethe power supply voltage will dropunder such a serious load. If you’relucky, the amplifier’s fuses will alsoblow before a fire starts, limiting thedamage to just the amplifier and thevictim loudspeaker.Fire insuranceNow the only safe way to preventa major fault occurring while you’renot listening to your music system isto turn it off at the wall socket. Butfaults can still occur while you arelistening to the system and if you’renot actually in the room at the time toturn it off when a major fault occurs,the results will be costly. So to preventdamage to your expensive speakersyou need to build the Universal Loudspeaker Protector presented in thisarticle.The Universal Loudspeaker Protec-Advantages Of This New ProtectorThis is not the first loudspeakerprotector circuit we have published.The last one was featured in the July1991 issue of SILICON CHIP. This newcircuit was produced as a result ofdevelopment work we have been doingon a high-power bridge amplifier. Thenew circuit is built onto a substantiallysmaller PC board and copes with anamplifier fault condition that would beignored by the previous circuit.By using separate monitoring circuits for each channel of the amplifier,the ULP can respond to a DC faultcondition in one or both channelsof a stereo amplifier. The previousLoudspeaker Protector (published July1991) had only one monitoring circuitwhich summed the active lines fromthe loudspeakers.If the amplifier in question failedsimultaneously in both channels, itis possible that one channel wouldproduce a positive DC fault and theother channel a negative DC fault. Ifa common sensing circuit was used,these two fault conditions would effectively cancel each other out andthe Loudspeaker Protector would failto operate.Is it possible for both channels of anamplifier to fail at once? And with oppo-site faults in both channels? Definitely!It is certainly possible althoughwe admit that it is unlikely with conventional stereo amplifiers. However,where a stereo amplifier is driving asingle loudspeaker in bridge mode, itis highly likely.In most bridged amplifiers, onechannel gets its signal from the outputof the second channel. So if the secondchannel fails and its output goes high,the first channel will have its outputforced low. So the fault condition willexist in both channels and both channels must be sensed separately, asin the ULP.April 1997 55Fig.2: this version of the Universal Loudspeaker Protector is identical with thatshown in Fig.1 except that it derives its power from the amplifier’s DC supplyvia regulator transistor Q9.Fig.3: this version of theUniversal LoudspeakerProtector is mainly intendedfor protecting speakersconnected to bridged outputamplifiers in cars.tor (ULP) will continually monitor theDC conditions at the outputs of yourstereo amplifier. If a fault occurs, theULP will operate a relay to disconnectthe loudspeakers.As a bonus, the ULP has a delay atswitch-on and if it is built into a stereoamplifier, it will prevent switch-onthumps from the loudspeakers.Three versionsWe are describing three versionsof the ULP. One is self-contained and56 Silicon Chippowered with a 9V or 12V DC plug–pack. The second is intended to bebuilt into a stereo amplifier and hasits own on-board regulator. The thirdversion is intended for bridged amplifiers in cars. We’ll talk about these twolatter versions later in this article.Fig.1 shows the complete circuitdiagram of the self-contained version.Let’s talk about how Q1, Q2 & Q3monitor the active output terminal ofan amplifier. The active signal is fedvia a two-stage low pass filter networkconsisting of three 22kΩ resistors andtwo 47µF NP (non-polarised) electrolytic capacitors. This filter networkeffectively removes any audio frequencies and ensures that only DC signalsare fed to the following transistors.This is necessary because we don’twant normal audio signals to trip theULP in any way.Now let’s see how the three transistors operate together. The line fromthe low pass filter is connected to theemitter of transistor Q1 and the base ofThe self-contained version of the Universal Loudspeaker Protector is housed ina plastic case and powered from a 9V or 12V DC plugpack. Note the resistor inseries with the DC power socket. This is only required if a 12V DC plugpack isused (see text).transistor Q3. In effect, Q1 monitors fornegative DC signals while Q3 monitorsfor positive DC signals.If a positive DC signal of more than0.6V is present, Q3 will turn on. Similarly, if a negative DC signal of morethan 0.6V is present, the emitter of Q1will be pulled below its base and so Q1will turn on and turn on Q2. Both Q2and Q3 have a common 56kΩ load resistor (R1) and this normally feeds basecurrent to Q7. Q7 feeds base currentto Q8 and so both of these transistorsand the relay are on.However, when either Q1 or Q3 turnon, the base current for Q7 is shuntedto deck and so Q7, Q8 and the relayare turned off, disconnecting thespeakers.The same working principle appliesto the monitoring of the second amplifier channel, with Q4 sensing negativeDC signals and Q6 sensing positiveDC signals. Q5 & Q6 share the samecommon 56kΩ load resistor as Q2 &Q3. So if either of these transistors areturned on by fault voltages, they willalso rob Q7 of base current and causeQ8 and the relay to turn off.Arc protectionWhen the relay operates to discon-nect the loudspeakers, the movingcontacts are shorted to the loudspeakerground lines via the “unused” contacts. This has been done because if alarge DC voltage (say more than 30V)appears at the amplifier outputs, theresulting high current can cause anarc across the relay contacts. Untilthat arc is extinguished, the loud-speaker is still being subjected to thehigh current and the possibility ofdamage.By shorting the moving contacts ofthe relay to the speaker ground lines,the arc current is diverted and theamplifier fuses will blow if the arcstill persists.The fact that this Universal Loudspeaker Protector can be used withhigh power amplifiers which can produce very large output currents meansthat a heavy duty relay must be used.The one specified has DPDT (doubleThe amplifier and loudspeakerconnections are run to the selfcontained unit via a terminalblock at one end of the case.April 1997 57Fig.4: use this diagram when wiring the self-contained version of the ULP. The missing componentsat the lefthand side of the PC board are for other versions.Fig.5: this is the wiring diagram for the built-in version of the circuit, as shownin Fig.2. Note that the external resistor RY is only required if the amplifier’s DCvoltage supply is above 40V.discharged and no base current canflow via 56kΩ resistor R1. C1 thencharges via 220kΩ resistor R3 andeventually sufficient voltage is presentto allow resistor R1 to turn on transistor Q7. This turns on Q8 and the relayand so the loudspeakers are connectedto the amplifier. This delay is severalseconds and it allows the voltageswithin the amplifier to stabilise, sowhen the speakers are connected, nothumps are heard.When power is removed from theULP circuit, the relay disconnects thespeakers almost immediately, preventing turn-off thumps.Note that this “thump” protection isonly available if the ULP is poweredfrom the supply rails of the amplifier, as in Figs.2 & 5. If it is built as aself-contained unit and powered froma DC plugpack, the thump protectionwill not be provided.Constructionpole, double throw; changeover) contacts rated at 10 amps.Power supplyAs noted above, we are presentingthree versions of this circuit. The firstversion, intended as a self-containedunit to be used with any amplifier ormusic system, can be powered with a9V or 12VDC plugpack.The second version, presented as aPC board to be built into a stereo amplifier, can derive its supply from thepositive amplifier DC supply rail andthis can range from +30 to +75V DC.Its circuit diagram is shown in Fig.2.In this case, the amplifier’s supplyrail is fed to transistor Q9 and associ58 Silicon Chipated components and these operate toprovide a regulated +12V supply forthe relay and other transistors.The third version, intended forbridged amplifiers in cars, takes itssupply directly from the 12V batteryline. Its circuit is shown in Fig.3.Turn-on delaySo far we have described the mainfunction of the ULP which is to prevent loudspeaker burnouts. The minorfunction, mentioned above, is to prevent thumps from the loudspeakerswhen the amplifier is turned on. Thisis achieved with resistors R1 & R3 andcapacitor C1.When power is first applied, C1 isLet’s now describe the constructionof the self-contained version. All theparts are mounted on a PC board coded01104971 and the wiring diagram isshown in Fig.4. As you can see, someparts are missing from one end of theboard. These are for the on-board regulator (Q9, etc) which are used onlyin the in-amplifier version.Fit the PC pins first and then theresistors. The four 47µF electrolyticcapacitors can go in either way aroundsince they are the non-polarised (NP)type. The 100µF capacitor is polarisedand must be inserted the correct wayaround.The eight transistors and the diodecan be inserted next. Check that youinsert the correct type in each positionand make sure that each is oriented exactly as shown in the wiringdiagram.Don’t forget to install the wire link,LK1. This has been provided to enable a thermal cutout to operate thecircuit but this feature is not usedhere.Finally, the relay can be installed.We mounted ours by soldering shortlengths of stout tinned copper wireto each relay pin. These wire leadsare then pushed through the relaymounting holes on the board and thensoldered. We understand that some kitset suppliers may provide a PC boardwith slotted holes so that the tinnedcopper wire may not be necessary.With the board complete, it’s timeto install it in the plastic case. Youmay elect to use a different case fromour prototype; as long as everythingfits, the case size and shape are unimportant.You will need to drill a hole at oneend of the case to take the DC socketfor the plugpack. At the other end youwill need to mount a six-way insulated terminal block and drill holes forwires to run inside the case. Install thePARTS LISTSelf-contained version1 plastic case, 150 x 80 x 60mm1 PC board, code 01104971,107mm x 55mm1 9V or 12VDC 150mA plugpackwith 2.1mm DC plug1 2.1mm DC socket10 PC board pins1 Relay DPDT 10A 240VAC, 12Vcoil <at> 75mA, Jaycar SY-4065or similar6 3mm x 20mm screws6 3mm nuts4 6mm spacers4 adhesive rubber feetSemiconductors5 BC547 NPN (Q1,Q3,Q4,Q6)2 BC557 PNP transistors (Q2,Q5)1 BC327 PNP transistor (Q8)1 1N4004 silicon diode (D1)largest terminal block you can obtainwhich will fit. The larger ones havelarger wiring holes which makes iteasier to connect the speaker wires,Capacitors1 470µF 16VW electrolytic1 100µF 16VW electrolytic4 47µF 50VW NP electrolyticResistors (1%, 0,25W)1 220kΩ 2 22kΩ 1W2 56kΩ 1 2.2kΩ4 22kΩ 1 39Ω 0.5W (RX)Extra parts for built-in version1 BD649 NPN transistor (Q9)1 13V 0.5W or 1W zener diode(ZD1)1 100µF/100VW electrolyticcapacitor1 2.7kΩ 1W resistor1 220Ω 5W wirewound (RY; seetext)1 U-shaped TO-220 heatsink(Altronics Cat H-0502 or equiv).particularly if you are using heavygauge cables.Note that we have shown a resistorin series with the supply from theApril 1997 59Bridged Amplifiers In Car Audio SystemsFig.6: this is the wiringdiagram for the bridgedversion of the ULP, asshown in Fig.3.MANY HIGH-POWERED amplifiers in cars operate in bridgedmode and they are often run at highpower for extended periods. When theyfail, the speakers are just as likely to bedamaged as the speakers in a homestereo system. And the possibility of afire is just as high. So to protect valuable loudspeakers in cars, the ULP isa wise investment.You will need one ULP for each stereoamplifier and one for each bridgedamplifier. In each case, the ULP canbe powered directly from the +12Vbattery line.The circuit for this bridged amplifierversion is shown in Fig.3 while thewiring diagram is shown in Fig.6.plugpack. It is marked RX on Fig.4. Ifyou use a 9V plugpack, this resistorshould not be necessary. However,the unloaded voltage of a typical 12VDC plugpack can easily be +15V oreven higher and that could cause anincrease in power dissipation in therelay. Therefore, the series resistor isnecessary. We suggest that RX be a 39Ω0.5W resistor. If the plugpack voltage ishigher still, increase RX to 47Ω.TestingWhen all the wiring is complete, itis time for a power test. Do not connect any wires from your speakers oramplifier at this stage. Just connectthe plugpack and apply power. Therelay should close after a short delayof about two seconds. If that happens,you are almost home and hosed.Next, you can simulate a fault condition with a 6V or 9V battery (or eventwo 1.5V cells in series). Connect thebattery across each of the inputs inturn, first with one polarity and thenthe other. In each case, the relay shouldimmediately open and then close assoon as the battery is removed.60 Silicon ChipFig.7: here is the full size etching pattern for the PC board.If you strike trouble, switch off andcheck the circuit for errors. Normally,you can expect the unit to work as soonas you switch it on so now it shouldbe merely a matter of wiring the unitin series with your loudspeakers andthen you can rest easy.Fig.5 shows the wiring of the builtin version. This is the same as for Fig.4except that the regulator componentsinvolving transistor Q9 are included.Note that Q9 is mounted on a U-shapedheatsink.In addition, if the amplifier’s DCsupply is above 40V, it will be necessary to connect an external 5W wirewound resistor (RY) in series with thecollector of Q9. This resistor is shownon Fig.5 and a table of values is shownon Fig.2. For example, if the amplifier’sDC supply is around 60V, resistor RYSCshould be 220Ω 5W.SILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Rod Irving Electronics Pty LtdSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:Rod Irving Electronics Pty LtdSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Rod Irving Electronics Pty LtdSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:Rod Irving Electronics Pty LtdSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Rod Irving Electronics Pty LtdTrain controller formodel railway layoutsThis easy-to-build Train Controller will givefull, realistic control of your model trains.One control provides full reverse to fullforward speed. The circuit provides inertiaand a brake switch and has automaticoverload protection.By RICK WALTERSThe big virtue of this new TrainController is its single knob control.The one throttle knob gives full reversespeed when it is fully anticlockwiseand full forward speed when it is fully clockwise. And when the knob iscentred, the train is stopped.This simple throttle control doesaway with the need for a forward/66 Silicon Chipreverse switch or a relay and thusreduces the possibility of derailmentswhich can damage expensive modelrolling stock. This is especially thecase if derailed rolling stock falls tothe floor!What is the problem with a forward/reverse switch or relay? Surely theyare simple enough and are reliable?Well, yes they are but it is amazinghow many people driving model trainsoperate the forward/reverse switch bymistake; it is quite easily done. And ifthe train is going at a fair pace, throwing it into reverse often just derailseverything, which doesn’t do a lot forrealistic operation (to say nothing ofthe possibility of damage).With this new Train Controllerthough, if you have the train goingforward and decide to throw it intoreverse by rotating the throttle knobquickly to full anticlockwise, thereis no drama. The train slows downsmoothly by virtue of the built-ininertia, comes to a stop and thenaccelerates equally smoothly in theother direction.Oh, and there is another virtue innot having a forward/reverse switch.For one reason or another, many peo-Fig.1: the circuit is essentially a combination of two complementary emitterfollowers controlled by the throttle potentiometer VR1. Overload protection isprovided by Q3 and Q4. These monitor the track current through the two 0.47Ωresistors. The complementary design does away with the need to include aforward/reverse switch.ple have trouble wiring them up correctly!Other features of the controller arepreset trimpots for maximum forwardand maximum reverse speed and atrimpot for adjusting the degree ofbraking; you can have it really swiftor more leisurely.Actually, if the brake is applied tostop the train without rotating thecontrol knob to the centre position, thetrain will stop as you would expect itto. But if the brake is then switched off,the train will gradually pull away andaccelerate until it reaches the previousspeed set on the control knob.Finally, although this is an “unseen”feature, the Train Controller has automatic overload protection. So if aloco derails or someone inadvertently(or deliberately) shorts out the track,the Train Controller will take care ofthe overload and once the short isremoved, normal operation will beinstantly restored.We’ve built our prototype into aplastic case, as shown in the photosbut we assume that many modellingenthusiasts will build the controllerunderneath their layout and will maketheir own control panel.Circuit operationThe complete circuit of the TrainController is shown in Fig.1. It isvirtually two speed control circuitsin one. For forward speed operation,transistor Q1 feeds voltage to thetrack while for the reverse operation,transistor Q2 does the work. It is thisscheme which allows us to do awaywith the forward/reverse switch.This controller works by feedingpure DC to the track. It does not usepulsed DC or unsmoothed DC. Whilethese other forms can give more reliable loco operation when the trackor the loco wheels are dirty, pure DCresults in the quietest operation of theloco motor. For some modellers this isa most important point.A transformer with a centre-tapped18V winding (ie, 9V a side) feeds abridge rectifier (BR1) and two 4700µF25VW capacitors to provide balancedsupply rails of ±12V (nominal). Asshown, the +12V rail feeds the collector of NPN Darlington power transistor Q1, while the -12V rail feeds thecollector of PNP Darlington powertransistor Q2.Trimpot VR2 is connected acrossthe +12V rail to provide the maximumforward speed setting while VR3 isconnected across the -12V rail. Thewipers of these two trimpots thenfeed each end of the throttle potentio–meter, VR1.Now let us see what happens whenthe throttle knob is rotated clockwisefrom its centre setting. Let’s also consider that switch S1 is set to the “Run”position. As we rotate the throttlecontrol clockwise, the voltage pickedoff by the wiper will rise accordinglyand it will charge the 4700µF capacitorvia the 470Ω series resistor.After a short delay, caused by thecharging of the 4700µF capacitor, thevoltage at the base of transistor Q1 willbe high enough to turn it on. Fromthere on, as Q1’s base voltage rises, itwill act like an emitter follower, reproducing the voltage fed to its base at theemitter, less the base-emitter voltageof about 1.3V.So if the base voltage to Q1 is +6.7Vfor argument’s sake, the voltage acrossthe track will be close to +5.4V. If aloco is connected across the track, itApril 1997 67Fig.2: the component overlay for the TrainController. Secure the mains wiring with cableties so that the leads cannot move if one comesadrift. The mains terminal block is secured usinga nylon screw and nut and all exposed mainsterminals are covered with heatshrink tubing.68 Silicon Chipwill be running in the forward direction.If the throttle control is now rotatedin the reverse direction, the 4700µFcapacitor is discharged via the 470Ωresistor and the wiper of VR1. As thevoltage across the 4700µF capacitorgoes below ground, the voltage at thebase of transistor Q2 will be sufficientto turn it on, while the same voltageapplied to the base of Q1 will turn itoff.Q2 now acts like an emitter follower,reproducing the negative volt–agesat its base, at the emitter, less thebase-emitter voltage of about 1.3V. Soif the base voltage is -6.7V under thesame argument, the voltage across thetrack will be close to -5.4V and theloco will be running in the reversedirection.BrakingWhen the brake switch is turnedon, the 4700µF capacitor is dischargedthrough the 470Ω resistor and thebrake trimpot VR4. The time it takesto discharge the capacitor and hencethe time it takes for the train to cometo a stop is determined by the settingof VR4. When the brake is switchedoff, the 4700µF capacitor will slowlycharge up again to the voltage on thewiper of VR1 and the train will eventually resume the speed set before thebrake was applied.The two Darlington power transistors (Q1 & Q2) are mounted on a U-shapedheatsink, as shown here. Note that Q2 requires an insulating washer & bush(see Fig.3 below).Short circuit protectionOne of the features of the circuitis short circuit protection and thisis provided by transistors Q3 andQ4. Q3 monitors the current throughthe 0.47Ω emitter resistor associatedwith Q1. If the emitter current of Q1rises above about 1.3A, the resultingvoltage across the 0.47Ω resistor willbe sufficient to bias Q3 on. This willcause Q3 to shunt base current awayfrom Q1, throttling it back.If the emitter current tends to risefurther, Q3 will turn on harder, shunting even more base current away fromQ1 and throttling it back further.A similar process applies to Q2 andQ4. Q4 monitors the emitter currentof Q2 via the associated 0.47Ω resistor.We have not included a warningdevice to indicate an overload as itshould obvious when the train hasstalled that something is wrong. Don’tignore the short as the conducting transistor will get very hot and the heatsinkFig.3: details of the heatsink mounting for Q1 & Q2. Note that Q2must be electrically isolated from the heatsink.temperature will rise rapidly. In otherwords, the protection feature is reallyonly intended to cope with short termoverloads.fiers to develop positive and negativeDC rails.We’ll talk more about these optionslater.Power supply optionsBuilding the controllerThe circuit of Fig.1 shows that twopossible power transformer connections can be used. The first option isfor a centre-tapped transformer, asdescribed above. The second optionis to use a single-winding 12V transformer. Whichever transformer isused, the circuit is unchanged. Whenthe single winding transformer is used,the bridge rectifier acts like separatepositive and negative halfwave recti-The Train Controller is housed ina plastic case measuring 203 x 68 x158mm. The components are mountedon a PC board measuring 89 x 120mmand coded 06104971.Fig.2 shows the wiring details forthe Train Controller. Begin construction by carefully checking the PC boardfor shorted tracks or breaks. Repairany defects before proceeding further.Mount the parts on the PC boardApril 1997 69Fig.4: this is the full-size etching pattern for the PC board. Check your boardcarefully for etching defects by comparing it with this pattern and fix anyproblems before installing the parts.exactly as shown, taking care to ensurethat all polarised parts are correctlyconnected.The two Darlington power transistors Q1 & Q2 are mounted on acommon U-shaped heatsink. Q1,the BDV65B, is mounted directly onthe heatsink while Q2, the BDV64B,is mounted using a mica insulatingwasher. By not using an insulatingwasher we get improved heat dissipation for Q1. Note that since theheatsink is electrically connected tothe collector of Q1, it will be “live” at+12V or whatever is the value of thepositive supply rail.Both transistors should be installedwith thermal compound applied totheir mounting surfaces. Fig.3 showshow the heatsink is effectively sandwiched between the transistors andthe PC board.When you have installed bothtransistors on the heatsink, use yourmulti–meter (switched to a high Ohmsrange) to check that the transistor col-lectors are isolated from each other.You can solder all the externalconnections directly to the PC boardor you can connect to solder stakesif you prefer. Use different colouredhook-up wire for the various off-boardconnections. It makes it a lot easierto troubleshoot the unit if it does notwork when you first fire it up.The transformer is screwed directlyto the base of the case and one mounting foot is earthed back to the Earthwire of the mains power cord.As discussed previously, you havetwo options for the power transformer.If you only have a small layout andwill be using one loco at a time, atransformer with a single 9V to 15V1A secondary winding can be used butif you intend to have a larger layout,it is worthwhile going for the largercentre-tapped transformer.You could also use a ±12V DC powersupply to feed the controller. If youdo this you can fit 470µF capacitorsinstead of the more expensive 4700µFunits specified. The PC board overlayallows for both sizes of capacitor.Note that whichever supply optionis used, the inertia capacitor must be4700µF.The front panel has only the mainthrottle control and brake switchmounted on it. Hence you will onlyneed to drill two holes for these components before they can be wired.On the back panel, you will need todrill holes for the two-way insulatedterminal block for the output leads, themains switch and the cordgrip grommet for the power cord. We used a snapPARTS LIST1 PC board, code 09104971, 120x 89mm1 mains transformer 18V CT 60VA,Altronics M-2165 or equivalent1 plastic case, 203 x 68 x 158mm1 3-core mains flex with 3-pin plug1 cordgrip grommet to suit mainsflex1 SPDT switch (S1)1 240VAC SPST snap-fitting rockerswitch (S2)1 large knob to suit VR11 U-shaped heatsink, DSE typeH-3401 or equivalent1 BDV64B mounting kit2 2-way mains terminal blocks70 Silicon Chip1 3mm x 10mm nylon screw & nut(to secure mains terminal block)4 6PK x 6mm screws3 3mm x 10mm bolts3 3mm nuts3 3mm shakeproof washers1 6A bridge rectifier (BR1)Semiconductors1 BDV65B NPN Darlingtontransistor (Q1)1 BDV64B PNP Darlingtontransistor (Q2)1 BC548 or BC338 NPN transistor(Q3)1 BC558 or BC328 PNP transistor(Q4)Resistors (0.25W, 1%)2 4.7kΩ 2 470Ω2 1.5kΩ2 0.47Ω 5W wirewoundCapacitors1 4700µF 50WV PC electrolytic2 4700µF 25WV PC electrolytic1 .0068µF 3kV ceramicPotentiometers2 10kΩ trimpots (VR2,VR3)1 5kΩ linear potentiometer (VR1)1 1kΩ trimpot (VR4)The Train Controller is built into astandard plastic instrument case. Makesure that the mains cord is firmlyanchored and that the mains wiring iscorrectly installed.fitting power switch which requires arectangular cutout. This can be easilymade in the plastic panel by drillinga suitable hole and then filing it outto the desired size.The 3-core mains flex is passedthrough the cordgrip grommet whichanchors it. The Active wire is terminated directly to one side of the mainson/off switch (S2) while the Neutralwire is terminated to a 2-way terminal block. The Active wire from theother side of the mains switch is alsoterminated at the terminal block. Thisblock, which is secured using a nylonbolt, also terminates the primary wiresfrom the transformer.Note that the .0068µF 3kV suppression capacitor is wired directly acrossthe mains switch S2. All connectionsto this switch should be fitted withheatshrink sleeving to prevent anychance of accidental contact.When all the wiring is complete, goover your work thoroughly and crosscheck it with the circuit and wiringdiagrams of Figs.1 & 2.TestingApply power and check the positiveand negative supply rails. They shouldbe roughly the same (absolute value)and will typically be about ±15V fora nominal 18V centre-tapped transformer, with no load connected to theoutput. This will drop when loaded.Now rotate VR1 fully clockwise andcheck that the output voltage graduallyrises towards the positive supply rail.We would expect a maximum value ofabout +13V, again with no load. Youcan tweak this value to whatever valueyou finally decide upon by adjustingtrimpot VR2.Similarly, rotate VR1 fully anticlockwise and check that the outputvoltage builds gradually to the valueof the negative supply rail. We wouldexpect a value of around -13V, with noload. Again, you can set the maximumnegative value by adjusting trimpotVR3.There will be some interaction between these two trimpots but a coupleof tweaks should get them just right.VR4 can be set at any time to give arealistic braking distance.With these checks done, it is time torun a train. Connect the Train Controlto your layout (or a loop of track) andconfirm that you can control a locomotive smoothly. When VR1 is at itscentre setting, the loco should slowlycome to a stop.If you want to remove the inertiafeature you can omit the 4700µFelectrolytic capacitor connected to S1.Alternatively, if you want to reduce theinertia effect then make the capacitorsmaller (1000-2200µF). The enginewill now come up to speed quickerand brake quicker.SCApril 1997 71SILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.altronics.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.altronics.com.auSILICONCHIPIf you are seeing a blank page here, it ismore than likely that it contained advertisingwhich is now out of date and the advertiserhas requested that the page be removed toprevent misunderstandings.Please feel free to visit the advertiser’s website:www.altronics.com.auORDER FORMBACK ISSUESMONTHYEARMONTHYEARPR ICE EACH (includes p&p)TOTALAustrali a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10(airmail ). Buy 10 or more and get a 10% discount.Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89;Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues arecurrently i n stock.$AB INDERSPl ease send me _______ SILICON CHIP bi nder(s) at$A12.95 + $5.00 p&p each (Australi a only). N ot avail abl eelsewhere. Buy five and get them postage free.$ASUBSCRIPTIONS New subscription – month to start____________________________ Renewal – Sub. No.________________ Gift subscription GIFT SUBSCRIPTION DETAILSRATES (please tick one) 2 years (24 issues) 1 year (12 issues)Australia (incl. GST) $A135 $A69.50Australia with binder(s) (incl. GST)** $A159 $A83New Zealand (airmail) $A145 $A77Overseas surface mail $A160 $A85Month to start__________________Overseas airmail _____________________________ $A250 $A125**1 binder with 1-year subscription; 2 binders with 2-year subscriptionYOUR DETAILSYour Name_________________________________________________Message__________________________________________________Gift for:Name_________________________(PLEASE PRINT)Address___________________________________________________(PLEASE PRINT)Address___________________________________________________State__________Postcode_____________________________________________Postcode_____________Daytime Phone No.____________________Total Price $A __________Signature Cheque/Money Order Bankcard Visa Card Master Card______________________________Card No.Card expiry date________/________Phone (02) 9979 56449am-5pm Mon-Fri.Please have your credit carddetails readyORFax (02) 9979 6503Fax the coupon with yourcredit card details24 hours 7 days a weekMail order form to:ORReply Paid 25Silicon Chip PublicationsPO Box 139, Collaroy 2097No postage stamp required in AustraliaApril 1997 75VINTAGE RADIOBy JOHN HILLA look at signal tracing, Pt.1About 10 years ago, I drove away from a housein Melbourne with a car full of old radios andother gear. Back then I had no idea what goodbuying it all was for $200. At that stage of mycollecting career, I was quite unaware of thevalue of mid-1930s Radiolettes – and there weretwo of them in the boot when I drove off.one at that. It was a tuned type tracerand was called a “Healing DynamicSignalizer”, to quote the name on thefront panel. The old tracer appearedto be of early postwar manufacture.Coming into vintage radio with little or no experience can be a decideddisadvantage at times. In this instanceI had acquired quite a useful piece oftest equipment but I didn’t know whatit was and promptly forgot all about it.Apart from some very collectibleradio receivers, my haul also includedsome bound volumes of Radio andHobbies and a test instrument that Iassumed was a radio frequency RFgenerator.Only a few weeks earlier I had obtained a working RF generator whichwas in excellent condition. I thereforepaid little attention to this latest acquisition and it was placed in a darkcorner of a cupboard where it lived inGetting it going againforgotten limbo for nearly a decade.However, a recent visit to a collectorfriend jogged my memory when heshowed me his signal tracer. It lookedvery similar to the instrument I hadassigned to the cupboard many yearsago, so I checked it out as soon as Ireturned home.Sure enough, when my long forgotten “RF generator” was removed fromits hiding place, it turned out to be asignal tracer – and a reasonably goodThis is the front control panel of Healing signal tracer. The output socketsconnect to the speaker voice coil, while the X sockets allow an external coil tobe connected to extend the instrument’s range of frequencies.76 Silicon ChipIt was time for some restorationwork. There is not much point in having a signal tracer that doesn’t work.Restoring an old signal tracer isnot unlike restoring a simple radioreceiver. In fact, a signal tracer willreceive any strong local transmissionin a broadly tuned manner, havingmuch the same degree of selectivityas a crystal set.The Healing has a 6D6 RF amplifier,a detector which uses the diodes inthe first audio valve, two audio stagesemploying 6B6 and 6V6 valves, plus ahigh-tension DC circuit similar to mostvalve radios (the loudspeaker fieldcoil is used as a choke). The rectifieris a 5Y3.As the tracer was in almost completely original condition, its restoration was a simple matter of replacingthe paper and electrolytic capacitors,plus a few carbon resistors that hadgone high with age. All four tuningcoils were OK, likewise the powertransformer, the loudspeaker field coiland the output transformer.All four valves checked out as newand were in excellent condition. Thisis not surprising – a signal tracer is atest instrument, not a radio receiverand, as such, it would have had onlyintermittent use.Because of this, one would notexpect that the single gang tuning capacitor would need attention. Not so!The problem here was that thegang had been poorly mounted andthe alignment of the control shaft tothe front panel was out by severaldegrees. In fact, the alignment was sobad that the dial cursor was touchingthe panel on one side while there wasa 10mm gap on the other. Somethinghad to be done as the crooked cursorlooked terrible.Perhaps the reason for this poorlyinstalled tuning capacitor was the factthat the chassis was not jig-drilled toaccurately locate the mounting holes.Instead, the original holes had beenmarked out using a pencil and thesemarkings were still clearly visible.Unfortunately, the hole positions wereway out from where they should havebeen.To correct this misalignment problem, the mounting holes were elongated with a small round file and thetuning capacitor raised slightly usingwashers. The unit was then carefullyadjusted so that the control shaft wascentred in the dial aperture at rightangles to the front panel.But that was not the only problem.The general construction quality ofthe Dynamic Signalizer was dreadful.For example, many long screw threadshad been shortened with side cutters,which not only produced sharp edgesbut also made it difficult to removethe nuts. And connections to the frontpanel sockets were soldered to thethreads instead of to solder tags.On the other hand, the front controlpanel looks quite good. It is paintedblack, with most of the control markings stencilled on in white. The frequency range selector switch and thetuning dial are colour coded for theirrespective frequency bands in white,blue, green and red.The condition of the front panelpaint work was excellent and it responded well to a gentle rub downwith automotive cut and polishcompound. A couple of small barespots were touched up with a black“Texta” pen.One minor problem with the frontpanel was a hole of about 14mm diameter in the top right corner. Thissomewhat roughly drilled hole detracted from the panel’s otherwisegood appearance. This problem wassolved by fitting a green panel light,which tidied up that corner of theThis view shows the probe sockets (left), the range (or band) selector switch,and the audio and RF (radio frequency) gain controls. The painted-on panelmarkings are in very good condition for a 50-year old instrument.This under-chassis view shows the cluster of tuning coils and their associatedtrimmer capacitors. These coils are connected to the selector switch at left.panel quite nicely The original panellight was disconnected.Switching onWith the restoration almost complete, it was time to see if the oldSignalizer would work. At switch-onthe panel light lit up, as did the fourvalves. After about 15 seconds or soa quiet hum could be heard from thespeaker. All seemed well!The touch of a finger on the audiosocket produced a loud response fromthe speaker which was easily regulated by using the audio gain control.Similarly, touching a finger on theradio frequency (RF) socket broughtin a soft response from a local radiostation. Rotating the dial tuned in thestation and it responded to both theaudio and radio frequency gain controls.When checking the tracer’s tuningranges with an RF generator, it wasfound that the dial was not particularlywell aligned to the tuning capacitoron all four tuning ranges. This wascorrected by adjusting the tuningcoils.These coils are fitted with adjustable iron cores for aligning thelow frequency end of the range andtrimmers for adjustments at the highfrequency end. After completing theseApril 1997 77ment helps to slightly reduce HT consumption.These two minor circuit alterationscut back the high tension current byabout 6mA. While the field coil stillgets fairly warm, it runs much coolerthan before.Making the probeThe Signalizer’s tuning capacitor was repositioned by elongating the mountingholes and packing it with washers. The nuts on top of the chassis hold thetuning coils in place.A Rola 5-inch (125mm) electrodynamic loudspeaker is used in the signal tracer.Note the missing mounting washer and nut – typical of the very rough buildingquality evident throughout the instrument.simple alignment procedures, the diallined up quite accurately on all fourfrequency bands.The Healing Dynamic Signalizerwas just about ready for trials butthere was one remaining problem.After operating the unit for half anhour or so, the speaker field windingbecame uncomfortably hot. Field coilsshould operate at warm temperatures– not hot. For some reason or otherthe high tension current appeared tobe excessive.Substitute valves were tried one ata time but this failed to reduce theHT current. Sometimes a faulty valve78 Silicon Chipcan consume a lot more current thanit should.In order to reduce the HT current,the 150Ω back-bias resistor for the 6V6output valve was increased to 250Ω.In addition to this, a 300Ω resistor wasplaced between the RF gain controlpotentiometer and the cathode of theRF valve.Because the RF gain control is, infact, a variable cathode resistor, itsupplies no resistance (and thus nobias) at all when it is fully on (hencethe 300Ω cathode resistor). Backingoff the RF gain control to zero whenusing the audio section of the instru-All that remained at this stage wasto make up some suitable probes anda chassis lead. But this simple projectturned out to be more time consumingthan expected.When one lives in a small countrytown, shopping for items such asbanana plugs, shielded wire, and RFprobes can prove a difficult task. Soit is usually a case of improvise withwhatever is available at home or travel80km to a major electronics dealer forsuitable supplies.The chassis lead was no trouble tomake. With an old style banana plugat one end and an alligator clip at theother, it did not take long to complete.The lead itself was made of some moderately heavy, yet fairly flexible, plasticcovered multi-strand wire.Unfortunately, I couldn’t find a suitable length of shielded wire to makethe audio lead. All that was availablewas a single length of the same wireused to make the chassis lead. Andnon-shielded audio leads are not usually recommended.It was decided to make up a dualpurpose RF/AF probe using un-shielded wire. The probe would allow thetracer to be tested and a shielded leadcould be fitted at some stage in the future. The idea behind the dual-purposestrategy was that the probe could bechanged from RF to AF at the flick ofa switch.A suitable RF probe for a signaltracer, such as the Dynamic Signalizer, requires a small high-voltagecapacitor of 3-5pF to be mounted inthe probe tip itself. This is necessaryto prevent the probe lead from loadingthe receiver’s RF circuits and detuningthem.Unfortunately, I didn’t have asuitable capacitor available and soI decided to make one by twistingtwo short lengths of enamel-coveredcopper wire together. With the aid ofa capacitance meter and a high voltagemegohmmeter, the home-made 4pF1000V capacitor passed all tests.The probe was made up by installing the home-made capacitor and theP.C.B. Makers !If you need:• P.C.B. High Speed Drill• P.C.B. Guillotine• P.C.B. Material – Negative orPositive acting• Light Box – Single or DoubleSided – Large or Small• Etch Tank – Bubble or Circulating– Large or Small• U.V. Sensitive film for Negatives• Electronic Components and• The restored chassis cleaned up quite well, as this top view shows. The valves,from left, are: 5Y3, 6V6, 6B6 and 6D6.• Equipment forTAFEs, Colleges and SchoolsFREE ADVICE ON ANY OFOUR PRODUCTS FROMDEDICATED PEOPLE WITHHANDS-ON EXPERIENCEPrompt and Economical DeliveryKALEX40 Wallis Ave E. Ivanhoe 3079Ph (03) 9497 3422FAX (03) 9499 2381• ALL MAJOR CREDITCARDS ACCEPTEDTRANSFORMERS• TOROIDAL• CONVENTIONAL• POWER • OUTPUT• CURRENT • INVERTER• PLUGPACKS• CHOKESThe fully-restored unit retains its original cabinet finish. The unit should proveinvaluable for tracing problems in old radio receivers.switch in a “Texta” pen body. Thecompleted probe was then testedwith an ohmmeter. When the switchwas in the RF probe position, the capacitor was switched into circuit andthe ohmmeter indicated open circuit.Conversely, with the switch in theAF probe position, the capacitor wasshorted and the meter responded accordingly.All that remained was to try theprobe with the Signalizer to see if itworked properly. As an RF probe, theunit functioned perfectly. But whenswitched to the AF position andplugged into the audio socket, the humwas overpowering.However, because the audio sectionof the Signalizer has two stages, it isnot necessary to operate the gain control at full on; a setting of 20 on a scaleof 100 is where the instrument worksbest. At that level of amplificationthe hum is barely audible and I won’tbother to make another probe with ashielded lead.So the old Healing Dynamic Signalizer is now fully operational. Nextmonth we will try it out and tracethrough the circuit of a receiver. SCSTOCK RANGE TOROIDALSBEST PRICESAPPROVED TO AS 3108-1994SPECIALS DESIGNED & MADE15VA to 7.5kVATortech Pty Ltd24/31 Wentworth St, Greenacre 2190Phone (02) 642 6003 Fax (02) 642 6127April 1997 79PRODUCT SHOWCASEEasy-start battery chargerfrom AltronicsThis clever device should largelyeliminate the need to carry jumpercables to start your car or somebodyelse’s. Called the “Easy-Start” it is anin-cable battery charger which plugsinto the cigarette lighter sockets of bothcars. The Easy-Start draws currentfrom the car with the good battery,steps up the voltage a little and feedsit to the cigarette lighter socket of thecar with the dead battery.After being connected for five minutes, the manufacturer claims thatmost cars with dead batteries shouldhave received enough charge to beable to start. Whether that is true ornot in most cases, we like the conceptbecause it eliminates the use of jumpercables. Jumper cables are potentiallydamaging to any car with an enginemanagement computer and most carmakers warn against their use. Usingjumper cables also brings the possibility of battery explosions and seriousdamage to the cars concerned.Our examination of the Easy-Startreveals that it employs a switchmodestep-up circuit and probably chargesat somewhere in the region of fiveamps, based on the appearance of theFluke 36clamp meterThe Fluke 36 measures true RMScurrent and voltage, DC current andvoltage, resistance and continuityand shows readings on a 2000count liquid crystal display. Rangesare 0-600A AC, 0-1000A DC, 600Vand 0-200Ω. The continuity beeperfunction operates for resistances ofless than 30Ω. The Fluke 36 has amaximum reading hold functionfor checking inrush currents onmotors or the maximum load ona circuit.Designed to UL, CSA and TUV,the Fluke complies with IEC 1010safety standards. It comes withFluke Hard Point test leads, aprotective soft carrying case, a 9Vbattery and is covered by a one-yearwarranty.80 Silicon ChipFor more information, contactObiat Pty Ltd, 129 Queen Street,Beaconsfield, NSW 2014. Phone(02) 9698 4111; fax (02) 9699 9170.components and the gauge of the connecting cables. No performance datais given on the packaging.When the Easy-Start is first connected, a green LED is lit and then when itis charging the dead battery, three redLEDs light in sequence. The overallcable length is 5.5 metres.The whole package is much easierand safer to use than jumper cablesand should be very popular, particularly with drivers who have a secondvehicle which is not driven often andtherefore prone to the occasional deadbattery.The Easy Start is available fromAltronics in Perth or any Altronicsreseller. It is presently available atan introductory price of $39.95. (CatA-0295).Low cost handheldprogrammerStag Programmers has launched theP301, a full-featured handheld portable programmer which includes a PCWindows and DOS software packagefor full control via a PC. The StagP301 also has wireless communicationwith a host PC through an infraredIrDA interface, as well as an RS232port.The P301 provides programming forup to 32-bit structures based on 8-bitdevices through a single wide bladesocket capable of accommodating 8,24, 28 and 32-pin DIP packages witheither 0.3-inch or 0.6-inch pitch. Itwill program EPROMs, EEPROMs,serial EEPROM s and Flash/ CMOSPROMs. Adapters are also available forPLCC, TSOP and SOIC devices.The device support library is fullyupdatable and is held in non-volatile63VA transformeris wiredThis 12V 60VA transformer wasdesigned for use with halogenlighting in homes.Fully encapsulated and enclosed, it is intended to be mounted inthe ceiling space. However, it couldbe used in almost any applicationwhere a continuously rated 12V63VA transformer is required. Itsoverall dimensions are 207 x 48x 42mm.flash memory which means that noadditional library support ROMs arerequired.Device selection is menu driven,either by the manufacturer’s part nameor automatically via the electronic IDto select the programming algorithmfor the device in the socket. Stag alsomakes device library updates availableA particular attraction of thetransformer is that it comes fittedwith a 2-core power flex and amoulded 2-pin power plug. Thetransformer is protected againstoverloads by a thermal cutoutwhich is in series with the primarywinding. The secondary connection is via two screw terminalswhich are shrouded by a plasticcover.The transformer is availablefrom all Jaycar Electronics storesat $24.95 (Cat. MP-3050).free-of-charge on its Web site.The unit is fitted with 128Kb ofRAM as standard, expandible to 512Kbor 1Mb and devices are programmedin blocks if the RAM fitted is smallerthan the device. 8-bit, 16-bit and 32bit structures are supported and areautomatically handled by “Interlace2”, Stag’s method of splitting andshuffling data without the interventionof the user.Either battery or mains-poweredfor both portable and desktop applications, the P301 features a 4 x 20character alphan umeric reflectivesupertwist LCD and 23 dedicatedfunction and cursor keys. The P301’sbattery can either be trickle chargedusing the supplied mains adapter orboost charged using the optional offline charging unit.For more information, call EmonaInstruments on (02) 9519 3933 or faxon (02) 9550 1378.Thin-film powerchip resistorsNew thin-film power chip resistorsrecently introduced by Philips areamong the first to offer the same pulsepower capability as leaded products.As well, the new PRC202 resistorscan handle higher pulse surges andsignificantly higher current densitiesthan equivalent thick-film types.The resistors are supplied in thesame package (ie, 1218) as the Philipsthick-film PRC201 series. This is thesame size as the standard 1812 packagebut with the terminations on the longerside. The PRC201 range has alreadydemonstrated that this significantlyimproves heat transfer and increasesthe strength of the solder joint. It alsoreduces stresses and hence improvesreliability.Nearest equivalents to the newPRC202 thin-film series offering comparable continuous power handlingTHE “HIGH” THAT LASTS IS MADE IN THE U.S.A.Model KSN 1141The new Powerline series of Motorola’s2kHz Horn speakers incorporate protectioncircuitry which allows them to be used safelywith amplifiers rated as high as 400 watts.This results in a product that is practicallyblowout proof. Based upon extensive testing,Motorola is offering a 36 month money backguarantee on this product should itburn out.Frequency Response: 1.8kHz - 30kHzAv. Sens: 92dB <at> 1m/2.83v (1 watt <at> 8Ω)Max. Power Handling Capacity: 400WMax. Temperature: 80°CTyp. Imp: appears as a 0.3µF capacitorTypical Frequency ResponseMOTOROLA PIEZO TWEETERSAVAILABLE FROM:DICK SMITH, JAYCAR, ALTRONICS ANDOTHER GOOD AUDIO OUTLETS.IMPORTING DISTRIBUTOR:Freedman Electronics Pty Ltd, PO Box 3, Rydalmere NSW 2116. Phone: (02) 9638 6666.April 1997 81capability are available only in thelarger 2512 size.The new resistors are availablein values from 0.1Ω to 100Ω withtolerances down to ±1% and withtemperature coefficients of less than200 ppm for values between 0.1Ω and1Ω, and 50 ppm for values between 1Ωand 100Ω. They are supplied in blistertape and can be placed by all standardsurface-mount assembly machines.For further information, contactPhilips Components, 34 WaterlooRoad, North Ryde, NSW 2113. Phone(02) 9805 4479; fax (02) 9805 4466.125W 12VDC to230VAC inverterThere are quite a few different 12Vto 240VAC inverters on the marketbut few are as compact and as neatlypackaged as this one. It comes in aneat extruded aluminium case whichfunctions as the heatsink for the internal electronics. It has a single 3-pinAC outlet on the top and a short cablefitted with a cigarette lighter plug forthe DC input. There are no switches–you just plug it in and it goes.Overall dimensions of the inverterKITS-R-USRF ProductsFMTX1 Kit $49Single transistor 2.5 Watt Tx freerunning 12v-24V DC. FM band88-108MHz. 500mV RMS audiosensitivity.FMTX2A Kit $49A digital stereo coder usingdiscrete components. XTALlocked subcarrier. Compatiblewith all our transmitters.FMTX2B Kit $493 stage XTAL locked 100MHzFM band 30mW output. Austpre-emphasis. Quality specs.Optional 50mW upgrade $5.FMTX5 Kit $98Both a FMTX2A & FMTX2B on 1PCB. Pwt & audio routed.FME500 Kit $499Broadcast specs. PLL 0.5 to 1watt output narrowcast TX kit.Frequency set with Dip Switch.220 Linear Amp Kit $4992-15 watt output linear ampfor FM band 50mW input.Simple design uses hybrid.SG1 Kit $399Broadcast quality FM stereocoder. Uses op amps withselectable pre-emphasis.Other linear amps and kitsavailable for broadcasters.82 Silicon Chipare 128mm wide, 122mm long and53mm high.There are three LEDs on the top panel – one indicates that it is operating,while the other two indicate whetherthe battery is good or low.The output waveform is a modifiedPO Box 314 Blackwood SA 5051Ph 0414 323099 Fax 088 270 3175AWA FM721 FM-Tx board $19Modify them as a 1 watt opNarrowcast Tx. Lots of good RFbits on PCB.AWA FM721 FM-Rx board $10The complementary receiverfor the above Tx. Full circuitsprovided for Rx or Tx. Xtalshave been disabled.MAX Kit for PCs $169Talk to the real world from aPC. 7 relays, ADC, DAC 8 TTLinputs & stepper driver withsample basic programs.ETI 1623 kit for PCs $6924 lines as inputs or outputsDS-PTH-PCB and all parts. Easyto build, low cost.ETI DIGI-200 Watt Amp Kit $39200W/2 125W/4 70W/8 from±33 volt supply. 27,000 builtsince 1987. Easy to build.ROLA Digital Audio SoftwareCall for full information aboutour range of digital cart players & multitrack recorders.ALL POSTAGE $6.80 Per OrderFREE Steam BoatFor every order over $100 receiveFREE a PUTT-PUTT steam boat kit.Available separately for $19.95,this is one of the greatest educational toys ever sold.square wave type and it is silent in operation. We tested the unit by pluggingit into a cigarette lighter socket andthen measured the RMS output voltagewhen the unit was driving a standardlamp fitted with two 60W globes. Witharound 12.6V, it delivered 200V withTeac 12-speed CD-ROMTeac Corporation in Japan has released a12-speed CD-ROM drive, the CD-512. The CD-512features a data transfer rate of 1.8Mb/s and a choiceof ATAPI (CD-512E) or SCSI (CD-512S) interface,MW DMA Mode 2 and PIO Mode 4 to minimiseCPU utilisation (CD-512E), motorised tray loading, an MTBF of 100 000 hours (10% duty cycle),horizontal or vertical mounting and compliancy toWindows 95 andWindow NT.The CD -512has an industrystanda rd 5.25inch format.The front panelscontrols includean eject button, astereo mini jack and a thumbwheel volume control.There is also an emergency CD release mechanismwhich can be used to release a CD if there is nopower available.This drive is compatible with the CD-DA, CDROM (mode 1, mode 2), CD-ROM XA mode-2 (form1, form 2) Multi Session Photo CD, CD-I, Video-CD,CD Plus and Enhanced CD disc formats.For further information, PO Box 25, Bangor NSW2234. Phone (02) 9749 2633; fax (02) 9749 2152.one 60W globe on while with two 60Wglobes the voltage dropped to 140V.At just below 12.6V, the low batterylight comes and the unit emits a loudwhistle.Having been warned, we started themotor and the battery voltage rapidlycame up to 14V. At this point, it woulddeliver 200V with one or two 60Wlamps on.The unit should be suitable for manyapplications, driving mains voltageequipment where no 240VAC is available. It is available from Altronics inPerth or any Altronics reseller. It ispriced at $140.00 (Cat. M-8105).PCB POWERTRANSFORMERS1VA to 25VAManufactured in AustraliaHarbuch Electronics Pty Ltd9/40 Leighton Pl. HORNSBY 2077Ph (02) 9476-5854 Fx (02) 9476-3231Philips “talkingremote” finds itselfWith Philips hifi stereo video cassette recorders (models VR656 andVR856), you will always be able to findyour remote control. No longer willyou need to throw a tantrum or glareat the children whenever the remotecontrol for your VCR or TV has beenmisplaced.The new Remote Locator videocassette recorders from Philips “call”the remote device with a “beep, beep”when you press the power button onthe deck. And once you’ve found theremote for the VCR, there’s a goodchance you won’t have to worry aboutthe one that’s missing from the TV. ThePhilips remote is multi-branded andmulti-functional, which means it canoperate most TVs as well.Both units are 6-head, hifi stereoVCRs with Incredible Picture(TM) chipcircuitry to improve the picture quality. The VR856 model is Multisystemcompatible which means it can recordand play back tapes from the varioussystems in use around the world.G-Code makes programming a cinchBassBox®Design low frequency loudspeaker enclosuresfast and accurately with BassBox® software.Uses both Thiele-Small and Electro-Mechanicalparameters with equal ease. Includes X. Over2.03 passive crossover design program.and the new “Turbo Drive Mechanism” gives faster access to all play,fast forward and rewind functions.Other features include audio andvideo front input sockets, digital audiotracking, widescreen-compatible playback, tape counter, NTSC playback(Model VR656 only), PAL, NTSC andSECAM record and playback (ModelVR856 only).Recommended retail prices are $769for the VR656 and $989 for the VR856.For further information, contact yournearest Philips retailer.With component test speeds saidto be several times faster than otherautomatic test equipment currentlyavailable, the 5200 Power MDA excels in situations where high faultcoverage and very high throughput areimportant. In practice, using the 5200Power MDA results in more than twicethe normal throughput in a typicalmanufacturing setup. The Windowsbased software ensures test programsand fixture designs can be quicklydeveloped manually or from CAD data.For further information, contactMarconi Instruments, 1/38 South St,Rydalmere, NSW 2116. Phone (02)9638 0800.SCManufacturing defectsanalyserThe new 5200 Power ManufacturingDefects Analyser (MDA) from Marconi Instruments is designed to meetthe needs of high volume PC boardmanufacturers. The 5200 Power MDAincludes vectorless testing (Marconi’sQ-test is configured as standard),Boundary-Scan and new “power-on”test techniques. Comprehensivesoftware for program generation anddebug tools ensure ease of use.$299.00Plus $6.00 postage.Pay by cheque, Bankcard, Mastercard Visacard.EARTHQUAKE AUDIOPH: (02) 9949 8071 FAX: (02) 9949 8073PO BOX 226 BALGOWLAH NSW 2093April 1997 83Silicon ChipBack IssuesSeptember 1988: Hands-Free Speakerphone; Electronic FishBite Detector; High Performance AC Millivoltmeter, Pt.2; BuildThe Vader Voice.Converter For Car Amplifiers; Wiper Pulser For Rear Windows;4-Digit Combination Lock; 5W Power Amplifier For The 6-MetreAmateur Transmitter; Index To Volume 3.January 1991: Fast Charger For Nicad Batteries, Pt.1; HaveFun With The Fruit Machine; Two-Tone Alarm Module; LCDReadout For The Capacitance Meter; How Quartz CrystalsWork; The Dangers of Servicing Microwave Ovens.February 1991: Synthesised Stereo AM Tuner, Pt.1; ThreeInverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To DesignAmplifier Output Stages.Wire Antenna Tuner For 6 Metres; Phone Patch For RadioAmateurs, Pt.2.April 1989: Auxiliary Brake Light Flasher; What You Need toKnow About Capacitors; 32-Band Graphic Equaliser, Pt.2; TheStory Of Amtrak Passenger Services.March 1990: Delay Unit For Automatic Antennas; WorkoutTimer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2;Using The UC3906 SLA Battery Charger IC; The AustralianVFT Project.May 1989: Build A Synthesised Tom-Tom; Biofeedback MonitorFor Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad.April 1990: Dual Tracking ±50V Power Supply; Voice-OperatedSwitch (VOX) With Delayed Audio; 16-Channel Mixing Desk,Pt.3; Active CW Filter; Servicing Your Microwave Oven.July 1989: Exhaust Gas Monitor; Experimental Mains HumSniffers; Compact Ultrasonic Car Alarm; The NSW 86 ClassElectrics.June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies;Speed Alarm For Your Car; Fitting A Fax Card To A Computer.September 1989: 2-Chip Portable AM Stereo Radio (UsesMC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2.July 1990: Digital Sine/Square Generator, Pt.1 (Covers0-500kHz); Burglar Alarm Keypad & Combination Lock; SimpleElectronic Die; Low-Cost Dual Power Supply; Inside A CoalBurning Power Station.October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFetPreamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio,Pt.2; A Look At Australian Monorails.November 1989: Radfax Decoder For Your PC (Displays Fax,RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2;2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc DriveFormats & Options; The Pilbara Iron Ore Railways.December 1989: Digital Voice Board; UHF Remote Switch;Balanced Input & Output Stages; Operating an R/C Transmitter; Index to Vol. 2.January 1990: High Quality Sine/Square Oscillator; ServiceTips For Your VCR; Phone Patch For Radio Amateurs; ActiveAntenna Kit; Designing UHF Transmitter Stages; A Look AtVery Fast Trains.February 1990: A 16-Channel Mixing Desk; Build A High QualityAudio Oscillator, Pt.2; The Incredible Hot Canaries; RandomAugust 1990: High Stability UHF Remote Transmitter; UniversalSafety Timer For Mains Appliances (9 Minutes); Horace TheElectronic Cricket; Digital Sine/Square Generator, Pt.2.September 1990: Low-Cost 3-Digit Counter Module; SimpleShortwave Converter For The 2-Metre Band; the Bose LifestyleMusic System; The Care & Feeding Of Battery Packs; How ToMake Dynamark Labels.October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; SurfsoundSimulator; DC Offset For DMMs; NE602 Converter Circuits.November 1990: How To Connect Two TV Sets To One VCR;Build An Egg Timer; Low-Cost Model Train Controller; 1.5VTo 9V DC Converter; Introduction To Digital Electronics; BuildA Simple 6-Metre Amateur Band Transmitter.December 1990: The CD Green Pen Controversy; 100W DC-DCMarch 1991: Remote Controller For Garage Doors, Pt.1;Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner,Pt.2; Multi-Purpose I/O Board For PC-Compatibles; UniversalWideband RF Preamplifier For Amateur Radio & TV.April 1991: Steam Sound Simulator For Model Railroads;Remote Controller For Garage Doors, Pt.2; Simple 12/24VLight Chaser; Synthesised AM Stereo Tuner, Pt.3; A PracticalApproach To Amplifier Design, Pt.2.May 1991: 13.5V 25A Power Supply For Transceivers; StereoAudio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1.June 1991: A Corner Reflector Antenna For UHF TV; 4-ChannelLighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers,Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV.July 1991: Loudspeaker Protector For Stereo Amplifiers;4-Channel Lighting Desk, Pt.2; How To Install Multiple TVOutlets, Pt.2; Tuning In To Satellite TV, Pt.2; The SnowyMountains Hydro Scheme.August 1991: Build A Digital Tachometer; Masthead AmplifierFor TV & FM; PC Voice Recorder; Tuning In To Satellite TV,Pt.3; Step-By-Step Vintage Radio Repairs.September 1991: Digital Altimeter For Gliders & Ultralights;Ultrasonic Switch For Mains Appliances; The Basics Of A/D& D/A Conversion; Plotting The Course Of Thunderstorms.October 1991: Build A Talking Voltmeter For Your PC, Pt.1;SteamSound Simulator Mk.II; Magnetic Field Strength Meter;Digital Altimeter For Gliders, Pt.2; Military Applications OfR/C Aircraft.November 1991: Build A Colour TV Pattern Generator, Pt.1; AJunkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For YourPC, Pt.2; Turn-stile Antenna For Weather Satellite Reception.ORDER FORMPlease send me a back issue for: July 1989 September 1989 January 1990 February 1990 July 1990 August 1990 December 1990 January 1991 May 1991 June 1991 October 1991 November 1991 April 1992 May 1992 September 1992 October 1992 April 1993 May 1993 September 1993 October 1993 February 1994 March 1994 July 1994 August 1994 December 1994 January 1995 May 1995 June 1995 October 1995 November 1995 March 1996 April 1996 August 1996 September 1996 January 1997 February 1997 September 1988 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 July 1995 December 1995 May 1996 October 1996 March 1997 April 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 July 1992 February 1993 July 1993 December 1993 May 1994 October 1994 March 1995 August 1995 January 1996 June 1996 November 1996 May 1989 December 1989 June 1990 November 1990 April 1991 September 1991 March 1992 August 1992 March 1993 August 1993 January 1994 June 1994 November 1994 April 1995 September 1995 February 1996 July 1996 December 1996Enclosed is my cheque/money order for $______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master CardSignature ___________________________ Card expiry date_____ /______Name ______________________________ Phone No (___) ____________PLEASE PRINTStreet ______________________________________________________Suburb/town _______________________________ Postcode ___________84 Silicon ChipNote: all prices include post & packingAustralia (by return mail) ......................$A7NZ & PNG (airmail) ..............................$A7Overseas (airmail) ..............................$A10Detach and mail to:Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097.Or call (02) 9979 5644 & quote your credit carddetails or fax the details to (02) 9979 6503.Card No.December 1991: TV Transmitter For VCRs With UHF Modulators;Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2;Index To Volume 4.Audio Amplifier Module; Level Crossing Detector For ModelRailways; Voice Activated Switch For FM Microphones; SimpleLED Chaser; Engine Management, Pt.6.January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8APower Supply, Pt.1; Baby Room Monitor/FM Transmitter;Experiments For Your Games Card.April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; UniversalStereo Preamplifier; Digital Water Tank Gauge; EngineManagement, Pt.7.March 1992: TV Transmitter For VHF VCRs; Thermostatic SwitchFor Car Radiator Fans; Telephone Call Timer; Coping WithDamaged Computer Directories; A Guide To Valve SubstitutionIn Vintage Radios.April 1992: IR Remote Control For Model Railroads; DifferentialInput Buffer For CROs; Understanding Computer Memory;Aligning Vintage Radio Receivers, Pt.1.May 1992: Build A Telephone Intercom; Electronic Doorbell;Battery Eliminator For Personal Players; Infrared RemoteControl For Model Railroads, Pt.2; Aligning Vintage RadioReceivers, Pt.2.June 1992: Multi-Station Headset Intercom, Pt.1; VideoSwitcher For Camcorders & VCRs; IR Remote Control ForModel Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look AtHard Disc Drives.July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger;Multi-Station Headset Intercom, Pt.2.August 1992: An Automatic SLA Battery Charger; Miniature 1.5VTo 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI Explained.October 1992: 2kW 24VDC - 240VAC Sinewave Inverter;Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier ForPersonal Stereos; A Regulated Lead-Acid Battery Charger.January 1993: Flea-Power AM Radio Transmitter; High IntensityLED Flasher For Bicycles; 2kW 24VDC To 240VAC SinewaveInverter, Pt.4; Speed Controller For Electric Models, Pt.3.February 1993: Three Projects For Model Railroads; Low FuelIndicator For Cars; Audio Level/VU Meter (LED Readout);An Electronic Cockroach; 2kW 24VDC To 240VAC SinewaveInverter, Pt.5.March 1993: Solar Charger For 12V Batteries; Alarm-TriggeredSecurity Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers.April 1993: Solar-Powered Electric Fence; Audio Power Meter;Three-Function Home Weather Station; 12VDC To 70VDCConverter; Digital Clock With Battery Back-Up.May 1993: Nicad Cell Discharger; Build The Woofer Stopper;Alphanumeric LCD Demonstration Board; The MicrosoftWindows Sound System; The Story of Aluminium.June 1993: AM Radio Trainer, Pt.1; Remote Control For TheWoofer Stopper; Digital Voltmeter For Cars; Windows-basedLogic Analyser.July 1993: Single Chip Message Recorder; Light Beam RelayExtender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator;Windows-based Logic Analyser, Pt.2; Antenna Tuners – WhyThey Are Useful.August 1993: Low-Cost Colour Video Fader; 60-LED Brake LightArray; Microprocessor-Based Sidereal Clock; Southern CrossZ80-Based Computer; A Look At Satellites & Their Orbits.September 1993: Automatic Nicad Battery Charger/Discharger;Stereo Preamplifier With IR Remote Control, Pt.1; In-CircuitTransistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach.October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IRRemote Control, Pt.2; Electronic Engine Management, Pt.1.November 1993: Jumbo Digital Clock; High Efficiency InverterFor Fluorescent Tubes; Stereo Preamplifier With IR RemoteControl, Pt.3; Siren Sound Generator; Engine Management,Pt.2; Experiments For Games Cards.December 1993: Remote Controller For Garage Doors; LEDStroboscope; 25W Amplifier Module; 1-Chip Melody Generator;Engine Management, Pt.3; Index To Volume 6.January 1994: 3A 40V Adjustable Power Supply; SwitchingRegulator For Solar Panels; Printer Status Indicator; MiniDrill Speed Controller; Stepper Motor Controller; Active FilterDesign; Engine Management, Pt.4.February 1994: Build A 90-Second Message Recorder;12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40VAdjustable Power Supply; Engine Management, Pt.5; Airbags- How They Work.March 1994: Intelligent IR Remote Controller; 50W (LM3876)May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control;Dual Electronic Dice; Simple Servo Driver Circuits; EngineManagement, Pt.8; Passive Rebroadcasting For TV Signals.June 1994: 200W/350W Mosfet Amplifier Module; A CoolantLevel Alarm For Your Car; 80-Metre AM/CW Transmitter ForAmateurs; Converting Phono Inputs To Line Inputs; PC-BasedNicad Battery Monitor; Engine Management, Pt.9.July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp2-Transistor Preamplifier; Steam Train Whistle & Diesel HornSimulator; Portable 6V SLA Battery Charger; ElectronicEngine Management, Pt.10.August 1994: High-Power Dimmer For Incandescent Lights;Microprocessor-Controlled Morse Keyer; Dual Diversity TunerFor FM Microphones, Pt.1; Build a Nicad Zapper; EngineManagement, Pt.11.September 1994: Automatic Discharger For Nicad BatteryPacks; MiniVox Voice Operated Relay; Image IntensifiedNight Viewer; AM Radio For Weather Beacons; Dual DiversityTuner For FM Microphones, Pt.2; Engine Management, Pt.12.October 1994: Dolby Surround Sound - How It Works; DualRail Variable Power Supply; Talking Headlight Reminder;Electronic Ballast For Fluorescent Lights; TemperatureControlled Soldering Station; Engine Management, Pt.13.November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; TwinCell Nicad Discharger (See May 1993); Anti-Lock BrakingSystems; How To Plot Patterns Direct To PC Boards.December 1994: Dolby Pro-Logic Surround Sound Decoder,Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot LowDistortion Sinewave Oscillator; Clifford - A Pesky ElectronicCricket; Cruise Control - How It Works; Remote ControlSystem for Models, Pt.1; Index to Vol.7.January 1995: Sun Tracker For Solar Panels; Battery SaverFor Torches; Dolby Pro-Logic Surround Sound Decoder,Pt.2; Dual Channel UHF Remote Control; Stereo MicrophonePreamplifier;The Latest Trends In Car Sound; Pt.1.February 1995: 50-Watt/Channel Stereo Amplifier Module;Digital Effects Unit For Musicians; 6-Channel ThermometerWith LCD Readout; Wide Range Electrostatic Loudspeakers,Pt.1; Oil Change Timer For Cars; The Latest Trends In CarSound; Pt.2; Remote Control System For Models, Pt.2.March 1995: 50W/Channel Stereo Amplifier, Pt.1; SubcarrierDecoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; RemoteControl System For Models, Pt.3; Simple CW Filter.April 1995: Build An FM Radio Trainer, Pt.1; A PhotographicTimer For Darkrooms; Balanced Microphone Preamplifier &Line Filter; 50-Watt Per Channel Stereo Amplifier, Pt.2; WideRange Electrostatic Loudspeakers, Pt.3; 8-Channel DecoderFor Radio Remote Control.May 1995: What To Do When the Battery On Your PC’sMotherboard Goes Flat; Build A Guitar Headphone Amplifier;FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs;16-Channel Decoder For Radio Remote Control; Introductionto Satellite TV.June 1995: Build A Satellite TV Receiver; Train Detector ForModel Railways; 1W Audio Amplifier Trainer; Low-Cost VideoSecurity System; Multi-Channel Radio Control TransmitterFor Models, Pt.1; Build A $30 Digital Multimeter.July 1995: Electric Fence Controller; How To Run TwoTrains On A Single Track (Incl. Lights & Sound); Setting UpA Satellite TV Ground Station; Door Minder; Adding RAMTo A Computer.August 1995: Fuel Injector Monitor For Cars; Gain ControlledMicrophone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How ToIdentify IDE Hard Disc Drive Parameters.September 1995: Keypad Combination Lock; The IncredibleVader Voice; Railpower Mk.2 Walkaround Throttle For ModelRailways, Pt.1; Jacob’s Ladder Display; The Audio Lab PCControlled Test Instrument, Pt.2.October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For ModelRailways, Pt.2; Fast Charger For Nicad Batteries; DigitalSpeedometer & Fuel Gauge For Cars, Pt.1.November 1995: Mixture Display For Fuel Injected Cars; CBTransverter For The 80M Amateur Band, Pt.1; PIR MovementDetector; Dolby Pro Logic Surround Sound Decoder Mk.2,Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2.December 1995: Engine Immobiliser; 5-Band Equaliser; CBTransverter For The 80M Amateur Band, Pt.2; SubwooferController; Dolby Pro Logic Surround Sound Decoder Mk.2,Pt.2; Knock Sensing In Cars; Index To Volume 8.January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller;IR Remote Control For The Railpower Mk.2; RechargingNicad Batteries For Long Life.February 1996: Three Remote Controls To Build; WooferStopper Mk.2; 10-Minute Kill Switch For Smoke Detectors;Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2;Use your PC As A Reaction Timer.March 1996: Programmable Electronic Ignition System;Zener Tester For DMMs; Automatic Level Control For PASystems; 20ms Delay For Surround Sound Decoders;Multi-Channel Radio Control Transmitter; Pt.2; Cathode RayOscilloscopes, Pt.1.April 1996: Cheap Battery Refills For Mobile Telephones;125W Power Amplifier Module; Knock Indicator For LeadedPetrol Engines; Multi-Channel Radio Control Transmitter;Pt.3; Cathode Ray Oscilloscopes, Pt.2.May 1996: Upgrading The CPU In Your PC; Build A HighVoltage Insulation Tester; Knightrider Bi-Directional LEDChaser; Simple Duplex Intercom Using Fibre Optic Cable;Cathode Ray Oscilloscopes, Pt.3.June 1996: BassBox CAD Loudspeaker Software Reviewed;Stereo Simulator (uses delay chip); Rope Light Chaser; LowOhms Tester For Your DMM; Automatic 10A Battery Charger.July 1996: Installing a Dual Boot Windows System On YourPC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-BandParametric Equaliser; Single Channel 8-bit Data Logger.August 1996: Electronics on the Internet; Customising theWindows Desktop; Introduction to IGBTs; Electronic StarterFor Fluorescent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; CathodeRay Oscilloscopes, Pt.4.September 1996: VGA Oscilloscope, Pt.3; Infrared StereoHeadphone Link, Pt.1; High Quality PA Loudspeaker; 3-BandHF Amateur Radio Receiver; Feedback On ProgrammableIgnition (see March 1996); Cathode Ray Oscilloscopes, Pt.5.October 1996: Send Video Signals Over Twisted Pair Cable;Power Control With A Light Dimmer; 600W DC-DC ConverterFor Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link,Pt.2; Multi-Media Sound System, Pt.1; Multi-Channel RadioControl Transmitter, Pt.8.November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost FluorescentLight Inverter; How To Repair Domestic Light Dimmers; BuildA Multi-Media Sound System, Pt.2; 600W DC-DC ConverterFor Car Hifi Systems, Pt.2.December 1996: CD Recorders – The Next Add-On ForYour PC; Active Filter Cleans Up CW Reception; Fast ClockFor Railway Modellers; Laser Pistol & Electronic Target;Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2;Index To Volume 9.January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; Control Panel For MultipleSmoke Alarms, Pt.1; Build A Pink Noise Source (for SoundLevel Meter calibration); Computer Controlled Dual PowerSupply, Pt.1; Digi-Temp Monitors Eight Temperatures.February 1997: Computer Problems: Sorting Out What’sAt Fault; Cathode Ray Oscilloscopes, Pt.6; PC-ControlledMoving Message Display; Computer Controlled Dual PowerSupply, Pt.2; Alert-A-Phone Loud Sounding Alarm; ControlPanel For Multiple Smoke Alarms, Pt.2.March 1997: Driving A Computer By Remote Control; PlasticPower PA Amplifier (175W); Signalling & Lighting For MadelRailways; Build A Jumbo LED Clock; Audible ContinuityTester; Cathode Ray Oscilloscopes, Pt.6.PLEASE NOTE: November 1987 to August 1988, October1988 to March 1989, June 1989, August 1989, May 1990,February 1992, September 1992, November 1992 and December 1992 are now sold out. All other issues are presentlyin stock. For readers wanting articles from sold-out issues,we can supply photostat copies (or tear sheets) at $7.00 perarticle (includes p&p). When supplying photostat articles orback copies, we automatically supply any relevant notes &errata at no extra charge. A complete index to all articlespublished to date is available on floppy disc at $10 includingpacking & postage.April 1997 85Pt.8: More Advantages Of Digital ScopesDigital storage scopes excel over analog scopeswhen displaying multiple inputs or very slowsignals. Some DSOs can provide grey scaling orcolour gradations to accentuate signal changeswhile averaging many recurrent waveformsimproves the trace and the accuracy ofmathematical calculations.By BRYAN MAHERIt is common to use an oscilloscopeto display two (or more) differentsignals simultaneously, usually tosee the timing relationships betweenthem. Let’s compare how this is doneon analog scopes and digital scopesand then we’ll see why the DSO issuperior.In Pt.4 (August 1996 issue) of thisseries, we described how an analogscope can display two input signalsin either alternate or chop modes. Theswitching principle is shown in Fig.1.Briefly, two input signals, channel 1and channel 2, are individually attenuated and preamplified in A1 andA2. Then a fast electronic switch, IC1,switches back and forth between channels 1 and 2, to select which signal isdisplayed on the screen.86 Silicon ChipIn alternate mode, IC1 selectschannel 1 signal during all of the firstsweep, then switches to channel 2 forall the second sweep. Then channel 1is displayed again on the third sweep,and so on.This is not practical at slow sweepspeeds, because the first waveformfades away before the CRT beam hastime to draw the second. At fastersweep speeds, the screen persistencecontinues to show the first waveformwhile the next sweep displays the second. Although they are actually beingdisplayed alternately, you see bothwaveforms on the screen continually.But because each input signal triggers its own sweep of the scope independently, all time relation betweenthe two waveform displays is lost.Comparative timing measurementsbetween traces in alternate mode aremeaningless. What should you do?Chop modeYou could select chop mode onyour analog scope. Now IC1 rapidlyswitches back and forth betweenthe two channels, typically at a rateof about 1MHz. The screen displaysmany chopped up segments of bothwaveforms, as one of the scope screenphotos in this article shows. We’veshown a special case here to show thechopping action. As you can see, bothtraces are chopped up.This chopping mode is usuallynot evident because the waveformfrequency and chopping speed areunrelated. Normally, all those littlesegments are blended into two continuous waveforms on the screen.One input signal triggers all sweeps,so comparative timing measurementsmade between the traces in chop modeare valid.But here a second disadvantageof chop mode becomes evident. Thescreen doesn’t show what happens inwaveform 1 while the scope is busydisplaying the next short segment ofwaveform 2 and vice versa. Half ofeach signal is invisible. In this wayyou could miss seeing elusive glitches.Fig.1: two channel analog scopes have a fast electronic switch (IC1) to selectbetween channels either at the sweep rate which is called alternate mode or atabout 1MHz, which is called chop mode.If you were to set an analog scopeto this low sweep speed (and on mostanalog scopes, you can’t), you wouldjust show one bright green spot, slowlymeandering up and down and taking100 seconds to cross a dark screen. Itwon’t make much sense.But this sort of waveform is routineto a digital scope. After the signal hasexecuted two full cycles, they will bestored complete in the memory. Thenthe whole waveform will be continually displayed on the screen, refreshedat the 60Hz rate.You can observe the linearity of theramp signal by eye or measure it if yourDSO supports a mathematical differentiation routine. Results of changesor adjustments can be seen after thenext two cycles are complete.Grey scalingFig.2: A digital oscilloscope displays multiple inputs by individually preamplifying, sampling and digitising every input signal. The four sets of data arestored in separate areas of RAM before being displayed.So neither alternate nor chop modeis ideal. What other choice is there?Two-gun CRTs having separateelectron beams were tried but theirmechanical alignment proved impossible. Cossor split-beam tubes displayed two inputs validly at any speedbut were limited to two signals only.Today, to investigate timing diagrams in digital circuits, you mightneed four simultaneous input channels at fast sweep speeds. The onlysatisfactory answer is to buy a digitalstorage oscilloscope.Multiple inputsDigital scopes can successfullydisplay two, three or four separateinput signals simultaneously, at anysweep speed, using a very differenttechnique. The block diagram of Fig.2gives us an idea of how it’s done. Eachinput signal passes through its ownattenuator and analog preamplifier,shown as A1 to A4. From there, eachsignal is individually sampled andconverted in separate A/D convertersA/D1 to A/D4. All the digital datafrom each channel is separately storedin different areas of the fast randomaccess memory (RAM).The process of reading the contentsof the RAM to its display on the screenis complex, especially in Tektronixscopes using InstaVu mode. Sufficeto say that neither chop nor alternateprocedures are used, and the wholeof each waveform is displayed on thescreen.Everything recorded in the RAM isfaithfully shown; nothing is lost. Theprocess operates equally well at allsweep speeds, slow or fast.All timing measurements made onthe screen and the phase relationshipsobserved are accurate. In displayingmultiple input signals, a digital storageoscilloscope is vastly superior to allanalog scopes.Low frequency displaysIf you need to display long pulses orramp signals, you’ll find digital scopesmuch better than analog scopes. Sayyou want to observe a ramp signal witha period of 50 seconds. Setting thetimebase to 10s/div, the scope wouldtake 100 seconds for one sweep acrossthe screen. That would display twofull cycles of the waveform.In the past, your trusty analog scopeeasily displayed compound signals,for example live TV waveforms ordigital data which contained intermittent faulty pulses. Your displaywas brighter in those parts of thesignal which repeat more frequently,because at those points thousands oftraces were overlaid. Sections of thewaveform which continually changedor occurred less often thus appearedless bright.These brightness gradations let youidentify rarely occurring spuriousinterferences or runt pulses. On thescreen they looked different from thenormal repetitive signals. Point one infavour of analog scopes!But the simple digital storage oscilloscope we discussed in last month’sissue (Pt.7) can’t do this. Rememberthat is had a 1-bitmap refresh bufferand as such, it could not display signals at varying intensity. The one-bitoutput has only two possible values,digital high or low. These correspondto the points on the screen being illuminated or not; on or off.So in that simple sort of DSO we sawin the previous chapter, everythinghas the same intensity on thescreen.But ideally we want a digital storagescope to be at least as good as analogscopes were in showing compoundsignals. With that in mind, we wouldlike 16 levels of brightness in thetrace. Frequently recurring parts ofthe signal should be brighter thaninfrequent anomalies and faultypulses.April 1997 87These two analog oscilloscope photos show the same pair of signals depicted in alternate mode (left) and chop mode(right). The problem with alternate mode is that because each alternate sweep is separately triggered, the precise timerelationship between the two waveforms is lost. In the chop mode, by contrast, the two signals have sections chopped outand this can lead to glitches being missed in the display.To achieve this aim, digital oscilloscope designers enlarged the bitmap refresh buffer to store four bits(instead of one previously) in each ofits memory locations. We imagine thisstructured as four planes of memoryelements, as illustrated in Fig.3.Each plane is like the single bitmemory map depicted last monthand contains 307,200 memory cells,arranged in 480 rows, each row containing 640 cells. In each plane, eachcell contains a single digital value, 1or 0; ie, either logic high or low.As we saw in the previous chapter,the XY address of each cell corresponds to one particular point on theCRT screen raster.In Fig.3, all four planes of the refreshmemory are addressed in parallel. Forexample, the top left cells in all planeshave the same address.So when the system reads the topleft address of the refresh buffer, itreads the contents of the top left cellin each plane simultaneously. Theoutput is then 4-bit data (one bit fromeach plane) carried on four parallellines A, B, C, D.That 4-bit digital data is used tocontrol the brightness of the spot onthe screen, by changing the G1-K biaspotential on the CRT cathode. But thattube is an analog component, so it requires a varying analog voltage signalon its cathode to alter the electronbeam current and trace brightness.Therefore, the 4-bit digital data readfrom the bit map refresh buffer on linesA, B, C, D must be converted to an88 Silicon Chipanalog signal in the digital to analog(D/A) converter (IC7).D/A converterIC7 contains four CMOS switch elements, SA, SB, SC & SD, powered byan accurate +5V reference. Each switchproduces output exactly equal to +5Vif its input is logic high or exactly 0Vif its input is logic low. The resistorgroup between IC7 and IC8 forms anR-2R ladder attenuator; resistors marked 2R have twice the value of thosemarked R.The combination of IC7 and theresistor ladder produces an analogvoltage proportional to the value ofthe 4-bit digital data fed into IC7. Thissignal is then raised to a high level andinverted by video amplifier IC8, whichis DC-coupled and must have a highinput impedance.This high voltage analog signalfrom IC8, applied to the CRT cathode,controls the electron beam current andthus the screen illumination at thatpoint. This is called Z-modulation.Thus the trace brightness at each pixelis set to a value representing how oftenthat element of the signal appears atthe scope input.Four-bit digital data can take only16 different values. So this schemeallows the trace on a digital scopeto display compound signals in 16different levels of brightness. This iscalled “grey scaling”.When the display processor IC5meets a regularly occurring part of theinput waveform, it writes a logic highat the appropriate memory address inall four planes of the bit map refreshbuffer IC6.When read from the refresh buffer,the output data on the four parallellines A, B, C, D will be 1111. TheD/A converter IC7 converts this to themaximum analog voltage and the CRTproduces the brightest spot at the corresponding point on the screen raster.Now let’s suppose a spurious pulseappears only sometimes at the scopeinput. Sensing this fact, the displayprocessor IC5 might write a logic highto the corresponding address only inmemory plane A of the refresh bufferIC6, and write a logic low to the sameaddress in planes B, C and D.On the next refresh cycle, when thatdata stored in the refresh buffer is read,the digital data on output lines A, B,C, D will be 1000. This correspondsto a screen dot of half brightness.This indicates that that part of thesignal appears less frequently; so yoususpect it’s some spurious blip or afaulty pulse.There are a number of variations onthis theme in modern digital scopes.When variable persistence is selected,rapidly changing waveform points cangradually decay through 16 levels ofbrightness. Some cheaper models support only two levels of grey scaling.You might ask where’s the advantage of digital scopes, when all analogscopes naturally showed brightnessscaling? The answer is that DSOs support grey scaling at all sweep speedsequally. But normal analog scopes,at top speed, are flat out providing avisible trace even on repetitive signals,with no potential left for scaling.Colour displaySome digital scopes can show acolour graded display, with differentcolours indicating how frequentlysome part of a compound waveform repeats. The very high frequency 50GHzTektronix 11801B uses a 228mmdiagonal screen with a vertical rasterscan. The display resolves 552 pixelshorizontally and 704 pixels vertically,from a palette of 262,144 colours.Early colour scopes used colour TVtechnology. The tube contained threeelectron guns and the familiar tri-colour phosphor and beam convergenceshadow mask. But a monochrome CRTis capable of a much sharper trace thanany TV tube with a multiple colourphosphor. Therefore many moderncolour digital scopes use a white phosphor CRT, overlaid by a three-layerliquid crystal colour shutter. An example of this is the Tektronix modelTDS684B which provides horizontalraster scan on a 177mm screen featuring full colour grading from a paletteof 256 colour levels.Signal averagingAnalog signals may be corrupted byextraneous interference which resultsin a noisy display. Worse still, noisein the signal reduces the accuracy ofmathematical operations performedThese two scopes from Tektronix both use a white phosphor CRT, overlaid bya 3-layer liquid crystal colour shutter. Both models are showing colour gradeddisplays, with different colours indicating how frequently some parts of thewaveforms repeatby the oscilloscope. The way aroundthis is to feed the noisy signal throughyour digital scope many times. Thenyou display the average of many passesof the repetitive input signal.Each pass will contain differentnoise, but random (white) noise averages out towards zero. So the averageof a number of passes of the samesignal will be more like the originaluncorrupted waveform.Say your digital scope takes a recordconsisting of 500 samples at each passof the signal. We saw previously howthe A/D converts each sample to an8-bit digital word which represents theFig.3: for grey scaling, the bit map refresh buffer containsfour memory planes A, B, C & D. In each plane, each cellstores one bit. So four planes store 4-bit data. IC7 and theR-2R ladder form a D/A converter. IC8 is a linear amplifier.April 1997 89Repeated from the February 1997 issue, these two oscilloscope waveforms show how the use of averaging can removemuch of the noise in a repetitive signal.These two digital screen printouts show the menu setups necessary on a Tektronix RDS 360 digital scope, in order toobtain a two-level greyscale signal. The video signal is an off-air TV channel. Note the use of “vector accumulate” and“contrast” menu options. The main trace is a normal video line signal while the background signal accumulation showsthe variation in signal of a period of 1.5 seconds. Note the faint spurious sync signal in between the two main sync pulses.This faint signal is a ghost of the sync pulse. Such a faint signal is unlikely to be shown on an analog scope.nearest voltage decision level belowthe sample voltage.In real life more than two passesof the signal are averaged to obtainsmoother results. Averaging fourpasses of an 8-bit signal yields 10-bitdigital data. And eight passes resultsin 11-bit data.Many scopes let you choose thenumber of passes that will be averaged; eg, 2, 4, 8, 16, etc up to 2048.But they only keep the result of 11 bitsand discard any further overflow. Ofcourse, all normal averaging requiresthe signal to be repetitive.High resolution modeSome of the Tektronix TDS series90 Silicon Chipscopes also feature a clever systemcalled Hi-Res Mode which allowsaveraging, to reduce interference andnoise, even on one shot signals. Inthese scopes the sampler always runsat the maximum speed. In normalmode, if you choose slow sweep speedthe scope cannot use all the millionsof samples taken. So only enough ofthe samples are kept to form the bestdisplay and the rest are thrown away.But in Hi-Res Mode the excesssamples are kept in a section of thememory. There each group of 16, 32or 64 contiguous samples are averagedto form one point on the display. Sucha point can be accurate to 12 or 13 ormore bits. This process is repeatedover all the waveform until a wholescreen-full is set up, then displayed.The slower the sweep speed in use,the more excess samples are availablefor this fast averaging. But of coursewhen you select top sweep speed,Hi-Res Mode is unavailable, becauseall samples taken are needed to formthe normal display.References: Tektronix: Technical BriefSC12/94.XBS.15M.AcknowledgementThanks to Tektronix Australia fordata and for some of the illustrations used in this article.ASK SILICON CHIPGot a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a lineand we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097.Problem withCHAMP amplifierI have a problem with the littleCHAMP amplifier board, publishedin the February 1994 issue. This is agreat little amplifier and I have usedseveral of these now for different tasks.However, I want to use it to boost theaudio output of the SteamSound Simulator, published in the October 1991issue and also in your publication “14Model Railway Projects”.I hooked up the input of the CHAMP(ie, the 50kΩ volume control) to theoutput of op amp IC1c, pin 14, butit won’t amplify at all. As I wind upthe volume control it seems to distortand then it seems to oscillate. Thisgets worse as I wind up the volumecontrol and then eventually it cutsout altogether. I also tried taking theoutput of the SteamSound Simulatorfrom the junction of the two outputtransistors and the result was muchthe same. What is the problem likelyto be? (G. S., Gosford, NSW).• This is probably a trap for youngplayers. When we designed theCHAMP PC board, it was assumedthat most sources likely to be hookedto it would have no DC offset. Thismeant that we could leave out the input coupling capacitor to the volumeSmall PAsystem wantedWe have a small theatrical groupin the village where I live andthe community hall in which weperform for the residents is sadlylacking a PA system. I wish toconstruct a small system using the25W Amplifier Module featured inthe December 1993 issue of yourmagazine.I have searched for a circuitwhich I could construct but to noavail. Is there one I could use? (M.H., Chain Valley Bay, NSW).• We have not described a smallcontrol and thereby make the PC boardas small as possible. This very smallsize has been one of the reasons thisproject has been so popular.However, by taking the signal forthe SteamSound Simulator from pin14 of IC1c, you inadvertently applieda voltage of +4.5V DC across the 50kΩvolume control of the CHAMP. Aswell as being an undesirable practice,because DC through pots makes themnoisy, the volume control also feedsthis DC to the non-inverting input, pin3, of the LM386. As the volume controlis wound up, more of this DC is fed tothe input and this no doubt causes theamplifier to latch up.The solution is quite simple. Youneed an input coupling capacitor tothe 50kΩ volume control. Normally,if you wanted good response downto low frequencies (say 20Hz), youwould need a value of around 0.47µFbut since you are using it with theSteamSound Simulator which produces mainly higher frequencies. You canget away with 0.1µF or .047µF.Faulty displayin DMMI have recently completed the DMMdescribed in the June 1995 issue andI have found a problem. When it isPA system but it would be a fairlystraightforward job to build a system based on the 25W amplifiermodule.A suitable preamplifier wouldbe the one featured in the 120WPA amplifier published in the December 1988 & January 1989 issuesof SILICON CHIP. This preamp hadtwo balanced/unbalanced microphone inputs and bass and treblecontrols. The preamplifier is notavailable as a kit but the PC boardcan be obtained from RCS RadioPty Ltd, 651 Forest Road, Bexley, NSW 2207. Phone (02) 95873491.switched to any range, it only displaysthe negative sign, the HV sign and thenumber 18.0.8. Moving the display canchange this slightly. I have installed allcomponents except R24 which brokeduring installation but I’m sure thisisn’t the problem because it’s only forthe transistor tester. (M. E., Tokoroa,NZ).• The symptoms you mention suggestthat the liquid crystal display is notsitting correctly in contact with theelastomeric connector. We suggest youtry repositioning it for correct contact.Failing that, the service departmentat Dick Smith Electronics should beable to help.Measuring colour temperatureIn respect to the capability of measuring colour temperature in Kelvindegrees, how is it possible? Do professional photographers simply takefor granted what is written on theirlight sources?I am keen to build a 240VAC-powered studio flash unit. I can understandthe danger that would be involvedwith most project builders but I ama licensed electrical contractor anddeal on a daily basis with equipmentand installations that, while not operating on kVs, carry much highercurrents.Therefore, would you consider, atleast, “guiding” me towards the aboveor perhaps suggesting certain books orpublications. (A. F., Warilla, NSW).• We are unable to answer your question about measuring colour temperatures although we understand that themeasurements involve the use of twofilters, red and blue. Perhaps one of ourreaders can provide more informationon this subject.We cannot provide informationon the design of a 240VAC powerflash unit other than to refer you tothe “Circuit Notebook” pages of theFebruary 1997 issue of SILICON CHIP.A suggested power supply for a flashgun was featured.April 1997 91• TheUnwantedbattery drainI have built the 6/12V SLA battery charger as described in theAugust 1992 issue of SILICON CHIP.On switching the charger on, itperformed as expected. However,when I turned the charger off, aftercharging the battery, I noticed a faintglow from LED1, the main chargerindicator LED. On checking this, Imeasured a 5mA current from thebattery to the charger. The troubleseems to be in the positive trackfrom the fuse to the 680Ω, 180kΩand 18kΩ sensing resistors and thenvia IC1, the charger IC.I would appreciate it if you couldadvise me how this 5mA flow can bestopped. (S. M., Townsville, Qld).• The simple answerto this problem is tomanually disconnectthe charger when it isturned off. If you wantto do it automatically,the solution is to usea relay to connect theQuestions about highpower invertersI am interested in the 600W DC toDC converter published in the October& November 1996 issues of SILICONCHIP. However, I don’t need such ahigh power converter as I only wantto run a twin 50W amplifier (±35V <at>2.5A). I also want to keep costs to aminimum.Can the power output of the 600Wconverter be reduced by using lessMosfets? What changes would benecessary to produce a power outputof around 200W using a similar setupto the 600W converter?Would it be easier to use the 12VDCto 70VDC converter (April 1993, SILICON CHIP) and will this supply around2.5 amps (not much more)? Also,could a 200W, 12VDC to 240V ACinverter be modified so it will produce50-60VAC. Any help you can give isgreatly appreciated. (S. G., Tewantin,Qld).• Changing this design to reduce theoutput power is not really practical.92 Silicon Chipcharger when power is presentand disconnect it when power isremoved. You could do this witha 12V relay connected to the DCinput to the charger; ie, across the4700µF capacitor. The relay coilwill need a series resistor to preventover-dissipation.The DC voltage across the 4700µFcapacitor can be expected to beabout 22V and the series resistorwill need to be the same value ora little less than the relay’s coil resistance. For example, if the relaycoil resistance is 160Ω, the addedseries resistor should be 150Ω witha 2W rating. The relay should havea contact rating of at least 5A.The accompanying diagramshows the concept.A better approach would be to usethe 100W DC-DC converter publishedin the December 1990 issue. We cansupply a back issue for $7.00 includingpostage.Modifying our 200W 12V to 240VACinverter to produce 60VAC wouldalso not really be practical althoughit could be done. The main invertertransformer would need to have a lower turns ratio (ie, less secondary turns)and the inverter feedback changed.Ideally you could also use lower ratedMosfets in the H-pack drive circuitry.High powerdimmer doesn’tI have recently constructed thehigh power dimmer described in theAugust 1994 issue of SILICON CHIP butit doesn’t work. After connecting up,the lamp will come on at full brilliancewhen the slider pot is at 50% of itstravel. There is no dimming actionat all.I have checked the wiring and it allseems OK. (J. N., Leongatha, Vic).fact that you have no controlover the brightness sugg ests thatthe there may an open circuit in thewiring associated with op amp IC2dand the “set max brightness” trimpotVR3. Check your soldering carefullyto ensure that the connections to VR3and the associated series 4.7kΩ resistorare not open circuit.Electric fencehas no zingI have built the Electric Fence described in the July 1995 issue of SILICON CHIP. It has been impossible to gethigh enough output to deter anything.The fence is a single wire obviouslywell insulated but the output via thecoil can be hand-held without discomfort. On completion of the kit, anoutput spark of 2mm was observed butthe coil failed to click as mentioned inthe instructions.We used two coils which werefairly new and were meant to be usedin conjunction with a ballast resistor,one a Bosch GT40 and the other anEchlinttil Performance. Both are inexcellent condition and there is nodiscernible difference in performance.This kit was put together with all duecare and we’ve been scratching ourheads ever since. Could you pleaseadvise what the problem is?The length of the fence is well below1km, somewhere slightly above ½km,so it was thought most appropriate forthis installation and it has operatedsuccessfully with a borrowed DakenB20 12V energiser. (R. D., Boonah,Qld).• The 2mm length of spark from thehigh tension output would indicatethat the controller is not functioningcorrectly. We have modified the Electric Fence Controller circuit sincepublication to provide a 10kV hightension output rather than the original5kV. This change requires a 1.2Ω 1Wresistor in place of the 6.8Ω resistor inseries with the coil.Apart from the need for this change,there should not be any problem withthe circuit unless a component isfaulty or incorrectly oriented or positioned. The 555 timer is probablyfunctioning correctly since you say aspark is produced, however, it may notbe driving Q1 fully into saturation toprovide sufficient base current for Q2.Check that the collector of Q1 goesfully high when switched on and thatthe base voltage of Q2 when switchedon is about 1V. Note that the 1.5kΩresistor between pins 6 and 7 of IC1will need to be changed to a valueof about 1MΩ to extend the time tomeasure this switching when using amultimeter. Take the coil out of circuitwhen doing this since it will drawexcessive current due to the long ontime.DiscoLightdouble triggersI have a technical query regardingthe DiscoLight which was describedin the August 1988 issue of SILICONCHIP. I have just built one which worksperfectly in all modes except it triggerstwice on each bass beat. Strobe seemsOK but the ALT and Chaser moves intwo steps and as there are only fourchannels only two lights effectivelyoperate. It triggers fine via the Oscillator. Are there any errata for the triggeror squaring circuit? Have you heard ofthis problem? Any suggestions? (S. S.,Melbourne, Vic).• Double beating when used to triggerfrom sound is probably caused by therebeing too much signal. Try adjustingthe sensitivity down. You may alsofind that decreasing the 1MΩ resistorbetween pins 8 & 10 of IC1c to 180kΩwill improve the result. This providesa much greater hysteresis on Schmitttrigger IC1c.OverheatingTaragoI have been trying to overcome along-standing heating problem in myTarago van. After checking thermostatand repairing the radiator, the hoses,clamps and the head and having theauto transmission checked, all seemsto be OK. But I still have an unexplained loss of water and elevatedtemperature after driving about 100120km. As a result I am forever toppingup the water after every second tripand can never really have any peaceof mind when travelling.I want some circuitry to monitorK-type thermocouples to sense thetemperatures of the automatic fluidand engine coolant, both leaving andreturning after cooling, as well as theengine oil and ambient air temperature entering the radiator. I’d like todisplay the readings in pairs usingthe alphanumeric LCD (May 1993,Poor gas mileagein the KingswoodI installed the programmableignition system (March 1996) inmy 1974 Holden HQ approximately four months ago. I though thiswould be the solution I was waiting for, to allow me to change mytiming on the fly when changingfrom petrol to gas and vice versa.Overall, I am very impressedwith its operation, and I have noticed a marked increase in power.But after playing with varioussettings constantly for the last fewmonths, I am still experiencinga fairly large drop in my gas fueleconomy. Before installing the system, I could drive from MelbourneSILICON CHIP) and be able to recall themaximum reading later.I feel that by monitoring all the heatsources simultaneously, I can observethe thermal runaway building andcatch the offender. I think the troubleis linked to the way the auto is cooled.The engine radiator has a small heatexchanger for the transmission fluid.It seems that at a particular ambientair temperature the radiator cannothandle the load from the auto and thisstarts the heating cycle off.At least, I suspect that this is what isgoing on as it appears to occur duringthe warmer months of the year. I planto transplant the system to a friend’s4-wheel drive when I have fixed myproblem. I will include the transfercase and both differentials as he doessome very serious driving. (T. F., Bundaberg, Qld).• We have not published any circuitsto suit a K-type thermocouple andwe do not have any plans to do so inthe near future. However, it may bepossible to modify the Digi-Temp, asfeatured in the January 1997 issue ofSILICON CHIP.As published, this circuit will readthe temperature at up to eight separatelocations at up to 99°C. We have spoken to the designer, Graham Blowes,and he is confident that it could bemodified to read temperatures to about120°C. This could make it suitable foryour application.However, while it is not our normalto Benalla and back on one tank ofgas, a round trip of approximately420km. Now, I find that I can onlyjust make the one way trip. Anyway, I am hoping that someonecan provide me with some suitablesettings to allow for better timingfor gas. Please! The price of gas inthe country is double that of thecity! (R. B., Melbourne, Vic).• Unfortunately we do not haveany information on ignition timingfor cars and especially not for usewith gas. We can only suggest youtake the car to a speed shop whichhas a dynanometer and exhaust gasanalysis equipment. They shouldenable you to obtain the bestcompromise between power andeconomy for your car.province to give automotive advice,we think that you have a leak in thecooling system, not a mechanicaldefect which will be revealed by atemperature monitoring system.The reasoning is this: if the enginecoolant is overheating and causing theradiator cap to vent, no fluid shouldbe lost; it will all go into the overflowbottle. The fact that you have to topup the system frequently points to aleak.We think that the elevated temperature is caused by the loss of coolant,not the other way around. We strongly suggest that you take your car tothe local Toyota service people fora thorough investigation. Leaving itunrepaired will eventually lead to afailure of the alloy head and that willbe very expensive to repair.Notes & ErrataDigi-Temp Digital Thermometer, January 1997: the designer of this projecthas advised that the pinout diagramfor the DS1820 sensors is reversed;the GND terminal should be on therighthand side and the +5V on thelefthand side. No damage appears tooccur when this wrong connectionis made.Smoke Alarm Panel, January 1997:one of the array of 100µF capacitorson the circuit of page 29, January 1997should be 10µF. The component overSClays are correct.April 1997 93MARKET CENTRECash in your surplus gear. Advertise it here in Silicon Chip.FOR SALECLASSIFIED ADVERTISING RATESTo run your classified ad, print it clearly on a separate sheet of paper, fill outthe form below & send it with your cheque or credit card details to: SiliconChip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02)9979 6503._____________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ __________________________ _____________ _____________ _____________ _____________Enclosed is my cheque/money order for $__________ or please debit my Bankcard Visa Card Master CardCard No.Signature__________________________ Card expiry date______/______Name ______________________________________________________Street ______________________________________________________Suburb/town ___________________________ Postcode______________94 Silicon ChipC COMPILERS: Ever ything youneed to develop C and ASM software for 68HC08, 6809, 68HC11,68HC12, 68HC16, 8051/52, 8080/85,8086 or 8096: $140.00 each. MacroCross Assemblers for these CPUs+ 6800/01/03/05 and 6502: $140.00for the set. Debug monitors: $70 for6 CPUs. All compilers inc ‘HC12,XASMs and monitors: $480. 8051/52or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75.Try the new C-FLEA Virtual Machinefor small CPUs, build a “C-Stamp”.Demo disk: FREE. All prices + $5 p&p.GRANTRONICS PTY LTD, PO Box275, Wentworthville 2145. Ph/Fax (02)9631 1236 or Internet: http://www.mpx.com.au/~lgrant.WEATHER FAX DECODERS: for HF,VHF/UHF use with JVFAX, MAXISATand SATFAX. Details D. G. Hopkins, 4Handsworth Street, CAPALABA 4147.(07) 3390 3328.MICROCRAFT PRESENTS: Dunfield(DDS) products are now availableex-stock at a new low price; pleaseask for our catalogue. Micro C, theaffordable “C” compiler for embeddedapplications. Versions for 8051/52,8086, 8096, 68HC08, 6809, 68HC11or 68HC16 $139.95 each + $3 p&h •Now on special is the SDK, a package of ALL the DDS “C” compilersfor $399 + $6 p&h • EMILY52 is a PCbased 8051/52 high speed simulator$69.95 + $3 p&h • DDS demo disks$7 + $3 p&h • VHS VIDEO from theUSA (PAL) “CNC X-Y-Z using caraltern ators” (uses car alternators ascheap power stepper motors!) $49.95+ $6 p&h (includes diagrams) • Deviceprogramming EPROMs/PALs etc from$1.50 • Fixed price electronic designand PCB layout • Credit cards accepted • All goods sent certified mail• Call Bob for more details. MICROCRAFT, PO Box 514, Concord NSW2137. Phone (02) 9744 5440 or fax(02) 9744 9280.✂Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus50 cents for each additional word. Display ads (casual rate): $25 per columncentimetre (Max. 10cm). Closing date: five weeks prior to month of sale.RAIN BRAIN AND DIGI-TEMP KITS:8-station controller and 8-chann el,RS232 digital thermometer uses theincredible DS1820 sensor. Call Mantis Micro Products, 38 Garnet St,Niddrie, 3042. P/F/A (03) 9337 1917.http://www.home.aone.net.au/mantismpSIMPLE PIC84 PROGRAMMER:LED model 6 lights $65, LCD 16x2char. $75, P+H $3. Also low-costdesign, prototyping and microcontroller programming service. EasternElectronics (02) 9789-3616, Fax (02)9718-4762.MicroZed ComputersPO Box 634, ARMIDALE 2350 (296 Cook’s Rd)Ph (067) 722777 – may time out to Mobile 014 036775Fax (067) 728987 (Credit Cards OK)http://www.microzed.com.au/~microzedSEND A BLANK MESSAGE to help<at>dontronics.com for details on howto join our SiClub and List ServerSupport group. We have a free BasicInterpreter for the PIC16C84. Largestrange of PIC related products Southof the Equator.SATELLITE DISHES: internationalreception of Intelsat, Panamsat, Gorizont,Rimsat. Warehouse Sale – 4.6mdish & pole $1499; LNB $50; Feed $75.All accessories available. Videosat,2/28 Salisbury Rd, Hornsby. Phone(02) 9482 3100 8.30-5.00 M-F.WARNING! WARNING! WARNING!WARNING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!VIDEO CAMERA MODULES Bewareof higher or lower prices for a similarcamera! BUY A BETTER CAMERA AT A SIMILAR PRICE! With aCHOICE OF . . . . . 380, 460 & 600TVL resolution.0.05 lux low light & IRsensitive. TEENY WEENY 28mm x28mm PCBs. ELEVEN board lenses.FOUR pinhole lenses. IR cut/pass &polarising filters. 800+ nm 52 mW/Sr IRLEDs. Ancillary equipment. BEFORE& AFTER-SALES SERVICE, HELP& ADVICE! Before you buy! Ask forour detailed, illustrated price list withapplication notes. Also available CCTVtechnical, design & reference manu-With third party supportingproducts, all in stockEasy to learn, easy to use sophisticated CPU based controllersCredit cards OK Send two 45c stamps for infoMEMORY * MEMORY * MEMORYSPECIAL! (Ex Tax)4Mbx9 – (3 Chip) 60ns $47CAR/RALLY COMPUTER KIT: including fuel sensor & speed sensor.68HC05 & HC11 DEVELOPMENTSYSTEMS: Oztechnics, PO Box 38,Illawong NSW 2234. Phone (02) 95410310. Fax (02) 9541 0734.http://www.oztechnics.com.au/HOMEMADE GENERATORS: how toinstructions. Eight pages free text andcolour photos on the Internet at:http://www.onekw.co.nz/onekwBASIC STAMPS& PIC Tools651 Forest Rd, Bexley 2207makes all the project PCBspublished in SILICON CHIPand other Australian magazinesTel +61 2 9587 3491 Fax 9587 5385E-mail rcsradio<at>cia.com.auals & inter-active CD ROM. AllthingsSales & Services 09 349 9413; fax 09344 5905.JAPANESE QUALITY & TECHNOLOGY at very competitive importer-di-SIMMS (Parity/No Parity)4Mb 30 PIN-70 $47 $414Mb 72 PIN-70 $51 $238Mb 72 PIN-70 $96 $5916Mb 72 PIN-70 $162 $13232Mb 72 PIN-70 $306 $264EDO SIMMS (60ns)4Mb/8Mb $35/6316Mb/32Mb $132/26264Mb/128Mb $1080/2112LASER PRINTER MEMORY4Mb HP 4&5 $378Mb HP 4 & 5 $111All other models available $CallLIFETIME WARRANTY!!COMPAQ8Mb ARMADA 1100 $96All other models available $CallTOSHIBA8Mb Portege/ Sat EDO $11816Mb Portege/ Sat EDO $19216Mb Tecra 500/610 Sat $237All other models available $CallIBM16Mb T.Pad 755, 360 EDO $240All other models available $CallDIMMS4Mb - SO - 72 PIN $368Mb - SO - 72 PIN $7216Mb - SO - 72 PIN $1268Mb/16Mb - 168 PIN $60/12332Mb/64Mb - 168 PIN $267/514SYNCHRONOUS (SDRAM)168 PIN - 16Mb $150168 PIN - 32Mb $322168 PIN - 64Mb $696Ex Tax Pricing – Delivery $8. Pricing as at 04/03/97. Phone for latest.Sales Tax 22%.Credit Cards Welcome. We Also Buy And Trade-In Memory.PELHAMPTY LTDSuite 6, 2 Hillcrest Rd,Ph: (02) 9980 6988Pennant Hills, 2120.Fax: (02) 9980 6991Email: pelham1<at>ozemail.com.aurect prices. Automatic IRIS, manualIRIS & varifocal CS LENSES. Manualiris from $49. Auto iris from $93.Varifocal from $75. Allthings Sales& Services 09 349 9413; fax 09 3445905.SILICON CHIP FLOPPY INDEXWITH FILE VIEWERNow available: the complete index to all SILICON CHIP articlessince the first issue in November 1987. The Floppy Index comeswith a handy file viewer that lets you look at the index line byline or page by page for quick browsing, or you can use the search function. Allcommands are listed on the screen, so you’ll always know what to do next.Notes & Errata also now available: this file lets you quickly check out the Notes& Errata (if any) for all articles published in SILICON CHIP. Not an index but acomplete copy of all Notes & Errata text (diagrams not included). The file vieweris included in the price, so that you can quickly locate the item of interest.The Floppy Index and Notes & Errata files are supplied in ASCII format on a3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the FileViewer requires MSDOS 3.3 or above.Price $7.00 each + $3 p&p. Send your order to: Silicon Chip Publications, PO Box139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or faxthe details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc.April 1997 95460 & 600 TVL HI RESOLUTION 0.05lux VIDEO CAMERA MODULES IR& low light sensitive from $96. 09 3499413.VIDEO CAMERAS C/CS from $87.MICRO C/CS MOUNT from $145.DOME CEILING from $131. A.S. & S.Fax 09 344 5905.COLOUR 420 TVL MODULES & C/CS MOUNT CAMERAS auto shuttersmall light 12 VDC from $306. Ph 09349 9413.DIY CCTV 5.5' plug-in sets completewith IR LED-Audio-Camera, 20Mcable & plugpack from $269. 09 3499413.VIDEO AUDIO TRANSMITTERS 7'wireless CCTV sets. TX/RX modulepair only $80. 09 349 9413 fax 09344 5905.!!!!!!! THE TINIEST !!!!!!! VIDEOCAMERA MODULE. PCB 28 x 28 mm,IR & low light sensitive, with 2.8, 3.7or 5.5 mm pinhole lens. A.S. & S. 09349 9413 fax 09 344 5905.DIY SECURITY ALARM SUPPLIESProfessional grade equipment PIRs,autodialler alarm panels, CCTV, cable etc. Send for price list. All priceswholesale. AFFORDABLE ALARMS,7 Firefly Crescent, Lawnton, Qld. 4501.DATAMAN EPROM PROGRAMMERS: Dataman S4 world’s leadinghandheld programmer/emulator,onscreen editor, over 1500 devicetypes including EPROMS/EEPROM/Microprocessor ForDigital Effects UnitThis is the 68HC705-C8P programmed microprocessor IC for the DigitalEffects Unit (see Feb. 1995).Price: $45 + $6 p+pPayment by cheque, money order orcredit card to: Silicon Chip Publications. Phone (02) 9979 5644; Fax (02)9979 6503.Av-Comm.......................................6Dick Smith Electronics..... 8,9,34-37Earthquake Audio........................83Emona.........................................59Freedman Electronics..................81Flash up to 8Mbits. Dataman-48 upto 48pin DIL. DOS/Win software, freeupdates. Call or email for details.DIGITAL GRAPHICS P/L, PO Box281, North Ryde, 2113. Phone (02)9888 3105dgriffo<at>ozemail.com.auhttp://www.ozemail.com.au/~dgriffoKIT OF THE MONTH – CAR ALARMfeatures entry/exit time, ultrasonic,bonnet/boot, back up, low cost. CCDCAMERA low light/high resolution32x32x27mm, $125. COMMERCIALTV AUDIO/VIDEO transmitter to suit:$15 when purchased with camera. IRILLUMINATOR also available. OATLEYELECTRONICS Ph (02) 9584 3563Fax (02) 9584 3561. Much more infoon our WEB SITE:http://www.ozemail.com.au/~oatleyVINTAGE TUBES AND CAPACITORBANK: Electros for vintage radio work.New stock. Low prices. Thousands ofparts. Call P.A. Savell on 03 5871 1921or write to P.A. Savell, 25 Wirbill Street,Cobram, Victoria 3644.SILICON CHIP BINDERSThese binders will protect your copies ofSILICON CHIP.★ Heavy board covers with 2-tone greenvinyl covering★ Each binder holds up to 14 issues★ SILICON CHIP logo printed ingold-coloured lettering on spine & coverPrice: $A14.95 each (incl. postage in Aust). NZ & PNG orders please add$A5 each for p&p. To order, just fill in & mail the order form in this issue to:Silicon Chip Publications, PO Box 139, Collaroy 2097; Or phone (02) 99795644 & quote your credit card details or fax (02) 9979 6503.96 Silicon ChipAdvertising IndexAltronics................................. 72-74Harbuch Electronics....................83Instant PCBs................................95Jaycar ............................IFC, 45-52Kalex............................................79Kits-R-US.....................................82Macservice....................................3MicroZed Computers...................95Pelham.........................................95RCS Radio...................................95Rod Irving Electronics .......... 61-65Silicon Chip Back Issues....... 84-85Silicon Chip Bookshop...............IBCSilicon Chip Binders....................96Silicon Chip Model RailwayProjects Book..........................OBCSilicon Chip Software..................43Tortech.........................................79_____________________________PC BoardsPrinted circuit boards for SILICONCHIP projects are made by:• RCS Radio Pty Ltd, 651 ForestRd, Bexley, NSW 2207. Phone (02)9587 3491.• Marday Services, PO Box 19-189,Avondale, Auckland, NZ. Phone (09)828 5730.electronic design, and applications.The sixth edition has been expandedto include chapters on surface mounttechnology, hardware & softwaredesign, semicustom electronics &data communications. 63 chapters,in hard cover at $120.00.Silicon Chip BookshopRadio FrequencyTransistorsNewnes Guideto Satellite TVInstallation, Reception & Repair.By Derek J. Stephenson. Firstpublished 1991, reprinted 1994(3rd edition).This is a practical guide on theinstallation and servicing ofsatellite television equipment. Thecoverage of the subject is extensive, without excessive theory ormathematics. 371 pages, in hardcover at $55.95.Guide to TV & VideoTechnologyBy Eugene Trundle. First publish-ed 1988. Second edition 1996.Eugene Trundle has written formany years in Television magazineand his latest book is right up dateon TV and video technology. 382pages, in paperback, at $39.95.Servicing PersonalComputersBy Michael Tooley. First published 1985. 4th edition 1994.Computers are prone to failurefrom a number of common causes& some that are not so common.This book sets out the principles& practice of computer servicing(including disc drives, printers &monitors), describes some of thelatest software diagnostic routines& includes program listings. 387pages in hard cover at $59.95.format and R-DAT. If you want tounderstand digital audio, you needthis reference book. 305 pages, inpaperback at $55.95.The Art of LinearElectronicsBy John Linsley Hood. Published1993.This is a practical handbook fromone of the world’s most prolificaudio designers, with many of hisdesigns having been published inEnglish technical magazines overthe years. A great many practicalcircuits are featured – a must foranyone interested in audio design.336 pages, in paperback at $49.95.Components, Circuits & Applications, by F. F. Mazda. Published1990.Previously a neglected field, powerelectronics has come into its own,particularly in the areas of tractionand electric vehicles. F. F. Mazdais an acknowledged authority onthe subject and he writes mainlyon the many uses of thyristors &Triacs in single and three phasecircuits. 417 pages, in soft coverat $59.95.Digital Audio & CompactDisc TechnologyElectronics Engineer’sReference BookHard coveProduced by the Sony ServiceCentre (Europe). 3rd edition,published 1995.Prepared by Sony’s technicalstaff, this is the best book oncompact disc technology that wehave ever come across. It coversdigital audio in depth, includingPCM adapters, the Video8 PCMPower ElectronicsHandbookYour Name__________________________________________________PLEASE PRINTAddress_________________________________________________________________________________________Postcode_____________Daytime Phone No.______________________Total Price $A _________❏ Cheque/Money Order rEdited by F. F. Mazda. version nowavailableFirst published 1989.6th edition.This just has to be the best reference book available for electronicsengineers. Provides expert coverageof all aspects of electronics in fiveparts: techniques, physical phenomena, material & components,❏ Bankcard ❏ Visa Card ❏ MasterCardCard No.Signature_________________________ Card expiry date_____/______Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097.Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503.Principles & Practical Applications. By Norm Dye & HelgeGranberg. Published 1993.This book strips away the mysteries of RF circuit design. Writtenby two Motorola engineers, itlooks at RF transistor fundamentals before moving on to specificdesign examples; eg, amplifiers,oscillators and pulsed power systems. Also included are chapterson filtering, impedance matching& CAD. 235 pages, in hard coverat $85.00.Surface Mount TechnologyBy Rudolph Strauss. First published 1994.This book will provide informativereading for anyone consideringthe assembly of PC boards withsurface mounted devices. Includeschapters on wave soldering, reflowsoldering, component placement,cleaning & quality control. 361pages, in hard cover at $99.00.Audio ElectronicsBy John Linsley Hood. Published1995.This book is for anyone involvedin designing, adapting and usinganalog and digital audio equipment. Covers tape recording,tuners & radio receivers, preamplifiers, voltage amplifiers, poweramplifiers, the compact disc &digital audio, test & measurement,loudspeaker crossover systemsand power supplies. 351 pages, insoft cover at $52.95. Title Newnes Guide to Satellite TV Guide to TV & Video Technology Servicing Personal Computers The Art Of Linear Electronics Digital Audio & Compact Disc Technology Power Electronics Handbook Electronic Engineer's Reference Book Radio Frequency Transistors Surface Mount Technology Audio ElectronicsPrice$55.95$39.95$59.95$49.95$55.95$59.95$120.00$85.00$99.00$52.95Postage: add $5.00 per book. Orders over $100are post free within Australia. NZ & PNG add$10.00 per book, elsewhere add $15 per book.TOTAL $AApril 1997 97 This content requires the Adobe Flash Player. Get Flash |