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Especially For Model Railway Enthusiasts Order Direct From SILICON CHIP Order today by phoning (02) 9979 5644 & quoting your credit card number; or fill in the form below & fax it to (02) 9979 6503; or mail the form to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. This book has 14 model railway projects for you to build, including pulse power throttle controllers, a level crossing detector with matching lights & sound effects, & diesel sound & steam sound simulators. If you are a model railway enthusiast, then this collection of projects from SILICON CHIP is a must. Price: $7.95 plus $3 p&p Yes! Please send me _______ copies of 14 Model Railway Projects Enclosed is my cheque/money order for $­_________ or please debit my  Bankcard    Visa Card    Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date_____/_____ Name _________________________Phone No (____)_____________ PLEASE PRINT Street ___________________________________________________ Suburb/town __________________________ Postcode____________ Vol.7, No.10; October 1994 THIS DUAL RAIL POWER supply is capable of providing 11 switched output voltages ranging from ±1.25V to ±15V DC at currents up to 500mA. It runs off a plugpack supply, to eliminate mains wiring – see page 26. FEATURES FEATURES   4 Dolby Surround Sound: How It Works by Leo Simpson The sound of the theatre in your living room 14 Electronic Engine Management, Pt.13 by Julian Edgar Electronic transmission control PROJECTS PROJECTS TO TO BUILD BUILD 26 Beginner’s Dual Rail Variable Power Supply by Darren Yates A plugpack supply eliminates mains wiring EVER LEAVE YOUR CAR’S headlights on & flatten the battery? This Talking Headlight Reminder will warn you if you accidentally leave your lights on, or can be used as a solid state message recorder – see page 37. 37 Build A Talking Headlight Reminder by Darren Yates It tells you when you’ve left your lights on 42 Electronic Ballast For Fluorescent Lights by John Clarke High efficiency, instant starting & no flicker 65 Temperature Controlled Soldering Station by Jeff Monegal Lets you adjust tip temperature from 100°C to over 450°C SPECIAL SPECIAL COLUMNS COLUMNS 40 Serviceman’s Log by the TV Serviceman Two symptoms – one fault or two? IF YOU CAN’T AFFORD one of those fancy temperature controlled soldering stations, then build this one instead. It can adjust the tip temperature from 100°C to over 450°C – turn to page 65. 78 Vintage Radio by John Hill The winners of the Hellier Award 88 Computer Bits by Darren Yates Placing directories into programs DEPARTMENTS DEPARTMENTS   2 3 23 24 70 84 Publisher’s Letter Mailbag Order Form Circuit Notebook Bookshop Product Showcase 90 92 93 94 96 Back Issues Ask Silicon Chip Notes & Errata Market Centre Advertising Index REPLACE THE INTERNALS of your fluorescent light fittings with this electronic ballast. It is highly efficient, gives instant starting, eliminates flicker & has no hum or buzz. Cover concept: Marque Crozman October 1994  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Advertising Enquiries Leo Simpson Phone (02) 979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER Writing to SILICON CHIP Over the past few months, we have been receiving more let­ters from readers and that is very gratifying. We try to reply as promptly as possible but sometimes there is a delay because production of the magazine does take precedence over all other tasks. Hence, at some times of the month, correspondence does get pushed to one side. However, we do answer all letters we receive. Be that as it may, there are some things that correspond­ents can do to ensure that their letters are answered as soon as possible. The first of these is to make sure your address is at the top of the letter. That might seem fairly fundamental but it is surprising just how many people don’t put their address on their letters or on their envelopes. That makes it frustrating for us because sometimes we will prepare an answer and then find that we don’t know where to send it to. So if you have been frustrated with the lack of a reply, please ask yourself, “Did I include my address at the top of the letter?” Second, please keep your letters reasonably brief and to the point. If you write pages and pages, your letter will tend to gravitate to the bottom of the pile until there is more time to read it thoroughly. Third, if you have access to a fax machine or have a fax/modem on your computer, by all means fax your letter to us and we will reply by fax. Again, if your letter is reasonably brief and the question is straightforward, we should be able to reply on the same day or pretty soon afterwards. On the other hand, if you ask a lot of questions which require us to do some searching through the magazine archives, the reply will inevi­tably take longer. Still on the subject of faxing, if you want a reply by fax, please make sure that there is someone at home who knows how to operate the unit. There are times when we want to fax a reply but the person who picks up the phone does not know how to switch over to fax operation. This becomes doubly frustrating when the call is long distance STD and no postal address has been provided as an alternative. Please send all mail to PO Box 139, Collaroy, NSW 2097. We fulfil orders for books, back issues, software and binders on the day that they are received and they are usually in the post on the same day or by the next morning. Please include your phone number on all orders, just in case we have a query and need to check on some aspect. If we can’t fulfil an order, we can then phone you to suggest an alternative, etc. If you want to submit an article for publication, please phone Leo Simpson or Greg Swain beforehand for information on our requirements. By doing this, you can save yourself, and us, a lot of work. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains 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 killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations 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 Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG Radio control projects wanted After reading electronics magazines for years, I have finally been able to get involved in a practical way, thanks to external university study. The first lesson – get a breadboard, that helps a lot. Now instead of wondering how modern technology works, I can explain it to people who don’t know and try to think how it could be improved. As I’ve noticed that SILICON CHIP is more directed to the experimenter, I would be interested to know if there are any radio control projects coming. I remember the UK magazine “Every­ day Electronics” published a 3-channel proportional R/C system some time around 1983. In the last 10 years, electronics must have made it easier to make and build transmitters and receivers. R. Williams, Brisbane, Qld. Comment: Bob Young currently has a radio control transmitter and receiver under development. We hope to begin publication in the December issue. BIOS interrupts available in DOS 4 I read with interest your article on BIOS interupts in the July 1994 issue but find that this function is found in DOS 4 upwards, ie: MODE CON: RATE = rate DELAY = Delay time rate = 1 to 4, Delay time = 1 to 32. It can be put into the AUTOEXEC. BAT file and does the same job as your Keyboard Repeat Rate Utility. Hope it’s useful! In the Feburary 1994 article on Engine Management, concern­ing exhaust emissions, I think that the NO/x and hydrocarbons graphs are backwards; ie, the leaner the mixture, the greater the NO/x and the less parts per million of carbon monoxide (CO). Could you please check this? D. Kuenne, Ascot Vale, Vic. Comment: the graph on page 43 of the February 1994 issue is back to front. This graph came from a manufacturer’s instruction course so we wonder how the technicians are managing to service cars. Valve amplifiers not superior to solid state I am in total agreement with your editorial of the July 1994 issue. The performance of yesterday’s technology of valve audio amplifiers is not superior to solid state. Your editorial caused me to dig out my old copy of Radio­tron Designer’s Handbook, edited by F. Langford Smith. My copy is the fourth impression of the fourth edition and my page number references are from this volume. I give these references not in support or denial of any argument, but rather to illustrate that the matters were in need of discussion. Remember, this book was considered by all to be the real authority for circuit design, especially where valves were involved, (what else was there). Langford Smith wrote the book as an employee of a company selling valves. He doesn’t talk about any of these being a problem; he is telling designers how to get around the limita­tions of valve performance. You mentioned microphony; that is acknowledged in an arti­cle on testing for audio frequency valve microphony performance (p1311). Looking up the subject index in the back of the book gives 60 references to capacitance effect in valves ranging from hum problems caused by capacitance coupling of filament current (p798, 1296, 1197, 1198) to the effects of grid input capacitance (p323 and others). I would like to point out that in the heyday of valves, the arguments were real; one could hear differences and the arguments were informed, not imaginations of some enthusiast with little actual knowledge of electronics. There were arguments about whether triodes or pentodes were better, arguments about whether current feedback or voltage feedback from the voice coil was better and about damping of loudspeakers (p317, 841). Then there was the really big problem – the design of the transformer which was absolutely necessary to SILICON CHIP, PO Box 139, Collaroy, NSW 2097. couple high im­pedance valves to low impedance loudspeakers. Leakage inductance was a problem (p219) and the tricks used to overcome inter-winding capacitance, as well as leakage inductance get a mention (p223). It seems to me that if some of the techniques such as voice coil velocity and positional feedback were looked at, there could be an improvement in the performance of solid state amplifiers. But I wonder if anyone would hear that improvement. Bob Nicol, Armidale, NSW. Comment: the editor of the English magazine “Elementary With Practical Electronics” saw fit to quote from the abovementioned editorial in the September 1994 issue and he agreed with the propositions therein. Philips actually manu­ factured a range of active loudspeakers with motional feedback about 10 years ago but they never really caught on. Low voltage supply for soldering iron Recently, I had reason to repair a PC board and only having a 20W 240V iron, the work resulted in some of the tracks lifting, due to overheating. This set me wishing for a lower voltage iron with variable temperature. After deciding I couldn’t afford a soldering station, I purchased a 12V iron from Dick Smith Electronics. I made a power supply based on an ETI project 221 but modified it to give variable voltage between 9-16V, using a 10kΩ pot. The transistors used were 2N3055 (on a heatsink), BC337 and BC327, and the emitter resistor of the 2N3055 was tailored to give maximum current of 1.5A, thus giving a maximum wattage of 24W. This works extremely well. The iron is earthed on the negative side (ie, to the collector of 2N3055) and this avoids the need of a TO-3 insulator. I hope this idea for a poor man’s safe iron is of use to to other readers. The iron uses 1/8-inch copper bits (easily obtain­able). B. Porter, Port Macquarie, NSW. October 1994  3 By LEO SIMPSON Dolby Surround Sound: How It Works You’ve been to the movies. You’ve seen the pictures. You’ve heard the sound. And now you want it all at home, in your living room. And while you may not be able to afford the latest widescreen TV or LCD video projection system, you can at least have the big sound of the movies. Read on, to find out how Dolby Surround Sound works. Many people, if they think about it at all, may assume that the latest Dolby Surround Sound used to such great effect in today’s action movies is somehow related to the “failed” surround sound systems of the early 1970s. These were variously referred to as surround, four channel and quadraphonic. There where three competing systems, all of which were incompatible with each other and all required two additional speakers in the rear corners of the listening room, to reproduce extra channels from specially encoded stereo LP records. Older readers will remember the names of those systems as “Sansui QS”, CBS “SQ” and JVC’s CD-4. Fig.1: this shows the arrangement of speakers used in a typical Dolby stereo cinema system. The film sound track provides two stereo channels & these are fed to the Dolby processor to provide four main channels, Left, Centre, Right & Surround, together with an optional Subwoofer channel for extra bass. LEFT SUB “SQ” and “QS” sound systems were “matrixed” systems in which the rear channel signals effec­ tively rode on top of the normal stereo signals and were recov­ered with relatively simple phase-splitting circuitry. The re­sulting rear channels did not have much separation from each other or from the front channels (about 7dB) but they did give an illusion of extra space or “ambience” to the sound quality. The CD-4 4-channel system, by contrast, was much more ele­gant and did provide quite good separation between front and rear channels (up to 20dB) but it was also much more expensive, push­ ing the existing LP recording technology to the absolute limits. Briefly, a CD-4 encoded record has the regular stereo sign­als plus a high frequency carrier at 30kHz. This was phase and frequency modulated with rear difference signals (up to 45kHz) CENTRE SCREEN POWER AMPLIFIERS OPTIONAL SUBWOOFER RIGHT Lt Rt DOLBY STEREO CINEMA PROCESSOR CENTRE LEFT SURROUND SURROUND 4  Silicon Chip RIGHT DOLBY A-TYPE NR OR DOLBY SR Lt Rt BASS EXTENSION 4-CHANNEL DECODER OPTICAL PREAMP ADAPTIVE MATRIX 7kHz LOW-PASS FILTER AUDIO DELAY MODIFIED DOLBY B-TYPE NR DECODER Fig.2: the block diagram of the Dolby stereo cinema processor. The key point to note is that the surround channel is fed via an audio delay of typically 20 milliseconds. This is partly to provide ambience or reverberation & partly to allow your ears get the cue for direction from the front speakers. which were subsequently recovered from the outputs of the RIAA preamplifier. It required a phono cartridge with a special elliptical (Shibata) stylus, very low compliance and extra special tracking capability. If you played a CD-4 disc with a conventional stereo cartridge, the high frequency carrier would quickly be ploughed out and the disc would no longer provide four channel sound. After a few years, consumers were so confused with the claims and counterclaims for the different systems that they avoided the issue entirely and four channel sound just died. Dolby Surround Sound Dolby Surround Sound is quite different from all three of the above ill-fated systems and is continually growing in its acceptance by movie-goers and consumers in the home. So let’s see how Dolby works. Dolby stereo surround sound based on optical sound tracks was introduced to movie theatres in the mid-seventies but its arrangement of the channels is quite different to that used in previous home surround sound systems. Fig.1 shows the arrangement of channels and speakers used in a typical Dolby stereo cinema system. In essence, the film sound track provides two stereo channels, Lt (left total) and Rt (right total) and these are fed to the Dolby processor or decoder to provide four main channels, Left, Centre, Right and Surround, together with an optional Subwoofer channel for extra bass. Notice that all the Surround speakers are fed with the same signal – there is no left rear and right rear, just surround and this signal happens to be delayed, by 20 milliseconds or more, with respect to the front speakers. Why three front speakers? The trouble with having just two stereo speakers in a cinema is that the screen is too wide. For people at the sides of the theatre, the nearest speaker predominates. This sounds and looks silly when the source of the sound is clearly at the centre or on the other side of the screen. This is where the centre channel comes into its own and provides much better sound localisation. The centre channel should not be thought of as merely a “fill-in” speaker but as quite separate from that provided by the two stereo channels. Indeed, when the centre channel is used in a typical movie, it is used only for dialogue and the stereo speakers are silent while it is in use. Once you become aware of it, you SUBWOOFER 3rd OCTAVE EQUALISER RIGHT 3rd OCTAVE EQUALISER CENTRE 3rd OCTAVE EQUALISER LEFT PARAMETRIC EQUALISER SURROUND will often notice the profound switch between stereo sound over to the centre channel and then back out again. In effect, Dolby provides three separate front channels: they are used separately for dialogue while the left and right are used for stereo music accompaniment. The surround speakers are used during action scenes, with the delay providing a great deal of ambience, reverberation, echo or whatever. While you may think that having all the surround speakers driven from the one source would make rear sounds some­what vaguely located, your ears get their cues from the front speakers so that the apparent localisation is quite strong. Dolby decoding Fig.2 shows the block diagram of the Dolby stereo cinema processor which is featured in the setup of Fig.1. This shows input preamplifiers for the projector’s optical pickups, followed by Dolby A noise reduction, and then the two stereo signals are fed to the 4-channel decoder. This is partly based on the 4-channel matrix systems of the early 1970s and the key to it is the box labelled “Adaptive Matrix”. The outputs of this matrix become the LEFT CENTRE Lt -3dB SURROUND -3dB BPF DOLBY NR ENCODER +90ø -90ø RIGHT Rt Fig.3: the basic Dolby surround encoding setup. The encoder accepts four separate input signals – left, centre, right & surround (L, C, R & S) – & creates two final outputs, left-total & right-total (Lt & Rt). October 1994  5 DIGITAL DECODER A systems both are four channel sys­tems, their method of operation is quite different. MONO Dolby encoding While you might expect the Dolby signal encoding process to be complicated, it LEFT is actually simpler in princiDIGITAL 2 CHANNEL DECODER ple than the decoding. Fig.3 STEREO B shows the basic encoding setRIGHT up. The encoder accepts four separate input signals, left, DOLBY SURROUND DIGITAL PROGRAM MATERIAL centre, right and surround (L, C, R & S), and creates two LEFT 4 CHANNEL ANALOG DIGITAL final outputs: left-total and CENTRE ANALOG PRO LOGIC DECODER DOLBY RIGHT right-total (Lt & Rt). DECODER C SURROUND SURROUND The L and R inputs go straight to the Lt and Rt outputs without modification. LEFT The C input is divided equalCENTRE ly to Lt and Rt but with a 3dB DOLBY 5 OR 5.1 CHANNEL DOLBY RIGHT SURROUND SURROUND DIGITAL level reduction (to maintain DIGITAL LEFT SURROUND (SUBWOOFER OPTIONAL) a constant acoustic power in DECODER RIGHT SURROUND the mix). SUBWOOFER The S input is also dividFig.4: this diagram shows the various decoding possibilities from Digital Dolby ed equally between Lt and Surround which is encoded on to optical tracks between the film sprocket holes. Rt but it goes through three Note that it provides left & right surround channels but this is not possible via Dolby more processing steps: (1) encoded video tapes. bandwidth limiting from 100Hz to 7kHz, (2) encoding four channels – left, centre, right and After the delay line, the surround with modified Dolby B noise reducsurround – but the surround signal signal is filtered to remove any noise tion, and (3) ±90° phase shifts which goes through a little more process- above 7kHz and then passed through are applied to produce a 180° phase ing before it is fed to the surround a modified Dolby B noise reduction difference between the signal compoamplifiers. decoder so that the net result is that nents added to Lt and Rt. First, it goes through an audio delay when no surround signal is supposed A number of points should be made line which is there for two reasons. to be present, the rear speakers are about the overall encod­ing process. First, it provides the echo or reverber- quiet. First, there is no loss of separation ation which results in the “big” sound Note that all channel signals are between the original left and right of cinemas. Second, by delaying the subjected to substantial equal­isation signals. Second, there is also no theo­ surround sound, your ears get the cue before being fed to their amplifiers retical loss of separation between the for direction from the front speakers and loudspeak­ers. It should be clear centre and surround sign­ als. This and this provides the localisation re- by now that while Dolby Surround follows because the surround signal ferred to above. and the ill-fated quadraphonic sound is recovered by taking the difference INPUTS Lt Rt LEFT INPUT BALANCE CONTROL RIGHT SURROUND MASTER VOLUME CONTROL L-R L/R BALANCE SURROUND TRIM SURROUND ANTIALIAS FILTER AUDIO TIME DELAY 7kHz LOW PASS FILTER MODIFIED DOLBY BTYPE NOISE REDUCTION UNIT Fig.5: this is the block diagram of a “passive” Dolby surround sound decoder which does not incorporate the directional enhance­ment feature of Pro-Logic decoders. 6  Silicon Chip OUTPUTS LEFT RIGHT SURROUND Lt VCA LEFT VCA RIGHT L+R VCA CENTRE L-R VCA SURROUND PASSIVE DECODER Rt Fig.6: directional enhancement could be provided if each decoded output had its own voltage controlled amplifier (VCA). However, this does not work well as dialogue in the centre channel could cause the music in the stereo tracks to be pumped up & down. CONTROL CIRCUIT between the Lt and Rt signals and any identical centre channel components will be cancelled in the surround output. Similarly, since the centre channel (when decod­ed) is derived from the sum of Lt and Rt, the equal and opposite surround sound components will be cancelled out. This concept of precise cancellation to maintain separation between the centre and surround channels presupposes that the two main transmission channels have virtually identical gain and phase characteristics. If they don’t, separation between the centre and surround channel signals will be poor. Digital Dolby In 1992, a new 35mm format called SR.D was introduced by Dolby Laboratories. Between the film sprocket holes on SR.D prints is a 6-channel digital sound track. The older Dolby stereo Surround information is also present so that cinemas without the digital sound equipment can still show them. Dolby Surround at home All the movies which have been subsequently released on videotape or broadcast from TV stations have the original Dolby surround encoding information still present in their stereo sound tracks. In 1982, Dolby introduced a surround decoder for the home. When driving the required number of amplifiers and loud­ speakers, this can provide a convincing reproduction of theatre sound in the home. Dolby Pro-Logic The most recent development in home surround sound equip­ ment is the Dolby Pro-Logic decoder, first introduced in 1987 and now more or less standard in deluxe home theatre systems. This gives a substantial enhancement to sound localisation compared with the so-called “passive” decoder depicted in Fig.5. Before we describe the Pro-Logic system we should discuss some other means of directional enhancement which have been tried. Directional enhancement refers to any technique that attempts to improve the separation between channels by modifying the outputs of the matrix decoder. The first of these is “gain riding” whereby each decoded output has its own voltage controlled amplifier (VCA), as shown in Fig.6. Consider the case where the dialogue is present in the centre channel (so that Lt = Rt). This means that the centre channel will have the dialogue but so will the left and right hand speakers. To enhance the centre channel, the decoder could increase the gain of the centre amplifier and reduce that for the stereo channels. The same procedure could be used to isolate the left channel when only left LEFT Lt INPUTS The new digital system provides five full range channels for left, centre and right speakers, plus separate left surround and right surround speaker arrays in a configuration known as stereo surround. A sixth, bass only channel for subwoofers gives rise to the de­ scription “5.1 channels”. Fig.4 shows the various decoding possi­bilities from Digital Dolby Surround. Dolby’s digital sound has been a major factor in the suc­cess of recent movies, particularly “Jurassic Park”. Fig.5 shows the block diagram of a Dolby surround sound decoder and this can be compared with the Dolby stereo cinema processor shown in Fig.2. Note that the centre channel is lacking. At present, the six channel digital sound encoding is not available via the video tape format but it may become available on future digital video discs. DOLBY PROLOGIC ADAPTIVE MATRIX INPUT BALANCE CONTROL Rt MASTER VOLUME CONTROL RIGHT CENTRE CENTRE TRIM SURROUND NOISE SEQUENCER ANTIALIAS FILTER SURROUND AUDIO TIME DELAY L/R BALANCE 7kHz LOW PASS FILTER MODIFIED DOLBY BTYPE NOISE REDUCTION UNIT SURROUND TRIM OUTPUTS LEFT RIGHT CENTRE SURROUND Fig.7: the block diagram of a Dolby Pro-Logic decoder. If you compare this with the passive decoder depicted in Fig.5, you will see that the main difference is in the Pro-Logic Adaptive Matrix & the addition of the centre channel. October 1994  7 INPUTS Lt Rt FULL-WAVE RECTIFIER BANDPASS FILTERS FULL-WAVE RECTIFIER LEFT/RIGHT DOMINANCE SENSE LOGDIFFERENCE AMPLIFIER DUAL TIME CONSTANT E POLARITY SPLITTER ER THRESHOLD SWITCHES L+R L-R FULL-WAVE RECTIFIER FULL-WAVE RECTIFIER LOGDIFFERENCE AMPLIFIER DUAL TIME CONSTANT Below: this photo shows our soon to be published Dolby Pro-Logic Sur­ round Decoder which is presently being assessed by Dolby Labora­tories in California, USA. 8  Silicon Chip EL E ER E CL EC E SL ES OUTPUTS LEFT COMBINING NETWORKS RIGHT CENTRE SURROUND E POLARITY SPLITTER FRONT/REAR DOMINANCE SENSE Fig.8: this diagram shows the Adaptive Matrix used in the Dolby Pro-Logic decoder. The four signals are fed to full wave rectifiers & then to logarithmic detection circuits to determine the dominant signal for subsequent directional enhancement. channel signal was present, by turn­ing down the gain of the other channels. Unfortunately, this system of gain riding with VCAs does not work with real film sound tracks. In particular, stereo music is usually present along with dialogue. If dialogue is the domi­ nant factor and is used to vary the gain of relevant channels, the volume of music will inevitably be pumped up and down. E To solve this problem, Dolby has come up with the concept of “signal dominance” – the sound that is most dominant in the sound mix at any instant in time. This can then be used to vary the gains of the relevant channels and thus give the desired direc­tional cues. Dolby also suggest that if a decoder is to detect and use signal dominance to set the channel gains, it needs two addition­al characteristics to work effectively. First, it must be fast enough to provide enhancement on an instantaneous basis when the signal peaks are prominent enough to be heard as separate events. Second, it must sense when the relative signal dominance ES 8VCAs falls below a threshold where it is no longer necessary to provide any substantial directional enhancement. For these reasons, the Pro-Logic decoder has sensing circuits which ignore the absolute signal levels but respond to the logarithmic difference in levels between signals and thereby determine direction of signal dominance. Thus it can provide the correct degree of directional enhancement or gain adjustment of the four channels. Fig.7 shows the block diagram of a Pro-Logic decoder. If you compare this with the so-called passive decoder depicted in Fig.5 you will see that the main difference is in the Pro-Logic Adaptive Matrix and the addition of the centre channel. The detail of the Adaptive matrix is shown in Fig.8 and it has two sections: Left/Right dominance sense and The construction of our proposed Dolby Pro-Logic Sur­round Decoder will be quite straightforward, with most of the parts mounted on a single large PC board. It is based on a Dolby Pro-Logic chip set from Mitsubishi. Front/Rear dominance sense. In practice, the decoded channels from a Dolby Pro-Logic decoder can have a separation of up to 30dB which is more than adequate to provide strong directional information. The proof is in the listening, of course, and any action movie gets a major benefit from the Dolby sound track. Loudspeakers & amplifiers For a typical home Dolby surround setup you need quite a lot of equipment, apart from either a hifi stereo VCR (if you wish to play back Dolby encoded tapes) or a stereo TV set. If you have a conven­tional stereo VCR (ie, without hifi sound) you’ll be wasting your money since tape hiss will be a problem. You will need a stereo amplifier and a pair of stereo speakers for the front channels and a stereo amplifier for the rear speakers. It is normal practice to have a stereo amplifier to drive the rear speakers so that you can easily set the balance between them. For the centre channel, you have two approaches. The first is to use the “phantom channel” option available on most Dolby decoders. This divides the centre channel sound bet­ween the front stereo speakers and can give a good result in most home living rooms. The second approach is to use a centre channel amplifier and centre channel speaker which sits on top of or below the TV screen. Centre channel speakers must have full magnetic screening otherwise they will seriously degrade the picture quality from your TV, to the point where it is completely unwatchable. To emphasise this point, if you place a conventional unshielded loudspeaker within 30cm of your TV’s screen, you will magnetise the shadow mask inside and thoroughly “screw up” the colour purity. This will cause horrible colour blotch­es all over the screen and the set will then require de-guassing to restore its picture quality. The big problem about using a centre channel speaker, even if it is shielded, is that it should have the same sound quality as the main ste- reo speakers, as far as the treble and midrange is concerned. If it is a lesser quality speaker, the transition from centre to stereo speakers will be very no­ticeable – the centre channel will “squawk”. Most Dolby decoders have integral amplifiers for the rear and centre channel speakers and of course, you can purchase a full-on stereo receiver with Dolby Pro-Logic decoding builtin. This will have five power amplifiers so that external power amplifiers will not be necessary. Rear speakers Since the frequency bandwidth of the surround signal is limited to between 100Hz and 7kHz, the requirements for the rear surround speakers are not demanding and virtually any small pair of speakers will do the job. Do-it-yourself Pro-Logic Dolby Pro-Logic decoders are licensed by Dolby Laboratories who maintain strict control over technical standards. As this article is being written, a fully licensed design by SILICON CHIP staff is currently under review by Dolby Laboratories. We hope to SC publish the design very soon. October 1994  9 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Electronic Engine Management Pt.13: Electronic Transmission Control by Julian Edgar Anyone who has driven a car equipped with an automatic transmission has, in a sense, driven a computer-equipped car. Even if it’s a 1965 Valiant, the gear changes of the automatic transmission were computer-controlled – in this case, by an analog computer. Traditionally, an automatic transmission uses pressurised hydraulic fluid to control the movement of valves. However, in more recent times, the analog computer has been replaced by a digital version. The automatic transmission The automatic transmission is the most sophisticated me­chanical component in a car. A simple 3-speed transmission (ie, a unit with three forward ratios) uses a gear set comprising an annulus gear, forward and The Holden Jackaroo V6 uses full electronic control for its transmission. This view shows the Transmission Control Unit (TCU). 14  Silicon Chip reverse sun gears, and short and long pinions mounted in a planetary pinion carrier. Controlling these gears are two multi-plate clutches, front and rear braking bands, and a one-way clutch. The action of these friction elements is in turn controlled by four shift valves, two hydraulic pressure regulator valves, a governor valve, and five other valves per­forming one-way or other functions. Central to automatic transmissions are planetary gear sets. Fig.1 shows a planetary gear set with three pinions. All the gears remain enmeshed at all times, with different ratios gained by driving a particular gear member while the others are held stationary. This makes the system amenable to automatic operation, with hydraulically-operated clutches or bands being used to control the rotation of parts of the planetary gear set. The single gear set shown in Fig.1 would not provide suffi­cient forward ratios for a car. Either two simple gear sets connected together or a compound gear set (which shares some gears between two planetary sets) is required to provide the correct ratios and direction of rotation for a car transmission. Four (and now five!) speed auto transmissions require even more internal gears but all use various combinations of planetary gear sets. A torque converter connects the automatic transmission to the engine. This internal speed sensor is from a Magna electronically-con­trolled automatic transmission. This acts as a sophisticated fluid coupling. Hydrau­lic oil is driven around inside the housing by the action of spinning blades and torque is transferred from the impeller (which rotates at engine speed) to the turbine (which is attached to the transmission input shaft). When the turbine is stationary (ie, the car is stopped) but the impeller is spinning quickly (ie, the engine is being revved), the engine’s output torque is multiplied by the convert­er by a ratio which may be as high as 2:1. This torque multipli­cation is reduced as the rotational speeds of the two spinning elements become closer. However, while the action of the torque converter is advan­tageous during acceleration, some slippage will always occur when the car is being driven at a constant speed. Conventional control Conventional transmission control is by means of an hydrau­lic computer (in reality, the transmission’s valve body) and this uses oil pressure to perform its function. Oil is pressurised by an internal pump and this pressure is modulated by two main variables: (1) road speed, and (2) throttle position. In the simplest two-speed transmission, these two variables oppose each other by bearing on opposite ends of the same spool valve. Fig.2 shows a schematic of this type of control system. A spring holds the shift valve in the “first gear” position, to allow the car to start off in low gear. If throttle pressure is high (ie, the accelerator is hard down), then the shift valve will resist the rising governor pressure (which is proportional to road speed). However, when the throttle pressure Fig.1: automatic transmissions use several sets of these plane­tary gears. This allows the ratios to be changed while the gears are in constant mesh. FIRST GEAR SECOND GEAR SPRING GOVERNOR (ROAD SPEED) INPUT THROTTLE PRESSURE SHIFT VALVE PRESSURE REGULATOR INPUT Fig.2: the basis of hydraulic transmission control is the spool valve, which is subject to varying hydraulic pressures. This diagram shows a simple 2-speed system. Fig.3: this diagram shows the pressure flow for a simple 2-speed hydraulicallycontrolled transmission. THROTTLE VALVE PUMP PRESSURE REGULATOR X FIRST GEAR SHIFT SECOND GEAR GOVERNOR VALVE X X = DRAIN October 1994  15 Fig.4: an automatic transmission is the most complicated mechani­cal component in a car. This cutaway drawing is of the Jatco L4N71B 4-speed transmission which uses hybrid electro-hydraulic control. drops (ie, the accel­erator has been lifted) or the road speed rises sufficiently, then the governor pressure will cause the valve to move to the right. A 1-2 gear change will then occur as the valve directs fluid to the correct planetary gear control clutch and/or band. Obviously, if gear changes are to be completed quickly and aspects such as kickdown are required, then some additions to Fig.2’s simple system are required. A manual control valve (so that P-R-N-D-1 can be selected) is also needed. However, all hydraulic transmissions are essentially controlled using this type of valve-pressure approach. Fig.3 shows a flow diagram of this simplified version. The transmission’s hydraulic control valves are located in the valve body at the base of the transmission. Machined to very fine tolerances, these valves generally work for very long serv­ice lives with little maintenance, as long as regular transmis­ sion fluid changes are carried out and overheating of the oil does not occur. Electro-hydraulic control With the hydraulic control of automotive transmissions very well entrenched, full electronic control was not immediately introduced when the technology became available. The high cost of transmission development meant that hybrid transmissions appeared next, using some elements of electronic control matched to FUSE CONVERTER CLUTCH SOLENNOID CONTROL UNIT 17 OD CANCEL SOLENOID DOWNSHIFT SOLENOID 2 1 POWER SHIFT SWITCH INHIBITOR SWITCH 18 6 7 10 5 8 THROTTLE VALVE SWITCH 3 22 11 VEHICLE SPEED SENSOR 16  Silicon Chip 4 CONTROL UNIT 9 21 KICKDOWN SWITCH 12 1-2 2-3 16 3-4 15 TEMP SENSOR 19 THROTTLE VALVE SENSOR Fig.5: hybrid control transmissions generally have a limited range of electronic control capabilities. This unit is able to override the hydraulics only in the selection of overdrive (fourth gear), kickdown and torque converter lockup (Holden). Fig.6: this Bosch system integrates engine & transmission manage­ment into one unit. This allows the easy use of sophisticated techniques like retarding the ignition timing during gear chang­es. Many of the input sensors for the engine & transmission control are the same. trans­ missions which are essentially hydraulically controlled. Generally, the electronic control exercised in these hybrid transmissions is for features such as kickdown and torque con­verter lock-up. One example is the Jatco L4N71B, as used in the Holden VL Commodore, Nissan Skyline and some Mazda models. This transmission is a real “Grandpa’s axe”, with the 1970s 3-speed 3N71B having had an overdrive unit added and then some electronic control juxtaposed on top! Fig.4 shows this transmission in cutaway form. Ten input signals to the Transmission Control Unit (TCU) are used and the system controls three transmission functions. Fig.5 shows the circuit for this system. The electronics is able to override the hydraulics only in the selection of overdrive (fourth gear), kickdown and torque converter lock-up. The TCU uses vehicle speed, throttle position, transmission fluid temperature, and the positions of the hydraulic shift valves as its main in- B A Jatco’s hybrid electro-hydraulic controlled transmission uses a solenoid (A) to control kickdown & a temperature sensor (B) to indicate transmission fluid temperature to the control unit. puts. By using a switch mounted on the gear lever, the driver can select between “power” and “economy” modes, with different shift behav- iour experienced in each mode. Fast acceleration will also automatically select the power mode. In this mode, the upshift and downshift points October 1994  17 The traditional hydraulic control system uses valves mounted inside an intricate valve body to determine when gear shifts occur. Hydraulically-operated wet multiplate clutches are used in all auto transmissions – whether they are controlled electronically or not. the transmission oil temperature is less than 45°C; (2) during acceleration; (3) during a gear change; (4) when the throttle is closed; and (5) when the transmission is in first and second gears. Actual control of the clutch operation is hydraulic, with the TCU operating a bleed-off solenoid. Full electronic control All automatic transmissions use planetary gear sets. They are compact & remain permanently engaged – even during ratio changes. generally occur at higher engine rpm than in economy mode. The electronic module controls the overdrive function, with change into overdrive inhibited when the accelerator is floored, when the transmission is in power mode, and when the transmission fluid is at a temperature of less than 45°C. The latter inhibition occurs because exhaust emissions would suffer if using low rpm and wide throttle angles when the engine was still relatively cold. (Note that with this system, the engine management 18  Silicon Chip and transmission control electronics are entirely separate – there is no engine coolant temperature input to the transmission control). Because of the intrinsic slippage experienced in torque converters during cruise conditions, manufacturers have started building in lock-up converter clutches. However, if the torque multiplication function is still to occur, then the clutch should not lock-up under certain conditions. For example, the L4N71B torque converter will not lock-up (1) when With the adoption of transmissions expressly designed for full electronic control, a different approach to the design could be taken. The fundamental sensor requirements for gear selection control could be re-evaluated and greater versatility and accura­cy built-in. Electronically-controlled transmissions still use hydraulics to apply the clutches and bands but all the valves are triggered by the electronic control unit. Up to 14 inputs are used in some transmissions, with sometimes six internal hydraulic solenoids controlled by the electronics. In many cars, the engine and transmission management computers are integrated, allowing the manufacturer to include refinements such as retarding the ignition during gear changes to give smoother progress. In one car (Subaru Liberty), the electronic transmission control is divided Fig.7: a “hot” chip can be used to reprogram a fully electroni­cally-controlled automatic transmission. This diagram shows the results obtained from a Holden Jackaroo V6 using a Fueltronics-modified transmission control unit. into six areas. These areas are: (1). Gear Shift Control: here, the TCU controls the gear change points using different internal maps, depending on whether the economy or power pattern has (automatically) been selected. It also holds fourth gear longer when the cruise control is being used (thereby stopping unnecessary down-shifts) and locks the transmission in third gear when the anti-lock braking system (ABS) is operating. If the transmission fluid temperature is too low, it prevents the use of fourth gear. It also holds each gear when the gear selector is being manually used. (2). Lock-Up Control: the TCU determines when torque converter lock-up will occur. This depends on the gear used, the throttle position and vehicle speed. (3). Over-Running Clutch Control: engine braking is performed by using the TCU to determine the operation Even the simplest automatic transmission is a complex mix of hydraulic valves, gear sets and friction elements. Electronic control is now taking over from full hydraulic control. of an over-run clutch. The operation of this clutch depends on the power/ economy range being used, vehicle speed, and cruise control operation. When the cruise control is in operation, full engine braking is imposed to prevent speed build-up when coasting down hills. (4). Line Pressure Control: during gear shifting, the hydraulic oil pressure is dropped to reduce “shift shock”. As vehicle speed increases, the line pressure is brought up to provide better hy­draulic clamping of the clutches and bands. During engine start­ ing, the hydraulic pressure is reduced to impose less cranking load on the starter motor. (5). Automatic Power/Economy Selection: when the speed of the throttle opening exceeds an internal value, the TCU switches over to its power shift map and then returns to the economy mode when the throttle opening falls below a preset amount. (6). Shift Timing Control: by using variations in hydraulic pressure at the appropriate times, the TCU is able to smooth up-shifts and down-shifts. Incidentally, with full microprocessor control, new programs can now be written which modify the change points. By using a “hot chip”, for example, the power mode can be made to kick down at higher speeds than for the standard chip, with the intermediate gears holding on for longer before SC changing up. October 1994  19 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) Australi 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 are currently i n stock. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. 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Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia October 1994  23 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Test GPO for workshops This test GPO provides a simple means of connecting proto­type equipment to the mains without blowing fuses, tripping circuit breakers or overloading transformers. It consists of a 1500W radiator permanently wired in series with the Active terminal of a GPO (General Purpose Outlet). In parallel with the radiator is a 150W globe. Both are mounted on the ceiling above the general work area. Additional lamp sockets are wired in series with the test GPO. Parallel connected switches allow various combinations of series-connected lamps to limit load currents that are rated for currents much less than the radiator element; eg, low voltage plugpacks. If a load causes the 150W globe on the wall (wired in parallel with radiator) to light up brightly and remain that way, there is a major problem (providing of course that the test load is rated at less than 1500W). The system is particularly suitable for testing computer switch­mode power supplies. The initial surge current of N GPO 10A 240V A 10A CB 150W 150W 150W 150W 1.5kW RADIATOR S1 S2 S3 24  Silicon Chip N E 1 10W E 1 10W 1 10W 1 10W S4 NC TEST TERMINALS these power supplies causes a 150W series connected globe to light up brightly, then dim to barely visible. If, however, one of the capacitors or rectifier diodes is faulty (a common fault), the globe will remain brightly lit. This simple method prevents the usual arcing from occurring when a partial short circuit exists. It also prevents further damage to equipment using conventional step-down transformers Flashing battery monitor This battery monitor flashes when the voltage drops below the preset trip level. The circuit is a normal astable multivi­brator using a CMOS 555 for low battery consumption. A clamp circuit is added to prevent pin 6 from exceeding 4V. VR1 is used to adjust the internal threshold of the timer and thus sets the onset of operation. In normal operation with a 555 timer, the capacitor at pin 6 charges between 1/3Vcc and 2/3Vcc, as set by the internal com­parators of the chip. This circuit, however, has pin 6 clamped to 4V, as set by zener A with faulty circuitry connected to their sec­ondary side. The series resistors in the Earth circuit allow checks to be made for earth leakage currents. The terminals across the resistor allow the AC voltage drop to be measured with a standard DMM set to 200mV (AC). The measured value is the current in mil­liamps. H. Peter Harle, Mt. Druitt, NSW. ($25) +9V 100k 7 3k D1 1N4148 ZD1 3.3V 100k 6 100  8 4 IC1 7555 2 LED1 3 1.7k 5 1 VR1 100k  0V The circuit for the battery monitor is based on a 7555 timer. It flashes LED 1 when the battery voltage falls below 6V. 10 16VW diode ZD1 and diode D1 and so the circuit does not oscillate. However, if the battery voltage drops to below +6V, the upper threshold of the chip will be below +4V and so the capacitor at pin 6 will be able to charge and discharge in the normal way and so the LED connected to pin 3 will flash on and off. VR1 is used to artificially lower the internal thresholds of the chip and so sets the battery voltage at which the circuit starts to flash. V. Erdstein, Highett, Vic. ($20) PC Alert – a simple watchdog alarm This device was constructed to monitor a special purpose PC in an office environment. The PC is running constantly to provide queued file transfer between a mainframe and a network. However, due to the vagaries of network and mainframe communications, the PC may occasionally “hang”. To detect this, the PC-Alert circuit is connected to the parallel port of the PC and provided the signal on pin 2 (Data bit 0) of the port changes at least every 80 seconds, all is quiet. However, if a change does not occur in the allotted time the alarm will sound and draw attention to the state of the PC application. Naturally, the PC is programmed to toggle the state of pin 2 frequently. IC1 and IC2 are arranged as oneshot timers, with timing intervals of about 80 seconds for the values shown. When the output (pin 3) of either 555 goes low the buzzer will sound. If pin 2 of the parallel port is high, Q3 will conduct and continu­ously retrigger IC2, so its output will remain high. However, if pin 2 goes low, the output of IC2 will remain high for the speci­ fied time interval, after which the Auto-shutoff for battery circuits If a multi-cell nicad battery pack (or cells used in series) are dis­charged to below 1.1V per cell, then the stronger cells will reverse charge the weak ones, which will cause permanent damage to those cells. This circuit will prevent reverse charging. It is connected between the batteries and the load and it shuts off the power when the voltage reaches 1.1V per cell. In more detail, switch S1 starts the circuit by shorting the NO (normally off) contacts of the relay. The battery voltage is taken from a divider and compared against a 3.9V reference. Normally the voltage at the non-inverting input will be greater than the inverting input. This will make the op amp’s output high and turn on RLY1 via transistor Q1. The relay’s contacts +9V 560  6.8k D1 1N4004 D2 1N4004 4 2 BUZZER 3 IC1 555 6 Q2 BC547 4.7k Q1 BC547 8 7 2.7k 2.7k  LED1 PIN 2 1.5M 5 1 .001 47 16VW TANT D3 1N4004 PIN 19 S1 1.5M 2.7k D4 1N4004 7 D5 1N4004 8 IC2 555 6 Q3 BC547 4 2 +9V D6 1N4004 3 5 1 .001 47 16VW TANT output will go low and the buzzer will sound. IC1 behaves similarly, except that Q2 is used to invert the signal from pin 2. Therefore, IC1 will sound the alarm about 80 seconds after pin 2 goes high and IC2 will sound it about 80 seconds after pin 2 goes low. So, as long as pin 2 keeps changing between low and high the alarm will be dormant. If the alarm does sound, pressing S1 rests both ICs and switches off the alarm for another 80 seconds. R7 and D7 are simply to provide power on indication. I. Hogan, Mulgrave, Vic. ($25) S1 BATTERY VOLTAGE RLY1 R1 D1 1N4004 10k 7 3 3.9k 2 IC 741 6 4 RLY1 10k Q1 BC548 TO LOAD R1 6 1.6k 7.2 2.7k 8.4 3.9k 9.6 4.7k 10.8 6.2k 12 7.3k ZD1 3.9V are now closed and current will flow through it with S1 released. When the voltage at pin 3 falls below 3.9V, the op amp’s output goes low, de-energising the relay and shutting off power to the circuit and load. The accompanying table shows the battery voltage and the appropriate resistor required for R1. Devices which draw a heavy surge current may not be used satisfactorily with this circuit. This is because the battery voltage can dip below the cutoff voltage and false trigger the circuit. A. Chin, Heidelberg, Vic. ($20) October 1994  25 A Beginner’s Variable Dual-Rail Power Supply If you’re just beginning in electronics, then you’ll probably baulk at building a mainsoperated power supply. This project uses a plugpack which means that you can make your own variable dual-rail power supply without worrying about mains wiring. By DARREN YATES When it comes to experimenting in electronics, power sup­plies are a bit of a “chicken and egg” situation. To experiment with circuits, you need a power supply but unless you have the necessary knowledge already, building a mains-powered supply is beyond most beginners. The alternative is to run all of your circuits from batter­ies or buy a readymade supply. Either option is expensive. So in the interests of making it easier to start experimenting, we’ve 26  Silicon Chip come up with this dual-rail power supply which runs from a 16V AC plugpack. It’s capable of providing output voltages ranging from ±1.25V DC to ±15V DC at currents up to 500mA (see Fig.1). The beauty of this design is that it doesn’t require any external mains wiring! All the mains wiring is contained inside the plugpack, leaving you with just the low-voltage AC output which connects straight into the project. In order to keep costs down, the output voltage is varied in 11 switched steps. This eliminates the need for an output voltage meter since the precise value can be directly read off the switch position. The 11 switched voltage ranges are: 1.25V, 1.5V, 3V, 4.5V, 5V, 6V, 7.5V, 9V, 12V, 13.5V & 15V. Both supply rails are protected against short circuits and voltages generated by external loads, while a LED indicator lights if the supply stops regulating. Another worthwhile feature is the provision of a “load” switch. This allows the power to the load to be switched on and off while keeping the supply switched on. The output current capabilities of the supply are relative­ly modest but should be more than adequate for most projects. Fig.1 plots the maximum current that can be delivered at various output voltages. As can be seen, the supply is capable of deliv­ ering 250mA or more for voltages Fig.1: this graph plots the maximum output current from the supply for voltage settings between 1.5V & 15V (16VAC 1A plugpack). The supply is capable of delivering 250mA or more over most of the range. from 1.5V up to about 14V, with a maximum of 500mA at 7.5V. Note that these figures assume a 16VAC 1A plugpack supply. By now, some readers will be asking “what is a dual-rail power supply?” It’s quite straightforward really – a dual-rail power supply has both positive and negative output voltage rails, as well as the ground (or zero volt) rail. Most projects and cir­cuits you build will only require the positive output and the ground rail. This is basically the same as if you connected a battery of the same voltage to the circuit you’re building. However, you’ll also come up against circuits which use operational amplifiers (op amps) and these require both posi­ tive and negative supply rails. That’s where the dual-rail power supply comes in. It can power op amp circuits with ease and so is just that much more versatile than a standard single rail supply. An important feature of this design is that the negative supply rail automatically tracks the positive supply rail. This means that the two rails always have the same absolute value. Thus, if you set the positive output to +12V, the negative rail will be at -12V. And here we should clear up a common misconception regard­ ing dual rail supplies. Despite what many people think, it’s quite possible to use the positive and negative rails to obtain a much higher output voltage than is possible by simply connecting between one of these rails and the 0V rail. For example, if you want a 30V single-rail supply, simply set the supply to give ±15V and connect the circuit across these outputs. Another way of looking at this is simply to con­sider that there is 30V between the two outputs. So a dual-rail ±1.25-15V variable power supply can also function as a 2.5-30V single rail supply. How it works The circuit for the Beginner’s Dual Rail Power Supply uses only standard components which you can find in any virtually electronics store. If you’ve got a parts bin handy, you’ll prob­ably have a few parts that are suitable already. Let’s take a look at the circuit – see Fig.2. The plug pack takes care of all of the mains wiring and steps the 240VAC mains voltage down to a suitable 16VAC for our circuit. This is fed via power switch S1 to rectifier diodes D1 & D2 to produce unregulat­ed plus and minus DC rails of about 20V. These DC rails are filtered by two 470µF electrolytic ca­ pacitors and fed to LM317 and LM337 3-terminal regulators. These provide the adjustable plus and minus supply outputs respec­tive­ly. In the case of the positive rail, the LM317 (REG1) does most of the work. Its output voltage is set by the 120Ω and 2.7kΩ resistors on its ADJ terminal and by the resistive divider string associated with switch S3. These components form the feedback network around the regulator IC. Basically, switch S3 sets the output voltage from REG1 by setting the resistance between the ADJ terminal and the 0V rail. When the ADJ terminal is connected to 0V, the output voltage is +1.25V. This voltage can then by PARTS LIST 1 plastic case, 198 x 113 x 62mm 1 PC board, code 04110941, 102 x 57mm 1 front panel label 1 red 4mm binding post 1 black 4mm binding post 1 blue 4mm binding post 1 SPDT toggle switch (S1) 1 DPDT toggle switch (S2) 1 12-position 1-pole rotary switch (S3) 1 knob to suit S3 2 LED bezels 1 16VAC 1A plugpack 1 3.5mm power socket 2 mini U heatsinks 4 rubber feet Semiconductors 1 LM358 dual op amp (IC1) 1 LM317 3-terminal regulator (REG1) 1 LM337 3-terminal regulator (REG2) 6 1N4004 rectifier diodes (D1-D6) 6 1N914 diodes (D7-D12) 2 15V 1W zener diodes (ZD1,ZD2) 2 5mm red LEDs (LED1,LED2) Capacitors 2 470µF 25VW electrolytics 2 100µF 25VW electrolytics 4 1µF 63VW electrolytics 1 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 4.7MΩ 2 330Ω 2 47kΩ 1 270Ω 1 22kΩ 1 220Ω 2 3.3kΩ 1 180Ω 1 2.7kΩ 2 150Ω 3 1kΩ 2 120Ω 1 680Ω 1 56Ω 1 560Ω 1 27Ω 1 470Ω Miscellaneous Machine screws & nuts, washers, hook-up wire. stepped up to a maximum of +15V by using S3 to progressively switch in additional resistors in the string. The 1µF capacitor between the ADJ pin and ground ensures that any residual noise from the mains is kept to a minimum. Finally, the output voltage October 1994  27 28  Silicon Chip POWER LED1 1k 470 25VW 470 25VW D1 1N4004 330  ZD2 15V ZD1 15V 330  -15V 47k +15V 47k 22k 1 8 +15V -15V IC1a 2 LM358 4 1 1 1 OUT 2.7k LM317 REG1 ADJ 3 IN BEGINNER'S POWER SUPPLY  D2 1N4004 FROM 16VAC PLUG-PACK POWERT S1 D3 1N4004 1 120  100 25VW 15V 13.5V 12V 9V 7.5V 6V 5V 4.5V 3V 1.5V 1.25V S3 D4 1N4004 REG2 ADJ IN LM337 OUT 1k 560  470  680  270  220  150  56  180  150  27  120  D5 1N4004 3.3k 3.3k 0.1 D7 AO I LM317 D8 2x1N914 100 25VW 6 5 4.7M IC1b D6 1N4004 A IO LM337 7 1k A K 4x1N914 D9-D12 LED2 DROPOUT  M1 R2 R1 S2b LOAD S2a 0V V V This is the view inside the prototype. Note the two small heatsinks fitted to the two 3-terminal regulators. Take care to ensure that the regulators are correctly oriented – each device is installed with its metal tab towards the centre of the PC board. from REG1 is filtered by a 100µF electrolytic capacitor and fed to the load via switch S2a. Negative regulation The negative regulator (REG2) works in a similar manner to REG1. It’s made to track the positive rail by using IC1a to provide a mirror of the voltage on the ADJ terminal of REG1. For example, if the ADJ voltage of REG1 is at 10.75V (to produce a 12V output), then IC1a will act to produce -10.75V on the ADJ terminal of REG2. This is achieved by connecting IC1a as a unity gain invert­ ing amplifier. Its inverting input (pin 2) is fed from the ADJ terminal of REG1 via a 47kΩ Fig.2 (left): the circuit uses two adjustable 3-terminal regulators (REG1 & REG2) to provide the positive & negative supply rails. IC1a inverts the control voltage applied to the ADJ terminal of REG1 to drive REG2, while IC1b drives D9-D12 & LED 2 to provide dropout indication. resistor, while the associated 47kΩ feedback resistor sets the gain to -1. The non-inverting input is biased to 0V via a 22kΩ resistor to ensure minimum output offset. The output of IC1a drives the ADJ terminal of REG2 via a 1kΩ resistor. This 1kΩ resistor is inside the feedback loop and is there so IC1a can actually drive the ADJ terminal to the maximum required value of -13.75V (when the output voltage is set to ±15V). This is outside the operating range of the LM358 because its supply rails are ±15V. The result of all this is that the negative output voltage of REG2 tracks the positive output voltage of REG1. The ±15V supply rails for IC1 are produced by zener diodes ZD1 and ZD2, while LED1 provides power indication. Diodes D3, D4, D5 and D6 protect the regulators from any reverse voltag­es which may be generated by capacitive or inductive loads con­ nected across the outputs. Dropout detection When the regulators are working as intended, the ripple voltage superimposed on the DC rails will be very low. However, if the current drain is higher than the regulators can supply while still maintaining about 2V between their IN and OUT termi­nals, the ripple voltage will suddenly become quite high. At this point, the output voltage will fall quite rapidly if even more current is called for and the ripple will go even higher. What this means of course is that the power supply is unable to provide sufficient current to the load and is dropping out of regulation. This undesirable condition is indicated by the dropout indicator circuit and this is based on IC1b and diodes D9-D12. IC1b is connected as an inverting amplifier with a high gain, as determined by the ratio of the 4.7MΩ feedback resistor to the impedance of the 0.1µF input capacitor and the 3.3kΩ resistors which monitor the positive and negative supply rails. The two back-to-back diodes, D7 & D8, limit the maximum input signal to ±0.7V. When ever either regulator drops out of regulation (eg, if an output is shorted to ground), the ripple output increases greatly. Because it operates with such high gain, IC1b squares up this signal to produce a square-wave October 1994  29 LED1 K S1 V+ 180  150  27  A 0V V-  150  56 1 S3 1 11 56 0 0W 22 27 0 680  47 LED2 K S2 0 2 3 4 A D3 ZD1 1 1k 1uF REG2 1k PLUGPACK SOCKET output at pin 7. This output drives a bridge rectifier consisting of D9-D12 via a 1kΩ current limiting resistor. The bridge rectifier in turn drives LED 2 and this begins to glow when the ripple at one of the regulator outputs exceeds about 4mV peak-to-peak. By the time the ripple reaches 19mV p-p, the LED is fully alight. An optional metering circuit is also shown on Fig.2, although we haven’t included it in the prototype (the appropriate connection points are on the PC board). All you have to do is calculate what resistance should be added in series with the meter to give a full-scale reading at 30V. For example, if you have a 0-1mA meter movement, then by Ohm’s Law R = V/I = 30/.001 = 30kΩ. Making R1 30  Silicon Chip 4 3 IC1 LM358 470uF 330 2 1 120  3.3k 0.1 D10 D7 D6 D12 100uF D11 1uF 100uF R1 3.3k D2 470uF D9 47k 330 1uF ZD1 D8 22k D1 1k 4.7M 2.7k 1uF 120  47k REG1 D5 R2 METER D4 Fig.3: use medium-duty (24 x 0.2mm) hookup wire for all wiring connections & take care to ensure that switch S3 is wired exactly as shown. Resistors R1 & R2 can be left out of circuit if you don't intend installing an output meter. = 27kΩ and R2 = 2.7kΩ will be near enough, especially when the internal impedance of the meter is taken into consideration. Construction All of the components for the Beginner’s Power Supply are installed on PC board coded 04110941 and measuring 102 x 57mm. Before commencing construction, check the board carefully against Fig.4 for any shorts or breaks in the tracks. If you find any, use a dash of solder or a small artwork knife where appropriate to fix the problem. Fig.3 shows the parts layout on the PC board. Start by installing PC stakes at the external wiring points, followed by the wire links, resistors, diodes, capacitors and ICs. Make sure that all polarised parts are correctly oriented and check the resistor values on your multimeter before mounting them on the board. Table 1 shows the resistor colour codes. Note that diodes D1-D6 are all 1N4004 types, while the remaining diodes are the smaller 1N914 types. Pin 1 of the IC is adjacent to a small notch or dot in one end of the plastic body. The metal tabs of the two 3-terminal regulators must be oriented exactly as shown on Fig.3; ie, the metal tab of each device goes towards the centre of the board. Do not confuse these two regulators – REG1 is an LM317 type while REG2 is an LM337. Once mounted, they can be fitted with small finned heatsinks to aid cooling. After the board assembly has been completed, you can in­stall the resistors around switch S3. As supplied, this switch will be a 12-position type. It is easily converted to an 11-position type by lifting the locking ring at the front of the switch bush and rotating it to position 11. This done, solder the resistors to the switch terminals exactly as shown on Fig.3, starting at terminal 1 and continuing in an anticlockwise direction to termi­ nal 11 (note: in most cases, the terminal numbers are marked on the back of the switch). If you have a switch that doesn’t have the terminals marked, here’s an easy way to find terminal 1. All you have to do is rotate the switch fully anticlockwise, then use your multi­ meter to find which terminal is now connected to the wiper. This will be terminal 1 and you can begin by soldering the 27Ω resis­ tor to it. The remaining resistors can then be installed exactly as shown. Check the resistor values carefully as they are mounted. If you make a mistake, then one or more of the voltage ranges will be wrong. It’s also a good idea to trim the resistor leads back as you go so that you don’t end up with a tangled mess. Don’t forget the wire link between the switch wiper (near Fig.4: this is the full-size etching pattern for the PC board the centre) and terminal 11. The Beginner’s Power Supply is designed to fit into a plas­tic zippy case measuring 198 x 113 x 62mm. The front panel is actually one of the long sides of the case, while the PC board is mounted on the bottom of the case. The whole unit is then turned upside down so that the lid becomes the base. The first step is to attach the front panel label (bottom nearest the lid), then use this as a drilling template for the front panel items. The PC board can also be used as a template to mark out its four mounting holes, while an additional hole will be required in the rear panel to accept a 3.5mm power socket. Note that it’s best to initially drill all holes to 3mm. These can then be enlarged where necessary using a tapered ream­er. Final assembly Once the holes have been completed, mount the various items in place. Fig.3 shows where each component should be placed. Note that the range switch (S3) must be oriented so that RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  2 ❏  1 ❏  2 ❏  1 ❏  3 ❏  1 ❏  1 ❏  1 ❏  2 ❏  1 ❏  1 ❏  1 ❏  2 ❏  2 ❏  1 ❏  1 Value 4.7MΩ 47kΩ 22kΩ 3.3kΩ 2.7kΩ 1kΩ 680Ω 560Ω 470Ω 330Ω 270Ω 220Ω 180Ω 150Ω 120Ω 56Ω 27Ω 4-Band Code (1%) yellow violet green brown yellow violet orange brown red red orange brown orange orange red brown red violet red brown brown black red brown blue grey brown brown green blue brown brown yellow violet brown brown orange orange brown brown red violet brown brown red red brown brown brown grey brown brown brown green brown brown brown red brown brown green blue black brown red violet black brown 5-Band Code (1%) yellow violet black yellow brown yellow violet black red brown red red black red brown orange orange black brown brown red violet black brown brown brown black black brown brown blue grey black black brown green blue black black brown yellow violet black black brown orange orange black black brown red violet black black brown red red black black brown brown grey black black brown brown green black black brown brown red black black brown green blue black gold brown red violet black gold brown October 1994  31 For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 553 1763; Fax (03) 532 2957 32  Silicon Chip Additional heatsinking As the unit stands, the output current capability is limit­ed by the modest amount of heatsinking. That’s because the two 3-terminal regulators have inbuilt thermal overload protection which means that they automatically throttle back when they start to get too hot. As an option, you can slightly increase the output current capability by increasing the heatsinking. This - DROPOUT 0V 13.5 1.5 + 15 1.25 POWER LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE Now for the smoke test. Connect a 16VAC 1A plugpack supply, switch on and use your multi­meter to check the voltage between the “+” and “0V” terminals for each switch posi­ tion. In each case, the measured voltage should correspond to the switch position. The negative rail can then be checked in similar fashion; ie, by connecting the multimeter between the “-” and “0V” terminals. If everything checks out, the power supply is ready for use. If you strike problems, check the supply rails to the 3-terminal regulators and to IC1. You should find +20V on the IN terminal of REG1, -20V on the IN terminal of REG2, +15V on pin 8 of IC1, and -15V on pin 4 of IC1. If any of these voltages are incorrect, switch off and check D1, D2, ZD1 and ZD2 as appro­priate. If the measured output voltages don’t correspond to the switch settings, check the resistor string around S3. You may have some of the resistors in the wrong positions. 12 Testing 3 DISHES 60m to 3.7m FROM ...........$130 LOAD FEEDHORNS C.BAND FROM .........$95 9 FEEDHORNS Ku BAND FROM ......$45 4.5 LNB’s C FROM .................................$330 DUAL TRACKING POWER SUPPLY LNB’s Ku FROM ..............................$229 7.5 SATELLITE RECEIVERS FROM .$280 6 Aussat systems from under $850 5 SATELLITE SUPPLIES the pointer on the knob aligns with the 1.25V marking on the front panel when the switch is rotated fully anticlockwise. Binding posts are used for the three output terminals. We suggest that you use red for positive, black for 0V and blue for the negative. The PC board is secured in the case using machine screws and nuts, with additional nuts under each corner of the board acting as spacers. The wiring can now be completed as shown in Fig.3. It’s a good idea to use different coloured wire for each section, as this will make it easier to check your wiring later on. Take care with the orientation of the LEDs – the anode lead is always the longer of the two and the cathode will be adjacent to the flat edge on the LED bevel. Fig.5: this full-size artwork can be used as a drilling template for the front panel. additional heat­ sinking can be obtained by substituting an aluminium lid for the plastic lid of the case. The two regulators are then bolted to the lid using TO-220 isolating kits (ie, a mica washer and insulating bush) to provide electrical isola­tion and their leads connected to the PC board via flying leads. SC SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Build this talking headlight reminder Ever leave your car’s headlights or parking lights on? Flatten the battery too? If so, you need this talking headlight reminder. If you accidentally leave your headlights on, it tells you to switch them off. By DARREN YATES Most headlight reminders are quite simple devices. Typical­ly, they sound a beeper if the ignition is switched off while the headlights are still on. In some cars, the beeper is not activat­ed until a door is opened but regardless of the triggering method used, a headlight reminder can save you from a great deal of inconvenience. Of course, if you drive an old car, then it’s quite prob­able that is lacks this very useful feature. This Talk- ing Head­ light Reminder is actually far more elaborate than a headlight reminder needs to be but it’s easy to build and it has one big advantage over other such units – you can record your own mes­sage. After all, what could be more attention-getting than “you’ve left yer lights on stupid”, or something equally hard hitting? The recorded message is continually replayed over a 30-second period, after which the device automatically switches itself off. The heart of the Talking Headlight Reminder is a 16-second sound recorder IC, the ISD1416 from Information Storage Devices. This is a second generation device and is based on the original ISD1016 which we used in the 16-Second Message Recorder described in July 1993. Like the original device, the ISD1416 features 16 seconds of recording time but now has the added features of optional edge-level control and automatic power down. Edge-level control simply means that playback can be initiated by momentarily press­ing the PLAY button, although that feature is not used here. Power for the circuit is supplied via the headlights switch, while the trigger input monitors the ignition switch. The sound comes from an external speaker and this can be October 1994  37 INTERNAL CLOCK XCLK MIC MIC REF AGC DECODERS AMP ANA OUT ANALOG TRANSCEIVERS ANTIALIASING FILTER ANA IN PREAMP pling rate. The signal is then sampled and stored in the EEPROM array, ready for playback. During playback, the stored samples are clocked out of the EEPROM array and passed through a 5-pole smoothing filter. The recovered signal is then fed to an internal audio amplifier and this can either drive a small loudspeaker directly or an external power amplifier. Thankfully, the circuitry inside the IC takes care of all the difficult jobs such as providing clock signals and sampling rates. All we have to do is apply the signal, make sure that the correct lines are either high or low, and that’s about it. SAMPLING CLOCK TIMING SP+ SMOOTHING FILTER SP- AMP 128K CELL NONVOLATILE ANALOG STORAGE ARRAY AGC POWER CONDITIONING VCCA VCCD ADDRESS BUFFERS DEVICE CONTROL A0 A1 A2 A3 A4 A5 A6 A7 REC PLAYE PLAYL RECLED Fig.1: this block diagram shows the main components of the ISD1416 sound recorder IC. It uses a 128K-cell EEPROM to store up to 16 seconds of audio in analog form, a technique that eliminates the need for A/D & D/A converters. mounted either under the dashboard or under a seat. OK, that’s just one application for this device. It could be used anywhere you need a solid-state message recorder that re­ p eats a recorded message over a 30-second interval. All you have to do is connect the appropriate supply voltage and trigger input. ples the incoming audio signal and stores the samples as analog voltages in a 128,000-cell EEPROM (electric­ ally erasable programmable read-only mem­ ory). This technique provides much better sound quality than can be obtained from a similar digital device and means that the recording is retained in memory when the power is removed. And because the information is stored in the EEPROM in analog form, there’s no need for A/D and D/A converters. In greater detail, the incoming audio signal is amplified and fed through a 5-pole anti-aliasing filter to remove frequen­cies greater than half the sam- Sound storage Refer now to Fig.1. This shows the block diagram of the ISD1416 and we’ll go over the principles of this chip briefly. During recording, the device sam- How it works Let’s now take a look at the circuit for the Talking Head­light Reminder –see Fig.2. As you can see, there are just three ICs involved: a 555 timer Fig.2 (below): the circuit is based on the ISD1416 sound recorder (IC2). If the ignition is switched off before the lights, IC1 turns Q1 on for 30 seconds & IC2 repeats the recorded message until the timing period ends. IC3 is the audio amplifier stage. D2 1N4004 REG1 78L05 OUT GND 1k 1k 0.1 10k RECORD LED1 0.22 A K 18 0.22 17 10 16VW MIC 24  25 PLAYE MIC MIC REF RECLED 1M 100k FROM IGNITION SWITCH 1k D1 1N4004 100k 7 6 0.1 PLAY S1 Q1 BC548 C 4 8 3 100k B REC S2 IC1 E 555 5 2 1 22 25VW 0.1 B E C E B C VIEWED FROM BELOW TALKING HEADLIGHT REMINDER 38  Silicon Chip IN CHASSIS OUT 100 16VW 1 14 1k 20 GND REG2 7809 100k 27 REC 23 AIN PLAYL 1 A0 AOUT 2 A1 3 A2 XCLK 5 A4 6 AGC A5 VSSD VSSA 12 13 V+ FROM HEADLIGHT SWITCH 100 16VW 28 VCD 16 VCA A3 4 9 A6 10 A7 IC2 SP+ ISD1416 10k IN 1 VOLUME VR1 10k 6 3 IC3 2 LM386 7 21 4.7k 10 16VW 5 4 100 8W EXT. SPKR 0.1 10  26 19 470k 4.7 25VW A K I GO I GO LED1 MIC 100k 100uF 1uF 1k REG2 100uF 0.22 IC3 LM386 1 IC2 ISD1416 0.1 TO IGNITION SWITCH 1 S1 (IC1), the ISD1416 (IC2) and an LM386 audio power amplifier (IC3). D1, IC1 and transistor Q1 form the playback trigger circuit for IC2. If the headlights are off when the ignition is switched off, nothing happens since no power is applied to the circuit. However, if the ignition is switched off first, D1 is forward biased (since its cathode is pulled low) and a short Below: the PC board is mounted on the back of the lid using 19mm long spacers & secured using machine screws & nuts. Note the method used to mount the two switches. S2 470k 1uF D1 TO SPEAKER TO SPEAKER CHASSIS 1k 100k 100k D2 +V FROM LIGHT SWITCH 0.1 4.7k 22uF 1k 100uF VR1 10  1 REG1 0.1 10k 0.22 Fig.2: install the parts on the PC board as shown here, taking care to ensure that all polarised components are correctly oriented. The two pushbutton switches (S1 & S2) are mounted by soldering their pins to the tops of PC stakes (see photo below). K 1k 10uF 0.1 IC1 555 10k Q1 100k 1M A 4.7uF negative-going pulse is applied to pin 2 (the trigger input) of IC1. IC1 is wired in monostable configuration. When triggered, its output at pin 3 goes high for approximately 30 seconds. This turns on transistor Q1 which in turn pulls the PLAYL input (pin 23) of IC2 low. PLAYL stands for “PLAY LEVEL”, which indicates that it is a level-triggered input rather than an edge-triggered one. Thus, IC2 only plays back the recorded message during the 30-second period that Q1 is on (ie, for as long as the PLAYL input is held low). Note that the address lines (A0- A5) of the ISD1416 are all connected to ground. This places the device into “loop” mode, so that the recorded message is repeatedly replayed during the 30-second period. Alternatively, IC1 (and thus IC2) can be manually triggered by pressing switch S1 (PLAY). Normally, this switch would not be used once the device is installed in a car. It’s there simply to provide a convenient way of triggering the recorded message during the setting up procedure. The audio output from IC2 appears at pin 14 and is AC-cou­pled to pin 2 of IC3, an LM386 audio amplifier. Its October 1994  39 PARTS LIST The ISD1416 sound recorder IC is mounted in an IC socket while the two remaining ICs are soldered directly to the PC board. Take care to ensure that the two switches are oriented correctly (ie, flat side to the right). 1 PC board, code 01109941, 102 x 58mm 1 plastic zippy case, 130 x 68 x 41mm 1 front-panel label 1 green snap action momentary switch (S1) 1 red snap action momentary switch (S2) 1 8-ohm 1W loudspeaker 1 electret microphone insert 1 28-pin machined IC socket 1 10kΩ 5mm trimpot (VR1) 1 5-pin 0.1-inch header 13 PC stakes 4 19mm spacers 4 3 x 30mm machine screws plus nuts & washers Semiconductors 1 NE555 timer (IC1) 1 ISD1416 16-second sound recorder (IC2) 1 LM386 low-power audio amplifier (IC3) 1 78L05 5V 100mA regulator (REG1) 1 7809 9V regulator (REG2) 1 BC548 NPN transistor (Q1) 2 1N4004 silicon diodes (D1,D2) 1 5mm red LED (LED1) Fig.4: this is the full size etching pattern for the PC board. output ap­pears at pin 5 and drives an 8-ohm loudspeaker via a 100µF ca­ pacitor. Trimpot VR1 functions as the volume control, while a Zobel network consisting of a 10Ω resistor and series 0.1µF capacitor is connected across the output of IC3 (pin 5 & GND) to ensure stability. Power for IC3 is derived from the headlight switch via reverse polarity protection diode D2 and 9V regulator REG2. Regulator REG1 provides a 5V rail to power the rest of the cir­cuit. Recording The recording mode is activated by pressing switch S2 (RECORD). This pulls the REC line (pin 27) of IC2 low, which then pulls the RECLED line (pin 25) low via internal logic circuitry. When this happens, the electret microphone turns on and feeds the incoming audio signal into pin 18 for storage in the EEPROM. At 40  Silicon Chip the same time, LED 1 (RECORD) turns on to indicate that the unit is in the recording mode. Recording either ceases after 16 seconds or when the RECORD button is released, which ever comes first. In either case, pin 25 goes high again and LED 1 and the microphone turn off. Capacitors 3 100µF 16VW electrolytic 1 22µF 25VW electrolytic 2 10µF 16VW electrolytic 1 4.7µF 25VW electrolytic 2 1µF 63VW electrolytic 2 0.22µF 63VW MKT polyester 4 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 1MΩ 2 10Ω 1 470kΩ 4 1kΩ 4 100kΩ 1 4.7kΩ 2 10kΩ Construction Most of the parts for the Talking Headlight Reminder are installed on a PC board coded 01109941. Fig.3 shows the parts layout. Begin the assembly by installing 2-pin and 3-pin headers at the LED and microphone wiring points respectively, then install PC stakes at the switch mounting positions and at all remaining external wiring points. This done, solder in the wire links, followed by the resistors, capacitors, diodes and transistors. Make sure that all polarised parts are correctly oriented and note that the 22µF capacitor near IC1 should be mounted with its body flat against the PC board – see photo. Table 1 lists the resistor colour codes but it’s also a good idea to check them on a digital multimeter as some of the colours can be difficult to decipher. The ISD1416 (IC3) is installed using a 28-pin machined IC socket. This is done because the chip is rea­sonably expensive to replace. The other ICs on pins 4 & 8 of IC1 and pins 24 & 28 of IC2. If these checks prove OK, check that Q1’s collector switches low for about 30 seconds when the PLAY button is pressed. If it doesn’t, check the circuit around IC1 and Q1. Assuming that everything works correctly, the unit can now be installed in your car. There are just three wiring connections to be made: (1) to the negative side of the headlight switch; (2) to chassis; and (3) to the negative side of the ignition switch. In addition, you will have to run two leads to the external speaker. These should be passed through a grommeted hole in the side of the case. Perhaps the easiest way of connecting to the headlight switch circuit is to simply tap into the positive lead to the tail lights. This has two advantages: (1) ease of access (gaining access to the back of the headlights switch is usually quite difficult); and (2) the tail lights come on in both the parking lights and headlights switch positions, so you don’t have to find the parking lights terminal. Note: the unit should warn if either the parking lights or the headlights are left on. Use automotive connectors to interface to the car’s wiring and make sure that all wiring is installed in a professional manner. The last thing you want is a fault in your car’s lighting system due to sloppy wiring. Finally, check that the unit operates correctly in the car and adjust VR1 to give the desired volume level. We recommend that you keep the volume setting low, to minimise any annoyance on those occasions when you do SC trigger the unit. TALKING HEADLIGHT REMINDER MIC + + PLAY REC REC ON + + Fig.5: this full size artwork can be used as a drilling template for the front panel. can then be installed in the normal manner, followed by the two 3-terminal regulators. The two pushbutton switches can now be mounted in position by soldering their leads to the tops of the PC stakes. Use a green switch for S1 (PLAY) and a red switch for S2 (RECORD). Make sure that the two switches are correctly oriented; ie, the flat side of each switch must go to the right – see Fig.2. The microphone and LED 1 are connected to their respective pin headers on the board using light-duty hook-up wire. Take care to ensure that these devices are connected with the correct polarity. Final assembly The PC board is installed on the lid of a small zippy case (130 x 68 x 41mm) and is mounted on 19mm spacers so that the snap action switches just protrude through the front panel. The first step is to attach the front panel and then use this as a drilling template for the four mounting holes. Holes will also have to be drilled for the two pushbutton switches, the microphone and the LED. Note that the larger holes should be made by first drilling small pilot holes and then carefully enlarging them to the correct size using a tapered reamer. Both the LED and the microphone should be a push fit into their respective holes. They can be finally secured in position using a small dab of epoxy adhesive. This done, the board can be mounted in position and secured using machine screws and nuts. Test & installation To test the unit, connect a 12V power supply to the V+ and chassis terminals, then hold down the RECORD button while you speak into the microphone. The message should now replay when you press the PLAY button and should continually repeat for a period of 30 seconds. If it doesn’t work, first check for +5V at the output of REG1 and on pin 6 of IC3. Check also that +5V appears TABLE 1: RESISTOR COLOUR CODES Value 4-Band Code (1%) 5-Band Code (1%) ❏  1 1MΩ brown black green brown brown black black yellow brown ❏  1 470kΩ yellow violet yellow brown yellow violet black orange brown ❏  4 100kΩ brown black yellow brown brown black black orange brown ❏  2 10kΩ brown black orange brown brown black black red brown ❏  1 4.7kΩ yellow violet red brown yellow violet black brown brown ❏  4 1kΩ brown black red brown brown black black brown brown ❏  2 10Ω brown black black brown brown black black gold brown ❏ No. October 1994  41 An electronic ballast for fluorescent lamps Do you hate fluorescent lights with their inevitable flick, flick, flicker at switch-on, the flicker while they are running & the buzz or hum of the ballast? Now you can replace the internals of your fluorescent light fittings with this elec­ tronic ballast. It is highly efficient, gives instant starting & has no flicker, buzz or hum. By JOHN CLARKE Fluorescent lights are good. They are much more efficient than any incandescent light, they are free of glare and cast very little shadow. But fluorescent lights can also be a pain, espe­cially when they are first turned on. If the tube or the starter is a bit old or the temperature is low, there will be this inevi­table flick, flick, flicker and then maybe it will come on fully. These and the other irritations associated with fluorescent lights can be eliminated with this electronic ballast. It fits directly into a stand- WARNING! This circuit operates at voltages which are potentially lethal. No part of the circuit should be worked upon while it is connected to the 240VAC mains. If the project is to be used in a permanent domestic installation, it should be connected to the 240VAC mains by a licensed electrician. 42  Silicon Chip ard fluorescent light batten and can be built to suit 18W, 20W, 36W and 40W tubes. The electronic ballast gives a virtually instant start and since the tube is run at a very high frequency (around 100kHz), there is absolutely no sign of flicker. Nor is there any audible, buzz hum or whistle. As a bonus, electromagnetic interference to radio reception is low. Power factor control The electronic ballast design can also be said to be “green” in that it has less impact on the environment. This comes about because of its use of a power factor controller chip. Let’s discuss this point. Electricity supply authorities are constantly after ways to reduce power losses. This not only improves power station effi­ciency (meaning that less coal is burnt) but can keep costs down for the consumer. One of the major ways is to maintain the load current directly in phase with the supplied voltage. For loads such as incandescent lights and bar radiators, the current is in phase with the voltage but for inductive loads such as Shown almost actual size, the PC board is designed to fit into a standard 18W or 36W fluorescent batten fitting. It lights the tube almost instantaneously & produces no audible buzz or hum. motors and conventional fluorescent lights, the current lags the voltage considerably. Fig.1 shows roughly how the current lags the voltage for a conventional fluorescent tube. Here the current lags the voltage by 45° so that the power factor is 0.7 (cosine 45°). Since the supplied power is the RMS voltage x the RMS current x the power factor, the supplied current must therefore be some 41% greater than if it was exactly in phase (ie, power factor of 1 or unity) with the applied voltage. • • • • • • • • • • • Fig.1: this diagram shows the phase relationship between the voltage & current in a conventional fluorescent light fitting; the current lags the voltage. Note that in reality, the fluores­cent light current is not sinusoidal but it is shown in this way for simplicity. Features Suitable for 18W/20W and 36W/40W tubes Replaces existing ballast and starter High efficiency Fast start without flicker Noiseless operation High frequency drive Filament preheat Constant lamp brightness from 200V-280VAC input Fuse protection for faulty tubes 0.99 power factor Low electromagnetic radiation Fig.2: in a conventional electronic ballast, pulses of current are drawn at the crests of the 240VAC 50Hz waveform. This leads to poor line utilisation & a less than desirable power factor. October 1994  43 2.5V REF ZERO CURRENT 5 DETECT INPUT CURRENT 4 SENSE INPUT 8 UNDER VOLTAGE DETECTOR ZERO CURRENT COMPARATOR 7 DRIVE OUTPUT LATCH, PWM, TIMER, LOGIC VREF OVER VOLTAGE COMPARATOR 1.08xVREF 1 MULTIPLIER 3 INPUT Fig.3: block diagram of the MC34262 power factor controller IC. The heart of the chip is the two input multiplier. VCC MULTIPLIER ERROR AMP QUICKSTART 2 VOLTAGE FEEDBACK INPUT VREF 6 A +353V 0V 240VAC C1 HIGH FREQUENCY BYPASS N Dx Lx 3 1 Q1 7 IC1 MC34262 4 6 C2 STORAGE Iavg +400V LOAD R1 VIN ILI Iavg Block diagram ON Q1 OFF Fig.4: simplified boost circuit employing the MC34262 power factor controller chip. Q1 is switched on & off for varying times during each AC half-cycle so that the current drain is evenly spread out. Fig.5: the fluorescent driver circuit. This takes the 400V DC from the boost circuit & uses an oscillator running at 100kHz to drive the fluorescent tube. This gives appreciably more light output than the same current at low frequency; eg, 50Hz. 44  Silicon Chip This extra current requirement when the power factor is less than unity contributes to substantial power losses in the mains distribution system all the way back to the alternators at the power stations. Since the power losses follow a square law (ie, I2R), increasing the current required by 41% will double the power losses! As a consequence, most commercial and industrial lighting installations are required to include power factor correction in the light fittings, by adding a capacitor across the supply. This is not required in domestic light fittings but perhaps it should be. Most electronic ballasts (and indeed all power supplies) have a similar drawback as far as the energy authorities are concerned. This is because they use a bridge rectifier and ca­pacitor filter. Typical electronic ballasts, as used in compact fluorescent lamps, use the circuit shown in Fig.2 to derive a 353VDC supply. These circuits draw a large pulse of current at the crest of each mains half-cycle and while the current is essentially in phase with the voltage, the fact that it has such a short duty cycle means that again, power losses are higher than they otherwise would be. The effective power factor for this type of circuit is between 0.5 and 0.7. By contrast, the SILICON CHIP electronic ballast incorporates a power factor controller chip which ensures that the current drawn from the 240VAC mains is spread more evenly over each half-cycle, and thus reduces losses in the distribution system. Fig.3 shows the internal details of the Motorola MC34262 power factor controller IC while Fig.4 shows how it is connected to boost the incoming mains voltage. It drives a boost converter using Mosfet Q1, inductor Lx, diode Dx and capacitor C2. The incoming 240VAC mains is fed to a bridge rectifier to provide positive-going half sinewaves. Capacitor C1 functions as a high frequency filter. Mosfet Q1 is rapidly switched on and off and each time Q1 is switched off, the energy stored in Lx is trans­ferred to capacitor C2 via diode Dx. IC1 monitors the DC output voltage, the current through Q1 (via resistor R1) and the raw DC input waveform. As a result, Q1 is switched on for longer times at the beginning and end of each A 47k 1W 750k 47k 1W 12-35VDC 470 35VW 750k 8 3 12k 22k 5 T1 S2 N2 .01 2 Q1 BUK547600B 10  G 7 S1 D6 BY229/ 600 D C2 6x1 400V S .018 1 150k 150k 150k 820k 680pF 3kV 12k ZD1 12V 1W 330  D8 1N5062 +2.5V 27k T2 N2 .018 27k 150k R1 43k 6 F2 2x 330  1W 820k D7 50822800 .0068 TP2 +400V 47  4 10 16VW F1 N1 F2 IC1 MC34262P T1 : EFD25/13/9 TRANSFORMER ASSY 3F3 CORE WITH 200um AIR GAP T2 : RCC 12.5/7.5/5 3F3 RING CORE L1, L2 : 26T 0.4mm DIA ENCU ON RCC/23/14/7 3F3 RING CORE L3 : 60T 0.4mm DIA ENCU ON EFD/20/10/7 TRANSFORMER ASSY 3F3 CORE WITH 150um AIR GAP D5 1N4936 DIAC1 ST2 0.1 63V 68k 2x 330  1W 0.12 A D1-D4 4x1N5062 F1 .01 250VAC L1 270k 240VAC ZD2 12V 1W 330  N3 0.1 250VAC 270k .01 250VAC L2 TP1 CASE +360V 0V C3 .001 3kV Q3 BUK457600B D G S D A C1 0.22 400V N FL1 FLUORESCENT TUBE C4 0.1 250VAC L3 900uH N1 22  100Hz NOTCH FILTER Q2 BUK457600B D G S GD S K A E CASE T1 FL1 F1 F2 36W 5A 500mA 7T 0.25mm DIA ENCU 18W 5A 250mA 10T 0.25mm DIA ENCU N2 T2 N1 N1 N2, N3 R1 84T 0.4mm DIA ENCU 14T 6T, 6T 0.4mm DIA ENCU 1.5  120T 0.4mm DIA ENCU 24T 3T, 3T 0.25mm DIA ENCU 3.3  ELECTRONIC BALLAST FOR FLUORESCENT TUBES Fig.6: the circuit is more complicated than typical electronic ballasts because it uses the MC34262 power factor controller (IC1). Note that the entire circuit is powered directly from the 240VAC 50Hz mains supply. half-cycle and for shorter times at the crest of each half cycle, as depicted in the waveforms associated with Fig.4. So in effect, the current drain of the circuit is spread more or less evenly over each half-cycle and the power factor is close to unity. The MC34262 has a number of other features which we will discuss later. The 400VDC output from the power factor controller circuit drives the fluorescent tube but it must be converted into a high frequency AC voltage using the scheme depicted in Fig.5. This uses an oscillator to drive the tube via a resonant circuit consisting of inductor L3 and capacitor C3. A starter circuit is also required to fire the tube after which the oscillator is essentially free running. Main circuit Fig.6 shows the complete circuit of the electronic ballast. The 240VAC mains is applied via fuse F1 and an interference filter comprising L1 and L2 and associated capacitors. L1 & L2 are wound onto a common toroid in antiphase so that the inductor works to eliminate common mode high frequency signals without saturation from the line current. The .01µF capacitors act to shunt high frequency signals to ground while the 0.1µF capacitor in conjunction with the inductance of L1 and L2 forms a low pass filter to block high frequency signals which would otherwise be radi­ated by the mains wiring. October 1994  45 PARTS LIST 1 PC board, code 11309941, 362 x 45mm 1 18W or 36W fluorescent batten with tube fitted 1 EFD25/13/9 3F3 core, former and retaining clips (2 x Philips 4312 020 4116 1, 1 x 4322 021 3524 1, 2 x 4322 021 3516 1) - T1 1 RCC23/14/7 3F3 ring core (Philips 4330 030 3499 1) -L1,L2 1 RCC12.5/7.5/5 3F3 ring core (Philips 4330 021 3515 1) - L3 4 M205 PC-mount fuse clips 1 5A M205 fuse (F1) 1 500mA M205 fuse (36W version) 1 250mA M205 fuse (18W version) 1 3-way mains terminal block 1 transistor insulating bush 6 9mm tapped standoffs 1 3mm Nylon screw & nut 2 small cable ties 12 3mm diameter screws 4mm long 2 3mm diameter screws 12mm long & two 3mm nuts 8 PC stakes 1 cord clamp 1 mains cord and plug 1 150mm length of 0.8mm tinned copper wire 1 11.25-metre length of 0.4mm enamelled copper wire 1 1-metre length of 0.25mm enamelled copper wire Semiconductors 1 MC34262P power factor controller (IC1) 3 BUK457-600B Mosfets (Q1-Q3) The AC mains waveform is full wave rectified using diodes D1D4 and partially filtered with the 0.22µF 400V capacitor. The resulting raw DC waveform is fed to Q1 via transformer T1 and to pins 3 & 8 of IC1 via series-connected pairs of 750kΩ & 47kΩ resis­tors. The 47kΩ resistors provide the initial power for the chip to pin 8 but once it is in running mode, it derives its power from the secondary winding of T1 via diode D5. 46  Silicon Chip 5 1N5062 800V 2A transient protected diodes (D1-D4,D8) 1 1N4936 400V 1.5A fast recovery diode (D5) 1 BY229-600 600V 7A fast recovery diode (D6) 1 5082-2800 Schottky diode (D7) 1 ST2 Diac (DIAC1) 2 12V 1W zener diodes (ZD1,ZD2) Capacitors 1 470µF 35VW PC electrolytic 1 10µF 16VW PC electrolytic 6 1µF 400VDC metallised polyester (Philips 2222 368 55105 or equivalent) 1 0.22µF 400VDC metallised polyester (Philips 2222 368 55224) 1 0.12µF MKT polyester 2 0.1µF 250VAC metallised polyester film & paper (Philips 2222 330 41104) 1 0.1µF MKT polyester 2 .018µF MKT polyester 2 .01µF 250VAC metallised polyester film & paper (Philips 2222 330 1103) 1 .01µF MKT polyester 1 .0068µF MKT polyester 1 .001µF 3kV ceramic 1 680pF 3kV ceramic Resistors (0.25W, 1%) 2 820kΩ 2 12kΩ 2 750kΩ 4 330Ω 1W 5% 2 270kΩ 2 330Ω 4 150kΩ 1 47Ω 1 68kΩ 1 22Ω 2 47kΩ 1W 5% 1 10Ω 1 43kΩ 1 3.3Ω 5% 2 27kΩ 1 1.5Ω 5% 1 22kΩ The seriesed 750kΩ resistors and a 12kΩ resistor divide the raw DC waveform down to a level suitable for the multiplier input at pin 3. The multiplier has two inputs (which it multiplies together): the input at pin 3 which provides phase and voltage information on the incoming rectified AC waveform, and the output of the error amplifier at pin 2. The error amplifier input at pin 1 monitors the +400V DC output from diode D6 via two 820kΩ resistors which reduce the voltage to +2.5V before it is fed via a 100Hz notch filter (to pin 1). Thus, the internal multiplier has two jobs to do as it controls the pulse width modulation drive to the gate of Mosfet Q1 via pin 7. First, it must regulate the DC output to +400V and second, it must ensure that Q1 is turned on and off so that the current drawn from the AC mains is evenly spread throughout each AC half-cycle. Note that while Q1 is draws current from the raw DC input in the form of very short pulses (typically about 20 microsec­ onds) long, the pulses are longer at the start and finish of each AC half-cycle than they are at the crest. This pulse current is filtered by the input filter consisting of L1, L2, C1 and the associated 250VAC capacitors so that the actual current drawn from the AC mains is 50Hz with relatively low harmonic content. Q1 draws current through winding N1 of transformer T1 (equivalent to inductor Lx in Fig.4) and each time Q1 turns off, diode D6 is forced to conduct and deliver charge to C2 which consists of six 1µF 400V metallised polyester capacitors. The secondary winding of T1 drives diode D5 and a 470µF capacitor to provide power to the chip itself. Current limiting for Q1 is provided by pin 4 which monitors the voltage drop across R1. The current waveform is filtered by the 47Ω resistor and a .0068µF capacitor while Schott­ ky diode D7 is included to clip turn- off voltage spikes due to the inductance between ground and the source of Q1. These spikes would otherwise cause circuit instability. OK, so we have a +400V DC supply and this needs to be turned into high frequency AC to drive the fluorescent tube and a circuit is required to initially fire the tube. These functions are performed by the fluorescent driver circuit which is depicted schematic­ ally in Fig.5. The circuit we have used is very similar to that featured in the fluorescent inverter circuit published in the November 1993 issue of SILICON CHIP. Fluorescent driver The fluorescent tube driver comprises Mosfets Q2 and Q3, transformer T2 and associated components. The fluorescent tube is driven via inductor L3 and the N1 winding of transformer T2. The gates of Q2 and Q3 are driven 5 6 F2 S1 4 7 3 8 9 S2 2 10 F1 1 4 5 3 6 2 7 1 8 L3 T1 WINDING DETAILS L1 N2 N1 N3 T2 WINDING DETAILS L2 Fig.7: winding details for the toroid filters and ferrite cored transformers. Note particularly that the two windings of L1 & L2 are wound in different directions. from the N2 and N3 windings which are connected in antiphase. When power is first applied, there is 400V DC between the drain of Q2 and the source of Q3. The 0.1µF capacitor adjacent to Diac1 begins to charge via two series 150kΩ resistors. When the voltage reaches about 30V the Diac breaks down and dumps the 0.1µF capacitor’s charge into the gate of Q3. Zener diode ZD2 protects the gate from overvoltage. Mosfet Q3 now switches on and current can flow from the +400V supply via the fluorescent tube top filament, the .001µF 3kV capacitor, the second tube filament, the 0.1µF 250VAC capaci­tor, inductor L3 and the N1 winding of T2. The current flow in N1 will apply gate drive to Q2 via N2 and switch off gate drive to Q3 via N3 (due to the polarity of the windings of T2). If oscillation does not occur, the Diac will again fire Q3. Ultimately, when oscillation occurs, Mosfets Q2 & Q3 will switch on and off in alternate fashion. The frequency of operation is set by the combined inductance of L3 and N1 which resonates with the .001µF capacitor, C3. The oscillator current heats the fluorescent tube’s fila­ ments and after a short period (less than a second) the tube ignites. Capacitor C3 is now effectively shunted by the discharge within the tube and the oscillation frequency is set by the core saturation properties of T2. Current through the tube is limited by the saturation of T2 and the impedance of L3. Once normal oscillation occurs, the start-up circuit com­prising Diac1 and the 0.1µF capacitor is disabled by diode D8. This diode discharges the 0.1µF capacitor every time Q3 switches on and hence prevents the Diac from firing. Gate drive to Q2 and Q3 is limited using two parallel 330Ω gate resistors and 12V zener diodes which clamp the gate voltage to a safe value. The 330Ω resistor from This shows the mains voltage waveform (the larger of the two set to 10V/div) & the current waveform (set to 90mA/ div) when the electronic ballast is driving a 36W tube. Note that the current is directly in phase with the voltage. The flattening of the 240VAC waveform is not a circuit function but was present at the time these photos were taken. These are the starting pulses as seen at the drain of Q3 with no tube in circuit. Pulses from Diac1 drive the gate of Q3 & switch it on. The voltage scale is 100V/div & the frequency is about 1kHz. This is the waveform at the drain of Q3 when driving a 36W tube. The vertical scale is 100V/div & the frequency is about 100kHz. October 1994  51 A TP1 D5 .01 250VAC 750k 0.22 400V IC1 1 .0068 0.18 TP0V MC34262 470uF 43k 270k N L2 10uF .01 12k E 0.1 250VAC 270k 47k 1W 0.18 0.12 27k 27k 10  1 22k Q1 820k 47k 1W 820k 47  R1 A L1 K D6 D1-D4 12k 68k .01 250VAC 750k F1 D7 T1 TO EARTH TERMINAL OF BATTEN Fig.8 (above & facing page): the component overlay diagram of the PC board. Note that quite a few different diodes & zener diodes are employed & they must not be mixed up. This close-up view shows how transformer T2 is secured to the PC board with a Nylon screw & nut & a transistor insulating bush. gate to source provides a load for the T2 windings to accurately set the core saturation. Q2 and Q3 switch on and off at about 100kHz (150kHz for the 18/20W version) but do not require heatsinks. However, during the switch-over process, the Mosfet which is switched off, is forced to commutate whereby its internal reverse diode briefly conducts. This commutation can lead to high dissipation in the Mosfets and must be prevented otherwise they would ultimately be destroyed. To reduce this dissipation to a low value, a snubber capacitor network comprising the 680pF 3kV capacitor and the series 22Ω resistor is connected from the source of Q2 to the 0V line. The two 150kΩ resistors connecting the snubber network to the 400V supply provide a load for the circuit if the fluorescent tube is not present or is effectively open circuit. Circuit variations Depending on whether the circuit is to be used with an 18W or 36W fluorescent tube, there are a number of variations to the winding details of transformers T1 & T2, and the values of fuse F1 and resistor R1. These are shown on the table included on the diagram of Fig.6. These changes are also relevant to 20W and 40W tubes. Transformer T2 has different wind­ ings to set the frequency of operation for each tube type. For the 18W tube load, the fre­quency is set to around 150kHz, while for 36W loads the frequency is set to about 100kHz. This difference in frequency allows us to keep the same value of inductance for L3. The input filter, comprising L1 & L2 on a common toroid, is secured using two plastic cable ties. 52  Silicon Chip Construction The PC board for the circuit is K Q2 TP2 150k 150k 330  1W 150k D6 150k A T2 ZD1 1uF 400V 1uF 400V 1uF 400V 1uF 400V D8 1uF 400V ZD2 TP0V coded 11309941 and measures 362 x 45mm. It is designed to fit inside a standard 18W or 36W fluorescent batten fitting. Construction can begin by winding the toroids and the transformers. Let’s start with the larger of the two toroids which has two windings, L1 and L2. Fig.7 shows how they are wound, using 26 turns of 0.4mm enamelled copper wire (ENCU). Note that each winding must be wound in the direction shown on the diagram; ie, L1 is wound in a different direction to L2 so that they end up in antiphase. Transformer T2 is wound on the smaller of the two toroids and again, its windings must be wound as shown. The wire gauge and number of turns depend on whether you are building the 18W or 36W version. Use the table on the circuit of Fig.6 to find the number of turns for N1, N2 and N3. 22W DIAC1 T1 N2 330  680pF 3kV 1 .001 3kV TUBE END L3 N1 0.1 1uF 400V F2 330  1W 330  TUBE END N3 330  1W 330  1W 0.1 250VAC Q3 Both T1 and L3 are wound on ferrite transformer bobbins. The larger of the two is for T1. Both require the centre leg of one of the core halves to be filed down so that a precise air gap is formed when the cores are clipped together. You will need a small file and a set of feeler gauges. Initially, for each core set place the two core halves together and observe that there is no gap between the mating surfaces of the two. Now file the centre leg of one core half, making sure that you are filing squarely and evenly across the face. The required gap is 200µm (0.2mm) for the larger core (T1) and 150µm (0.15mm) for L3, the smaller core. The whole process should not take more that a few minutes since the ferrite material is quite soft. Take care when filing down the centre leg of each core to ensure that you do not exceed the gap required. The secondary winding of T1 (N2) is wound first using 0.25mm enamelled copper wire – see Fig.6. Start the N2 winding on pin 2 and wind on the required number of turns before terminating at pin 6. Now apply a layer of insulating tape over the winding. The primary (N1) of T1 can now be wound using 0.4mm enamelled copper wire. This must be wound in the same direction as the secondary winding. Start at pin 4 and wind on the requisite number of turns neatly, side by side, placing a layer of insulating tape over each layer. The end of the winding terminates on pin 1. The transformer can now be assembled by fitting the core halves into the bobbin and securing with the clips. L3 is wound using 60 turns of 0.4mm ENCU wire, starting on pin 2 and finishing at pin 3. Again, insulate RESISTOR COLOUR CODES ❏ No. ❏  2 ❏  2 ❏  2   ❏  4 ❏  1 ❏  2 ❏  1 ❏  2 ❏  1 ❏  2 ❏  4 ❏  2 ❏  1 ❏  1 ❏  1 ❏  1 ❏  1 Value 820kΩ 750kΩ 270kΩ 150kΩ 68kΩ 47kΩ 43kΩ 27kΩ 22kΩ 12kΩ 330Ω 330Ω 47Ω 22Ω 10Ω 3.3Ω 1.5Ω 4-Band Code (1%) grey red yellow brown violet green yellow brown red violet yellow brown brown green yellow brown blue grey orange brown yellow violet orange brown yellow orange orange brown red violet orange brown red red orange brown brown red orange brown orange orange brown brown orange orange brown brown yellow violet black brown red red black brown brown black black brown orange orange gold brown brown green gold brown 5-Band Code (1%) grey red black orange brown violet green black orange brown red violet black orange brown brown green black orange brown blue grey black red brown yellow violet black red brown yellow orange black red brown red violet black red brown red red black red brown brown red black red brown orange orange black black brown orange orange black black brown yellow violet black gold brown red red black gold brown brown black black gold brown orange orange black silver brown brown green black silver brown October 1994  53 between each layer with insulating tape and apply a layer of tape over the final windings. Assemble the ferrite cores into the bobbin and secure with the clips. PC board assembly Fig.8 shows the component layout for the PC board. Before installing the components, check the board for shorts or breaks in the copper tracks and make any repairs that may be necessary. Also check the holes for correct sizing for each component. You will need 3mm diameter holes for the six PC board mounting holes, inductor L3 and the cable tie holes for the large toroid input filter (ie, L1 & L2). Start the board assembly by inserting all the PC stakes plus the four M205 fuse clips. This done, insert the resistors, links and diodes, followed by IC1. The diodes and IC must be oriented as shown, while the ST2 (Diac1) can be inserted either way around. Take care with the diodes since there are several types used on the board. The 1N5062 diodes (D1-D4 and D8) are axial lead types with spherical bodies. The 1N4936 diode (D5) is an Why is it called a ballast? The circuit presented here is called an “electronic ballast” because it replaces the ballast choke found in all conventional fluorescent lamp fittings. Electronic ballasts are more efficient than conventional ballast chokes and the fact that they operate the tube at very high frequencies also improves the efficiency. Which leads to the question “Why is the choke in a fluorescent fitting referred to as a ballast?” A ballast or more correctly, a ballast resistor, is used in a circuit to limit the operating current to a safe value. A fluo­rescent tube requires a ballast because its mercury vapour dis­charge has a negative resistance characteristic, ie, if the current increases, the voltage across the tube decreas54  Silicon Chip es. If the ballast choke was not in the circuit, the current through the tube would not be limited and it would be burnt out. Hence, the ballast choke maintains the current through the tube at a more or less constant value. And why are fluorescent light fittings called battens? Standard fluorescent light fittings for use in domestic and commercial installations are usually referred to as “battens”. This is because they are screwed to the timber battens which secure the Gyprock or fibrous plaster ceiling material to the rafters. In the same way, incandescent lamp holders which screw to a wall or ceiling are usually sold as “batten holders”. axial lead type with a black and light grey cylindrical body. D6 is a two-lead TO220 encapsulation, while the two zeners (ZD1, ZD2) are axial lead types with an orange body. D7 is a small axial lead type with a clear transparent cylindrical body. When installing the capacitors, take care with the orienta­tion of the electrolytic types which are polarised. Note that the capacitors must be as specified. In particular, don’t substitute 630V DC capacitors for those specified at 250VAC. Transformer T1 and inductor L3 must be installed with pin 1 oriented correctly. The input filter toroid is mounted using two cable ties as shown in the photos, while T2 is secured using a transistor mounting bush together with a Nylon screw and nut. Install the Mosfets (Q1-Q3) and fit the fuses into the fuse clips. The terminal block is mounted using two 3mm screws and nuts. Connections from the PC board to the terminal block are made with short lengths of tinned copper wire. Installation of the PC board We recommend that the PC board be installed into the fluo­rescent batten before testing because the voltages on the board are potentially lethal. Before installation, the existing ballast, starter and starter socket should be removed from the batten. The existing three-way insulated terminal block should be left in place as it will still be required to terminate the incoming mains supply wiring. Testing Now it is ready for testing. Insert a fluorescent tube into the fitting and apply power. The tube should initially start with a blue glow at the tube ends and then light up. After about a second the power factor controller will start up and the tube will reach full brilliance. If the circuit does not power the tube, switch off immediately and dis- connect it from the mains. Check that the fuses are intact and if so check your board for incorrectly located components. You should also check that the inductors and transformers have been wound correctly. Voltage checks Note that this circuit is potentially lethal to work on and that all points of the circuit float at mains voltage. If you do use a multimeter to make voltage checks, make sure it has shrouded probes and do not handle the meter while you are actual­ ly measuring voltages. Under no circumstance should an oscilloscope be connected to the circuit unless it has differential inputs or the circuit is powered via a line isolating transformer. You can check that the DC supply section of the circuit is operating by connecting a multimeter (set for 1000VDC) between TP0V and TP2. At switch-on, the voltage will initially be some­what lower than 400V and after a second or so it will settle at 400V DC. The power supply for IC1 can be measured between TP0V and on the cathode of D5. This voltage should gradually rise to about 12V, whereupon the circuit will start and the voltage should then sit at about SC 20-25V. Fig.9: this is the PC artwork reduced to 70.7%. To reproduce it full size, use a photocopier with an expansion ratio of 1.41. Check the board carefully before mounting any parts. Drill holes in the base of the batten to accommodate the six PC board standoffs. If the unit is to be used as a free standing lamp, then any holes in the metalwork of the batten should be covered to prevent accidental contact with the live PC board or its components. After installing the PC board into the batten, the tube leads and mains wiring should be connected to the PC board. Use a 2-way insulated terminal block to make the extension in the wires to the far-end tombstone (tombstones are the sockets used at each end of the fluorescent tube). It is important to earth the metal case of the batten to the green/yellow Earth wire in the mains lead. This should be done using the earth contact provided on the batten via the insulated terminal block mentioned earlier. The centre terminal of this contact is screwed onto an integral lug in the batten. The Active (brown) lead and the Neutral (blue) lead should connect to the A and N inputs on the PC board. Clamp the cord so that it cannot be pulled out of the terminal block. The assembled PC board fits neatly at one end of the batten fitting and is secured with six screws. Remember that the whole circuit is potential lethal since it is powered directly from the 240VAC mains supply. SERVICEMAN'S LOG Two symptoms – one fault or two? I’ve got a really weird one this month – two quite different visual symptoms & two faulty parts mixed up in a crazy tug-o’-war. Less traumatic was the set that went green; it fooled the customer more than me. The weird story is about an AWA colour TV set, model 4303, using one of the “Q” series chassis. It would be about 10 years old and is one of several in a local motel. As with many other AWA chassis types, the “Q” series are actually made by Mitsu­bishi. I first heard of the problem when the motel proprietor rang me, identified the set, and explained that one of his guests had reported that the set had lost colour. When he later checked the report it was quite correct. There was no colour but, as he added, there was also a black line or strip about 50mm wide at the top of the picture. That should have alerted me – well, alerted me more than it did. But I did speculate as to whether I had two separate faults – which seemed most likely – or whether it was a single fault with a funny origin; and I didn’t mean funny ha-ha. As it transpired, there weren’t any laughs anywhere in the episode. I don’t know what the record is for frustration factor but, on a scale of 1-10, this must have been nudging the nine mark. Having thus set the scene, let’s get down to details. No ordinary fault The customer delivered the set to the workshop and I turned it on while he was there. And yes, his description was fairly accurate; there was no colour and there was a black band about 50mm wide at the top of the picture. But there was more to it than that and I quickly realised that this was no ordinary fault. For a start, it was obvious that the black band was not simply a result of reduced vertical scan, involving either a compressed or non-linear image. What image was there was normal and the black band was, as it were, overlaid on the image. In other words, the scan was normal, but there was some kind of spurious blanking problem. The other thing I noticed immediately was that the junction between the picture and the black band was not a straight line, as one would have expected. Rather, it was a “wavey” line, per­haps best described a rough, shallow sinewave of about 12 cycles. I also discovered that I was able to brute force the set into momentary bursts of colour by carefully fine tuning it, although there was no setting that would hold it. But having noted all this, I was no wiser as to whether it was one fault or two, although I tended to favour the two fault theory. In any case, I could only tackle one set of symptoms at a time, so I decided to tackle the blanking problem, mainly because I felt more confident about where to start. Unfortunately, there was one other trap waiting for me. I didn’t have a “Q” chassis circuit for this particular model, which uses a 90 degree picture tube. The closest I had was one for a 110 degree tube but, as far as I knew, Fig.1: the faulty section in the AWA 4303. Part of IC201 is shown on the left, with pin 9 in its bottom right hand corner. Diode D204 is below it & to the left, while diode D203 is to the right near transistor Q213. The burst gate transistor (Q601) is at extreme right. 56  Silicon Chip the sets were iden­ tical in all other respects. And I fell right into the trap. I spent a great deal of time trying to find my way around the chassis from this circuit and found that I was getting nowhere. I eventually realised that it was almost the same but not quite, Finally, a colleague came to the rescue with the correct circuit. Having cleared that hurdle, I started all over again. I was concentrating on the circuitry around IC201 and, in particular, around pin 9, which apparently feeds blanking pulses into the blanking section – see Fig.1. There are two diodes connected to this pin – D204 and D404. D204 is adjacent to this pin on the circuit, while D404 is some distance away down near the scan coil assembly, being associated with a small resistor network (R417, R418, R419 & R420). Also under suspicion were some electrolytic capacitors, including C414, C409 and C408, in the adjacent vertical output stage. I replaced these first, without any result, and also checked various resistors in this part of the circuit. They all measured spot on. That left the diodes still under suspicion. But first I decided it would be a good idea to do a voltage check around IC201. Fortunately, all the pin voltages are shown on the circuit and, with one exception, they all measured well within tolerance. As you may have guessed, the exception was pin 9. It is marked 6.1V but I measured only about 2V. So did we have a faulty IC? I had a spare on hand and it was not a big job to fit it. It made no difference but at least I had cleared it of suspicion, a point about which I was thankful later on. That left the diodes as the next prime suspects. I went to D204 first. The simplest and most reliable way to check it was to pull it out and fit a new one, which I did. Now, at the risk of seeming to state the obvious, there would appear to be only one of two possible results from such a move: either the fault would be cured and that would be the end of the exercise, or (2) it would make no difference and the diode would be cleared of suspicion. Surely, those are the rules? At least, that’s what I thought until I replaced diode D204. But no; this circuit had its own ideas. We now had complete picture cutoff; in other words, the situation was worse than before. My first reaction was to suspect that the replacement diode was either faulty or unsuitable. I didn’t have a direct replacement but had used a 1N914 small signal diode, which I felt was adequate. I tried another 1N914, then several other types, but always with the same result; total picture cutoff. I checked the origi­nal diode for leakage and although the indication was only slight, I felt sure it was leaky. Yet when I refitted it, I could at least get the original picture. To say that I was confused would be putting it mildly. It really threw me; what on earth was going on? Although I eventual­ly decided that the original diode was faulty and that the re­placement was OK, I was no closer to an explanation. About the only thing that was clear was that there was another fault some­where which still had to be found. Apparently, the original “two-faults” concept was valid but not in the manner I had envisaged. A real clue But speculation didn’t help in a practical sense and I was at something of a loss as to what to do next. In desperation, I went back to pin 9. And this provided the first real clue; the voltage here had now jumped from a too-low value of around 2V to a too-high value of about 8.4V. Well, I suppose that made sense in a way; excessive voltage into the blanking circuit would do just that – it would blank the picture. But where was this excessive voltage coming from? In order to follow the next steps, it is necessary to study this part of the circuit carefully. First, there are three resistors in ser­ ies, R209, R223 and R224 (in that order), from pin 9 to the 12V rail. Their job is to establish the 6.1V at pin 9 shown on the circuit. Also connected to pin 9 is R210, C217 and diode D204. And somewhere via that network a spurious voltage October 1994  57 was being intro­duced. All I had to do was find out how. The first thing I did was to disconnect R224 at the 12V rail, which should have removed all voltage from pin 9. But it didn’t; we still had the 8.4V. Next I disconnected R210. Well that achieved something; the pin 9 voltage dropped to zero. Thus inspired, I abandoned the circuit and began tracing the copper pattern from R210, checking with the meter probe as I went. Of course the pattern was far more complex in reality than it appears on the circuit and I ran up a lot of garden paths and encountered a lot of brick walls over the next 15 minutes or so. But suddenly I struck oil; a diode marked D203 (near Q231), the other side of which connected to the 12V rail. More importantly, its polarity was such that it was opposing the 12V. I had no idea what its real function was – and still haven’t – but it was obvious that, if it was leaky, it could be the culprit. So out it came. And was it leaky? A sieve is the only com­parison I can offer. So in went a new one and all our troubles were over. With the benefit of hindsight, it 58  Silicon Chip appears that I might have been better advised to stick with the circuit, because the of­fending diode is right alongside IC201, connecting to the 12V rail where this emerges from the 12V regulator transistor (Q231). But of course it was a lot further away on the board than it appears on the circuit. So that was the solution. But it had been a most frustrat­ing exercise. It is bad enough to have two components fail at the same time but they usually produce distinctive symptoms. In this case, not only were both failures in the same part of the circuit but, worse than that, they were actually opposing one another in the effect they had. Thus, while the leak in D203 was attempting the raise the voltage on pin 9, the leak in D204 was pulling it down – and succeeding rather too effectively. But this was the only reason the set was producing any image at all; as I found out when I replaced D204 and made matters worse. Which is all delightfully simple to explain when looking backwards; it only we could look forward as easily. And what about the colour failure? How can that be ex­plained? Again, once the fault was tracked down and corrected, the connection became obvious (no pun intended). If we go back to the junction of R210 and C217 and follow this circuit to the right, we come first to the anode connection of diode D203, which caused all the bother. From here the circuit continues to the right, connects to the cathode of D205, and then to resistor network R586, R584 & R585 (this network connects to the horizontal output transformer, from which it picks up horizontal pulses). The circuit then leaves the main board, via connector pin 10, and goes to connec­tor pin 10 on the chroma board, then via R624 to the base of Q601. And Q601 is the burst gate transistor. Most importantly, this is a DC circuit all the way; whatev­er spurious voltage appeared on this line from D203 would appear on the base of Q601, modified only by the divider network of R624 & R625. And, incidentally, R625 is incorrectly shown as 22kΩ; it is, in fact, only 2.2kΩ. Even so, there would be a lot more voltage at this point than normal, effectively upsetting the burst gate function. Of course it was a happy ending for the customer but only partially so for Yours Truly. I was glad to have solved the problem but I wish I’d done it a little quicker. Little green pictures And now for something a little more straightforward, although it did have its period of confusion. Among other things, it demonstrated how a customer’s description of a fault, no matter how well intentioned, can set one thinking in the wrong direction. It involved an HMV colour set, model 12641. The same chas­sis is used in the model 12642 and in the JVC model 7765AU. The owner first brought the set in several months ago, with the complaint that,”... the picture goes green – but only sometimes”. Well, the “only sometimes” didn’t exactly cheer me up but otherwise I assumed it would be a fault in the picture tube drive system; either the green gun being turned hard on, or the red or blue gun (or perhaps even both) being turned down in some way. I turned the set on while he was there and, sure enough, it was producing a normal picture. I suggested he leave it with me for a few days and so the set sat in a corner of the bench and ran all day and every day for the next week or so. And it never missed a beat; there was not even a suggestion of a green cast. Finally, I suggested that as we weren’t getting anywhere, it might be better if he took the set back home until the fault became more predictable. And that was the last I heard about it for the next three months or so. In fact, I had almost forgotten about it when the owner suddenly turned up with it, saying, “It’s real crook now – goes green every day.” And so it was back into the corner of the bench. But he was right this time. It had been running for less than half an hour when the fault suddenly appeared. But as soon as it did, I re­ alised that I had been thinking along completely wrong lines. It wasn’t a green cast; instead, it was green faces, with all other colours similarly incorrect. Well that put a different complexion on things (oops, sorry about that) and that meant a completely different approach. It was in no sense a picture tube drive problem; it was phase fault which meant an inversion, shift, or upset of some kind. But the interesting aside here is that it was only the green flesh tones that attracted attention. That’s not surprising in one way, I suppose, since these are normally the centre of attention. At a more practical level, the most likely cause of such a problem would be failure somewhere in the half-line frequency (7.8kHz) chain, starting at the phase discriminator, where this frequency is generated in the process of pulling the crystal oscillator into phase with the burst frequency. The 7.8kHz frequency is used to operate the reversing switch which changes the colour phase on each alternate line in synchronism with the transmitter. And when it misbehaves, which it can in variety of ways, it can do dreadful things to the colour. (In order for the receiver to perform this switching in correct phase with the transmitter, the PAL system employs a swinging burst signal. This 4.43MHz reference burst is shifted 45 degrees, plus or minus, on alternate lines and the receiver uses this shift as a code to identify each line. The high Q of the crystal oscillator averages these two shifts, while the phase discriminator, which controls the crystal phase, also provides the half-line frequency for the reversing switch). Fig.2: the 7.8kHz oscillator circuitry in the HMV 12641. This oscillator consists of transistors X304 & X305, with X303 desig­nated as a 7.8kHz killer. The 7.8kHz signal is fed to the demodu­lator IC (IC302) at top right. In this set, one of the easiest points of access to the 7.8kHz chain is at transistors X304 and X305, described jointly as the 7.8kHz oscillator – see Fig.2. This feeds a 7.8kHz signal into the demodulator IC (IC302). There is also X303, which is described as a 7.8kHz oscillator killer. However, X304 and X305 were the most likely suspects. But ease of access was not the only reason I selected this point. The transistor type used here, 2SC458, is one that I regard as a mite unreliable, being prone to intermittent be­haviour. Finally, a brief check with the CRO confirmed that this was where the frequency was running into trouble. So it really boiled down to which of the two transistors was the most likely culprit. Well, it was a 50-50 chance and I took a punt on X305. And for once I picked it in one; I fitted a replacement and all the faces were back to normal. I ran the set on the bench for several days with no sign of the problem and, although I remembered it had done this before, decided to pass it back to the customer with the least possible delay. But I warned him to contact me immediately at any sign of the trouble. Subsequent checks have confirmed that there has been no recurrence of it. So that was it. It wasn’t a highly scientific exercise but was more a result of previous experience, plus a certain amount of luck. And it does happen that way sometimes. But the custo­mer’s description did throw me initially. Back to wireless To finish off this month, I’m breaking right away from the usual to indulge in a little nostalgia. In the hurly burly of modern high-tech electronics – and the high-tech service equip­ment which it demands – we sometimes forget, or perhaps never knew, about electronics in its infancy. It wasn’t known as electronics then of course – it was radio or, before that, wireless. Which was fair enough, because the wireless set was virtually the only manifestation of what was to become electronics. But regardless of what it was called, or the state of the art, the equipment of the day needed servicing. For the wireless enthusiast of the day, or the local garage mechanic who doubled as a wireless expert, this was more often than not undertaken on the “by guess and by God” basis. As for service equipment – well this was often limited to a few basic tools – pliers, screwdrivers and a soldering October 1994  59 iron. And diagnosis was on the basis of visible faults: loose terminals, broken leads, unlit valve filaments, or obviously defective controls. Which was OK up to a point. But wireless sets used batter­ ies – and that, as they say, was the ‘ard part. Meters were few and far between, quite crude, and very expensive. They didn’t even approach the simple 1000Ω/volt multimeter which was later to become the mainstay of radio servicing. The accompanying photograph is of one of the very early attempts at a meter for use with wireless sets. It was passed over to me by a colleague, who acquired from a non-technical friend who found it in some junk in his workshop. Apart from that, its origin and history remain a mystery. It was a highly specialised piece of equipment. With a 0-50V scale and with prominent markings at 22.5V and 45V, it could have had only one role in life: to test B batteries. For the benefit of younger readers, the B battery – or high tension battery – came as a 45V unit, tapped at 22.5V. A small set (eg, one valve with 60  Silicon Chip earphones) would use one light duty version, while larger sets would use at least two heavy duty types to give 90V, or three to give 135V. And they were horribly expensive. Advertisements from wireless magazines of that era suggest that the keenest price for a 45V heavy-duty battery would be £1/5/0 ($2.50), or £3/15/0 ($7.50) for Fig.3: this pocket meter was the latest thing in test equipment in the 1920s. All it could do was test the B bat­tery. a set of three. But the basic wage was then only around £3/12/6 ($7.25). Most people earned a little more than that, say around £4/0/0, but a set of batteries would still make a mess of a week’s wages (work that out in modern terms)! With average use, but without wastage, a set would provide 6-9 months of use. And that, by any standards, made a wireless set an expensive thing to run. So nobody discarded them until they were convinced that they really were exhausted – and that the deteriorating perfor­ mance was not due to some other cause. Hence the popularity of the little meter portrayed here. For the repair man, it provided the proof needed to sell another set of batteries. And the enthu­siast who owned one was the envy of his peers; his popularity – and a regular invitation to dinner – was assured. The meter itself is almost certainly a moving iron type, renowned for its simplicity rather than sensitivity, and recog­nised by non-linearity at the low end of the scale. The colleague who passed it over to me checked it against his “u-beaut” digital meter and, to the accuracy with which he could read the simple scale, pronounced it “spot on”. He also checked its sensitivity, and found that at 45V it drew about 10mA. This was probably more by accident than by design but it would not have been an unreasonable load with which to test these batteries. Typical current drains would have been 10-15mA. How old is it? I’ve passed it around to several old timers but no-one’s game to admit to ever having seen one in actual use, for fear of revealing their age. However, history suggests that it would have been popular in the early 1920s, or about 70-plus years ago. Having said all that, the thing that stands out most in my mind is the point I made at the beginning; the very narrow appli­cation for the device. It could do only one job – test individual B batteries. As a general purpose meter for use in the wireless set itself, it was virtually useless. Unless the set used only one 45V battery, it could not be used even to confirm that the HT voltage was present anywhere in the set itself. A meter to do that was several years down the track. But that’s how things were in the SC good old days. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Build a temperature controlled soldering station Can’t afford one those fancy new temperature controlled soldering stations? Never mind, build this one instead & save a bundle. It features a grounded tip to prevent damage to delicate MOS devices & is fully adjustable from 100°C to over 450°C. Design by JEFF MONEGAL Temperature controlled soldering irons are highly desirable but many electronics enthusiasts can’t afford them. Now you can build your own and learn about the technology at the same time. It uses a high quality replacement heating element which comes with a thermocouple built into the barrel. A LED bargraph indicator shows the temperature setting and another LED shows when the heater element is on. The principle of this temperature controlled soldering iron is simple. It uses a transformer with a 24V secondary and a Triac to switch the heating element on or off, depending on the feed­back from a thermocouple mount­ed in the soldering iron barrel. The heart of the project is the standard replacement soldering element which has four wires, two for the element and two for the thermocouple connections. This replacement soldering element is available from Dick Smith Electronics (Cat. T-2008) and is priced at $19.95. In essence, the circuit has two parts, one for show and one for go. The part for show is IC3, the LM3914 LED display driver and the associated LEDs in the bargraph. The rest of the circuit, the part that actually does the work, uses two op amps in an LM324 quad op amp package, a transistor and an optocoupler to drive the Triac. Now let’s refer to the circuit diagram of Fig.1 to see how it all comes together. The thermocouple TH1 is connected to pin 3 of op amp IC1a which is configured as a non-inverting amplifier October 1994  65 +2.4V K LED13 A POWER  ON K 47  470  47k 10 4 3 IC1a 2 LM324 100k 1 +8V 470 16VW LED2 HEATER ON 4.7M VR1 25k 5 +0.75V 6 IC1b 7 11 8.2k 1 OUT K 470  1 6 IC2 MOC3021 TRIAC1 BT139-600 A2  2 10k 47k B 1k 470 25VW A  BR1 W04 +18V IN GND 1k +3V 560  D1 1N914 TH1 REG1 7808 +7.4V A LED1 D2 1N914 VCC 470  4 C G A1 0V 12V 24V HEATER ELEMENT Q1 BC548 E 4.7k E N 240VAC A VCC 9 B E A K LEDS 3-12 VIEWED FROM BELOW 10 K 5 K A LEDS 1, 2 AND 13 C 3 LED12  11 6 12 K LED10  13 14 K I GO A1 A2 G 2.7k IC3 LM3914 7 4 8 2  15 16 K 4.7k LED8 LED6  17 18 K LED4  1 COLD A HOT K A K A K A K A K LED11 A  LED9 A  LED7 A  LED5 A  LED3 A  TEMPERATURE CONTROLLED SOLDERING IRON Fig.1: the circuit uses the feedback from a thermocouple inside the soldering iron’s barrel to control the switching of a Triac. The Triac is not phase controlled but turns on or off depending on the temperature control VR1. with a gain of 48. The 470Ω resistor provides a current of 5mA through the thermocouple and the resulting small voltage developed across the thermocouple is added to the voltage generated due to the “See­beck effect”; ie, the voltage generated by a junction of two wires of dissimilar metals. The voltage at pin 3 of IC1a is amplified (by 48 times) and the output at pin 1 is fed, via a filter network consisting of a 100kΩ resistor and 1µF capacitor, to pin 6 of IC1b. This second op amp is connected as a comparator. It compares the voltage from pin 1 of IC1a with the preset voltage from potentiometer VR1, the temperature set control. When the voltage at pin 5 of IC1b is above that at pin 6, the output at pin 7 66  Silicon Chip is high and this causes transistor Q1 to turn on. Q1 then turns on the internal LED in optocoupler IC2 and this turns on the Triac, to heat up the soldering iron element. The collector current of Q1 also passes through LED2 and this serves as an indication that the heater element is cycling. A 4.7MΩ resistor is connected between pins 5 and 6 of IC1a to give the comparator a degree of hysteresis; ie, positive feedback. Thus, when pin 6 rises above pin 5 (due to increased voltage from the thermocouple TH1), the output at pin 7 flicks low and because of current flow through the 4.7MΩ resistor, pin 5 is actually pulled slightly lower than it would otherwise be. Thus the vol­tage at pin 6 has to drop further than it otherwise would before the output at pin 7 flicks high again. This “hysteresis” action prevents the circuit from rapidly hunting on and off. Temperature indication IC3, the LM3914 dot/bar display driver, is used to give an indication of the temperature setting. Its pin 5 input is tied to pin 6 of IC1b, while the pin 6 input is tied to the +3V side of VR1. When the soldering iron is cold, the voltage at pin 5 of IC3 is only a few millivolts. This means that the first LED in the 10 LED bargraph will not light until the iron has reached a significant temperature above cold. In other words, if the iron is not warm enough to melt solder then no LEDs in the bargraph will light. The arrangement of the power transformer and rectifier is a little unusual. The transformer is a multi-tap unit (DSE Cat. M-1991) with the 12V and REAR PANEL SOLDERING IRON SOCKET EARTH LUG MICA INSULATOR TRIAC1 A1 A2 G EARTH (GREEN/ YELLOW) 1 MAINS CORD 2 ACTIVE (BROWN) BROWN BLUE 24V 12V PRIMARY PRIMARY NEUTRAL (BLUE) 0V POWER TRANSFORMER LEDS 2-13 MOUNTED ON COPPER SIDE OF BOARD K 2 1 TRIAC1 IC1 LM324 Q1 470uF 1uF 47k 1 1k 47uF 470  470  8.2k 10k 4.7k 4.7M 100k 470uF 10uF 1 K A LED13 47k IC2 MOC3020 1k BR1 D2 VR1 REG1 7808 12V OV TRANSFORMER SECONDARY A LED2 A A A A A A A A A A 560  LED3 K LED4 K LED5 K LED6 K LED7 K LED8 K LED9 K LED10 K LED11 K LED12 K 470  2.2k IC3 LM3914 4.7k 1 LED1 K D1 A Fig.2: this wiring diagram must be followed carefully, particular­ly the details of the mains cord termination & the wiring to the Triac. October 1994  67 24V taps being used. 12VAC is fed to the bridge rectifier and the resulting DC is smoothed by the 470µF 25VW electrolytic capacitor. The is fed to a 7808 8V 3-terminal regulator which supplies most of the circuit. 24V AC supplies the soldering iron element via the Triac. Note here that the 0V tap on the transformer does not connect to the earth of the circuit but that the 0V rail, depicted by the familiar earth symbol, does connect to the 240VAC mains Earth via the mains cord. The barrel of the soldering iron is earthed via the thermo­ couple connection. We’ll discuss this point later in the text. Construction Most of the circuit components are mounted on a PC board measuring 132mm wide by 65mm deep. This board is slot mounted vertically in an Arlec case measuring 140mm wide, 70mm high and 130mm deep. The sides of the PC board need to be tapered slightly at top and bottom to make sure it fits snugly into the case. The case comes with a plastic front panel and steel rear panel and these will require drilling before the assembled PC board can be mounted. But let’s talk about board assembly first. The component overlay diagram can be seen in Fig.2 which shows all the wiring. Before you begin any soldering, check the board thoroughly for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. If all is OK, you can start assembly by inserting all the resistors and capacitors. Remember to watch the ori- The PC board is mounted vertically inside the case & the trans­former must be placed so that its terminals do not contact com­ponents on the board. Note how the indicator LEDs are mounted so that they sit flush with the front panel. entation of the electrolytic capacitors. Next, insert the diodes, bridge rectifier and transistor Q1. If you want to use sockets for IC1, IC2 and IC3 then insert them now. Finally, insert and solder the regulator. It is laid flat on the topside of the PC board and secured with a screw and nut. All of the LEDs except LED1 are soldered to the copper side of the PC board. Their lead length should be about 18mm to allow them to protrude through holes in the front panel. 3mm LEDs are used for the bargraph while the others can be 3mm or 5mm types. The 25kΩ potentiometer VR1 is also mounted on the PC board and secured with a nut and lockwasher. Before it is mounted, its shaft should be cut to a length of RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  2 ❏  1 ❏  1 ❏  2 ❏  1 ❏  2 ❏  1 ❏  3 68  Silicon Chip Value 4.7MΩ 100kΩ 47kΩ 10kΩ 8.2kΩ 4.7kΩ 2.7kΩ 1kΩ 560Ω 470Ω 4-Band Code (1%) yellow violet green brown brown black yellow brown yellow violet orange brown brown black orange brown grey red red brown yellow violet red brown red violet red brown brown black red brown green blue brown brown yellow violet brown brown 5-Band Code (1%) yellow violet black yellow brown brown black black orange brown yellow violet black red brown brown black black red brown grey red black brown brown yellow violet black brown brown red violet black brown brown brown black black brown brown green blue black black brown yellow violet black black brown SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from 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 the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card 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. 70  Silicon Chip semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer’s Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 ing a mica washer and bush and smear the mounting surface lightly with heatsink com­pound. Check with your multimeter, switched to the “Ohms” range, to confirm that the metal tab of the Triac is actually isolated from the metal panel. Make sure that the mains wiring is as depicted in Fig.2. Both the rear panel and the transformer case must be connected to the 240VAC mains earth, while the Active and Neutral wires should be terminated in a 2-way insulated terminal block. The 240VAC connections to the transformer should be fitted with heat­shrink sleeving to make them safe. Soldering iron assembly Make sure that the mains cord is securely anchored using a cordgrip grommet & note that the rear panel & the transformer case must be connected to the mains earth. Bind the wiring that runs between the rear panel & the PC board using cable ties as shown in this photograph. about 25mm. This will allow sufficient shaft to protrude through the front panel and have a knob fitted. Drilling the case Quite a few holes need to be drilled in the case. On the front panel, you will need to cut a slot for the 3mm bargraph LEDs, plus holes for the other two LEDs and the potentiometer shaft. The latter hole can be 8-10mm in dia­meter. The base of the case needs to be drilled for the transform­er mounting screws and a screw for the insulated 2-way terminal block. On the rear panel, you will need holes for the cordgrip grommet (for the mains cord), for the Triac, for the earth solder lug and for the 4-pin screw-in soldering iron socket. When drilling the base of the case for the transformer, you will need to offset it so that its voltage terminals do not foul components on the PC board. Check the relevant photo in this arti­cle to clarify this point. Mount the Triac on the rear panel us- Where to buy the parts A kit of parts for this project will be available from CTOAN Electronics. This will comprise the PC board plus all on-board components, Triac, mains cord and moulded plug. The soldering iron element, transformer and case are available from any Dick Smith Electronics store. The cost of the kit is $33.00 plus $5.00 for postage & packing. Ctoan Electronics will also be selling built and tested PC boards for $58.00. A repair service will also be available. Contact CTOAN Electronics at PO Box 1031, Jimboomba, Qld 4280. Phone (07) 297 5421. Note: copyright of the PC board associated with this project is retained by CTOAN Electronics. There are several approaches you can take to make the com­plete soldering iron. The specified soldering iron element, DSE Cat. T-2008, comes with the thermocouple already embedded in the metal barrel so you only have to connect the four wires, two for the thermocouple and two for the heater element, to a 4-way cable and plug to match the socket on the rear of the con­ troller’s case. The tricky bit comes in making or obtaining a suitable handle. If you already have a defunct soldering iron, you may be able to adapt its handle to the specified element. Alternatively, you could buy a cheap iron such as the model T-2100 from Dick Smith Electronics. You could then discard its element and replace it with the temperature element under discussion. The prototype pictured in this article was made from an old paint roller handle, with a short length of dowel inside to provide something for the screws to be anchored in. Make sure that what ever you use as a handle will not melt because the base of the heating element gets quite warm. Take care when making connections to the soldering iron element. All connections must be well anchored and should be well insulated to eliminate any possibility of shorts. The two white wires are for the heating element while the other two are for the thermocouple: green is the direct connection to the barrel while black is the positive output which ultimately connects to pin 3 of IC1a. When all wiring is complete, thoroughly check it all against the circuit and wiring diagrams of Fig.1 and October 1994  71 PARTS LIST 1 PC board, code CE/94, 75mm x 130mm 1 soldering iron element (Dick Smith Cat. T2008) 1 soldering iron handle (see text) 1 multitap transformer, DSE Cat M-1991 or equivalent 1 Arlec plastic case, 140 x 70 x 130mm, DSE Cat. H-2516 1 3-core mains flex & moulded 3-pin plug 1 cordgrip grommet to suit mains cord 1 knob 1 4-way mic plug, DSE Cat. P-1824 1 4-way mic socket, DSE Cat. P-1834 1 25kΩ linear pot (VR1) The soldering iron is connected to the controller via a 4-way microphone plug & socket. Two of the leads are for the heater, while the other two leads go to the thermocouple. Make sure that all leads to the soldering iron are securely anchored, to avoid any possibility of shorts. setting – the iron should get hotter. At the minimum setting the first LED may not be on. The indicator only serves as an indication that the temperature is rising, falling or steady. It is not meant to accurately indicate tip temperature. Fig.4: isolate the Triac from the rear panel using On the prototype, a mica washer & insulating bush, as shown it was found that a in this mounting diagram. Smear all mating good soldering temsurfaces with heatsink compound before bolting perature was obtain­ the assembly together, then use your multimeter ed when two of the (switched to the “Ohms” range) to confirm that green LEDs were on. the metal tab of the Triac is indeed isolated from The red LEDs are the metal panel. meant to indicate a very hot tip and on our units the tip Fig.2. You are now ready for the big actual­ ly changed colour when all moment. Connect the soldering iron LEDs were on. and switch on the power and watch If everything did not happen as it for anything abnormal such as sparks, is supposed to then switch off and go fire or explosions. Both the power and back over your work. Disconnect the heater LEDs should come on. After a iron and connect a 100Ω pot is place few seconds you should be able to feel of the thermocouple (ie, between pin the iron barrel getting hot. 3 of IC1a and 0V). By rotating the pot Rotate the temperature control fully you can simulate the rising and falling anticlockwise. The heater LED should of the iron temperature. cycle on and off with the temperature You can also check out the various being quite low. It will of course be too voltages on the circuit to see if they hot to touch but may only just melt are correct. The voltage at pin 1 of solder. Now increase the temperature IC1a should rise and fall with the 72  Silicon Chip Semiconductors 1 LM324 quad bipolar op amp (IC1) 1 MOC3021 optocoupled Triac trigger (IC2) 1 LM3914 dot/bar display driver (IC3) 1 LM7808 8V 3-terminal regulator (REG1) 1 BC548 NPN transistor (Q1) 1 BT139-600 Triac (see text) 1 W04 bridge rectifier (BR1) 2 1N914 silicon diodes (D1,D2) 2 5mm red LEDs (LED1,2) 3 3mm yellow LEDs (LED3,4,5) 5 3mm green LEDs (LED6-10) 2 3mm red LEDs (LED11,12) 1 5mm green LED (LED13) Capacitors 1 470µF 25VW electrolytic 1 470µF 16VW electrolytic 1 47µF 16VW electrolytic 1 10µF 16VW electrolytic 1 1µF 16VW electrolytic Resistors (0.25W, 5%) 1 4.7MΩ 2 4.7kΩ 1 100kΩ 1 2.7kΩ 2 47kΩ 2 1kΩ 1 10kΩ 1 560Ω 1 8.2kΩ 3 470Ω Miscellaneous Hook-up wire, nuts, bolts, solder. rotation of the 100Ω pot. Whenever the voltage at pin 2 is below pin 3, Q1 should turn on, as indi­cated by SC the heater LED. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd VINTAGE RADIO By JOHN HILL The winners of the Hellier Award As explained in last month’s Vintage Radio column, the Vintage Radio Club of North East Victoria Inc has a special annual activity – the Hellier Award. This year, the award centred around building a crystal set & there were two categories in­volved: open and vintage. Last month’s Vintage Radio story was about the crystal set I built for this year’s Hellier award. I enjoyed making the set and it had been my intention for the past six years to make that receiver. Previously I never found the time; that is, until the Club’s award activity motivated me sufficiently to get on with the job and get it done. As a result, I have built my “Classic Crystal Set”, I par­ticipated in the Club activity, and now the little receiver makes an excellent display item. It is a good “show and tell” attrac­tion to have when other collectors come to visit me. So other vintage radio clubs take note. A club project centred around a common theme is good for club morale. In the case of the Hellier award, interest in what others are doing is good socially and the collective display on judgement day can be interesting and wide ranging. The North East Club had 15 crystal sets entered for the Hellier award, with about a 50/50 representation in each cate­gory. It took several hours to demonstrate the receivers and judge them. The demonstration consisted of hooking up each crystal set to the aerial and earth supplied. The set’s output was then relayed through a small au- dio amplifier so that all those present could hear how well, or not so well, each set performed. The judging was done by the club members themselves. They were issued with score sheets and points were allotted as fol­lows: (1) Open Class – performance 30, design 30, construction 20, cabinet 20. (2) Vintage Class – performance 20, design 20, construction 30, cabinet 30. It would appear from these point scores that the vintage receivers were not expected to perform as well as the open cate­gory sets, nor would their design be as innovative. The vintage models were given more points for construction and cabinet. If that was the assumption then it proved to be false, because many of the vintage receivers were amongst the top per­formers, with some having quite elaborate circuits. The four scoring categories – performance, design, con­ struction and cabinet – were not as straightforward as they may seem, as each category had Harvey Utber’s winning open class entry featured twin coils, twin tuning capacitors & a variable coupling capacitor (top). This receiver was not only easy to operate but was a very good performer too. Harvey made the comment that the stations line up very well to the nonexistent dial pointers! 78  Silicon Chip many aspects to it. Let’s take a look at each category in turn. • Performance: how many stations could be received, how well the stations were separated, and the strength and clarity of output. • Design: ease of adjustment, ability to operate on different aerial lengths, originality of design and innovation (circuit and relevant information to be supplied). • Construction: neatness, winding of coils, accessibility of controls, connections, joints and soldering. • Cabinet: baseboard, front panel, finish, style, authentici­ty, aesthetics and general appeal (all very subjective stuff). This photo shows the control panel of Bob Young’s winning vin­tage class entry. Several hours of intense training is required before one gains complete mastery over the controls. Performance tests If we can go back to the performance aspect of these crys­tal sets, it is interesting to note that they were being tested in Benalla, Victoria. In such a locality, it was found that the better sets could receive four stations: the local Radio Nation­al, 3NE Wangaratta, 3SR Shepparton and 2CO Corowa. Not all of the crystal sets could pull in these four trans­missions, with some of the simpler sets being restricted to Radio National, which was by far the strongest signal. Just to make things difficult, the aerial that had been erected was approximately 55 metres long. As one of the design criteria was the ability to work with different aerials, this extra long aerial made it more difficult for sets of simple design. Those crystal sets that could pull in all four stations without inter-station interference were indeed well designed. What’s more, a surprising number of receivers were capable of doing just that. A rear view of Bob’s crystal set. The two coils behind the front panel are wound with Litz wire, while the loading coil at the end is a slider type. All connecting wires are of square busbar. The set has been built for display purposes. The winners Well the big moment finally arrived. The scores had been totalled and the results were read out. In the open category, Harvey Utber was first, Pat O’Shannessy second and Marcus Chick third. In the vintage category, Bob Young was first, Yours Truly second and Ralph Robertson third. After the judging, it was time to talk, look, ask ques­tions and take photographs. Because the crystal sets were spread over several tables, it was not possible to photograph them all, nor would it have been possible to include all of them here in Vintage Radio. How- Also entered into the vintage category was this neat set built into a wooden box. Note that both coils have sliders instead of the more usual taps. ever, the winners and some of the other sets are shown in the accompanying photographs. It is amazing to think that in this “high-tech” age, so many grown men would want to build a crystal set. Yet October 1994  79 "Scruffy Mk.1” was entered in jest to prove just how rough a simple crystal set can be & still work. Unfortunately, it per­formed dismally on the extra-long aerial & came last in the open section. The “boulder” mounted between the coil and tuning ca­pacitor is a large lump of galena. many did just that and they all enjoyed the experience. It is interesting to note that the vintage category winner, Bob Young, is actually in the computer business. Even so, Bob still likes to tinker around with old radios and crystal sets in particular. Currently Bob is writing a book about crystal sets and I have had the privilege of reading some of the early chapters. I can only say that it is a brilliant work which should be eagerly sort after when the book is complete. Bob’s writing technique is wonderfully straightforward. He has the ability to make complex issues understandable and his writing style has a touch of humour about it as well. Whether one is interested in crystal sets or not, there’s heaps of good basic information in the book. I hope to review it when it is complet­ed. Well that’s about all there is to report about the Hellier Award and the activities of the Vintage Radio Club of North East Victoria Inc. If anyone in that area wishes to contact the club, they can write or phone the secretary, Mr Ian Milne, 48 Smythe St, Benalla 3672. Phone (057) 62 5841. Germanium diodes In what space is left, I will continue with the crystal set theme and relate what I recently discovered regarding crystal detectors and germanium diodes. As a young lad, I built many crystal sets and well remember my father coming home one day with one of These vintage sets captured the true look of the 1920s. Most early crystal sets were enclosed in solid timber home-made cabinets. 80  Silicon Chip the new “u-beaut” germanium diodes –the wonder device that would solve all my crystal detector problems. To cut a long story short, the new diode was not as sensitive as the old crystal detector and recep­tion was noticeably weaker when it was in use. All I can say is that it was one of the first of its type and it never lived up to expectations. I have since had to reconsider diode performance and now know that a modern germanium signal diode is as good as anything, not to mention the convenience factor of such a component. But have you ever tested various diodes with an ohmmeter? I have and they vary quite a bit. Their forward resistance is about the same at around 3kΩ, while the reverse resistance varies from 0.5-2MΩ This neat and unusual crystal set uses a form of variometer tuning, whereby one coil slides over the other. A match box receiver (not shown) also operated on the same principle. or more. When used as a detector in a “crystal” set, they all perform much the same. Testing a “Neutron” crystal (a commercially made crystal for crystal sets) was a bit of a shock. “Good spots” produced approximately the same 3kΩ forward resistance as a germanium diode, while the reverse resistance amounted to less than 50kΩ, with most readings about 10-20kΩ. As mentioned in last month’s story, alternately switching from this crystal detector to a germanium diode detector shows no discernible difference if the crystal detector is properly ad­justed on a good spot. And while that seems to be contrary to what are generally accepted “facts”, practical experimenting proves the point. Regarding the crystal sets entered in the previously men­tioned Hellier Award, the open class mainly used signal diodes for detectors, whereas the vintage class used crystal detectors. Many of the top performers were in the vintage category, so the difference (if any) is negligible. But a germanium diode sure is conSC venient to use! Now here’s a clock radio with a difference! A clock & crystal set complete with its BSA badge placed this outfit in the unoffi­cial novelty section. October 1994  81 SPECIALS BY FAX If your fax has a polling function, dial (02) 579 3955 and press your POLLING button to get our latest specials, plus our item and kit listing. Updated at the start of each month. HF ELECTRONIC BALLASTS Brand new “slim line” cased electronic ballasts. They provide instant flicker free starting, extend tube life, reduce power consumption, eliminate flicker during operation (high frequency operation), and are “noise free” in operation. The design of these appears to be similar to the one published in the Oct. 94 SILICON CHIP magazine. One of the models even includes a DIMMING OPTION!! Needs external 100K potentiometer or a 0-10V DC source. We have a good but limited stock of these and are offering them at fraction of the cost of the parts used in them! Type A: Designed to power two 32W - 4' tubes, will power two 40W - 4' tubes with no noticeable change in light output, has provision for dimming: $26 Type B: Designed to power two 16W - 18" tubes, will power two 18W - 18" tubes with no noticeable change in light output: $18 MISCELLANEOUS FLAT NOSE PLIERS: $4 per pair. BATTERY CHARGER: S2 accessory set for Telecom Walkabout “Phones”. Includes cigarette lighter cable, fast rate charger, and desktop stand. Actually charges 6 series connected AA Nicad batteries: $27. BATTERY PACKS: Contain 6 AA Nicad batteries wired in series, can easily be pulled apart, used units, satisfaction guaranteed: $2 per pack. LITHIUM BATTERIES: Button shaped with pins, 20mm diameter, 3mm thick. A red led connected across one of these will produce light output for over 72 hours (3 days): 4 for $2. CIGARETTE LIGHTER LEADS: Cigarette lighter plug with 3 metres of heavy duty fig. 8 flex connected. Should suit load currents up to 20A: 5 for $5. SUPERCAPS: 0.047F/5.5V capacitors: 5 for $2. HOUR METER: Non resettable, mains powered (50HZ), WARBURTON FRANKI, 100,000 Hours maximum, 0.01Hr resolution: $15. PCB MOUNTED SWITCHES 90 deg. 3A-250V, SPDT: 4 for $2. AC POWER SUPPLY: Mains in, two separate 8.5V/3A outputs, in plastic case with mains power lead/plug and output leads/plugs: $15 Ea. MONITOR PCB’s: Complete PCB and yoke assembly for high resolution monochrome TV monitors (no tube). Operate from 12V DC, circuit and information provided: $15. MODEMS: Complete mains powered non standard 1200 baud Telecom approved modems. We should have brief information available. Limited stock at below the price of the high quality case that these are housed in: $30 for 2 modems. MEDICAL LASER One only water cooled medical laser with selectable outputs: Argon (7W multiline) or Dye laser (1W red). Large water cooled unit with a separate control box and accessories (350kg): $15,000 LEVEL RECORDER One only, Bruel & Kjaer level recorder type 2305, in good condition: $300 82  Silicon Chip DIE CAST BOXES These large (187 x 120 x 56mm) aluminium die cast boxes have several holes drilled in them and have a C&K toggle switch and a 6.25mm phono socket fitted. New units from an unfinished production project: $4 Ea. WELLER SOLDERING IRON TIPS New soldering iron for low voltage Weller soldering stations and mains operated Weller irons. Mixed popular sizes and temperatures. Specify mains or soldering station type: 5 for $10. NICAD BATTERY PACKS Brand new Toshiba 7.2V-2.2AHr Nicad Battery packs in a plastic assembly: $20 Ea. If you purchase three packs we will supply a matching fast charger (90min.) that can charge up to three of these batteries (one at a time). Modern unit that employs “delta V” voltage detection to terminate charge, needs an external 12V-2.2A unregulated supply: $60 for three battery packs and a three way charger. PLUGS/SOCKETS 3 pin chassis mounting socket and a matching covered three pin plug. Good quality components that will handle a few amperes at low voltage: $5 for 4 pairs. DYNAMIC MICROPHONES Low impedance dynamic microphones with separate switch wiring, 3.5mm mic. plug, 2.5mm switch plug, as used on most cassette recorders: $4 Ea. 40mW IR LASER DIODES New famous brand 40mW-830nM IR laser diodes, suit medical and other applications: $90 Ea. Constant current driver kit to suit: $10. HIGH POWER LED IR ILLUMINATOR This kit includes two PCBs, all on-board components plus casing: Switched mode power supply plus 60 high intensity 880nm IR (invisible) LEDs. Variable output power, 6-20VDC input, suitable for illuminating IR responsive CCD cameras, IR night viewers etc. Professional performance at a fraction of the price of the commercial product. COMPLETE KIT PRICE: $60 LOW COST 1-2 CHANNEL UHF REMOTE CONTROL Late in October we will have available a single channel 304MHz UHF remote control with over 1/2 million code combinations which also makes provision for a second channel expansion. The low cost design includes a complete compact keyring transmitter kit, which includes a case and battery, and a PCB and components kit for the receiver that has 2A relay contact output! Tx kit $10, Rx kit $20. Additional components to convert the receiver to 2 channel operation (extra decoder IC and relay) $6. INCREDIBLE PRICES: COMPLETE 1 CHANNEL TX-RX KIT: $30 COMPLETE 2 CHANNEL TX-RX KIT: $36 ADDITIONAL TRANSMITTERS: $10 FIBRE OPTIC TUBES These US made tubes are from used equipment but in excellent condition. Have 25/40 mm diameter, fibre-optically coupled input and output windows. The 25mm tube has an overall diameter of 57mm and is 60mm long, the 40mm tube has an overall diameter of 80mm and is 92mm long. The gain of these is such that they would produce a good image in approximately 1/2 moon illumination, when used with suitable “fast” lens, but they can also be IR assisted to see in total darkness. Our HIGH POWER LED IR ILLUMINATOR kit, and the IR filter are both suitable for use with these tubes. The superior resolution of these tubes would make them suitable for low light video preamplifiers, wild life observation, and astronomical use. Each of the tubes is supplied with an 9V-EHT power supply kit. INCREDIBLE PRICES: $120 for the 25mm intensifier tube and supply kit. $180 for the 40mm intensifier tube and supply kit. We also have a good supply of the same tubes that may have a small blemish which is not in the central viewing area!: $65 for a blemished 25mm intensifier tube and supply kit. $95 for the blemished 40mm intensifier tube and supply kit. SIEMENS VARISTORS 420VAC 20 joule varistors that are suitable for spike protection in Australian 3 phase systems: 10 for $5. TAA611C ICs TAA611C Audio power amplifier ICs, no more information: 5 for $5. INTENSIFIED NIGHT VIEWER KIT SC Sept. 94. See in the dark! Make your own night scope that will produce good vision in sub-starlight illumination! Has superior gain and resolution to all Russian viewers priced at under $1500. We supply a three stage fibre-optically coupled image intensifier tube, EHT power supply kit, and sufficient plastics to make a monocular scope. The three tubes are supplied already wired and bonded together. $290 for the 25mm version $390 for the 40mm version We can also supply the lens (100mm f2: $75) and the eyepiece ($18) which would be everything that is necessary to make an incredible viewer! MAINS POWERED GAS LASER Includes a professional potted mains power supply and a new 3mW red tube to suit. One catch, this supply requires a 4-6V (TTL) enable input which is optically isolated, to make the unit switch ON. Very low consumption from a 4.5V battery. $100 for a new 3mW tube plus a TTL mains power supply to suit. SUPER DIODE POINTERS - HEADS These pointers probably represent the best value when you compare them on a “brightness per dollar” basis. They are about 5 times brighter than 5mW/670nm pointers! They have an output of 2.5mW at 650nm, which is about equal in brightness to a 0.8mW HE-NE tube!! SPECIAL INTRODUCTORY PRICE: $150 We will also have available some of the 3V diode modules used in these pointers at approximately $125, and also some 2.5mW/635nm laser diode modules with special optics at approximately $280. VIDEO TRANSMITTERS Low power PAL standard UHF TV transmitters. Have audio and video inputs with adjustable levels, a power switch, and a power input socket: 10-14V DC/10mA operation. Enclosed in a small metal box with an attached telescopic antenna. Range is up to 10m with the telescopic antenna supplied, but can be increased to approximately 30m by the use of a small directional UHF antenna. INCREDIBLE PRICING: $25 TDA ICs/TRANSFORMERS We have a limited stock of some 20 Watt TDA1520 HI-FI quality monolithic power amplifier ICs, less than 0.01% THD and TIM distortion, at 10W RMS output! With the transformer we supply we guarantee an output of greater than 20W RMS per channel into an 8ohm load, with both channels driven. We supply a far overrated 240V-28V/80W transformer, two TDA1520 ICs, and two suitable PCBs which also include an optional preamplifier section (only one additional IC), and a circuit and layout diagram. The combination can be used as a high quality HI-FI Stereo/Guitar/P.A., amplifier. Only a handful of additional components are required to complete this excellent stereo/twin amplifier! Incredible pricing: $25 for one 240V-28V (80W!) transformer, two TDA1520 monolithic HI-FI amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. LIGHT MOTION DETECTORS Small PCB assembly based on a ULN2232 IC. This device has a built in light detector, filters, timer, narrow angle lens, and even a siren driver circuit that can drive an external speaker. Will detect humans crossing a narrow corridor at distances up to 3 metres. Much higher ranges are possible if the detector is illuminated by a remote visible or IR light source. Can be used at very low light levels, and even in total darkness: with IR LED. Full information provided. The IC only, is worth $16! OUR SPECIAL PRICE FOR THE ASSEMBLY IS: $5 Ea. or 5 for $20 GAS LASER SPECIAL We have a good supply of some He-Ne laser heads that were removed from new or near new equipment, and have a power output of 2.5-5mW: very bright! With each head we will supply a 12V universal laser power supply kit for a ridiculous TOTAL PRICE of: $89 AA NICADS Brand new AA size Saft brand (made in France) 500mA Hr. batteries, also have solder connections (can be removed): $2 Ea. or 10 for $ 16. TWO STEPPER MOTORS PLUS A DRIVER KIT This kit will drive two stepper motors: 4, 5, 6 or 8 eight wire stepper motors from an IBM computer parallel port. Motors require separate power supply. A detailed manual on the COMPUTER CONTROL OF MOTORS plus circuit diagrams/descriptions are provided. We also provide the necessary software on a 5.25" disc. Great “low cost” educational kit. We provide the kit, manual, disc, plus TWO 5V/6 WIRE/7.5 Deg. STEPPER MOTORS FOR A SPECIAL PRICE OF: $42 CAMERA FLASH UNITS Electronic flash units out of disposable cameras. Include PCB/components and Xenon tube/reflector assembly. Requires a 1.5V battery. $2.50 IR LASER DIODE KIT auto iris lens. It can work with illumination of as little as 0.1Lux and it is IR responsive. Can be used in total darkness with Infra Red illumination. Overall dimensions of camera are 24 x 46 x 70mm and it weighs less than 40 grams! Can be connected to any standard monitor, or the video input on a Video cassette recorder. NEW LOW PRICE: $199 IR “TANK SET” A set of components that can be used to make a very responsive Infra Red night viewer. The matching lens tube and eyepiece sets were removed from working military quality tank viewers. We also supply a very small EHT power supply kit that enables the tube to be operated from a small 9V battery. The tube employed is probably the most sensitive IR responsive tube we ever supplied. The resultant viewer requires low level IR illumination. Basic instructions provided. $140 BRAND NEW 780nm LASER DIODES (barely visible), mounted in a professional adjustable collimator-heatsink assembly. Each of these assemblies is supplied with a CONSTANT CURRENT DRIVER kit and a suitable PIN DIODE that can serve as a detector, plus some INSTRUCTIONS. Suitable for medical use, perimeter protection, data transmission, IR illumination, etc. For the tube, lens, eyepiece and the power supply kit. 5mW VISIBLE LASER DIODE KIT We include a basic diagram-circuit showing how to make a small refrigerator-heater. The major additional items required will be an insulated container such as an old “Esky”, two heatsinks, and a small block of aluminium. $40 Includes a Hitachi 6711G 5mW-670nm visible laser diode, an APC driver kit, a collimating lens - heatsink assembly, a case and battery holder. That’s a complete 3mW collimated laser diode kit for a TOTAL PRICE OF: $75 BIGGER LASER We have a good, but LIMITED QUANTITY of some “as new” red 6mW+ laser heads that were removed from new equipment. Head dimensions: 45mm diameter by 380mm long. With each of the heads we will include our 12V Universal Laser power supply. BARGAIN AT: $170 6mW+ head/supply. ITEM No. 0225B We can also supply a 240V-12V/4A-5V/4A switched mode power supply to suit for $30. 12V-2.5 WATT SOLAR PANEL SPECIAL These US made amorphous glass solar panels only need terminating and weather proofing. We provide terminating clips and a slightly larger sheet of glass. The terminated panel is glued to the backing glass, around the edges only. To make the final weatherproof panel look very attractive some inexpensive plastic “L” angle could also be glued to the edges with some silicone. Very easy to make. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE until the end of 94!: $20 Ea. or 4 for $60 Each panel is provided with a sheet of backing glass, terminating clips, an isolating diode, and the instructions. A very efficient switching regulator kit is available: Suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. CCD CAMERA Monochrome CCD camera which is totally assembled on a small PCB and includes an SOLID STATE “PELTIER EFFECT” COOLER-HEATER These are the major parts needed to make a solid state thermoelectric cooler-heater. We can provide a large 12V-4.5A Peltier effect semiconductor, two thermal cutout switches, and a 12V DC fan for a total price of: $45. ITEM No. 0231 RUSSIAN NIGHT VIEWER We have a limited quantity of some passive monocular Russian made night viewers that employ a 1st generation image intensifier tube, and are prefocussed to infinity. CLEARANCE: $180 INFRA RED FILTER A very high quality IR filter and a RUBBER lens cover that would fit over most torches including MAGLITEs, and convert them to a good source of IR. The filter material withstands high temperatures and produces an output which would not be visible from a few metres away and in total darkness. Suitable for use with passive and active viewers. The filter and a rubber lens cover is priced at: $11 DOME TWEETERS Small (70mm diam., 15mm deep) dynamic 8ohm tweeters, as used in very compact high quality speaker systems: $5 Ea. We also have some 4" woofers: $5 Ea. VIDEO ZOOM LENSES Wire antenna - attached, Microphone: Electret condenser, Battery: One 1.5V silver oxide LR44/G13, Battery life: 60 hours, Weight: 15g, Dimensions: 1.3" x 0.9" x 0.4". $25 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 Ea. MORE KITS-ITEMS Single Channel UHF Remote Control, SC Dec. 92 1 x Tx plus 1 x Rx $45, extra Tx $15. 4 Channel UHF Remote Control Kit: two transmitters and one receiver, $96. Garage/Door/Gate Remote Control Kit: Tx $18, Rx $79. 1.5-9V Converter Kit: $6 Ea. or 3 for $15. Laser Beam Communicator Kit: Tx, Rx, plus IR Laser, $60. Magnetic Card Reader: professional assembled and cased unit that will read information from plastic cards, needs low current 12VDC supply-plugpack, $70. Switched Mode Power Supplies: mains in (240V), new assembled units with 12V-4A and 5V-4ADC outputs, $32. Electric Fence Kit: PCB and components, includes prewound transformer, $28 High Power IR LEDs: 880nm/30mW/12deg. <at> 100mA, 10 for $9 Plasma Ball Kit: PCB and components kit, needs any bulb, $25. Masthead Amplifier Kit: two PCBs plus all on board components: low noise (uses MAR-6 IC), covers VHF-UHF, $18. Inductive Proximity Switches: detect ferrous and non-ferrous metals at close proximity, AC or DC powered types, three wire connection for connecting into circuitry: two for the supply, and one for switching the load. These also make excellent sensors for rotating shafts etc. $22 Ea. or 6 for $100. Brake Light Indicator Kit: 60 LEDs, two PCBs and ten Rs, makes for a very bright 600mm long high intensity Red display, $30. IEC Leads: heavy duty 3 core (10A) 3M LEADS with IEC plug on one end and an European plug at the other, $1.50 Ea. or 10 for $10. IEC Extension Leads: 2M long, IEC plug at one end, IEC socket at other end, $5. Motor Special: these motors can also double up as generators. Type M9: 12V, I No load = 0.52A-15,800 RPM at 12V, 36mm Diam.-67mm long, $5. Type M14: made for slot cars, 4-8V, I No load = 0.84A at 6V, at max efficiency I = 5.7A-7500 RPM, 30mm Diam-57mm long, $5. EPROMS: 27C512, 512K (64K x 8), 150ns access CMOS EPROMS. Removed from new equipment, need to be erased, guaranteed, $4. Green Laser Tubes: Back in stock! The luminous output of these 1-1.5mW GREEN laser diode heads compares with a 5mW red tube!: $490 for a 1-1.5mW green head and a 12V operated universal laser inverter kit. 40 x 2 LCD Display: brand new 40 character by 2 line LCD displays with built in driver circuitry that uses Hitachi ICs, easy to drive “standard” displays, brief information provided, $30 Ea. or 4 for $100. RS232 Interface PCB: brand new PCB assembly, amongst many parts contains two INTERSIL ICL232 ICs: RS232 Tx - Rx ICs, $8. Modular Telephone Cables: 4-way modular curled cable with plugs fitted at each end, also a 4m long 8-way modular flat cable with plugs fitted at each end, one of each for $2. 12V Fans: brand new 80mm 12V-1.6W DC fans. These are IC controlled and have four different approval stamps, $10 Ea. or 5 for $40. Lenses: a pair of lens assemblies that were removed from brand new laser printers. They contain a total of 4 lenses which by different combinations - placement in a laser beam can diverge, collimate, make a small line, make an ellipse etc., $ 8. Polygon Scanners: precision motor with 8 sided mirror, plus a matching PCB driver assembly. Will deflect a laser beam and generate a line. Needs a clock pulse and DC supply to operate, information supplied, $25. PCB With AD7581LN IC: PCB assembly that amongst many other components contains a MAXIM AD7581LN IC: 8 bit, 8 channel memory buffered data acquisition system designed to interface with microprocessors, $29. EHT Power Supply: out of new laser printers, deliver -600V, -7.5KV and +7kV when powered from a 24V-800mA DC supply, enclosed in a plastic case, $16. Mains Contactor Relay: has a 24V-250ohm relay coil, and four separate SPST switch outputs, 2 x 10A and 2 x 20A, new Omron brand, mounting bracket and spade connectors provided, $8. FM Transmitter Kit - Mk.II: high quality high stability, suit radio microphones and instruments, 9V operation, the kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip, $11. FM Transmitter Kit - Mk.I: this complete transmitter kit (miniature microphone included) is the size of a “AA” battery, and it is powered by a single “AA” battery. We use a two “AA” battery holder (provided) for the case, and a battery clip (shorted) for the switch. Estimated battery life is over 500 hours!!: $11. High Power Argons: the real thing! Draw pictures on clouds, big buildings etc., with a multiline water-cooled Argon laser with a few watts of output. “Ring” for more details. Argon-Ion Heads: used Argon-Ion heads with 30-100mW output in the blue-green spectrum, will be back in stock soon, priced at around $400 for the “head” only, power supply circuit and information supplied. Two only 10:1 video zoom lenses, f=15150mm, 1:1.8, have provision for remote focus aperture and zoom control: three motors, one has a “C” mount adaptor, 150mm diam. by 180mm long: OATLEY ELECTRONICS MINIATURE FM TRANSMITTER Phone (02) 579 4985. Fax (02) 570 7910 $390 Ea. Not a kit, but a very small ready made self contained FM transmitter enclosed in a small black metal case. It is powered by a single small 1.5V silver oxide battery, and has an inbuilt electret microphone. SPECIFICATIONS: Tuning range: 88-108MHz, Antenna: PO Box 89, Oatley, NSW 2223 Bankcard, Master Card, Visa Card & Amex accepted with phone & fax orders. P & P for most mixed orders: Aust. $6; NZ (airmail) $10. October 1994  83 PRODUCT SHOWCASE PIR detectors from DSE Passive infrared detectors are becoming cheaper and their uses more varied. They are used to detect movement and are most commonly found in alarm systems, automatic doors and lighting systems. The sensor consists of two infrared elements on a single substrate which is heated to operating temperature. One element is exposed to incoming infrared radiation with the other protected. With a static background, the amount of infrared radiation seen by the exposed element remains constant, but when a body moves across the background, it alters the amount of heat seen by the element, causing a voltage shift between the two elements. Placing a Fresnel lens in front of the sensor maximises the change in heat seen by breaking the background into zones. As a person moves across the sensor's field, he or she moves from zone to zone causing a pulsing heat signal to be seen by the exposed element. This difference is detected by the electronics and if enough pulses are detected in a set time the detector opens a relay to indicate that it has seen movement. People are not the only sources of heat, so care has to be taken when installing the detectors so that sources of heat do not lead to false triggering. Common sources of false triggering are direct sunlight, air conditioners and heaters. Stickers can be placed on the inside of the Fresnel lens to blind particular zones from the source of interference. Three PIR detectors are available from Dick Smith Electronics. The first Low cost video enhancer If your VCR is in tiptop condition you probably have no need for a video enhancer but if you want to dub between VCRs or want to send video signals over a longish cable, then this SuperBooster II model from Jaycar may be for you. It has controls for video boost and the stereo audio levels and will provide a maximum video gain of two (+3dB). Note that it does not boost the video high frequencies which would enhance picture detail. If you want a detail enhancer. Jaycar has another model, the JVE-1. 84  Silicon Chip The video enhancer is powered by an external 9V 200mA DC plugpack (not supplied) and sells for $39.95 (Cat. AV-6500). It is available from all Jaycar Electronics stores. (DSE PIR detector) is a budget version and has a fixed 90° field of view. The sensitivity is adjustable and a LED gives visual indication of detection to help with setup procedures. A tamper switch inside detects any attempt that is made to open the case. The detector needs a 12V supply and has an N/C (normally closed) alarm output (Cat. L-5011). The second detector (Everspring 180 degree PIR) is a half hemisphere in shape and uses mirrors above the sen­sor to gain a 180° view. It can have the Fresnel lens mounted vertically or horizontally to tailor the field of view to wide or tall. Four lenses are included to provide further response tailoring and are la­ belled wide angle, long distance, pet and curtain. Detection pulses are counted over a time frame to mini­mise false triggering. Tamper protec­tion and LED indication are also in­cluded. The unit needs a 9-16V sup­ply and has N/C tamper and alarm outputs (Cat. L-5015). The last detector (Ir-tec IR-820 PIR) has three different Fresnel patterns in its lens to detect motion. The patterns are designated wide angle, long range and finger curtain. Stickers are included to mask out any zone that has a source of interference. The sensor can also be moved in relation 12-PPM laser printers from Hewlett Packard SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands 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 a complete copy of all Notes & Errata text (diagrams not included). The file viewer 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 a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM Hewlett-Packard has introduced two new 12-page-per minute (PPM) laser printers that are 30-40% faster, on average, than their predecessors. Called the HP LaserJet 4 Plus and HP LaserJet 4M Plus, these printers fea­ture 600 x 600 dots per inch (dpi) resolution and a 12-ppm print engine with a 25MHz Intel i960 RISC processor with cache, advanced memory management and other performance enhancements. HP's Memory Enhancement technology (MEt) effectively doubles the printer's memory and enables it to print more complex pages with stand­ a rd memory in PCL, while u s e r­c o n f i g u r a b l e i n p u t / o u t p u t (I/O) buff­ering allows the printer to accept print data faster, returning control of the host computer to the user sooner. The resource-saving feature retains downloaded fonts, logos, forms and macros, eliminating the time normally needed to download this information again when switching between PCL and Postscript. Job overlap enables the printer to process one print job while it is printing another. This re­ sults in faster printer throughput when multiple jobs are sent to the PRICE ❏ 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): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ to the lens to alter the response pattern. A gauge on the PC board helps in align­ment. LED indication is jumper selectable and can be turned off once setup is complete, thereby not letting an intruder know that he has been detected. Tamper protection and pulse count­ing are also included. The detector needs 9-16V and has N/C tamper and alarm outputs (Cat. L-5014). These PIR detectors sell for $39.95, $59.95 and $89.95 respectively and are available from all Dick Smith Electronics stores. October 1994  85 printer, particularly if the jobs alternate between PCL and PostScript. The HP LaserJet 4M Plus printer offers improved greyscale capability when printing in Postscript. The result is reduced visual banding so transitions in grey tones appear smoother and more even, while scanned images are reproduced with better detail. The new LaserJet comes standard with 2Mb of RAM while the LaserJet 4M Plus includes 6Mb of RAM. Addi­ tional memory can be used in both printers to increase I/O buffer space for faster return to the user's application and for saving of downloaded fonts, forms and macros. The HP LaserJet 4 Plus and 4M Plus are upgradable to 66Mb and 38Mb, respectively. For further information on HP products and services, phone 131 347 (toll free, no STD area code required). Ultra-thin toroidal transformers from Tortech Conventional toroidal transformers are readily available from several sources in Australia but if you want to place a toroidal transformer with a reasonable high VA rating in a one-unit high rack case, you have a problem. Or at least you did, until now. Pictured above are two toroids, one a conventional unit and one an ultra-thin unit measuring only 20mm thick and having a rating of 50VA. Want to know more? It is available from Tortech Pty Ltd, 24/31 Wentworth Street, Greenacre, NSW 2190. Phone (02) 642 6003. Replace your mouse with a tablet from DSE Dick Smith Electronics has two new graphics tablets to improve your CAD and drawing ability on the PC. The Acecat II is a high resolution digitising tablet with up to 2000 line per inch (LPI) resolution. Using the supplied WinTab multi-pointer soft­ware driver, the tablet can be used alongside a stand­ard mouse or trackball in the Windows environment as a template overlay for easy tracing of existing drawings or creating free­hand drawings. 86  Silicon Chip For CAD users, the tablet uses "absolute" positioning which means that where you point on the tablet is exactly where your cursor will appear on the screen. This, it is claimed, makes the selection of icons and drawing faster than using a conventional mouse or trackball. The programmable 2-button stylus comes with replaceable tips on either a 5-inch square or 12-inch square tablet. The right mouse button is on the barrel of the stylus and is controlled by your index finger, while the left mouse button is actuated by pressing the sty­lus more firmly on the tablet. The smaller tablet is about the size of a mouse pad and can be used in the palm of the hand or on the desk, whereas the larger tablet is intended for desk use. Supplied with five software drivers and various testing utilities, the Acecat II can be software configured to suit your favourite program and connects to any serial port. The Win Tab driver appears as an icon in the Windows envi­ r onment and may be clicked on to change parameters such as tracking areas, tablet sensi­tivity and button configura­tions. The smaller tablet (5 x 5-inch) retails for $199 and the larger (12 x 12-inch) sells for $399. Both come with a quickstart guide and comprehen­sive user's manual. For more information, contact the Dick Smith Electronics store nearest you. Beyer kick drum microphone The new TG-X mic from Beyer Dynamic is designed primarily for close miking of kick drums in re­ cording and live performance ap­plications. It is also useful for miking high sound pressure levels such as musical instruments. The heart of the microphone uses a pressure gradient dynamic transducer with a hypercardioid pattern. The capsule has a quoted frequency response of 15Hz to 18kHz (no dB limits). The microphone body is constructed of diecast zinc with a matt black finish and it is fitted with a standard 3-pin XLR connec­tor. Standard accessories are a mic clip and padded carry bag. Options include a range of mic and boom stands and cables with Neutrik jack and XLR connec­t ors. Recommend­ed retail price of the Beyer TG-X 50 is $495. For more information, contact Amber Technology, Unit B, 5 Sky line Place, Frenchs Forest 2086. Phone (02) 975 1211. October 1994  87 COMPUTER BITS BY DARREN YATES Placing directories into programs Unless you have Visual BASIC or some other high level language, getting DOS directories into your programs is not always easy. This month, we show you how you can do it with QBasic and QuickBASIC 4.5. This month’s column is the result of a letter from a reader wanting to know how to get a directory listing from the screen into one of his programs. This is actually a quite common thing to do, particularly if you work with Windows or Visual BASIC. However, it’s a little more difficult to do it in Quick BASIC than just clicking on an icon. Firstly, there is no direct command in BASIC you can use apart from the FILES command and this simply displays a list of files on the screen. You can determine which files come up –not how they appear – by using the familiar wildcard commands. In fact, the files appear pretty much as they would get if you used the DOS command “DIR/W”. Most of the time, this isn’t very use­ful, particularly if you type FILES C:|WINDOWS (for example) and 100+ files fly past your eyes, or if you need to know the size of a certain file before loading it into the system. For QuickBASIC users, there are essentially two methods. The first is to take it directly from the drive. This can be done using some extra DOS interrupts that we have yet to cover. You can do what’s called an “absolute read” of a certain sector of a track where DOS stores this information. This is by far the most elegant method but it can be dangerous if you plug in the wrong command. It doesn’t take much to rewrite your directory and upset the whole disc. It’s also fairly 88  Silicon Chip difficult to do and that’s with the right information at hand. The DOS interrupts also allow you to do an “absolute write” to any sector of any track but you don’t get any second warnings. In fact, you don’t even get a first warning that you will lose any information currently stored in that location. It simply wipes over the top. The redirect command The second method is more cumbersome but is much safer and easier to do. It involves using the DOS redirect command, “>”. Every time you do a DIR in DOS, your PC directs the directory output to your screen so you can see all of the files. However, by using the “>” command, you can direct this output into an ASCII file on disc. For example, if you type the command “DIR > DIRLIST.TXT”, DOS will create the file DIRLIST.TXT and dump the complete list­ ing of the current directory into that file. You can then use EDIT to do what you like with that file. More importantly, you can now use Quick/QBasic to do what you like with the file. The good thing about the file is that it is columnated; ie, each subpart of the directory listing begins at a particular column. For example, the first part of the filename begins at column 1 and has a maximum of eight letters; the three-letter maximum extension begins at column 10. The size of the file begins at column 14 and the start of the date at column 24. And finally, the time begins at column 34. You can easily extract each of these five file parameters by using the MID$ command. An example of this is shown in the program DIRSPLIT.BAS – see listing. This program is designed to handle a directory which has up to 400 files. If you expect to have a bigger directory, simply extend the dimension from 400 to whatever you think you need. The next series of dimension statements set up our five parameter arrays, one each for filename, extension, file size, date and time. Using the LINE INPUT statement to read in one line of the directory listing at a time, the WHILE NOT EOF(1) loop and the MID$ command enables us to extract each of the parameters. These parameters are then stored in suitably named arrays: FILENAME, EXTENSION, FILESIZE, DATE and TIME. The dimension of each array is arranged so that the first element of each array refers to one file, the next element to the next file and so on. The second half of the program prints this information on screen. The TAB statements ensure that the directory listing uses the whole screen rather than just half of it as the normal DIR statement uses. The VIEW PRINT command allows the top two lines (ie, the column titles) to stay on screen at all times, while the FOR NEXT loop enables you to page through the directory. This is handy when you have more than one screen of files in a directory. To run the program, you simply type DIRSPLIT<enter> and it will display the contents of the current disc and directory. Copies of DIRSPLIT.BAS/OBJ/EXE will be available on 3.5-inch or 5.25- Basic Listing For Dirsplit.bas Utility • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES DIM dirline$(400) DIM filename(400) AS STRING * 8 DIM extention(400) AS STRING * 3 DIM filesize(400) AS STRING * 9 DIM date(400) AS STRING * 8 DIM time(400) AS STRING * 7 start = 0 SHELL “DIR > DIRLIST.TXT” OPEN “dirlist.txt” FOR INPUT AS #1 WHILE NOT EOF(1) lineno = lineno + 1 LINE INPUT #1, dirline$ ‘FILENAME filename(lineno) = MID$(dirline$, 1, 8) ‘EXTENSION extension(lineno) = MID$(dirline$, 10, 3) ‘FILESIZE filesize(lineno) = MID$(dirline$, 14, 9) ‘DATE date(lineno) = MID$(dirline$, 24, 8) ‘TIME time(lineno) = MID$(dirline$, 34, 7) WEND CLOSE #1 CLS PRINT TAB(1); “File”; TAB(15); “extension”; TAB(30); “File size”; TAB(50); “Date”; TAB(70); “Time” PRINT “————————————————————————————­­” VIEW PRINT 3 TO 24 WHILE linenum < lineno FOR linenum = start + 5 TO start + 24 IF linenum > lineno - 2 THEN GOTO endnext PRINT TAB(1); filename(linenum); PRINT TAB(15); extention(linenum); PRINT TAB(30); filesize(linenum); PRINT TAB(50); date(linenum); PRINT TAB(70); time(linenum); endnext: NEXT linenum PRINT : PRINT “Press <ENTER> key to continue. . .” a$ = INPUT$(1) start = start + 19 WEND inch discs for $7 plus $3 p&p from SILICON CHIP, PO Box 139, Collaroy Beach, NSW 2097. Alternatively, you TRANSFORMERS can order by phoning (02) 979 5644 or faxing (02) 979 6503 and quoting a SC credit card number. STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 Silicon Chip Binders These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­ tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A11.95 plus $3 p&p each (NZ $6 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. October 1994  89 Silicon Chip With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). June 1990: Multi-Sector Home Burglar Alarm; LowNoise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. 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 Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/ Square Wave Generator, Pt.2. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Conver ter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone ORDER FORM Please send me a back issue for: ❏ September 1988 ❏ November 1988 ❏ April 1989 ❏ May 1989 ❏ June 1989 ❏ July 1989 ❏ September 1989 ❏ October 1989 ❏ November 1989 ❏ December 1989 ❏ January 1990 ❏ February 1990 ❏ March 1990 ❏ April 1990 ❏ June 1990 ❏ July 1990 ❏ August 1990 ❏ September 1990 ❏ October 1990 ❏ November 1990 ❏ December 1990 ❏ January 1991 ❏ February 1991 ❏ March 1991 ❏ April 1991 ❏ May 1991 ❏ June 1991 ❏ July 1991 ❏ August 1991 ❏ September 1991 ❏ October 1991 ❏ November 1991 ❏ December 1991 ❏ January 1992 ❏ February 1992 ❏ March 1992 ❏ April 1992 ❏ May 1992 ❏ June 1992 ❏ July 1992 ❏ August 1992 ❏ September 1992 ❏ October 1992 ❏ January 1993 ❏ February 1993 ❏ March 1993 ❏ April 1993 ❏ May 1993 ❏ June 1993 ❏ July 1993 ❏ August 1993 ❏ September 1993 ❏ October 1993 ❏ November 1993 ❏ December 1993 ❏ January 1994 ❏ February 1994 ❏ March 1994 ❏ April 1994 ❏ May 1994 ❏ June 1994 ❏ July 1994 ❏ August 1994 ❏ September 1994 ❏ October 1994 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PCCompatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio 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-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; Build A Fax/Modem For Your Computer; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. May 1992: Build A Telephone Intercom; Low-Cost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard 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; Electronics Workbench For Home Or Laboratory. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 Micro­controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags: More Than Just Bags Of Wind; Building A Simple 1-Valve Radio Receiver. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6; Switching Regulators Made Simple (Software Offer). April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver Circuits; Electronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up; A Look At The Digital Compact Cassette. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/ CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electronic Engine Management, Pt.9 December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Index To Volume 4. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; The Micro­soft Windows Sound System. July 1994: SmallTalk – a Tiny Voice Digitiser For The PC; Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2 August 1994: High-Power Dimmer For Incandescent Lights; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Simple Crystal Checker; Electronic Engine Management, Pt.11; Philips’ Widescreen TV Set Reviewed. February 1992: Compact Digital Voice Recorder; 5 0 - Wa t t / C h a n n e l S t e r e o Powe r A m p l i f i e r ; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­controller – Lesson 1; Antenna Tuners – Why They Are Useful. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Aircraft Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, December 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ories; Valve Substitution In Vintage Radios. April 1992: Infrared Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memor y; Aligning Vintage Radio Receivers, Pt.1. September 1993: Automatic Nicad Battery Charger/ Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach Servicing An R/C Transmitter, Pt.1. October 1994  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Information on inductive loops I would like to pick your brains for the design of induc­tive loops for hearing aids, as used in a public address system. I have a basic understanding of how they work but would like to know if there is any design formula that relates to the number of turns required, the power amplifier requirement for a given area, etc. What sort of load does the loop provide to the amplifier? Is a Zobel network required to maintain stability to the amplifier? Can you use the small aluminium fasteners that electricians use for mains wiring to mount an inductive loop to a wall? Does the aluminium surrounding the loop constitute a “shorted turn” effect? Similarly, can the loop be put through an RSJ steel beam without upsetting the magnetic field? (M. M., Hamilton, NZ). • We do not have any published information about this subject but we Burp charging of nicads I have noticed the proliferation of nicad battery charger designs over the years and they all seem to use the “constant current” charging method. Is there any other way? The reason I ask is that some years ago, (1987 to be precise), I was involved in a trials team testing radios and part of my job as a technician was to “play” with various battery chargers. One caught my atten­tion because of the way it charged the batteries and the speed with which it charged them. The charger was made by an American company called “Christie” and had all the bells and whistles (microprocessor control and the ability to recall stored settings for different battery types depending on the cable connected). I didn’t have much information 92  Silicon Chip can make the following comments. The impedance of the loop must be within the range able to be driven by the amplifier and this must normally be between 4Ω and 8Ω for most audio amplifi­ers. Also, the more powerful the amplifier, the better. Run as many turns as you can around the area to be served while keeping the total resistance under 8Ω, in order to maximise the power. You can use the nail type Nylon fasteners to secure the loop although the aluminium type you refer to should work without problems. If the amplifier design incorporates a Zobel network, then it will not be necessary to add one externally. Cray computers & touch screens I have a number of questions which I would like answered if you could. For many years I have heard many references to the Cray super-computer. on the beast except for Christie’s colour glossies, which basically explained the pro­cess. They called the charging method “Reflex” (which had a trade mark on it) or “burp” charging. The theory was that you could charge a battery at double the normal charging current but that current was pulsed. Christie used the analogy of feeding a baby. You feed them a bit, burp them to get rid of their wind, then feed them some more. Apparently the charger did the same thing with the battery, applying a negative voltage to prevent gassing and “memory” effect. I did manage to run a few crude tests using 1.2Ah nicads. On the normal trickle charge, which took overnight to charge, I got 47 minutes at 1.2A on discharge (this was another feature of the charger). After one charge using the “burp” charger (which took 25 minutes to What is so special about this computer and how does it compare with the latest in computers? Some new Ameri­can computers are running at nearly 300MHz. I have seen computer display systems with options on the menu selected by touching certain areas on the screen. How do these systems work and how does it know which square you are touching? I would like to do some experimenting with vacuum fluorescent displays but I am not sure how they are operated. I believe you need an AC supply and an DC supply. I can get plenty of displays from junked VCRs and I prefer the green displays rather than LED displays. Perhaps you can let me know of a suitable book that gives information on these displays. Concerning generators and alternators in car charging sys­tems, I have noticed cars with generators tend to have a notice­ able increase in light output as they accelerate away from complete), I got one hour and 10 minutes on discharge under the same conditions! The charger also had a “maintenance mode” where­by the battery was discharged and burp charged three times. Christie claimed this would remove the memory from almost all batteries. Do you have any information on this method of charging? If so, how about a design? After seeing what the Christie charger did, I would be very interested. (I. B., Watsonia, Vic). • We do not have any information on burp charging of nicad batteries but we can refer you to the microprocessor controlled charger published in the September 1993 issue of SILICON CHIP. We also recommend the fast charger based on the TEA1100 chip, as featured in the May 1994 issue and in the data article published in September 1994. a stop, whereas cars with alternators don’t seem to have this problem. And why do modern cars generate AC first then rectify to DC rather than just generating DC? What are the pros and cons of both systems? I have read about digital video transmission systems where instead of transmitting complete new pictures they transmit only the difference between frames. This much I understand but what happens when you first turn on your TV; there is no picture to compare with for your first frame? I look forward to some inter­esting answers. (D. H., Kamerunga, Qld). • We know very little about the Cray computer except that it achieves its very high speeds by parallel processing. For these very powerful machines the clock speed is not the measure of speed but rather the number of instructions they can handle per second. Machines like the Cray are rated in “MIPS” which stands for “million instructions per second” and “MFLOPS” which stands for “million floating point operations per second”. Computers with touch screens have a row of infrared LEDs along the top and one side of the screen and matching rows of infrared detector diodes along the other edges. When your finger touches the screen, it breaks one of the horizontal and vertical infrared beams and the logic does the rest, just as in the rows and columns of a numeric keyboard. Note that your finger does not actually have to touch the screen for the system to work. We have little information on vacuum fluorescent displays. They are normally custom designs intended to to be directly driven by the microprocessor in the appliance. Junked displays from VCRs and other appliances are just that – junk. Modern cars use alternators because they are much more efficient than generators and they have no need for a commutator which wears out. When you think about it, a generator actually produces AC and this is “rectified” by the switching action of the commutator. Modern alternators also come with much better voltage regulators and so their voltage output is more constant, regardless of engine revs. The digital video transmission systems you refer to do take an appreciable time to transmit the first frame. After that, the compression algorithm Notes & Errata 40V/3A Adjustable Power Supply, January & February 1994: some readers have experienced difficulty with the wiring of switch S4 and potentiometer VR1. Unfortunately, with multi-turn pots, the pinouts are not necessarily the same for all brands. Usually, the pin arrangement is shown on the body and the correct wiring can be worked out from this. Basically, you only need to find the wiper and connect it to the PC board on terminal 21 as shown on the wiring diagram. Terminal 22 goes to one end of the pot. If the output voltage from the power supply is a maximum when the pot is turned fully anticlockwise and a minimum when rotated fully clockwise, connect the wire from terminal 22 to the other end of the pot. takes over and only transmits the video information which changes from frame to frame. Component substitutions I am building several SILICON CHIP projects at present and have some queries on them. The first concerns the 40V/3A Power Supply described in January and February 1994. What altera­tions would I need to make to use a 10kΩ 10-turn pot in place of the 50kΩ unit specified for VR1? My second query concerns the Nicad Cell Discharger de­ scribed in the May 1993 issue. This specified at BZX79C5V1 5.1V 500mW zener diode for ZD1. All I can get is a 5.1V 400mW type. It this OK? Finally, would the 25W amplifier module described in the December 1993 issue be suitable as a small guitar amplifier. If so, what would I need to add for guitar and microphone inputs. (A. M., Melrose Park, SA). • To replace the 50kΩ pot for VR1 with a 10-turn 10kΩ pot you will need to reduce the value of the 1.5kΩ resistor connected to pin 4 of IC1. The new value should be 300Ω. This can be made up with a 330Ω resistor paralleled by 3.3kΩ. For S4, the switch specified in the parts list is an Altron­ics S-1394 momentary pushbutton type which has the wipers of the double pole switch at one end rather than the centre as is cus­tomary with toggle switches. If a momentary pushbutton switch with the wipers in the centre of the switch is used, the wiring will have to be changed as mentioned on page 71 of the February 1994 issue. Finally, the orientation required for S4 on the wiring diagram is with the common terminals facing the mains switch S1. 12-240VAC 200W Inverter, February 1994: the 1kΩ resistor which connects to pin 6 of IC3 on the overlay should be 10kΩ as shown on the circuit. Use of a 1kΩ resistor will cause the inverter to shut down prematurely. In the Nicad Discharger, you can substitute a 400mW or 1W zener diode for the specified 500mW type. The 25W amplifier featured in the December 1993 issue would be suitable as a guitar amplifier. If you need a preamp, the best approach would be to use the 4-Channel Guitar Mixer featured in the January 1992 issue. This is available as a kit from Dick Smith Electronics, Jaycar Electronics or Altronic Distributors in Perth. TL496C IC is hard to come by As an electronics hobby buff, I decided to make the Induction Balance Metal Locator from the May 1994 issue. I like making my own PC boards and gathering the necessary compon­ ents. I asked Coffs Harbour Electronics to get the TL496C con­verter and went ahead with the construction. Some time later, I was informed that this IC is only available with a kit. Is there a substitute or perhaps a supplier not known to Coffs Harbour Electronics? (D. K., Coffs Harbour, NSW). • This IC (TL496C) is very hard to come by and is not cheap. We have not been able to locate a retail source. Your best ap­proach may be to buy the kit from Jaycar at $13.95 (Cat KC-5122). October 1994  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES VINTAGE RADIO Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. VINTAGE RADIO SWAP meet/fair. Inc. military, amateur radio and antique sound. Sunday 23rd October, 1994 10am to 5pm. Glenroy Technical School Hall, Melbourne. Bookings: R. Howarth, PO Box 9, Junortoun 3551. Phone (054) 49 3207. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ FOR SALE REAL TIME ICE!!! The only way to go. MOTOROLA 6805 EMULATOR and programmers. Prices and data from Graham Blowes, Mantis Micro Products, 38 Garnet Street, Niddrie 3042. Phone (03) 337 1917 (a/h), (03) 575 3349 (b/h). Fax (03) 575 3369. AUSTRALIAN PRODUCT: Control Canaries, Cameras, Cars or Circuits from the printer port of your PC. 32 bits in. 32 bits out. Bare PCB, Software Disk and Data $38. Add-on Relay Board $15, or Demo/Promo Disk $2. Don McKenzie, 29 Ellesmere Crescent, Tulla­ marine 3043. Phone (03) 338 6286. SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 I/O pins, board space includes prototyping area. Program it on a PC (only 33 instructions) with development kit which includes one “BASIC STAMP” Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 Microprocessor For Stereo Preamplifier Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.-Oct. 1993). Also suits the Remote Volume Control (May & June, 1993). Price: $45 + $6 p+p Payment by chequeor credit card to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Phone (02) 9795644; Fax (02) 979 6503. TRANSFORMER REWINDS • • • • 350 Watt Power MOSFET Amplifier Module As published in the June 1994 issue of Silicon Chip. Kit price $159.00. Postage and handling $8.00. Payment by M/C, B/C, Visa, Cheque or Money Order. 3kg O/N Air Bag $10.00 Computer & Electronic Services Pty Ltd 27 Osborne Avenue, Trevallyn Launceston, Tasmania 7250 Phone 003-34 4218; Fax 003-31 4328 MEMORY & DRIVES PRICES AT SEPTEMBER, 1994 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $58/54 4Mb 30-pin $208/195 2Mb 72-pin $125 4Mb 72-pin $230/215 8Mb 72-pin $460/420 16Mb 72-pin $815/775 32Mb 72-pin $1690/1500 MAC 6Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $395 $90 LASER PRINTER HP with 2Mb $200 ALL TYPES OF TRANSFORMER REWINDS COMPAQ CONTURA TRANSFORMER REWINDS 8Mb $440 WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & Rtty receiving program. Suitable for CGA, EGA, VGA and Hercules cards. Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. FLUORESCENT INVERTER KIT (SC, Feb 91) (Soft Technology No. 46): 12V, 24V or 48V/16W version. Secondary wind, board plus compon­ents $30 plus $4 p&p. SOLAR BATTERY CHARGING REGULATOR: short form kit 12V or 24V (SC, Jan 94) 10A $54 plus $4 p&p. $8 $8 IBM PS.2 THINKPAD L40/N33 90/95 8Mb 4Mb 4Mb $655 $280 $230 TOSHIBA 3100SX 46/6400 4Mb 4Mb $245 $265 SUN SPARC 10/20 16Mb SPARC 10/20 64Mb $965 $4080 DRIVES – SEAGATE 214Mb 10ms 3yr w 528Mb 12ms 3yr w 1052Mb 9ms 5yr w $260 $465 $1075 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. 70ns 70ns Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for latest prices. Reply Paid No.7, PO Box 1058, St Marys, NSW 2760. Ph: (02) 833 1146. Fax: (02) 623 5559. ($249 plus S/T & post), extra modules ($66 plus S/T & post). Send 45c stamp for more information. Parallax distributor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­dale, NSW 2350. Facsimile (067) 72 8987. DRAM DIP 1Mb x 1 256 x 4 Additional Mosfet $8 and Schottky diode $5 to make 20A regulator. With every kit ordered FREE used LEAD SEALED BATTERY 12V/4Ah or 6Ah while stocks last. Good condition but no warranty. Only p&p is charged for battery. Ring for postage cost. Cheques and postal money orders accepted with mail orders. Send orders to: Otakar Priboj, PO Box 362, Villawood, NSW 2163, Australia. Phone (02) 724 3801. INTELLIGENT INFRARED RECEIVER (ref SILICON CHIP, March 94). Now with 8 outputs. Use your TV or VCR infrared remote control trans­mitter to control your TV or hifi appliances with an intelligent infrared receiver kit. Also available infrared transmitters, preprogrammed and learning models. For details call BENETRON P/L (018) 20 0108. THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PELHAM PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. VALVE AMPLIFIERS: Australian made. Mono, stereo, guitar using 2A3, 211, 6L6 or 807 valves. Williamson reproductions. Parts available for DIY constructors. Circuit diagrams and construction details for many types of valve amplifiers. Valve equipment repairs. Lancroft Pty Ltd, PO Box 439, Bexley 2207. Phone (02) 567 5390. THE 8051 MICRO-COMTROLLER book includes a simulator disk ($40). ROMLoader EPROM Emulator (EA Jan/Feb 92, EA June 94) (PCB $30). 8051 Proto-Boards (EA Feb 93) (PCB $30). Tantau Australia, PO Box 1232, Lane Cove, NSW 2066. Phone AH (02) 878 4715. CALLING ALL HOBBYISTS We provide the challenge and money for you to design and build as many simple, useful, economical and original kit sets as possible. We will only consider kits using lots of ICs and transistors. If you need assistance in getting samples and technical specifications while building your kits, let us know. YUGA ENTERPRISE 705 SIMS DRIVE #03-09 SHUN LI INDUSTRIAL COMPLEX SINGAPORE 1438 TEL: 65 741 0300    Fax: 65 749 1048 October 1994  95 SmallTALK for PCs: voice digitiser for 286's and up Play speech on your PC's speaker with no sound card! 3 minute version $34.95 HDD version $39.95 Optional QLB/LIB libraries $14.00 All orders add $3.05 p+p. Send your cheque/order to: RAT Electronics AUSTRALIA PO Box 641, Penrith, NSW 2750 Ph: (047) 77 4745 Fax: (047) 77 4745 ELECTROSTATIC LOUDSPEAKERS 3-PANEL FULL RANGE DESIGN, AVAILABLE IN KIT FORM OR FULLY ASSEMBLED. LOCALLY DESIGNED & MANUFACTURED. FOR INFORMATION BROCHURE, PHONE/FAX (09) 397 6212 OR WRITE TO: E. R. AUDIO, 119 BROOKTON HWY, ROLEYSTONE, WESTERN AUSTRALIA 6111. Advertising Index Altronics ................................ 20-22 Av-Comm................................69,81 Computer & Elect. Services.........95 David Reid Electronics ..............86 Dick Smith Electronics........... 10-13 Emona Instruments.....................87 E. R. Audio...................................96 Harbuch Electronics....................86 UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. BINARY CLOCK - OCTOBER 1993: complete documentation supplied, includes introduction to binary, how it works, PLD source list­ings, conversion tables. Kit with PC board and all components $75 plus $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 plus $5 p&p. Available from Prototype Electronics, 1/29 Stewart St, Parra­matta, NSW 2124. Phone (02) 890 2960; Fax (02) 630 3148. Pay by cheque, money order, credit card. TES FIELD STRENGTH meter, model MC661/F, VLF/VHF/UHF VGC complete with charger and manual. $300. (079) 28 0966. WANTED WANTED: made in USA or Western Europe for audio valves, vintage audio equipment and books about valve technology. Wai Kei Leung, Block B, 5th Floor, 7 Kweilin Street, Shamshuipo, Kowloon, Hong Kong. Fax: 852 387 5560. PC COMPUTERS (08) 364 0902 (08) 332 6513 36 Regent St, Kensington, South Australia High Power 2.5 Watt Transmitter Kit FMTX1 $69 This kit uses a single transistor to provide up to 2.5 watts into a 50-ohm load. It can be set on the FM band from 88-108MHz. Audio is 500mV P-P with Australian pre-emphasis. Power supply from 12-24 volts DC. Range up to 100 miles. Leaky coax distribution can be used with any of our transmitters, terminate up to 2km of coax with a 50-ohm resistor and no radiation occurs. Use a 150-ohm WW pot and you can set the level of radiation up to 300 metres from the coax. You can use this method to comply with DOTC schedule 3. Instant PCBs................................95 Jaycar ......................... 33-36,61-64 L & M Video.................................32 Macservice............................ 47-50 Oatley Electronics.................. 82-83 PC Computers.............................96 Pelham........................................95 Rat Electronics............................96 RCS Radio ..................................94 Rod Irving Electronics .......... 73-77 Silicon Chip Back Issues....... 90-91 Silicon Chip Binders....................89 Silicon Chip Bookshop.................70 Silicon Chip Projects Book......OBC Silicon Chip Software..................85 Silicon Chip Wallchart................IBC Tortech.........................................89 Transformer Rewinds...................95 Yokogawa..................................IBC XTAL Locked 30mW Transmitter (The best quality kit transmitter in Australia) FMTX2B $49 This transmitter is XTAL-locked on 100MHz (XTAL supplied) and is the most stable kit transmitter on the market. It features a 3-stage design with only two tuned circuits and a clean output. This design can be used as the basis of a station exciter. Yuga Enterprise...........................95 _________________________________ Digital Stereo Coder (All Digital Design With Australian Pre-emphasis) FMTX2A $49 This is a universal stereo coder able to be used with all of our transmitter designs and many others. Its performance is superior to domestic encoder single chip designs. Dozens have been sold to FM stations as a standby stereo coder or with the FMTX2B as an exciter. Printed circuit boards for SILICON CHIP projects are made by: Both FMTX2A and FMTX2B on 1 PCB as a complete stereo transmit­ter FMTX5 $99 MAX I/O Board for PCs (Talk To The Outside World) $169 This kit features 7 relays, ADC, DAC, stepper motor driver with sample software in Basic and connects to a PC’s parallel port. Now also available I/O bits software for MS Windows so you can program functions without being a programmer. Call relays by a name like stop relay, assign its own icon - uses a simple VISUAL interface to make your own PLC. Full developer’s version has DOS runtime so you do not require Windows and optional sup­port for LCD displays. Data logging ADC and DAC boards and more. MAX version $169. FM Band Linear Amplifier Kits (All Imported Kits) New 30mW to 1 watt linear coming in September 1994 (advance orders taken) 500mW to 5 or 10 watts $199 250mW to 25 watts 15 watts to 110 watts $599 40 watts to 300 watts Power supplies and heatsinks not included in short form kit price. $99 $249 $999 Other kits available. Call for a list or see Silicon Chip April-June 1994 or the Silicon Chip Model Railway Book. 96  Silicon Chip PC Boards • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590.