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BONUS DICK SMITH ELECTRONICS CATALOG* AUST. ONLY $4.50 JUNE 1993 NZ $5.50 INCL GST SERVICING — VINTAGE RADIO — COMPUTERS — AMATEUR RADIO — PROJECTS TO BUILD REGISTERED BY AUSTRALIA POST – PUBLICATION NO. NBP9047 WINDOWS BASED DIGITAL LOGIC ANALYSER ANTENNA RF AMPLIFIER MIXER IF AMPLIFIER AUDIO AMPLIFIER DETECTOR SPEAKER AGC LOCAL OSCILLATOR GANGED TUNING TO OTHER STAGES POWER SUPPLY DIGITAL VOLTMETER FOR YOUR CAR SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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 Vol.6, No.6; June 1993 THIS SUPERHET AM RADIO trainer has its circuit diagram screen printed onto the PC board so that you can easily trace through the various stages. Turn to page 12. FEATURES   6 Dick Smith’s Trans-Australia Balloon Attempt by Leo Simpson Listen in on 14.146MHz 88 The Story Of Electrical Energy, Pt.24 by Bryan Maher How aluminium is refined PROJECTS TO BUILD 12 Build An AM Radio Trainer by Marque Crozman Learn how a superhet radio receiver works 18 Remote Control For The Woofer Stopper by Darren Yates DON’T GET OUT of bed to press the Start button on the Woofer stopper. Just press the button on this hand-held transmitter instead – see page 18. Just press the button on a small hand-held transmitter 24 A Digital Voltmeter For Your Car by Darren Yates Don’t get caught on those cold winter mornings 36 Windows-Based Digital Logic Analyser by Jussi Jumppanen Has eight input channels & can be built for less than $220 64 Remote Volume Control For Hifi Systems, Pt.2 by John Clarke The full construction details SPECIAL COLUMNS 30 Serviceman’s Log by the TV Serviceman Some customers can be a real pain 53 Amateur Radio by Garry Cratt The Smith Chart – what it is & how to use it A CROOK BATTERY is the most common reason for car trouble during the winter months. This digital voltmeter will show how your car’s battery is faring & can also warn against over-charging. Details page 24 56 Vintage Radio by John Hill A look at high tension filtering 71 Computer Bits by Darren Yates Double your disc space with DOS 6 80 Remote Control by Bob Young Unmanned aircraft – the early developments DEPARTMENTS DEPARTMENTS   2   4 5 10 83 Publisher’s Letter Mailbag Order Form Circuit Notebook Product Showcase 86 93 94 95 96 Back Issues Ask Silicon Chip Notes & Errata Market Centre Advertising Index HERE’s YOUR CHANCE to build a PC based 8-channel digital logic analyser that uses software developed for Windows 3.0 or higher. The article starts on page 36. June 1993  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) PUBLISHER'S LETTER Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Marketing Manager Sharon Lightner Phone (02) 979 5644 Mobile phone (018) 28 5532 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 Editorial Advisory Panel Phillip Watson, MIREE, VK2ZPW Norman Marks Steve Payor, B. Sc., B. E. 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: Magazine Printers Pty Ltd, Alexandria, NSW; Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $42 per year in Australia. For overseas rates, see the subscription page in this issue. Liability: Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringment of such patents by manufacturing or selling any such equipment. Editorial & advertising offices: Unit 1a/77-79 Bassett Street, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. ISSN 1030-2662 2  Silicon Chip Back to the superheterodyne The month, we feature the first part of a 2-part constructional project for an AM broadcast radio using the standard superhet circuit. This is being featured for the benefit of TAFE college and secondary school students, beginners in electronics and anyone who wants to learn about or refresh their knowledge of the most important communications circuit – the superhet. We have had this project in mind for a while, conscious that this side of electronics has been neglected for quite some time. Back in the days of valves, every beginner "cut his teeth" on a crystal set and then went on to build a small valve radio. In doing so, he would come to grips with the principles of AM radio and the superheterodyne. In fact, by the time the enthusiast of those days had mastered the principles of the superhet, he was well on the way to being well-versed in electronics. These days the field of electronics is far more diverse and much bigger than anyone could have dreamed of 30 years ago. And so with the passing of valves and the takeover of electronics by semiconductors and integrated circuits, the good old AM superhet radio has been shunted out of the limelight. So much so, that probably a fair proportion of today's enthusiasts would admit, if pushed to it, that they are not familiar with the superhet. Well now is the time to correct that deficiency. Nor should readers think that superhets are somehow old fashioned or obsolete. The superhet in all its forms is in wider use than ever, in all TV and radio receivers, hifi tuners, amateur radio and communications gear in all fields, in radio control and so on. The difference today is that so much of the circuitry is buried in ubiquitous ICs and so there is little chance to trace a signal through all stages. The special feature of the AM Radio Trainer in this issue is that the top of the printed circuit board is actually screen printed with the circuit diagram and you insert each component onto the board in the exact position of the circuit symbol. We have designed it this way so that the constructor will have a more "hands on" feel for the circuit. At the end of it all you will have a working radio in which the signal path can easily be traced through, stage by stage. That can't be done in any standard pocket radio because the components are crammed too close together and there is liable to be damage if you make the attempt. The article starts on page 12 of this issue. Go to it. Leo Simpson MAILBAG A prizewinner’s thanks I have built a number of kits over the years and, of course, some of my own designs. Although I have suffered my fair share of dry joints, it is only over the past 12 months or so that I have realised the importance of temperature control of the soldering iron. I’d been promising to treat myself to a proper soldering station for some time but hadn’t quite managed to do so. To be one of the winners of an Altronics T2440 Soldering Station is absolutely fantastic! I’ve been purchasing SILICON CHIP since May 1988, and it’s something of a coincidence that the first project to front up to the soldering station will be the High Energy Ignition kit detailed in that particular issue. R. Hilton, Mt. Pleasant, WA. Suggestions for solar projects Like a number of people in Australia, I own a caravan and am interested in fitting it up with solar power. I wondered if you had any plans to publish construction articles in this area of electronics. Three areas need to be catered for: (1) a fully automatic 12V battery charger with high, medium & float charge that discon­nects itself from the battery when 240V is not available (I know that you published a version for 6V, 12V and 24V last year but the other two voltage ranges introduce compli­ cations when they are not required. Maybe the details for a cut­down version suitable only for 12V could be published); (2) a solar panel regulator; and (3) a device to take the 12V from the car, step it up to 14V and charge the van battery at 6-10A while travelling. The problem with a direct connection to the car battery is a drop in voltage between the car and the van. This results in a very small charge going into the van battery. In my case, I have a 4WD fitted with two batteries and the van battery is effective­ly in parallel with the second battery. Many chargers are not designed to 4  Silicon Chip work with deep cycle batteries and will not shut off, as the voltage never gets above 14.3V. They will cook the battery unless manually operated. I would be interested in your comments on these projects, as the growing number of caravaners going for solar power are not able to obtain these units commercially. Don Crago, Pooraka, SA. Comment: as you know, some of the projects we have already published skirt this general area. It should be possible to cut down the Thunderbird charger circuit so that it doesn’t provide 6V and 24V. This could be done easily by eliminating the relay and its driver transformer and permanently wiring the two trans­formers for the 12V condition. If other readers express interest in this area of electron­ics, we could consider publishing projects along the lines you suggest. Take care with old appliances Recently, my neighbour asked me to check out his old slide projector. He wanted to transfer some family slides onto video but the projector had shown no signs of life when unearthed from the cupboard after 20 or more years. The lamp checked out OK and then I looked at the mains wiring and the memory bells rang. Back in the fifties, a colleague of mine received a severe shock after fitting an Australian 3-pin mains plug to a labora­ tory balance of German manufacture without properly checking the cord’s coloured leads which were red, black and grey. Thinking that the Active and Neutral would be red and black and the Earth grey, he hooked the machine up with almost fatal results. In German wiring at the time, red was used as the earth, while black and grey were the Active and Neutral. When I checked this projector, the same situation applied. Apparently the owner had used an adaptor when the projector was new and somebody had decided to fit a 3-pin plug after SILICON CHIP, PO Box 139, Collaroy Beach 2097. losing the adaptor. When the machine did not work, they apparently abandoned the project, leaving it booby-trapped. I replaced the mains cord with a new moulded 3-pin plug and flex to make sure nobody got burned in future. The projector was a Braun Paximat, a good machine at the time. So if you encounter similar machines, replace the flex with the correct brown, blue and green-yellow variety, to avoid a potentially fatal accident. N. Marks, Pennant Hills, NSW. Praise for the high energy ignition system A little over eight weeks ago, I successfully built the High Energy Ignition unit, as described in the May 1988 issue of SILICON CHIP. The unit is installed on my 1969 Datsun 1600 with an L16 (1600cc) 4-cylinder engine, with a points-based distribu­ tor. On completion of assembly, the unit ran first go and has performed faultlessly for the last 5000km. The MJ10012 transistor runs slightly warm and the coil is hot to touch but I believe much of the coil’s temperature can be attributed to its closeness to the exhaust manifold. If the temperature becomes excessive in future use, an aluminium heatshield and a cool air duct should reduce this heat. As stated in the original article, the greatest single benefit is the increased time between tune-ups. The old days of burned and pitted points are gone. Also, I have noticed that the spark plugs operate cleaner – they do not foul due to combustion deposits. Add to this smoother running of the 4-cylinder engine right from idle. My thanks to SILICON CHIP for producing an excellent after-market ignition system. V. Smith, Toowoomba, Qld. Comment: the ignition coil will run hotter than in a Kettering system due to the higher average current through it. It would be a good idea to move it away from the exhaust manifold if you can. ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL 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. $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. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A84 ❏ $A42 ❏ $A105 ❏ $A53 ❏ $A130 ❏ $A65 ❏ $A130 ❏ $A65 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. 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 June 1993  5 Dick Smith’s As this issue goes to press, Dick Smith is making final preparations to cross Australia by balloon. Providing winds are favourable, he is expected to make the attempt early this month, starting from Carnarvon in Western Australia. By LEO SIMPSON The gondola: (1) Lift webs; (2) Burner fuel line; (3) Entry hatch and observation dome; (4) Lift cables; (5) HF anten­na; (6) Satellite transmission antenna; (7) VHF antenna; (8) Landing trail rope; (9) Lockers for food, water and batteries; (10) 80-litre LPG tanks (four each side); (11) Hand holds; (12) Hollow keels, flooded in sea landing; (13) Twin LPG burners; (14) LPG 240VAC generator; (15) Sand ballast; (16) GPS antenna; (17) Strobe light; (18,19) Liquid oxygen tanks; (20) Navigation and communications, flight instruments, GPS, Inmarsat, VHF radio, radar transponder, HF transceiver, weather fax; (21) satellite data printer; (22) chart table. 6  Silicon Chip s Trans Australia Balloon Attempt T HIS IS NOT THE first time some- one has attempted to fly across Australia by balloon. There have been six previous at­tempts but all have failed. The last attempt was in November 1984 and it landed near Broken Hill. The prevailing winds across Australia are from the west and so it should be feasible to start on the west coast and drift right across the continent to the east coast. Ever the optimist, Dick Smith is making an attempt this year but he will be taking a new approach in more ways than one and will have the bene­fit of technology that could only be dreamed about in previous attempts. A new type of balloon will be used for this attempt although the concept has been around for almost as long as ballooning has been feasible. The balloon is a Rozier type, named after Frenchman Jean Pilatre Rozier who in 1785 devised a hot air/hydrogen balloon. Rozier was actually a passenger with the Gondolfier Brothers in the first ever balloon flight in 1783. Hydrogen and hot air is a dangerous combination and the original balloon using these gases was doomed to failure but the Rozier concept does have merit. Helium gas Dick Smith will not be using hydrogen but helium, in a double compartment balloon. Helium will fill the top compartment while the bottom compartment will be occupied by air, heated by the LPG burners below. This system is claimed to have substantial advantages over a standard hot air balloon or a helium gas bal­loon, for the following reasons. For a trans-Australia attempt, any hot air balloon needs to carry a lot of LPG, stored in heavy cylinders. The more LPG you need, the bigger the balloon required and so on. Once you run out of LPG, the flight must end shortly afterwards because you lose the means of maintaining buoyancy. By contrast, a helium gas balloon needs to be very large and carry a lot of ballast. During the day, the helium expands considerably due to heat from the sun. The balloon needs to be able to cope with the large increase in volume. At the same time, the gondola may need oxygen or pressurising to enable the crew to fly at extreme altitude. At night, the gas cools down and loses buoyancy and so the crew needs to shed ballast to maintain alti­tude. If the trip lasts several days, the ballast will eventually run out and again, the journey can’t be maintained for much longer after that. This is where the Rozier balloon has the advantage because the dual compartment balloon has a more constant buoyancy from night to day and will need little use of the LPG burners during the day. Dick Smith’s balloon attempt will be made at heights of between 10,000 and 18,000 feet to take advantage of the prevail­ing jetstreams. He will be constantly updated with weather in­for­ma­ tion via fax machine so that he and his navigator can adjust the altitude so that the jetstream blows them where they want to go – east! Even so, Dick admits that they could end up anywhere between Cairns and Tasmania. Suspended below the huge balloon will be an enclosed gondo­la made from fibreglass. It will have such ancillaries as cylin­ders of LPG for the burners and oxygen for the crew. Suspended above the gondola will be a 240VAC generator powered from LPG. This will run the communications equipment and charge the batteries. In addition to normal navigation This map shows the predicted paths for six flights starting on different days last June. The predicted landing point is somewhere between Tasmania & Cape York. and flight instruments, the gondola will be equipped with an Inmarsat C receiver as well as a Trimble GPS re­ ceiver. (Trim­ble Navigations Ltd is a fast rising company in the field, having supplied 10,000 GPS receivers to the US army during the Gulf War). Australian CQs Another attraction of the balloon attempt is that amateur radio operators will be able to contact Dick Smith as he drifts above. He will be using a Yaesu FT-757 transceiver on 14.146-MHz. His call sign is VK-2DIK. The flight is expected to take two to three days and could take place at any time after 31st May, depending on favourable weather conditions. Readers will be able to obtain daily progress reports on the attempt in The Australian or by phoning 0055 29060 from anywhere in Australia. Acknowledgement: our thanks to Dick Smith and the staff of Australian Geographic magazine for their assistance in the prepa­ration of this article and for permission to publish SC the accompa­nying diagrams. June 1993  7 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. Add-on circuit for a sidereal clock This simple circuit can be used to convert a digital clock based on a TMS ­ 3450NL IC to sidereal time. One whole year has apMAINS proximately 366 sidereal SAMPLE days so a sidereal clock runs about 366/365 faster than a normal clock (ie, about 3 minutes 56 seconds per day faster). The principle used here is to count 365 “ticks” and then add one extra tick. I selected a cheap digital LED bedside clock running off the mains – a Technica T1 with a 12-hour display. However, I recommend a clock with a bigger box and prefer­ably a 24-hour display. In this case, a 50Hz mains frequency sample is applied to pin 25 of a TMS3450NL clock IC, which counts the pulses and displays the time. The 4040 binary counter (IC1) also counts the mains sample and Battery monitor for solar chargers Many solar battery chargers consist of just an array of solar panels connected in series, with a diode in one of the output leads to prevent the battery from discharging through the array in low sunlight conditions. The problem though is that a 12V solar panel can easily produce 15-18V DC output in very strong sunlight and this can lead to overcharging. Over extended periods of time, this won’t do the batteries much good. This circuit warns you if the battery voltage rises above 15V by sounding an alarm. It could also be used to warn of overcharging in a car or van. The circuit is based on op amp IC1 which is wired as a voltage comparator. Zener diode ZD1 provides a fixed 5.1V refer­ence on IC1’s inverting input (pin 2), while a sample of the battery voltage is applied to the non-inverting 10  Silicon Chip +V 0.1 390k 16 D1 1N4148 3 180k 10 CLK TO PIN 25, TMS3450NL CLOCK AND DISPLAY DRIVER 5 IC1 Q7 4040 Q6 11 Q3 12 Q1 8 3 14 13 9 10 Q4 C1 470pF 2 4 Q9 120k .033 2 5 4 7 R 1 RC A 14 16 C IC3a 4538 13ms B .001 Q 13 6 11 12 IC2 4068 R B 15 RC C Q IC3b 120uS Q A 10 9 8 11 when 365 (101101101) is reached, the 4068 NAND gate (IC2) initiates a 13ms pulse from mono­stable IC3a. When this times out, it initiates a 120µs pulse from IC3b and this is applied to the TMS3450NL clock chip via D1 to provide the “catch-up” tick for sidereal time. At the same time, IC3b’s Q output resets the 4040 counter. D1 isolates the normally high Q-bar output from the mains sample, while C1 filters out mains-borne hash which can speed up the clock. The mains sample also drives the display multiplexer, so every 7.3s, the out-of-phase 120µs pulse causes some of the display’s unlit segments to flash faintly (a handy test). The modification was powered from the clock’s own 13V supply. Assum­ing an exact 50Hz mains supply, the error rate is about +1 minute per year. J. Priestley, Paekakariki, NZ. ($30) D1 1N4004 220 16VW 1k 10k 2 ZD1 5.1V 400mW 3 7 IC1 LM741 6 ZD2 3.3V 400mW PIEZO SIREN 2.2k Q1 BC337 4 5.6k input (pin 3) via a voltage divider stage (10kΩ & 5.6kΩ). If the battery voltage rises above 15V, the voltage at pin 3 rises above the 5.1V reference and the output at pin 6 goes high. This turns on driver transistor Q1 and sounds the alarm. The 3.3V zener diode in series with pin 6 is there because IC1’s output does not swing all the way to ground. It ensures that Q1 is off when the battery voltage is less than 15V. Diode D1 provides reverse polarity protection for the 741 op amp if the supply leads are incorrectly connected. Darren Yates, SILICON CHIP. Refinement for the Interphone exchange This circuit solves a small problem with the Interphone Digital Exchange published in the August and September 1992 issues of SILICON CHIP. The problem is that as you hang up, after Repeater time-out indicator PTT If you have trouble keeping track of the time while you are working via a repeater, this circuit will avoid the embarrassment of a time-out. It can be built on a small piece of Veroboard or PC board and installed in the base of your desk microphone. Most modern transceivers have a few volts DC available in the PTT (press to talk) circuit and this can be used to provide the supply to this ancillary circuit which takes over the func­tion of the PTT switch and turns off the transmitter function before the repeater times out. The suggested “on” time is 2-2.5 minutes, while the “off” time is 25 seconds. IC1, a 555 timer, is connected in the astable mode with the period determined by the components connected to pin 2, 6 and 7. When power is first applied by the PTT switch, pin 3 of IC1 goes high and switches power to the PTT circuit in the transceiver, via IC2, a 4016 analog switch. Some older amateur transceivers, such as the Yaesu FT-290, may require a relay instead of using the 4016. Pin 3 of IC1 can drive a small relay directly, provided a reverse biased protection diode +5V +5V CUT 2.2k IC3 PIN 12 2.2k 33 BC548 1 5 47k 2 4 IC5 ORIGINAL CIRCUIT a call, each extension beeps and this causes confusion to other members of the household. This happens because the line voltage rises abruptly to 50V and this can trigger the ring detector circuit. The solution is to disable the ring detector circuit for half a second after hanging up and this is achieved with one transistor and a few other components. In the modified circuit, the ring detector optocoupler, IC5, is supplied from the collec­tor of the added transistor and its base is connected to pin 12 of IC3b via a 2.2kΩ resis­tor and 33µF capacitor. When the phone is placed on-hook, pin 12 of IC3b goes high and turns the transistor on for about half a second. This removes the supply from the ring detector (IC5) and thus prevents any extension from ringing for that brief interval. B. H, Goulburn, NSW. ($15) +A +5-14V 100k VR1 E 14 1.5M 4 8 3 7 47k IC1 555 6 2 6 5 8 1 9 IC2 4016B .01 TO PTT CIRCUIT IN EQUIPMENT 10k 1,2,3,4,5,10 11,12,13 47 16VW PTT TO +A +5V PLUG TO FT636 TO OUTPUT PTT E E E BASE OF DESK MIC BREAK DOTTED WIRE (OR TRACK ON PCB) AND INSTALL NEW WIRING SHOWN IN HEAVY LINES is connected between pin 3 and 0V, with anode to pin 3. Bob Beveridge, VK2JZ, (Address not supplied) ($20) Discrete step-down voltage converter This simple circuit uses only a handful of transistors but can convert any voltage from 6-18V DC to a steady 5V rail. Transistors Q1 and Q2 form an astable multivibrator which produces a pulse waveform at the collector of Q2. This signal is then inverted by Q3 which in turn provides the drive current to switch Q4. Each time Q4 turns on, the 470µF capacitor at the output is charged via inductor L1. This inductor consists of 50 turns of 0.4mm diameter enamell­ ed copper wire wound on a Neosid toroidal core (No.17-732-22). When Q4 turns off, D1 prevents the collector of Q4 from going below -0.7V. To produce a regulated 5V rail, a 5.1V zener diode is con­nected in series with a 4.7kΩ resistor between the output and the base of Q5. This feedback circuit regulates the output voltage by switching the multivibrator on and off. For example, if the output voltage rises above 5V, Q5 turns on and pulls the base of Q1 low, thus turning the pulse oscillator off. This then causes Q4 to turn off and so the output voltage falls. Conversely, if the output voltage falls below the zener diode threshold, Q5 turns off and the pulse oscillator switches back on again. By this means, the output is kept quite close to 5V DC. The maximum load current is about 100mA. Darren Yates, SILICON CHIP. +6-18V 4.7k 47k 47k 1k 4.7k .0015 .01 Q1 BC548 Q2 BC548 Q3 BC548 100  Q4 BC327 L1 D1 BY229 Q5 BC548 470 16VW 5V 100mA ZD1 5.1V 400mW 4.7k L1 : 50T, 0.4mm ENCU WOUND ON NEOSID 17-732-22 TOROID June 1993  11 BUILD THIS AM RADIO TRAINER Ever wanted to build a radio but haven’t seen a suitable circuit with easy to get parts? Well, now is the time to give it a try with this demonstration AM Radio Trainer project. It is intended for beginners, schools & TAFE students & will give you an understanding of how an AM radio works. By MARQUE CROZMAN & LEO SIMPSON When radio stations first began broadcasting in Australia and other countries, they all used the amplitude modulation (AM) system. In this system, the radio frequency carrier signal is modulated in proportion to the amplitude of the audio signal. 12  Silicon Chip The AM radio signal is radiated from the broadcast trans­mitter antenna and picked up by the radio. It demodulates the signal – the reverse of the amplitude modulation process –and the recovered audio signal is then amplified and fed to the radio’s loudspeaker so that you can listen to it. All of today’s AM radios are designed along the superheter­ odyne principle, which was invented by Edwin Armstrong in 1918. The first AM superhet radios were put on the market by Radio Corporation of America (RCA) in 1924. Later, RCA licensed other manufacturers so that the design was used world-wide. Prior to the superheterodyne, all radios were either crys­tal sets or used the tuned radio frequency (TRF) principle of which there are a number of variations. Essentially though, the TRF can be thought of as a crystal set with gain. In a TRF re­ceiver, all amplification up to the detector takes place at the frequency of the incoming signal. Left: all the parts for the AM Radio Trainer are mounted on a single large PC board. The circuit diagram is screened onto the component side, to show you where to mount the parts. The superheterodyne radio brought with it two major advan­ tages over previous circuits. The first was greatly increased gain. This was a big boost compared with TRF tuners which are strictly limited as far as maximum gain is concerned; any attempt to increase the gain over this limit and the circuit goes into oscillation – a loud squeal is the result. Second, the selectivity of the superheterodyne was a big improvement over previous circuits and this meant that weak stations could be separated out from strong stations which would otherwise tend to blanket half the dial. Finally, the superheterodyne re­ ceiver brought with it the possibili­ty of automatic volume control (AVC), although this did not become a feature until around 1930. AVC did away with the need for manual gain controls and meant that all stations came in with roughly the same loudness, as they do today, in spite of the fact that some stations may be very strong and some very weak. Since the advent of the superheterodyne receiver, or “superhet” for short, there have been relatively few changes to the basic circuit configuration although the components used have changed radically. Originally, valves (or vacuum tubes) were used and now transistors are used or a single integrated circuit with just a few external components may suffice. So if you decide to build this AM superhet receiver, you will be building a circuit configuration which has been around for over 70 years but one which is still just as relevant today. Let’s have a look at the operating principles of the super­het which are set out in block diagram form in Fig.1. Block diagram Fig.1 shows the general configuration of a superhet receiv­ er. The antenna at left feeds into an RF amplifier which has a parallel resonant circuit which is tuned by a variable capacitor. This is one section of a tuning gang capacitor. The other section of the gang capacitor varies the local oscillator which we’ll come to in a moment. The parallel resonant circuit is “tuned” by the variable capacitor so that the wanted signal is amplified and other sign­als are rejected. The signal from the RF Amplifier is then fed to the Mixer and this is where the “superheterodyne” process takes place. The word “heterodyne” refers to a difference in frequency or beat. “Hetero” is derived from the Greek word for “other” while “dyne” is derived from the French word for power. In the Mixer stage, the Local Oscillator signal is mixed with that from the RF Amplifier. The result is four signals: the original two signals plus the sum and difference frequencies. These are passed to an amplifier stage or stages which are tuned to the difference frequency which is now known as the Intermediate Frequency or IF (pronounced “Eye-Eff”). The IF stage amplifies only the difference frequency and rejects all the others. In most radios of this type, the Intermediate Frequency is 455kHz or 450kHz. The output of the IF stage is then applied to the detector which in transistor radios is usually a germanium diode, selected because of its small forward voltage drop. This rectifies the IF signal which is then filtered to remove RF components, leaving the original audio signal which modulated the transmitter. This audio signal is fed to the Audio Amplifier and this then drives a loudspeaker. Automatic gain control Apart from demodulating the IF signal, the detector is also used to produce the AGC voltage. AGC stands for “automatic gain control” which was previously referred to as AVC or “automatic volume control”. AGC was regarded as a wonderful innovation when it was introduced, as it eliminated the need for manual gain controls. These were needed to stop the IF stages from overload­ing on strong signals and to increase the gain for very weak signals. To derive the AGC voltage, the raw DC output from the detector is heavily filtered to remove all audio components, to produce a DC voltage which is proportional to the strength of the IF signal. This is then used to control the gain of the IF stages and June 1993  13 RF CARRIER DETECTED AUDIO COMPONENT APLIFIED IF CARRIER IF CARRIER AMPLIFIED AUDIO ANTENNA RF AMPLIFIER MIXER IF AMPLIFIER AUDIO AMPLIFIER DETECTOR SPEAKER OSCILLATOR WAVE LOCAL OSCILLATOR AGC TO OTHER STAGES POWER SUPPLY GANGED TUNING Fig.1: the general configuration for a superheterodyne radio receiver. The incoming RF signal is first mixed with the output from a local oscillator to produce an intermediate frequency (IF) signal & this is then fed to a detector stage to recover the original audio signal. perhaps also the RF stage, so that the signal is held to a more or less constant level. So why is this type of radio circuit referred to as a “superheterodyne”? Why couldn’t it just have been called a plain old heterodyne radio? It is not because the circuit has a “super you-beaut” performance, although it was a big step forward com­ pared to the TRF. The reason is that the intermediate frequency produced by the superhet was “supersonic” as opposed to circuits such as the beat frequency oscillator (BFO) which produced audi­ble heterodynes or beats. Hence, superhet is a contraction of “supersonic heterodyne”. The first superhets had an intermediate frequency of 50kHz which gave very sharp selectivity but poor audio response. Later, the standard IF was 175kHz and later still this was standardised at 455kHz. Interestingly, some references give the definition of superhet as referring to the fact that the Local Oscillator signal is above the incoming RF signal from the antenna – hence super, meaning “above”. Local oscillator Note that the Local Oscillator frequency always “tracks” the tuned frequency of the RF Amplifier. So if the radio is tuned to 1370kHz, the local oscillator will be set to 1370 + 455 = 1825kHz. Similarly, if the radio is tuned to 702kHz, the local oscillator will be at 702 + 455 = 1157kHz. All this happens automatically by virtue of the 14  Silicon Chip 2-section tuning gang – one section for the RF amplifier and the other for the local oscillator. Variations on a theme While we have just described the broad concept of the superhet, there are many variations on this theme. For example, many superhet circuits leave out the RF Amplifier stage and some do not have a local oscillator. Instead, the local oscillator is combined with the mixer stage in what is known as a “self oscil­lating mixer”. Others may have two or three IF stages and still others may have a separate detector to produce the AGC voltage. Another important variant is the double conversion superhetero­ dyne configuration which is used in some high performance communications re­ceiv­ers. The circuit to be described is a “single conversion” superhet, meaning that it performs just one conver­sion from the incoming RF frequency to the intermediate frequen­cy. In communications receivers which tune the higher frequency bands, double conversion may be used. The first local oscillator and mixer will produce an intermediate frequency of, usually, 10.7MHz. This will be passed through one or more IF stages before being mixed with a second (fixed) local oscillator to produce a second intermediate frequency of 455kHz. Other variations which are common include “permeability tuned” superhets and today’s frequency synthesised receivers which have digital readouts and microprocessor control. Perme­ability tuning was common in car radios and moved the slugs in inductors in tuned circuits rather than using tuning gangs which were more susceptible to vibration. Regardless of all the variations, you will find that all superhets have the same operating mode and same circuit functions as described by the block diagram of Fig.1. By the way, the Edwin Armstrong who produced the AM super­het receiver was the same brilliant inventor who later developed the principles of FM transmission and reception. One further note before we leave the origins of the super­het: apparently, radio (wireless?) circuits working along the same principle were used in British submarines during the First World War. 7-transistor circuit Now refer to Fig.2 which shows the complete circuit of our AM Radio Trainer. Each section of the circuit is labelled so that you can see how it relates to Fig.1. The circuit does not have an RF amplifier stage so the antenna signal is coupled directly into the mixer stage. The antenna coil is wound on a small ferrite rod and the primary coil is tuned in a parallel resonant circuit by one section of the tuning gang, VC1. VC2, also in the circuit, is a trimmer which is set during the alignment process. A secondary coil on the ferrite rod couples the tuned signal into the base circuit of transistor Q1 which functions as a self-oscillating mixer or mixer/oscillator. It oscillates at a frequency set by the parallel resonant circuit connected to its emitter. The oscillator is tuned by the second section of the tuning gang, VC3. VC4 is a trimmer which is set during the align­ment process. The oscillator coil (L2) has its secondary winding connected in series with the collector of Q1. The IF components of the collector current drawn by Q1 pass through the primary winding of the 1st IF transformer, T1. The secondary of this transformer couples the IF signal to the base of Q2, the 1st IF amplifier stage. The collector current of Q2 passes through the primary of IF transformer T2 and its secondary couples the signal to base of Q3, the second IF amplifier stage. It is virtually identical to the 1st IF stage and drives the third IF transform­er, T3. Transformer coupling These transformer coupled stages may seem odd to readers who are used to seeing circuits in which transistor stages are directly coupled; ie, without capacitors or transformers. There are several reasons for using transformers. The first is that each IF transformer is designed to resonate with the capacitor connected in parallel with its primary winding. During the alignment process, each IF transformer is tuned to 455kHz by adjusting its iron dust core (the threaded “slug”). By this means, the IF stages become very efficient amplifiers over a narrow bandwidth centred on 455kHz, while frequencies outside the wanted band are strongly rejected. Second, the IF transformers provide the right degree of impedance matching between the relatively high impedance of the collector circuits of the transistors and the relatively low impedance base circuit of the following transistor. Note that in each case, the collector current of the transistor passes through only a portion of the transformer primary and this is part of the intended matching process. Note also the tortuous path followed by the DC collector current for the mixer transistor Q1. The current passes through part of the primary of the 1st IF transformer (T1) and then via the secondary of oscillator coil L2 (which is also a transformer), before arriving at the collector of Q1. Detector diode We now come to a part of the circuit which looks to be quite simple but which has more going on than meets the eye: the detector diode (D1). This is driven by the secondary winding of the third and last IF transformer. The detector diode performs two tasks: (1) it detects or demodulates the amplitude modulated IF signal to produce an audio signal; and (2) it produces the AGC voltage which is used to control the gain of the 1st IF amplifi­er, Q2. D1 is an OA91 germanium diode, selected for its low forward voltage drop of about 0.2V. Note that the diode appears to be connected the opposite way around to what you might expect. The anode of the diode is connected to a .022µF capacitor which provides the first stage of RF filtering, and then via a 2.2kΩ resistor to a second 0.022µF capacitor which provides more filtering of the final audio signal which appears across the 10kΩ volume control potentiometer. The reason that the diode is connected back to front is so that it can develop a negative DC voltage as it rectifies the IF signal. This negative voltage is coupled via a 3.3kΩ resistor to a 10µF filter capacitor and thus becomes part of the bias voltage for the base of the 1st IF amplifier stage, Q2. The AGC works as follows: if a large signal is being picked up, diode D1 will produce a larger than normal negative DC vol­tage and this will tend to throttle back the bias voltage of Fig.2 (right): the circuit employs seven transistors in a fairly conventional arrangement. The incoming RF signal is picked up by a ferrite rod antenna & fed via the tuner stage to Q1 which functions as a self-oscillating mixer stage. The resulting signal is then coupled via T1 to the 1st & 2nd IF amplifier stages & detected by diode D1 to recover the audio signal. This then drives audio amplifier stage Q4-Q7 via volume control VR1. June 1993  15 Q2. Q2 will therefore conduct less current and its gain will conse­quently be reduced. The stronger the signal, the greater the gain reduction and hence the chance of signal overload is greatly reduced. Note the rather complicated bias network for the base of Q2. Current passes first via the 27kΩ resistor, the 3.3kΩ and 2.2kΩ resistors associated with diode D1, and then via the 10kΩ volume control pot VR1. The base current flows from the junction of the 27kΩ and 3.3kΩ resistors via the secondary of the 1st IF transformer (T1). Having the bias current flow through the volume control pot is not PARTS LIST 1 PC board, code 06106931, 275 x 90mm 1 50mm 8Ω loudspeaker 1 455kHz IF transformer/ oscillator kit (DSE R-5040) 1 60-160pF tuning gang capacitor (DSE R-2970) 1 ferrite rod with coil (DSE R-5100) 1 3.5mm socket 1 SPST toggle switch 1 9V battery holder 1 9V battery 1 10kΩ log. pot (VR1) 1 200Ω trimpot (VR2) Semiconductors 4 BC547 NPN transistors (Q1,Q2,Q3,Q4) 2 BC327 PNP transistors (Q5,Q7) 1 BC337 NPN transistor (Q6) 1 OA91 germanium diode (D1) 1 1N4148 signal diode (D2) Capacitors 1 470µF 16VW electrolytic 1 100µF 16VW electrolytic 5 10µF 16VW electrolytic 5 .022µF monolithic or ceramic 1 .01µF monolithic or ceramic 1 .0047µF monolithic or ceramic Resistors (0.25W, 1%) 1 1.2MΩ 1 10kΩ 1 1MΩ 1 4.7kΩ 1 820kΩ 2 3.3kΩ 1 56kΩ 1 2.2kΩ 1 47kΩ 2 1kΩ 1 39kΩ 1 470Ω 1 27kΩ 2 100Ω 1 12kΩ 16  Silicon Chip good engineering practice because pots with DC flowing through them generally become noisy after awhile. Potentiometers become even noisier if current is drawn off via the wiper but that does not happen in this circuit. Having DC flow though the volume pot is common in cheap transistor radios, hence we repeat the practice here. The signal from the volume control is fed to a 4-transistor amplifier consisting of Q4, Q5, Q6 & Q7. This amplifier is direct coupled throughout apart from the output capacitor which we’ll come to in a moment. Q4 is connected as a common emitter stage with all its collector current becoming the base current of the following PNP transistor, Q5. This is also a common emitter stage and provides most of the voltage gain of the amplifier. Its collector current flows partly into the bases of the output transistors, Q6 and Q7, while the rest goes through the 1kΩ resistor and 8Ω loudspeaker to ground. Output transistors Q6 and Q7 are connected as complementary emitter followers in class-AB mode. The two output transistors are slightly biased into forward conduction by the voltage devel­oped across diode D2 and trimpot VR2. VR2 provides quiescent current adjustment to minimise cross­ over distortion. Negative feedback from the output of the amplifier is pro­ vided by the 4.7kΩ resistor to the emitter of Q4. The AC voltage gain of the amplifier is set to about 47 by the 100Ω resistor from the emitter of Q4, while the series 10µF capacitor sets the bass roll-off of the amplifier. By now, you’ve probably realised that this is “minimum component count” radio, very similar in circuitry to most portable AM radios. Another place where components have been minimised is in the output stage where the 1kΩ resistor is connected to 0V via the speaker. The same DC bias conditions could have been obtained in the output stage by simply connecting the 1kΩ resistor direct­ly to the 0V line but there is good reason for doing it the way we have. Bootstrapping By connecting the 1kΩ resistor via the speaker we take advantage of the fact that the output stage transistors are emitter followers. In this mode, these transistors have a voltage gain just slightly less than one. This means that the AC signal voltage at the emitters of Q6 and Q7 (and hence across the speak­er) is only slightly less than the signal voltage at the bases of these two transistors. Because of this, the AC voltage applied across the 1kΩ resistor is very small and so little AC current flows. Hence, transistor Q5 “sees” a much higher collector load than the nomi­nal 1kΩ connected. This means it is able to provide more drive to the output stage and higher overall voltage gain. This technique is known as “boot­ strapping” and is commonly used in audio amplifiers. However, while this is an effective method which improves the overall performance, it does have one drawback. If the loudspeaker or headphone is not in circuit, no current can flow through the 1kΩ resistor. If this happens, the output stage is not biased on and the whole amplifi­er “latches up” and draws no current at all. This may not seem important because the speaker will nor­ mally always be connected. But if you try connecting a ceramic earpiece to the earphone socket, no current will flow through it and the amplifier won’t work. So don’t be trapped! One other little circuit trick needs to be noted before we finish this article and this involves the 470µF capacitor just after on/off switch S1. This relatively large capacitor may seem unnecessary since the circuit is intended to be powered from a 9V battery but it does have a distinct benefit. As the battery ages, its internal impedance rises. This means that it is less able to deliver the relatively high current pulses demanded by the amplifier and the result is more distor­ tion from the amplifier; ie, poor sound. By placing the 470µF capacitor across the 9V supply, we effectively reduce the AC impedance of the battery and thus enable it to deliver those higher current pulses. The result is better sound quality. Whew! Well, that’s it for this month. Next month we will show you how to assemble this AM Radio Trainer and give the alignment procedure. You will build an alignment oscillator to do this, so no special equipment will SC be required. 8MM VIDEO CASSETES These 120-minute 8mm metal oxide video cassettes were recorded on once for a commercial application and then bulk erased. They are in new condition but don’t have the record protect tabs fitted. The hole in the upper right corner will have to be taped over. $9 Ea. or 5 for $38 LARGE NIGHT VIEWERS One of a kind! A very large complete viewer for long range observation. Based on a 3-stage fibre optically coupled 40mm first generation image intensifier, with a low light 200mm objec­tive mirror lens. Designed for tripod mounting. Probably the highest gain-resolution night viewer ever made. ONE ONLY at an incredible price of: $3990 BINOCULAR EHT POWER SUPPLY This low current EHT power supply was originally used to power the IR binoculars advertised elsewhere in this listing. It is powered by a single 1.5V “C” cell and produces a negative voltage output of approximately 12kV. Can be used for powering prefocussed IR tubes etc. $20 IR BINOCULARS High quality helmet mount, ex-military binocular viewer. Self-powered by one 1.5V “C” size battery. Focus adjustable from 1 metre to infinity. Requires IR illumination. Original carry case provided. Limited stocks, ON SPECIAL AT: $500 IR FILTERS A high quality military grade, deep infrared filter. Used to filter the IR spectrum from medium-high powered spotlights. Its glass construction makes it capable of withstanding high temper­atures. Approx. 130mm diameter and 6mm thick. For use with IR viewers and IR responsive CCD cameras: ON SPECIAL $45 12V OPERATED LASERS WITH KIT SUPPLY Save by making your own laser inverter kit. This combination includes a new HeNe visible red laser tube and one of our 12V Universal Laser Power Supply MkIII kits. This inverter is easy to construct as the transformer is assembled. The supply powers HeNe tubes with powers of 0.2-15mW. $130 with 1mW TUBE $180 with 5mW TUBE $280 with 10mW TUBE MAINS OPERATED LASER Supplied with a new visible red HeNe laser tube with its matching encapsulated (240V) supply. $179 with 1mW TUBE $240 with 5mW TUBE $390 with 10mW TUBE GREEN LASER HEADS We have a limited quantity of some brand new 2mW+ laser heads that produce a brillant green output beam. Because of the relative response of the human eye, these appear about as bright as 5-8mW red helium neon tubes. Approximately 500mm long by 40mm diameter, with very low divergence. Priced at a small fraction of their real value $599 A 12V universal laser inverter kit is provided for free with each head. ARGON HEADS These low-voltage air-cooled Argon lon Laser Heads are priced according to their hours of operation. They produce a bright BLUE BEAM (488nm) and a power output in the 10-100mW range. Depends on the tube current. The head includes power meter circuitry, and starting circuitry. We provide a simple circuit for the supply and can provide some of the major components for this supply. Limited supplies at a fraction of their real cost. $450-$800 ARGON OPTIC SETS If you intend to make an Argon laser tube, the most expen­sive parts you will need are the two mirrors contained in this ARGON LASER OPTIC SET. Includes one high reflector and one output coupler at a fraction of their real value. LIMITED SUPPLY $200 for the two Argon LASER mirrors. LASER POINTER Improve and enhance all your presentations. Not a kit but a complete commercial 5mW/670nm pen sized pointer at ONLY: $149 LARGE LENSES Two pairs of these new precision ground AR coated lenses were originally used to make up one large symmetrical lens for use in IBM equipment. Made in Japan by TOMINON. The larger lens has a diameter of 80mm and weighs 0.5kg. Experimenters delight at only: $15 for the pair. EHT GENERATOR KIT A low cost EHT generator kit for experimenting with HT-EHT voltages: DANGER – HIGH VOLTAGE! The kit also doubles as a very inexpensive power supply for laser tubes: See EL-CHEAPO LASER. Powered from a 12V DC supply, the EHT generator delivers a pulsed DC output with peak output voltage of approximately 11kV. By adding a capacitor (.001uF/15kV $4), the kit will deliver an 11kV DC output. By using two of the lower voltage taps available on the transformer, it is possible to obtain other voltages: 400V and 1300V by simply adding a suitable diode and a capacitor: 200mA - 3kV diode and 0.01uF 5kV capacitor: $3 extra for the pair. Possible uses include EHT experiments, replacement supplies in servicing (Old radios/CRO’s), plasma balls etc. The EHT generator kit now includes the PCB and is priced at a low: $23 LED DISPLAYS National Seminconductor 7-segment common cathode 12 digit multiplexed LED displays with 12 decimal points. Overall size is 60 x 18mm and pinout diagram is provided. 2.50 Ea. or 5 for $10 BATTERIES Brand new industrial grade PANASONIC 12V-6.5AHr sealed gel batteries at a reduced price.Yes, 6.5 AHr batteries for use in alarms, solar lighting systems, etc. Dimensions: 100 x 954 x 65mm. Weight of one battery is 2.2kG. The SPECIAL price? $38 PIR DETECTORS What are the expensive parts in a passive movement dector as per EA May 89? A high quality dual element PIR sensor, plus a fresnel lens, plus a white filter. We include these and a copy of PIR movement detector circuit diagram for: $9 MASTHEAD AMPLIFIER KIT Based on an IC with 20dB of gain, a bandwidth of 2GHz and a noise figure of 2.8dB, this amplifier kit outperforms most other similar ICs and is priced at a fraction of their cost. The cost of the complete kit of parts for the masthead amplifier PCB and components and the power and signal combiner PCB and components is AN INCREDIBLE: $18 For more information see a novel and extremely popular antenna design which employs this amplifier: MIRACLE TV ANTENNA - EA May 1992: Box, balun, and wire for this antenna: $5 extra SODIUM VAPOUR LAMPS Brand new 140W low pressure sodium vapour lamps. Overall length 520mm, 65mm diameter, GEC type SO1/H. We supply data for a very similar lamp (135W). CLEARANCE AT: lenses: two plastic and one glass. The basis of a high quality magnifier, or projection system? Experimenters’ delight! $30 CRYSTAL OSCILLATOR MODULES These small TTL Quartz Crystal Oscillators are hermetically sealed. Similar to units used in computers. Operate from 5V and draw approximately 30mA. TTL logic level clock output. Available in 4MHz, 4.032MHz, 5.0688MHz, 20MHz, 20.2752MHz, 24.74MHz, 40MHz and 50MHz. $7 Ea. or 5 for $25 FLUORESCENT BACKLIGHT These are new units supplied in their original packing. They were an option for backlighting Citizen LCD colour TVs. The screen glows a brilliant white colour when the unit is powered by a 6V battery. Draws approximately 50mA. The screen and the in­verter PCB can be separated. Effective screen size is 38 x 50mm. $12 MAINS FILTER BARGAIN For two displays - one yellow green and one silver grey. SOME DIFFERENT COMPONENTS 1000pF/15kV disc ceramic capacitors ..............$5 20kV PIV - 5mA Av/1A Pk fast diodes .........$1.50 3kV PIV - 300mA / 30A Pk fast diodes ........... 60c 0.01uF /5kV disc ceramic capacitors ...........$1.80 680pF / 3kV disc ceramic capacitors .............. 30c Who said that power MOSFETS are expensive?? MTP3055 N-channel MOSFETS as used in many SC projects ............................$2 Ea. or 10 for $15 MTP2955 P-channel MOSFETS (complementary to MTP3055) ..........................$2 Ea. or 10 for $15 BUZ11 N-channel MOSFETS $3 Ea. or 10 for $25 Brief DATA and application sheet for above MOSFETS free with any of their purchases (ask) Flexible DECIMAL KEYPADS with PCB connectors to suit ...........................................................$1.50 1-inch CRO TUBES with basic X-Y monitor circuit CLEARANCE <at>..............................................$20 Schottky Barrier diodes 30V PIV - 1A/25A Pk. 45c 100 LED BARGRAPH DISPLAY Note that we also have some IEC extension leads that are two metres long at $4 Ea. Yes 100 LEDs plus IC control circuitry, all surface mounted on a long strip of PCB. SIMPLE - a 4-bit binary code selects which one out of the 10 LED groups will be on, whilst another 4-bit binary code selects which one of each group of 10 LEDs will be ON. Latching inputs are also provided. We include a circuit and a connecting diagram. VERY LIMITED QUANTITY WEATHER TRANSMITTERS FM TRANSMITTER KIT - MKll A complete mains filter employing two inductors and three capacitors fitted in a shielded metal IEC socket. We include a 40 joule varistor with each filter. $5 These brand new units were originally intended to monitor weather conditions at high altitudes: attached to balloons. Contain a transmitter (12GHz?) humidity sensor, temperature sensor, barometric altitude sensor, and a 24V battery which is activated by submersing in water. The precision all mechanical altitude sensor appears similar to a barometer and has a mechani­cal encoder and is supplied with calibration chart. Great for experimentation. $16 Ea. SOLAR CHARGER Use it to charge and or maintain batteries on BOATS, for solar LIGHTING, solar powered ELECTRIC FENCES etc. Make your own 12V 4 Watt solar panel. We provide four 6V 1-Watt solar panels with terminating clips, and a PCB and components kit for a 12V battery charging regulator and a three LED charging indicator: see March 93 SC. Incredible value! $42 6.5Ahr. PANASONIC gel Battery $35, ELECTRIC FENCE PCB and all onboard components kit $40. See SC April 93. $7Ea. This low cost FM transmitter features pre-emphasis, high audio sensitivity as it can easily pick up normal conversation in a large room, a range of well over 100 metres, etc. It also has excellent frequency stability. The resultant frequency shift due to waving the antenna away and close to a human body and/or changing the supply voltage by +/-1V at 9V will not produce more than 30kHz deviation at 100MHz! That represents a frequency deviation of less than 0.03%, which simply means that the fre­quency stays within the tuned position on the receiver. Specifications: tuning range: 88-101MHz, supply voltage 6-12V, current consumption <at>9V 3.5mA, pre-emphasis 50µs or 75µs, frequency response 40Hz to greater than 15kHz, S/N ratio greater than 60dB, sensitivity for full deviation 20mV, frequency stabil­ity (see notes) 0.03%, PCB dimensions 1-inch x 1.7inch. Construction is easy and no coil winding is necessary. The coil is preassembled in a shielded metal can. The double sided, solder masked and screened PCB also makes for easy construction. The kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip: $11 Ea. or 3 for $30 LARGE LCD DISPLAY MODULE - HITACHI These are Hitachi LM215XB, 400 x 128 dot displays. Some are silver grey and some are yellow green reflective types. These were removed from unused laptop computers. We sold out of similar displays that were brand new at $39 each but are offering these units at about half price. VERY LIMITED STOCK. $40 OATLEY ELECTRONICS $15 Ea. PO Box 89, Oatley, NSW 2223 STEPPER MOTORS Phone (02) 579 4985. Fax (02) 570 7910 $12 MAJOR CARDS ACCEPTED WITH PHONE & FAX ORDERS These are brand new units. Main body has a diameter of 58mm and a height of 25mm. Will operate from 5V, has 7.5deg. steps, coil resistance of 6.6 ohms, and it is a 2-phase type. Six wires. ONLY: PROJECTION LENS Brand new large precison projection lens which was original­ly intended for big screen TV projection systems. Will project images at close proximity onto walls and screens and it has adjustable focussing. Main body has a diameter of 117mm and is 107mm long. The whole assembly can be easily unscrewed to obtain three very large P & P FOR MOST MIXED ORDERS AUSTRALIA: $6; NZ (Air Mail): $10 June 1993  17 Remote control for the Woofer Stopper Don’t get out of bed to press the Start button on the Woofer Stopper. Just press the button on a small hand-held trans­mitter instead. By DARREN YATES The Woofer Stopper in last month’s issue is a great idea. It zaps barking dogs with a high-level supersonic tone that’s beyond the range of human hearing. While we cannot guarantee that it will work with every dog, the device has been very effective on the mutts that have been zapped so far. In fact, a dog belonging to one of our staff members was stopped in mid-howl when the START switch was pressed. But there is one drawback 18  Silicon Chip to the Woofer Stopper. If the mutt next door starts making a nuisance of himself, you’ve actually got to get out of your chair or out of bed to press the START button on the front panel. This UHF remote control unit solves that problem. It uses a small handheld transmitter to activate a receiver module mounted inside the Woofer Stopper case. Basically, the receiver output is wired in parallel with the START switch. When the transmitter button is pressed, the receiver output goes high and this simulates the START switch action. Rather than re-invent the wheel, we decided to base the project on the UHF Remote Control that was featured in the Decem­ber 1992 issue. This used a small key fob style transmitter and a compact receiver unit based on a pre-built front end module. The transmitter circuit is identical but we’ve considerably simplified the receiver circuit, since we no longer require the relays or the latching circuit. All we require is a momentary output and this can be derived using just the RF front-end module and the decoder IC. The front-end module comes prealigned (to 304MHz) and uses surface mount components to give an assem- Fig.1: the transmitter is based on trinary encoder IC1. When S1 is pressed, IC1 generates a series of pulses at its pin 17 output to switch transistor Q1 on & off. This transistor is wired as a Hartley oscillator & operates at 304MHz due to its tuned collector load & the SAW filter in the feedback path. bly that measures just 35 x 25mm. It is fitted with a pin connector along one edge and plugs into the receiver PC board just like any other component. This eliminates alignment hassles and means that you don’t have to wind any tricky coils. So there it is; the answer to your prayers. Now you can zap the barking fleaball next door by remote control. Let’s find out how this miracle of technology works. How it works – transmitter The transmitter is based on an AX5026 trinary encoder IC – see Fig.1. When pushbutton switch S1 is press­ ed, this IC gener­ ates a sequence of pulses at its output (pin 17). The rate at which these pulses are generated is set by the 1MΩ timing resis­tor between pins 15 and 16 (R1), while the code sequence is set by the connections to the address lines (A1-A12). Each of these address lines can be tied high, low or left open circuit, giv­ ing more than half a million possible codes – 531,441 to be exact. Security is not a prime consideration in this project, however. The coded output from IC1 drives RF transistor Q1. This transistor is connected as a Hartley oscillator operating at 304MHz, as set by a tank circuit consisting of L1 (etched on the PC board), C3, C4 and C5. In addition, a SAW resonator is used to provide a narrow-band feedback path. Its lowest impedance is at its resonant frequency of 304MHz and thus the tuned collector load must be set to this frequency in order for Q1 to oscillate. The SAW resonator ensures fre- quency stability and makes the transmitter easy to align. That’s because the oscillator will only start and pulse LED 1 when the tuned circuit is virtually dead on frequency. This arrangement eliminates trial & error adjustments. C3 is used to adjust the centre frequency of the tuned circuit. This point corresponds to maximum current consumption and is found by adjusting C3 to obtain peak brightness from the indicator LED (LED 1). Power for the transmitter is derived from a miniature 12V battery (GP23 or equivalent) and this is connected in series with the pushbutton switch (S1). When S1 is pressed, the current drawn by the circuit is only a few Main Features Range .....................................................100 metres (line of sight only). Transmitter Frequency ............................304MHz (set by SAW filter). No. Of Code Combinations .....................531,441. Receiver Frequency �������������������������������Preset to 304MHz by a factory assembled front-end module. Receiver Dimensions ..............................33 x 64 x 30mm (W x D x H). Receiver Output ��������������������������������������High for as long as transmitter button is held down. June 1993  19 Fig.2: the receiver uses a pre-built RF front-end module to pick up the pulses from the transmitter. The resulting digital pulse train from the front-end module is then decoded by Tristate decoder IC1. When the transmitter button is pressed, pin 17 of IC1 goes high. milliamps, the exact figure depend­ing on the code word selected at address lines A1-A12. How it works – receiver Fig.2 shows the circuit details of the receiver. Its job is to pick-up the coded RF pulses from the transmitter and decode these pulses to generate an output. As already mentioned, the receiver is based on a complete “front-end” module. This processes the received signal via a bandpass filter, an RF preamplifier, a regenerative detector, an amplifier and a Schmitt trigger. Its input is connected to a short antenna, while its output delivers a digital pulse train to the input (pin 14) of IC1. IC1 is an AX-528 Tristate decoder and is used to decode the 12-bit pulse signal that’s generated by the transmitter. As with the AX-5026 encoder, this device has 12 address lines (A1-A12) and these are connected to match the transmitter code. If the code sequence on pin 14 of IC1 matches its address lines, and the code sequence rate matches its timing (as set by R1), the valid transmission output at pin 17 switches high. This output connects to pin 8 of IC5b in the Woofer Stopper and simu­lates the action of the START switch. Thus, when the transmitter button is pressed, pin 17 of the AX-528 decoder goes high and the Woofer Stopper is activated and begins its 9-minute timing cycle. Pin 17 of the decoder IC then switches low again as soon as the transmitter button is released. Construction Fig.3 shows the assembly details for the transmitter. All the parts, including the battery terminals and the switch (S1), are mounted on a small PC board. Before mounting any of the parts, you must first file the edges of the PC board so that it will fit in the case. This also removes two shorting strips. One of these strips runs along the bottom of the board, while the other runs down the righthand edge (as viewed from the copper side). Make sure that these two short­ing strips are completely filed away; if they are not, the bat­tery terminals will be shorted and the positive battery terminal will be shorted to C3. The most important thing to remember with the transmitter assembly is that all component leads should be kept as short as possible. Apart from that, it’s simply a matter of installing the parts exactly as shown in Fig.3. Be sure to orient IC1 correctly and note that the flat side of the trimmer capacitor (VC1) is adjacent to one end of the board. The SAW resonator and switch should both be mounted flat against the board, while the transistor should only stand about 1mm proud of the board. Take care when mounting the switch – it must be correctly oriented, otherwise it will appear as a short and the transmitter will be on all the time (the switch will only fit comfortably in one direction). The LED should be mounted with its top about 7mm proud of the board, so that it later protrudes about halfway through a matching hole in the RESISTOR COLOUR CODE ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 20  Silicon Chip Value 1MΩ 6.8kΩ 1kΩ 150Ω 82Ω 4-Band Code (1%) brown black green brown blue grey red brown brown black red brown brown green brown brown grey red black brown 5-Band Code (1%) brown black black yellow brown blue grey black brown brown brown black black brown brown brown green black black brown grey red black gold brown ANTENNA A K 82W .001 S1 D1 K 6.8k C3 6.8pF LED1 A 1k 1M .0033 Q1 RECEIVER MODULE 4.7pF SAW 1 12V BATTERY 150  IC1 AX528 .001 1M IC1 AX5026 1 12V BATTERY Fig.3: make sure that the shorting strips are removed from the transmitter PC pattern before starting construction – see text. Keep all leads as short as possible when installing the parts & take care with the orientation of the encoder IC. lid. Be careful with the orientation of the LED – its anode lead is the longer of the two. Check the board carefully when the assembly is completed – it only takes one wrong component value to upset the circuit operation. This done, slip the board into the bottom half of the case and install the battery. Don’t worry if the LED doesn’t flash at this stage when you press the switch – that probably won’t occur because Q1 will not be oscillating. To adjust the oscillator stage, press the switch and tune C3 using a plastic tool until the LED flashes. When this hap­pens, the oscillator is working and you can tweak C3 for maximum transmitter output (ie, max­imum LED brightness). The lid of the case can now be snapped into position and secured using the small screw supplied with the kit. 12V PLUG-PACK D2 D1 220  1000uF 78L05 100k 10uF 0.1 IC1 4060 SEE TEXT 10M 33pF  1 33pF Fig.4: this is the full-size etching pattern for the receiver board. Fig.5 shows the parts layout on the receiver board. Install the parts exactly as shown, leaving the receiver Fig.5: install the parts on the receiver board & connect it to the main Woofer stopper PC board as shown in this diagram. The prebuilt receiver module is installed with its component side towards the .0033µF capacitor. June 1993  21 module till last. This component must be installed with its component side towards the .0033µF capacitor. The antenna consists of a length of insulated hook-up wire and can be either 250mm or 500mm long. The latter will give slightly greater range if this is important. When the receiver assembly is complete, it can be linked to the Woofer Stopper PC board via a 3-way cable. This done, apply power to the Woofer PARTS LIST Transmitter 1 transmitter case 1 PC board, 30 x 37mm 1 miniature PC-mount pushbutton switch 1 12V battery, GP23 or equivalent 1 304MHz SAW resonator Semiconductors 1 AX-5026 trinary encoder (IC1) 1 2SC3355 NPN transistor (Q1) 1 1N4148 silicon diode (D1) 1 3mm red LED (LED1) Stopper and use your DMM to check that pin 17 of the AX528 switches high when the transmitter button is pressed (be careful not to short any of the pins on the IC). Alternatively, you can check that unit operates when the transmitter button is pressed by modifying the Woofer Stopper circuit to produce a 2kHz tone, as described last month. Coding Because this is not a securityrelated project, coding of the transmitter and receiver can be considered optional. That said, it’s still a good idea to program in a simple code to avoid any possibility of interference with other units. Initially, all the A1-A12 address lines will be open cir­cuit but you can tie selected address pins high or low by con­necting them to adjacent copper tracks. In both the transmitter and the receiver, a +5V rail runs adjacent to the inside edge of the address pins, while a ground track runs around the outside edge of the address pins. For example, you might decide to tie A1 and A8 high, tie A3 and A6 low, and leave the rest open circuit. Short wire links can be used to make the connections but note that you will have to scrape away the solder mask from the adjacent rail at each con­nection point on the transmitter PC board so that the track can be soldered Make sure that the transmitter code matches the receiver code. Finally, the receiver board can be mounted on the bottom of the case, adjacent to the power supply terminals. Use the board as a template for marking out its mounting holes and secure the board using machine screws and nuts, with additional nuts used as spacers. An additional small hole in the far end of the case serves as an exit point for the antenna. Footnote: when activated, the Woof­ er Stopper sounds for nine minutes before switching off. To reduce this period to one minute, cut the track to pin 3 of IC3 and connect pin 1 of IC4 to pin 15 of IC3 instead (or to pin 14 SC for a 30-second period). Capacitors 2 .001µF ceramic 1 6.8pF ceramic 1 4.7pF ceramic 1 2-7pF miniature trimmer Resistors (0.25W, 5%) 1 1MΩ 1 150Ω 1 6.8kΩ 1 82Ω 1 1kΩ Receiver 1 PC board, code 03105932, 64 x 33mm 1 front-end module (aligned to 304MHz) 1 AX-528 Tristate decoder (IC1) 1 .0033µF MKT polyester capacitor 1 1MΩ resistor (0.25W, 1%) Where to buy the parts A kit of parts for this remote control unit is available from Oatley Electronics, PO Box 89, Oatley, NSW 2223, Australia. Phone (02) 579 4985. The price is $39.95 plus $2.50 for postage (incl. transmitter kit, receiver PC board and all parts for the receiver). The original Woofer Stopper project is available separately from other kit suppliers. 22  Silicon Chip The receiver module is mounted on the bottom of the Woofer Stopper case, adjacent to the power supply sockets. Run the antenna across the inside of the case & through an exit hole in the opposite end (near the tweeter socket). LED BRAKE LIGHT INDICATOR This “brilliant” brake light indicator employs 60 high intensity LEDs (550-1000mCd) to produce a display that is highly visible, even in bright sunlight. The intensity produced is equal to or better than the LED brake indicators which are now included in some late model “upmarket” vehicles. The LED displays used in most of these cars simply make all the LEDs turn on every time the brakes are applied. The circuit used in this unit can perform in this manner and, for non-automotive applications, it can be customised to produce a number of sweeps (110) starting at the centre of the display and with a variable sweep rate. It not only looks spectacular but also attracts more attention. All the necessary “electronics” is assempled on two identical PCBs and the resulting overall length of the twin bargraph dis­play is 460mm. It’s simple to install into a car since only two connections are required: Earth and the brake­ LASER SCANNER ASSEMBLIES These are complete laser scanners as used in laser printers. Include IR laser diode optics and a very useful polygon scanner ( motor-mirror). Produces a “fan” of light (approx. 30 deg) in one plane from any laser beam. We provide information on polygon scanner only. Clearance: $60 400 x 128 LCD DISPLAY MODULE – HITACHI These are silver grey Hitachi LM215XB dot matrix displays. They are installed in an attractive housing and a connector is provided. Data for the display is provided. BRAND NEW units at a low: $40 LASER OPTICS The collimating lens set is used to improve the beam (focus) divergence. The 1/4-wave plate and the beam splitter are used in holography and experimentation. All are priced at a fraction of their real value: 1/4 wave plate (633nM) ..............................$20 Collimating lens sets ..................................$45 Polarizing cube beam splitters ....................$65 GREEN LASER TUBES We have a limited supply of some 0.5mW GREEN ( 560nm) HeNe laser tubes. Because of the relative response of the human eye, these appear as bright as about a 2mW red tube: Very bright. We will supply this tube and a suitable 12V laser power supply kit for a low: $299 CCD ELEMENT BRAND NEW high sensitivity monolythic single line 2048 element image sensors as used in fax machines, optical charachter recognition and other high resolution imaging applications: Fairchild CCD122. Have usable response in the visible and IR spectrum. Supplied with 21 pages of data and a typical application circuit. $30 INFRARED TUBE AND SUPPLY These are the key components needed for making an INFRARED NIGHT VIEWER. The tubes will convert infrared light into visible light on the phosphor screen. These are prefocussed tubes similar to type 6929. They do not require a focus voltage. Very small: 34mm diameter, 68mm long. All that is needed to make the tube light connecting wire. The case for the prototype unit which would be suitable for mounting on the rear parcel shelf, was mainly made from two aluminium “L” brackets that were screwed together to make a “U” section. A metal rod and its matching holders (commonly available from hardware shops) are used for the supporting leg. $60 for both the PCBs, all the onboard components & instruc­tions: the 60 LEDs are included! We also have available a similar kit that does not have the sweeping feature. It produces similar results to the commercial units installed in cars: all the LEDs light up when power is applied. $40 for both the PCBs and all the onboard components. This kit is also supplied with the 60 LEDs and it uses different PCBs, that have identical dimensions to the ones supplied in the above­ mentioned kit. operational is a low current EHT power supply, which we provide ready made or in kit form: powered by a 9V battery and typically draws 20mA. INCREDIBLE PRICING: $90 For the image converter tube and an EHT power supply kit! All that is needed to make a complete IR night viewer is a lens an eyeiece and a case: See EA May and Sept. 1990. ALUMINIUM TORCHES – INFRARED LIGHTS These are high quality heavy-duty black anodised aluminium torches that are powered by four “D” cells. Their focussing is adjustable from a spot to a flood. They are water resistant and shock proof. Powered by a krypton bulb – spare bulb included in cap. $42 Note that we have available a very high quality INFRARED FILTER and a RUBBER lens cover that would convert this torch to a good source of IR: $15 extra for the pair. PASSIVE NIGHT VIEWER BARGAIN This kit is based on an BRAND NEW passive night vision scope, which is completely assembled and has an EHT coaxial cable connected. This assembly employs a high gain passive tube which is made in Russia. It has a very high luminous gain and the resultant viewer will produce useful pictures in sub-moonlight illumination. The viewer can also be assisted with infrared illumination in more difficult situations. It needs an EHT power supply to make it functional and we supply a suitable supply and its casing in kit form. This would probably represent the best value passive night viewer that we ever offered! BECAUSE OF A SPECIAL PURCHASE OF THE RUSSIAN-MADE SCOPES, WE HAVE REDUCED THE PRICE OF THIS PREVIOUSLY ADVERTISED ITEM FROM $550 TO A RIDICULOUS: $399 This combination will be soon published as a project in EA. NOTE THE REDUCED PRICE: LIMITED SUPPLY. Previous purchasers of the above kit please contact us. 24VDC TO MAINS VOLTAGE INVERTERS In the form of UNINTERRUPTABLE POWER SUPPLIES (UPS’s).These units contain a 300W, 24V DC to 240V 50Hz mains inverter. Can be used in solar power systems etc. or for their original intended purpose as UPS’s. THESE ARE VERY COMPACT, HIGH QUALITY UPS’s. They feature a 300W - 450W (50Hz) SINEWAVE INVERTER. The inverter is powered by two series 12V 6.5Ahr (24V). batteries that are built into the unit. There is only one catch: because these NEW units have been in storage for a while, we can not guarantee the two batteries for any period of time but we will guarantee that the batteries will perform in the UPS’s when these are supplied. We will provide a 3-month warranty on the UPS’s but not the batteries. A circuit will also be provided. PRICED AT A FRACTION OF THEIR REAL VALUE: BE QUICK! LIMITED STOCK! $239 ATTENTION ALL MOTOROLA MICROPROCESSOR PROGRAMMERS We have advanced information about two new STATE OF THE ART microprocessors to be released by Motorola: 68C705K1 and 68HC705J1. The chips are fully functional micros containing EPROM/OTPROM and RAM. Some of the features of these new LOW COST chips include: *16 pin DIL for the 68HC705K1 chip * 20 pin DIL for the 68HC705J1 chip * 10 fully programmable bi-directional I/O lines * EPROM and RAM on chip * Fully static operation with over 4MHz operating speed. These two chips should become very popular. We have put together a SPECIAL PACKAGE that includes a number of components that enable “playing” with the abovementioned new chips, and also some of the older chips. IN THIS PACKAGE YOU WILL GET: * One very large (330 x 220mm) PCB for the Computer/Trainer published in EA Sept. 93; one 16x2 LCD character display to suit; and one adaptor PCB to suit the 68HC705C8. * One small adaptor PCB that mates the programmer in EA Mar. 93 to the “J” chip, plus circuit. * One standalone programmer PCB for programming the “K” chip plus the circuit and a special transformer to suit. THE ABOVE PACKAGE IS ON SPECIAL AT A RIDICULOUS PRICE OF: $99 Note that the four PCBs supplied are all silk screened and solder masked, and have plated through holes. Their value alone would be in excess of $200! A demonstration disc for the COMPUTER/TRAINER is available for $10. No additional software is currently available. Previous purchasers of the COMPUTER/ TRAINER PCB can get a special credit towards the purchase of the rest of the above package. PLASMA BALL KIT This kit will produce a fascinating colourful changing high voltage discharge in a standard domestic light bulb. The EHT circuit is powered from a 12V supply and draws a low 0.7A. We provide a solder masked and screened PCB, all the onboard components (flyback transformer included), and the instructions at a SPECIAL introductory price of: $ 25 We do not supply the standard light bulb or any casing. The prototype supply was housed in a large coffee jar, with the lamp mounted on the lid – a very attractive low-cost housing! Diagrams included. LASER DIODE KIT – 5mW/670nm Our best visible laser diode kit ever! This one is supplied with a 5mW 670nm diode and the lens, already mounted in a small brass assembly, which has the three connecting wires attached. The lens used is the most efficient we have seen and its focus can be adjusted. We also provide a PCB and all on-board components for a driver kit that features Automatic Power Control (APC). Head has a diameter of 11mm and is 22mm long, APC driver PCB is 20 X 23mm, 4.5-12V operation at approx 80mA. $85 PRECISION STEPPER MOTORS This precision 4-wire Japanese stepper motor has 1.8 degree steps – that is 200 steps per revolution! 56mm diameter, 40mm high, drive shaft has a diameter of 6mm and is 20mm long, 7.2V 0.6A DC. We have a good but LIMITED supply of these brand new motors: $20 HIGH INTENSITY LEDs Narrow angle 5mm red LED’s in a clear housing. Have a luminous power output of 550-1000mCd <at> 20mA. That’s about 1000 times brighter than normal red LED’s. Similar in brightness SPECIAL REDUCED PRICE: 50c Ea or 10 for $4, or 100 for $30. IR VIEWER “TANK SET” ON SPECIAL is a set of components that can be used to make a complete first generation infrared night viewer. These matching lenses, tubes and eyepieces were removed from working tank viewers, and we also supply a suitable EHT power supply for the particular tube supplied. The power supply may be ready made or in kit form: basic instructions provided. The resultant viewer requires IR illumination. $180 We can also supply the complete monocular “Tank Viewer” for the same price, or a binocular viewer for $280: Ring. MINI EL-CHEAPO LASER A very small kit inverter that employs a switchmode power supply: Very efficient! Will power a 1mW tube from a 12V battery whilst consuming about 600 mA! Excellent for high-brightness laser sights, laser pointers, etc. Comes with a compact 1mW laser tube with a maximum dimension of 25mm diameter and an overall length of 150mm. The power supply will have overall dimensions of 40 x 40 x 140mm, making for a very compact combination. $59 For a used 1mW tube plus the kit inverter. OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 MAJOR CARDS ACCEPTED WITH PHONE & FAX ORDERS P & P FOR MOST MIXED ORDERS AUSTRALIA: $6; NZ (Air Mail): $10 June 1993  23 Have you ever experienced that sinking feeling when your car won’t start on those cold winter’s mornings? This digital voltmeter will show you how your car’s battery is faring. A digital voltmeter for your car By DARREN YATES Imagine this situation. It’s 6:30am, cold, dark and raining outside. It’s also time to go to work so you bolt for the car, fumble through your keys, unlock the door and dive in for all you’re worth! Made it; so far so good. Now to start ‘er up. You put the key in the ignition and crank the engine only to be greeted by an infuriatingly slow “rur, rur, rur” from the starter motor. Blast it! – crook battery. You’re not going anywhere; at least not until the battery has been recharged or replaced. The foregoing is not an unlikely scenario and, with only minor variations, has happened to most motorists. In fact, the battery is the most likely component in your car to fail during the winter months. This project won’t stop the battery from failing but it will tell you when the battery is on the way out. It accurately measures the battery voltage SUPPLY REGULATION V/F CONVERTER IC1 3-DIGIT COUNTER IC3 DISPLAY DRIVER IC4 TIMING CONTROLS IC2 3-DIGIT DISPLAY 24  Silicon Chip Fig.1: block diagram of the Car Digital Voltmeter. The battery voltage is fed to a voltage-to-frequency converter & this drives a 3-digit counter & the LED displays. over an 8-17V range and displays the result on a 3-digit LED display with 0.1V resolution. If the battery voltage consistently reads less than 12V, then either the charging system is not working correctly or the battery has reached the end of its life. Either way, it’s time to take action to avoid getting stranded. The Car Digital Voltmeter can also warn you if the battery is being overcharged, as can happen if the regulator in the alternator fails. By attending to this sort of problem quickly, you can not only avoid battery damage but also avoid damage to your car’s engine management computer. Block Diagram Refer now to the block diagram of Fig.1. This shows the basic circuit sections. Most digital voltmeters now use one of the Intersil 7106/7 series chips but, unfortunately, these are expensive in one-off quantities. As an alternative, our Digital Car Voltmeter uses an older but more economical circuit technique B E C E I GO B Q6 BC557 E C B IC2f .0022 100k .01 +5V 14 10 10 4 3 LE CLK 11 11 CAR DIGITAL VOLTMETER 15 MR 13 8 2 IC3 MC14553 D2 D1 D0 12 12 16 16 +5V IC2e 11 4 IC1b 8 470k .0033 6 10k 470k .0033 E IC2b 2.2M 0.1 CHASSIS 3 IC2a 4049B 2 VR1 2.2k 3.3k 0.1 5 47k 47k 4 100k 100 16VW 7 10k 47k C B Q1 BC547 2 3 .015 IC1a LM358 IC2c 0.1 100 16VW GND OUT 7805 IN +12V VIA IGNITION SWITCH D1 1N4004 IC2d 9 1 100k 0.1 1 10k 100k 10k +5V +5V 10 5 6 8 12 7 +5V C E VIEWED FROM BELOW B 3.3k 1 15 7 9 LE 8 5 C Q4 BC557 E B C Q2 BC557 E 3.3k B 5 6 6 2 1 7 A 3 3.3k 1k 10 10 B IC4 4511 C D f g 14 15 9 e d c b 13 a 4 Fig.2 shows the full circuit details. In addition to the LED displays, it uses three CMOS ICs, an LM358 dual op amp package and a handful of other parts. Let’s see how it all works. Op amps IC1a and IC1b together form the V/F converter sec­tion. IC1a is connected as an inverting integrator while IC1b is configured as a Schmitt trigger inverter. The incoming battery voltage is fed to a voltage divider consisting of a 3.3kΩ resistor and calibration trimpot VR1. From there, the sampled voltage is fed to the inverting (pin 2) input of IC1a via a 100kΩ resistor. It is also further divided by two and fed to the non-inverting input. In operation, IC1a’s output (pin 1) ramps up and down due to the presence of Schmitt trigger IC1b and transistor Q1 in its negative feedback loop. This Schmitt trigger has its upper and E 3 Q3 BC337 C B c d DISP1 HDSP-5303 10 9 2 11 11 6 4 12 7 e f g a b 1k Q5 BC337 3 DISP2 HDSP-5303 5 DP 180  7x 56  16 Circuit diagram Fig.2 (right): IC1a & IC1b form the V/F converter & this clocks IC3, the 3-digit counter. Its multiplexed outputs drive IC4, a 4511 display driver/decoder, & this then drives the displays via 56Ω current limiting resistors. The common cathodes of the displays are driven by the digit driver outputs (D0-D2) of IC3 via PNP/NPN transistor pairs Q2-Q3, Q4-Q5 & Q6-Q7. C 1k +5V Q7 BC337 3 DISP3 HDSP-5303 +5V that uses common parts. It connects directly to the positive and negative termi­nals of the battery and these are the only two connections to the car’s wiring – the circuit is powered directly by the battery it is measuring. As shown in Fig.1, the battery voltage is applied to a voltage regulator circuit and this provides a fixed +5V rail for the counter and display driver circuit. In addition, the battery voltage is applied to a voltage-to-frequency (V/F) converter based on IC1. This in turn produces a square-wave signal whose frequency is proportional to the battery voltage. The square-wave signal produced by IC1 clocks a 3-digit counter based on IC3. This counter is stopped and started by a timing circuit based on IC2, so that it essentially functions as a frequency meter. It’s outputs are fed into a 7-segment decod­er/display driver circuit which then drives the three LED dis­plays. June 1993  25 Q2 Q3 3.3k 1k +5V CLK GND 3.3k 1k MR Q6 LE 56  3.3k 1k DISP3 56  IC4 4511 IC3 MC14553 56  56  1 .0022 1 180  0.1 3.3k lower thresholds set to approximately 2/3Vcc and 1/3Vcc respec­tively by its two 100kΩ feedback resistors. When power is first applied, IC1a’s output ramps down line­arly until it reaches the lower threshold of IC1b (about 1.7V). When this point is reached, pin 7 of IC1b goes high and turns on Q1. This pulls pin 2 of IC1a low via a 47kΩ resistor and the voltage on pin 1 now rises as the .015µF capacitor charges in the opposite direction. When it reaches the upper threshold of the Schmitt trigger (about 3.4V), pin 7 of IC1b switches low and Q1 turns off. Pin 1 of IC1a now ramps down again and so the cycle continues indefinitely. As a result, a triangle waveform appears at pin 1 of IC1a, while a squarewave of the same frequency appears at pin 7 of IC1b. The frequency of this square-wave is directly proportional to the input voltage. It not only drives Q1 but also clocks pin 11 of IC3, a CMOS 4553 3-digit counter. IC3 contains three separate decade counters. Its 4-bit outputs appear in multiplexed fashion on pins 5, 6, 7 & 9 (Q0-Q3), while pins 15, 1 & 2 (D0-D2) are the digit driver outputs. The .0022µF capacitor between pins 3 & 4 sets the frequency of an internal oscillator and this in turn sets the speed at which the outputs are multiplexed. The 4-bit outputs are fed into the inputs (A-D) of IC4, a CMOS 4511 IC1 LM358 .015 Q1 10k 10k 10k VR1 1 .01 IC2 4049 1 10k 100uF 100k 470k 100k 100k 100uF 47k D1 26  Silicon Chip DISP2 Q7 7805 +12V VIA IGNITION SWITCH CHASSIS DISP1 Q5 56  56  56  Q4 0.1 0.1 47k 47k 100k Fig.3: install the parts on the two PC boards exactly as shown in this diagram. Make sure that all parts are correctly oriented & note that a small heatsink is fitted to the 7805 regulator to keep it cool. After completion, the two boards are wired together via their +5V, MR, CLK & GND connections. .0033 0.1 2.2M .0033 +5V CLK 470k GND MR LE 7-segment display driver/decoder IC. This converts the 4-bit BCD code into 7-segment outputs which directly drive the three LED displays via 56Ω current limiting resistors. In addi­ tion, pin 5 of DISP2 is permanently connected to the +5V rail via a 180Ω current limiting resistor so that its decimal point is always on. The other two decimal points are unused. Each display is switched on at the correct time via the digit driver outputs (pins 15, 1 & 2). These are active low outputs; ie, for a particular digit to light, its display output must go low. These outputs each drive a PNP/NPN transistor pair and these in turn switch the common cathodes of the display digits to ground. Of course, all this is done at high speed so that, as far as the observer is concerned, the three displays appear to be continuously lit. Timing To get the circuit to count correctly, we need to provide latch enable (LE) and memory reset (MR) timing signals for IC3. This task is performed by IC2a, a CMOS 4049 hex inverter IC. IC2a and IC2b form a basic squarewave oscillator with a frequency of about 2Hz. Its output appears at pin 4 and is cou­pled to pin 7 of IC2c via a .0033µF capacitor. Thus, each time pin 4 switches high, pin 7 also briefly switches high while the capacitor charges. As a result, pin 6 of IC2c generates a train of narrow negative-going pulses and these are fed into the LE input of IC3 (pin 10). Each time a pulse is received, the current count in IC3 is latched into the Q0-Q3 outputs and the display is updated (ie, the display is updated twice every second). Inverters IC2d and IC2e, along with the .0033µF capacitor and the 470kΩ resistor, provide a short time delay to ensure that all data lines are steady before the memory reset takes place. Normally, pin 12 of IC2e is low but when pin 6 goes high (at the end of the LE pulse), pin 12 goes high for a brief period. When pin 12 goes low again, pin 15 briefly goes high and resets IC3 to 000. As soon as the reset signal falls low again, IC3 begins counting the pulses on its clock input from the V/F converter. This continues until a latch enable signal arrives and the dis­play is updated as described above. IC3 is then reset again and so the cycle is continuously repeated every 0.5s, as set by the frequency of the oscillator based on IC2a & IC2b. Power for the circuit is derived directly from the battery via a 7805 3-terminal regulator. Diode D1 provides reverse polar­ity protection for the circuit, while the two 100µF capacitors provide supply line decoupling. During operation, the circuit draws approximately 140mA which means that the regulator dissipates about 1.2W. This means that a small heatsink must be fitted to the 7805 to keep it cool. Construction All the components for the Digital Car Voltmeter are installed on two PC boards and these are mounted backto-back on 9mm spacers. The first board (code 04105931) holds the V/F con­verter, power supply and timing circuitry, while the second board (code 04105932) holds the counter circuitry and the LED displays. Before installing any of the parts, carefully check both boards for etching defects by comparing them with the published patterns. When you’re happy that everything is OK, you can start with the display board assembly. Fig.3 shows the parts layout on the two PC boards, with the display board at the top. The first thing to do is to install the 12 wire links. Make sure you get these PARTS LIST Take extra care when installing the transistors on the display board, as it’s easy to confuse NPN & PNP types. The two ICs both face in the same direction, while the displays must be oriented with their decimal points at bottom right. This board carries the regulator & the V/F converter & timing circuitry. It is connected to the display board via a 5-way rainbow cable & the two boards then bolted together on 9mm untapped spacers. The trimpot at lower left allows the unit to be accurately calibrated. in the correct position and don’t forget the small link immediately beneath DISP3. If necessary, you can straighten the link wire by clamping one end in a vyce and then stretching it slightly by pulling on the other end with a pair of pliers. Once the links are in, install the resistors and the .0022µF polyester capacitor. Table 1 shows the resistor colour codes, although it’s also a good idea to check each resis­ tor with a multimeter before installing it on the board (the colours on some brands can be quite difficult to decipher). Note that there are four vacant holes in the display board, to the right of the .0022µF capacitor. These holes are not used in this project. They were originally provided to allow the deci­mal point of DISP1 to be turned on (by installing another link and another 180Ω resistor), a feature that might be handy in future projects based on this board. The six transistors all face in the same direction but be sure to use the correct type at each location. Q2, Q4 & Q6 are all BC557 PNP transistors, while Q3, Q5 & Q7 are all BC337 NPN types. Double check that these are all correctly mounted as it’s easy to get them mixed up. Note that each transistor should be 1 PC board, code 04105931, 102 x 55mm 1 PC board, code 04105932, 102 x 55mm 1 plastic zippy case, 130 x 67 x 42mm 1 red Perspex window, 46 x 20mm 1 front panel label, 125 x 62mm 1 small U-shaped heatsink 1 1-metre length red automotive cable 1 1-metre length black automotive cable 1 40mm-length 5-way rainbow cable 1 2.2kΩ 5mm horizontal trimpot 4 9mm-long untapped spacers 4 9mm-long tapped spacers 4 3mm x 15mm-long machine screws 5 3mm x 6mm-long machine screws Semiconductors 1 LM358 dual op amp (IC1) 1 4049 hex inverter (IC2) 1 MC14553 3-digit BCD counter (IC3) 1 4511 7-segment decoder\ driver (IC4) 1 7805 5V regulator 1 BC547 NPN transistor (Q1) 3 BC557 PNP transistors (Q2,Q4,Q6) 3 BC337 NPN transistors (Q3,Q5,Q7) 1 1N4004 silicon diode (D1) 3 HDSP-5303 common-cathode 7-segment LED displays (DISP1-3) Capacitors 2 100µF 35VW electrolytic 4 0.1µF 63VW MKT polyester 1 .015µF 63VW MKT polyester 1 .01µF 63VW MKT polyester 2 .0033µF 63VW MKT polyester 1 .0022µF 63VW MKT polyester Resistors (1%, 0.25W) 1 2.2MΩ 4 3.3kΩ 2 470kΩ 3 1kΩ 4 100kΩ 1 180Ω 3 47kΩ 7 56Ω 4 10kΩ Miscellaneous Tinned copper wire for links (100mm) June 1993  27 This view shows the two boards stacked together & mounted on the front panel. Make sure that there are no shorts between the two boards when the assembly has been completed. pushed down onto the board as far as it will comfortably go before soldering, so that it doesn’t later foul the front panel. The display board can now be completed by installing the three LED displays. Make sure that these are correctly oriented, with the decimal point of each display to bottom right. V/F converter board The assembly procedure for this board is similar to that for the previous board. Install the three wire links first, followed by the resistors, capacitors and semiconductors. The 7805 regulator is installed with its leads bent at right angles. A small heatsink is then slid under its metal tab and the assem­bly bolted to the PC board using a screw and nut. The two completed PC boards can now be placed side-by-side and their +5V, MR, CLK & GND terminals wired together using a short length of rainbow cable. This done, connect the power supply leads to the V/F converter board. Two 1-metre lengths of automotive cable should be used for this job. Use a red cable for the positive lead and a black cable for the negative lead. Once the wiring has been completed, the two boards can be stacked together on four 9mm untapped spacers and held using 12mm-long mounting screws inserted from the V/F converter board side of the assembly. The assembly is then secured by fitting a 9mm tapped spacer to each mounting screw on the display board side – see photo. All that remains now is to install the module inside the specified plastic case. As shown in the photos, the module is mounted on the lid of the case, with the three LED displays visible through a perspex window. The first step is to attach the front-panel label to the lid and use it as CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ Value 0.1µF .015µF .01µF .0033µF .0022µF IEC Code 100n 15n 10n 3n3 2n2 EIA Code 104 153 103 332 222 RESISTOR COLOUR CODE ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 2 4 3 4 4 3 1 7 28  Silicon Chip Value 2.2MΩ 470kΩ 100kΩ 47kΩ 10kΩ 3.3kΩ 1kΩ 180Ω 56Ω 4-Band Code (1%) red red green brown yellow violet yellow brown brown black yellow brown yellow violet orange brown brown black orange brown orange orange red brown brown black red brown brown grey brown brown green blue black brown 5-Band Code (1%) red red black yellow brown yellow violet black orange brown brown black black orange brown yellow violet black red brown brown black black red brown orange orange black brown brown brown black black brown brown brown grey black black brown green blue black gold brown a drilling template for the four mounting holes. This done, drill a series of holes around the inside perimeter of the display cutout area. The centre piece can now be knocked out and the job filed to a smooth finish so that the Perspex® window is a tight fit. You will also have to drill an entry hole for the supply leads, either at one end or at the rear. After that, it’s simply a matter of securing the module to the lid using four 6mm-long machine screws. If necessary, the Perspex® window can be secured by gluing it in position using epoxy resin (don’t use too much). Test & calibration To test the unit, connect the supply leads to a 12V battery and check that the three displays immediately light up. If they do, then the unit is functioning correctly. It can now be cal­ ibrated by first checking the battery’s voltage with your digital multimeter and then adjusting VR1 until you get the same reading on the Digital Car Voltmeter. If it doesn’t work, switch off immediately and check for wiring errors. In particular, make sure that all parts are cor­rectly mounted and that there are no missed solder joints or shorts between tracks due to solder splashes. If these checks reveal nothing, apply power once more and check that the output of the 3-terminal regulator is at +5V. Check that this voltage appears on the supply pins of the ICs and on the emitters of Q2, Q4 & Q6. After that, it’s a matter of trying to isolate the fault to a particular circuit stage. For example, if one display fails to Fig.4: check your PC boards for defects by comparing them against these full-size etching patterns. light, check its two driver transistors. If the display always shows 000, check the V/F converter stage based on IC1 and Q1. If the circuit fails to reset and count correctly, check the values of the resistors and capacitors associated with IC2. Installation Make sure that you install this unit in the car in a pro­fessional manner. + + VOLTS + DIGITAL CAR VOLTMETER + Fig.5: this full-size artwork can be used as a drilling template for the front panel. In particular, all wiring connections should be made using automotive style connectors which should be well-insulated to avoid any possibility of short circuits. The positive supply lead goes to the battery via the igni­ tion switch and a fuse in the fusebox. Finding a suitable point to tap into shouldn’t be too difficult. It’s simply a matter of finding a terminal in the fusebox that goes to +12V when the ignition is turned on (eg, the IGN terminal). Avoid using a terminal that also goes to +12V when the ignition switch is turned to the accessories position, however. Finally, you can reduce the size of the box sitting on your dashboard by mounting the three LED displays on a small satellite board. These can be housed in a small case and wired back to the main unit via an 11-way rainbow cable. Footnote: Dick Smith Electronics has advised us that they will be offering an optional satellite display board with their version SC of this kit. June 1993  29 SERVICEMAN'S LOG Some customers can be a real pain There is a good deal more to the service game than learning how to service TV sets, video recorders & other odd appliances which turn up from time to time. One also has to learn how to deal with customers – and that can sometimes be a lot harder! To be fair, most customers are not hard to get on with – not deliberately, anyway. Granted, their naive ideas about elec­tronic equipment and their clumsy attempts to describe symptoms can sometimes prove extremely frustrating but one learns to live with that. And a patient approach usually wins out in the end. But as I’m sure any of my colleagues will testify, every once in a while one encounters a really nasty one; someone who deliberately sets out to be as hard to get on with as possible. I imagine that, basically, it stems from an almost paranoid suspi­ cion that all service personnel – plumbers, electricians, motor mechanics and, of course, TV technicians – are rogues intent on ripping off the customer. 30  Silicon Chip Well, no doubt some of them are; it would be foolish to believe otherwise. And a healthy suspicion on the part of the customer is good protection –caveat emptor (let the buyer be­ware) and all that, as they say in the classics. But “all that” needs to be tempered with some discretion and common sense. The customer needs to take a little time and ask a few polite questions before reaching a conclusion. An honest technician will give logical, easy-to-understand answers; he has nothing to fear. How it started OK, so what started all this? First, in order that the reader can follow the story, it is necessary to provide a little background, before getting to the nitty-gritty. Some three or four years ago, a local dealer began handling Grundig TV sets. The Grundig is an up-market European brand which first appeared on the Australian market with the advent of colour TV. It remained on the market for a few years and then just seemed to fade away. The next I heard of Grundig was when the local dealer began stocking them. Initially, I had no particular interest in them until about a year ago when the dealer approached me about a set, still on his showroom floor, that was giving trouble. And, exhibiting an almost child-like confidence in my skill, he de­clared it was something which he was sure I could fix in five minutes! Naturally, it wasn’t that easy and the first thing I needed was a service manual. To obtain this, I rang the company responsible for importing these set’s and was put through to the managing director. He proved to be most obliging and helpful. Not only did he promise to put a manual in the post immediately but, when I quoted the set’s model number and the symptoms, he made some suggestions as to the likely cause of the problem. The manual arrived promptly and, with its aid and the suggestions, I quickly located the problem. A dry joint had destroyed the horizontal output transistor, plus an IC which drives this transistor. It was all perfectly routine and the set was repaired and returned to the dealer. And that started the ball rolling. My dealer colleague suggested I undertake warranty service for these sets, since he needed effective local warranty back-up as part of his sales package. I didn’t rush in; I needed to clarify the kind of deal I could expect from the importer; ie, technical back-up, parts availability and the financial basis for warranty jobs. This resulted in some telephone discussions and then a visit to their premises, which proved to be quite impressive. They were well organised, had a very good service set-up, an excellent stock of spare parts, and warranty payment and condi­tions in line with usual practice. And so a mutually satisfactory agreement was reached. Nothing much happened at this level for the next few months. By all accounts, Grundig TV sets are very reliable. Madam calls Then the phone rang and I quickly sensed trouble. The call­er, a woman with a rather imperious manner, indicated that she owned a Grundig TV set (model ST-70/460) which had failed and that she had been referred to me by the dealer. There was no suggestion of a warranty claim as the set was well outside this period, but she wanted me to come to her house, at that very instant, and fix the set. And it wasn’t simply a request; it was delivered more in the manner of a royal command. I replied, as quietly as I could, that I was very sorry but I could not come at that very instant; I was busy in the work­shop. I would be able to call the following afternoon, collect the set, bring it to the workshop, service it and return it. And I added that there would be a pick-up and delivery charge. “Oh no. That is totally unsatisfactory. No way. The set has to be repaired in the house”. Again I had to politely refuse. “I’m sorry but there is no way that I will attempt to repair the set in the house. I have no way of knowing what spare parts I will require, nor can I do a proper job without access to suitable test equipment”. Initially, she wouldn’t budge and tried to argue. But I wouldn’t budge either and I really had the whip hand. Eventually, very grudgingly, she agreed to let me take the set and so an ap­pointment was made for the following afternoon. Unfortunately, when I fronted up the next day, it was all to no avail. The front door wasn’t even opened. Instead, the husband came around the side of the house and informed me that my services were no longer required; the set was now OK. I accepted the situation in good grace and went on my way. But I wasn’t very happy. I felt that they might at least have had the decency to phone me and save me a time-wasting trip. But that’s the luck of the game. The truth is, I suspected that they had approached someone else to do the job. Madam complains In any case, I imagined that that was the end of the mat­ter. But no; about three weeks later I received a phone call from the managing director of the importing company. And I sensed that he was a mite put out. It appeared that he had been contact­ed by one of the party – presumably the woman – and told that I wouldn’t come to the house and look at the set. Well, I lost no time in putting him straight. And he didn’t take too much convincing. More to the point, he supported every­thing I had done and indicated his intention of ringing the customer and straightening things out. And he was as good as his word. Some 20 minutes later, a considerably mollified woman was on the phone wanting to know when I could pick up the set. It was early in the week and I had a pretty full schedule. The best I could offer was the following Saturday morning. No; that was no good. After some mumbling, she finally suggested that they would bring the set in themselves, on the Thursday afternoon. I said that that was fine by me and so that was how we left it. You’re not going to believe this next bit – or perhaps you’re way ahead of me. Thursday came and went with no sign of the set, as did Friday and Saturday. Then, on the following Wed­ nesday, the woman was on the phone again. I had been called away rather urgently at the time and had left the shop in the care of an assistant. And she copped the woman’s wrath full blast – a real tear-a-strip-off job because I hadn’t collected the set. Fortunately, my assistant was fully aware of situation and gave as good as she received. More specifically, she pointed out that the arrangement was for the customer to deliver the set. This was vigorously denied by the customer and so the conversation ended in a stalemate. Next morning I was on the phone first thing. The woman answered, which was fortunate since she seemed to be the one doing all the stirring. I reminded her of the arrangement whereby she and her husband were to deliver the set but again this was denied. She was obviously prepared to argue indefinitely over this until I pointed out that I had written the arrangement in my workshop diary. Only then did she stop arguing and agree that I should collect the set. And so a further appointment was made. And this time it worked. I was June 1993  31 SERVICEMAN'S LOG – CTD greeted at the door, almost affably, and shown into the lounge room. The house was very modern and the lounge room very large and expensively furnished. Along the full length of one wall was a built-in, glass fronted, cupboard which ran from the floor to about chest height. The TV set sat on top of this, along with an impressive hifi system. But what struck me was the fact that the shelf formed by the top of the cupboard was only just deep enough to accommodate the TV set. The point about all this was that it was quite a tricky job disconnecting the leads and plugs from the back of the set. As well as the antenna and power cord, there was a cable to the amplifier system which connected to the set via a European multi-pin SCART socket. Moving the set forward, or swinging it around, created a dangerously un- 32  Silicon Chip stable situation and I had to support it with one hand while working on these various leads. I managed OK but it was obvious that any idea of working on the set in-situ was completely out of the question, quite apart from any other con­ siderations. Nor were there any tables in the room; the only place to work was on the carpet. And I doubt whether Madam would have approved of that. Anyway, with some help from her husband, the set was even­tually loaded into the van and taken back to the shop. But one other point had been raised while I was there. Madam insisted that I submit a quote for the job, before proceeding. Madam’s quote Now this is something I normally do not do. Nor do most other servicemen that I know. It’s simply not practical in this game. In a great many cases, there is no way of assessing the cost until the job is finished, by which time one has already expended time and effort. And while the failure of one component may be obvious, there’s no way of knowing whether other compon­ ents have been damaged or how long it’s going to take to find the reason for the failure. When customers raise this matter, I point out that, if I did quote, it would have to be a high enough to cover almost all contingencies. But then, if it turns out to be something minor, I can be accused of ripping them off – or quoting a rip-off price. Most people accept this and I am always prepared to put a limit on costs, beyond which I will not go without consultation. Even this involves some risk but it’s one that I’m prepared to take. So what did I do about Madam’s demand? I’m afraid I took the coward’s way out. I’d had enough confrontation and, since I already had some idea of the likely fault, I reckoned I could break the rules for once and work around this one. And so, at long last, the set was on the bench and I could get on with the real job. At switch-on it was immediately obvious that the switchmode power supply had shut down. And the number one suspect in almost all such cases is the horizontal output transistor, or something very close to it. The relevant portion of the circuit is reproduced here (see Fig.1) and shows this transistor (T541, BU508A) and its associat­ed driver IC (IC500, TDA8140). This latter arrangement differs from that usually encountered, where a driver transistor and coupling transformer are used. Anyway, a quick measurement of T541 confirmed that it had cashed in its chips. And, acting on advice I had received from the importer, I suspected that the driver IC would also have failed. And so it proved to be. I had both these components in stock and it was a routine job to fit them. But I had no illusions that I had found the real fault; almost certainly, these were merely the victims. And again the service personnel’s advice proved to be spot on. I went to the tripler (K536) which, along with the horizon­ t al output transformer, is located in the right rear corner of the set. A close examination of this component revealed a small break in the plastic case. I fed the set from a Variac and wound the voltage up slowly while watching the tripler. Sure enough, as I approached the normal input voltage, a telltale corona appeared. I switched off immediately but I had also seen enough to suggest that the set would operate normally. So a new tripler was needed and I had one of these in stock also (they are not cheap, by the way). This was fitted and the set came good immediately. I made a few minor adjustments and the set was back to new condition. But what about Madam’s insistence on a quote before pro­ceeding? Well, of course, I had needed to “proceed” before I could assess the cost and this situation is a classic example of the futility of customers insisting on a quote. Anyway, I toted up the bill and as a matter of interest it worked out as follows: Labour plus transport ............$125.00 BU508A transistor .....................$8.00 Tripler ....................................$116.38 TDA8140 driver IC ..................$59.60 Postage on components .............$5.00 Total .......................................$313.98 I’d taken something of a punt, of course. How would I stand if, when I presented the above as a quote, the customer knocked it back? Well, of course, I hoped that it wasn’t going to happen. But considering the aggro I been through so far, I was even pre­ pared to offer to put the faulty parts back and give them back the set, no charge. Drastic? Of course – but I wonder what they would have done. In the event, it was all hypothetical. I rang the house and Madam herself answered the phone. Seeking to break the ice a little, I facetiously pulled the old gag of asking which she wanted first; the good news or the bad news. I should have known better; the gag fell completely flat (I doubt whether anyone ever laughs in that household). So I carried on bravely: “the good news is that there is no problem about repairing the set. The bad news is that it is going to cost you $314.00”. Madam agrees I fully expected a violent backlash at that figure. But no; all the woman Fig.1: the horizontal output stage in the Grundig ST-70/460 colour TV receiver. The use of an IC driver stage (IC500) for the horizontal output transistor (T541) is rather unusual. said was, “how soon can we have the set back?” I said it would take about three days. There were a couple of reasons for the delay. One was purely diplomatic; she had no idea that the job was finished. The other was genuinely technical; I wanted to give the set a good soak test before I returned it. The last thing I needed was for it to bounce. So another appointment was made and this time everything went without a hitch. I was greeted courteously, the husband helped me in with the set, and we set it up on the bookcase. I switched it on and the sight of a first class picture was ob­viously reassuring. This photo clearly shows the crack in the case of the tripler (K536). The small white plastic box houses the 30MΩ focus control variable resistor. Then I presented the itemised account. I was half expecting a grumble when the figure was digested. But no; the husband pulled out his wallet and handed me three $100 notes plus a twenty. I reached for the necessary change but he waved it away. “No way; that’s near enough. And I don’t even want the docket.” I protested that the gesture wasn’t necessary but he in­sisted and I gave in. But Madam showed her mettle by insisting on keeping the docket. Which was no skin off my nose; I had nothing to hide. Why did it happen? And that was the end of my ordeal. But why did it all hap­pen? Technically, I am now certain that the first failure was simply a power supply shut-down caused by the tripler but without any damage. Had they let me take the set then, I would have only needed to replace the tripler and they would have saved quite a few dollars. But when it came good temporarily, I was sent pack­ing. Domestically, there seems little doubt that there was a difference of opinion as to how and by whom the TV set should be repaired. This situation became quite clear when I encountered both parties together when I returned the set. The husband simply wanted the set fixed, without any hag­ gling or mucking about. Madam, on the other hand, treated me with rudeness and suspicion from the outset. She was June 1993  33 SERVICEMAN'S LOG – CTD was intrigued to learn about how this valve was to be used and in what kind of equipment. I took the valve with me the next time I went to town and as I handed it over to the salesman I asked if he could tell me who wanted it. All he knew was that it had been ordered by the local Cadburys chocolate factory but he had no idea what it was to be used for. He promised to enquire for me when someone from the company called to pick it up. Metal detector This is the Cintel IMD (Industrial Metal Detector) in the Cadburys chocolate factory. The 40-year old design can detect metal fragments that are just 0.5mm in diameter. also determined to have it all done her way and to drive the hardest possible bargain. Well, it didn’t turn out to be much of a bargain in the end. There’s one final snippet. I wasn’t the only one Madam dobbed in. While she was dobbing me in she also dobbed in my dealer colleague. Her story to the distribution company was that the dealer had indicated that he was no longer handling Grundig sets. This was her garbled version of the dealer’s state­ment that he did not service the sets; that they should be re­ferred to yours truly, as an accredited Grundig service agent. Fortunately, a few phone calls soon straightened things out but I think you can see what I mean by some people being delib­ erately hard to get on with. Apples & chocolates Well, after that, we need a complete change of scene. And who better to provide it than our old colleague, J. L. from Tas­mania, the land of apples and chocolates. This is his story about the latter. This is not a “Serviceman” story in the usual sense. In­stead, it’s a look at servicing in an entirely different field to that seen by most of us. What’s more, it turned out to be a very sweet exercise, in more ways than one! 34  Silicon Chip A few weeks ago the phone rang and the voice on the other end asked if I had a 6J6 that I could let him have. It turned out to be one of the staff at a city trade house and he wanted the item for one of their industrial clients. Now, I had to stop and think what a 6J6 was. You don’t hear words like that much these days. It turns out that a 6J6 was twin triode RF amplifier valve and, as you all know, RF amplifier valves went the same way as button-up boots. I’ve had no call for new valves for over 10 years and what is left of my stock is stowed away under the house amid thick dust and spider webs. But if someone actually wants to buy a valve, I don’t mind braving the creepy-crawlies to find one. So half an hour later I had found a 6J6, brand new in its original carton. It was the only one of its type I had and that made me wonder just what was special about this valve. Most other valve types are represented in my collection by the dozen. Why was this one there by its lonesome self? The 6J6 is an RF amplifier twin triode. It has the cathodes of each triode tied to a single base pin. I have never seen such an arrangement in any TV tuner (the most likely place to find RF amplifiers) nor in the front-end of any radio that I have ever worked on. So I The valve was duly collected but all he could learn was that it was for use in a metal detector and had been ordered by the purchasing officer. I was on my own if I wanted any more informa­tion. It occurred to me that any equipment that used valves should now be classified as “antique” and if some such equipment was still being serviced, then there must be a good story behind it. Ac­cordingly, I rang the factory the next day and spoke to the purchasing officer. He put me in touch with the assistant elec­trical engineer, who subsequently showed me through the factory and let me see the old valve-type metal detector that started this story. The equipment is a “Cintel IMD” (Industrial Metal Detector) and I learn­ ed that it, and some 20 others, had been installed in 1957/58 as part of the company’s on-going quality control pro­gram. About five of the machines remain in service, although only one is still in continuous operation. Their places have largely been taken by several different types of solid state detectors. The company’s Purchasing Officer was able to give me the full history of the remaining Cintel IMD. He brought out the original Assets Book and showed me where the machine had been ordered in September 1957, delivered in April 1958 and installed and working in June 1958. He was also able to tell me the price paid for it – 521 pounds (or $1042). When the Cintel finally retires, it will be replaced with a modern solid state machine costing just a shade under $250,000. I was also introduced to the Assistant Supervisor (electri­cal) and taken on a tour of the factory, to see how electronics had been introduced into the confectionery industry. The first thing we looked at was the Cintel IMD. This machine scans an 80cm wide production line conveyor belt, looking for any metal that may have been introduced into the product. When it was ordered, the specification was that the machine had to be able to detect a 2mm metal ball anywhere across the line. It easily succeeded in this task but, over the years, the technicians have tweaked and tuned it so that the Cintel can now detect a piece of metal only 0.5mm wide near the centre of the line, and even smaller at the edges. For all their refinement, the modern solid state machines can do no better. The power head of the Cintel IMD contains comparatively little electronics. There are only five valves in the unit, and all connections are hard-wired to terminal strips under the chassis. The 6J6 valve is used as an RF oscillator, followed by a buffer, a driver and a push-pull output stage. Apart from valve failures, the problem which started this story, there has been remarkably little trouble with the old machines. The most serious occurred some 10 years after they were installed, when there were a series of breakdowns when they were restarted after the Christmas shut-down. The problem was soon traced to defective paper capacitors and replacing these has prevented any further breakdowns. It’s a tribute to the 40-year old design and the robust British con­ struction that the machines still work perfectly after all these years, so long as replacement valves can be found. The Cintels are the only valve devices left at Cad­ burys. But there is hardly any part of the production line that is not supervised or mon­itored by electronics of one kind or another. Thank you J. L., for an interesting story. Its an area of electronics we seldom think about. And half your luck; I’ve always dreamed about being let loose in a chocolate factory. SC CEBus AUSTRALIA KITS CEBus Australia has opened the Circuit Cellar door to bring you a range of high quality, educational electronics kits. There are three types of kit available: an Experimenter’s Kit which includes the PCBs, manuals, any key components that are hard to find and the basic software required by the finished product. Then there is the Complete Kit which includes everything above plus the additional components required to complete the kit. Finally, there is the complete kit with Case & Power Supply. Regardless of which kit you purchase you get the same high quality solder masked and silk screened PCB and the same prime grade components. Our range of kits includes: HAL-4 4 Ch, EEG Monitor, Complete kit only ................... $356.00 Experimenter’s Kits: SmartSpooler, 256K print spooler ..................................... $214.00 IC Tester, Tests 74xx00 family ICs .................................... $233.00 Serial EPROM Programmer, For 27xxx devices ............... $214.00 Ultrasonic Ranger Board with Transducer.......................... $194.00 NB: The above prices DO NOT include sales tax. Don’t forget we also have the HCS II, Home Control System, available, Its features include: Expandible Network, Digital & Analog 1/O, X-10 Interface, Trainable IR Interface and Remote Displays. Call fax or write to us today for more information. Bankcard, Mastercard & Visa accepted. CEBus AUSTRALIA. Ph (03) 467 7194. Fax (03) 467 8422. PO Box 178, Greensborough, Vic 3087. June 1993  35 Windows-based digital logic analyser This PC-based digital logic analyser uses software dev­eloped for Windows 3.0 or higher. It features eight input channels & can be built for less than $220.00. By JUSSI JUMPPANEN There are basically three choices when it comes to debug­ging digital electronic circuitry. In order of preference, these are: (1) a commercial digital logic analyser (expensive); (2) an oscilloscope; and (3) a logic probe or digital multimeter. Of these, the latter method is the most common, although it is the least effective. Although far superior to a DMM or logic probe, a CRO suff­ers from several major drawbacks. First, it is specifically designed for testing analog 36  Silicon Chip circuits. Analog signals are more than likely to be of a periodic nature and a CRO requires a periodic signal for triggering. Unfortunately, many digital signals are non periodic and so cannot be displayed effectively on a CRO. For example, the read cycle of a RAM circuit or the one-shot action of a pushbutton circuit are difficult to debug using a CRO. In addition, the average CRO only has two channels. When analysing digital circuitry, the more channels that can be exam­ined simultaneously the better. After spending many a frustrating hour trying to debug digital electronic circuits using a 2-channel CRO, I decided that there had to be a better way. Unfortunately, commercial logic analysers are expensive and so this project was developed as a low-cost alternative. In particular, costs have been kept low by making the system PC-based. This provides a very effective display for the logic analyser. The control software is based on the Windows 3.0 platform and this not only simplifies the software development, but also results in an easy-to-use, professional-looking package – see Fig.1. The result is a 6.0MHz bandwidth, 8-channel digital logic analyser for less than $220.00. It boasts a host of features, including programmable trigger, variable sample fre­quency and external clock support. The programmable trigger allows the circuit to trigger on four of the eight input channels, while the frequency control allows the sampling frequency to be to be varied linearly from 100kHz to a maximum of 6.0MHz in 100kHz steps. If required, a lower sampling frequency can be provided by connecting an exter­nal clock to the unit. Software features The software is the heart of the project and was written using the Borland 3.0 C++ compiler in conjunction with the Bor­land Object Windows Library for Windows 3.0. It was initially tested on a machine running OS/2 2.0 using OS/2’s WinOS2 support but also runs on machines running Windows 3.0 and Windows 3.1. The software carries out three broad functions: (1) hard­ware configuration and control; (2) data storage and retrieval; and (3) data analysis and display. The hardware control is provided through the use of I/O read and write ports. The software allows the user to program the trigger point at which the logic analyser starts sampling and program the frequency at which the sample should run. Normally, once started, the sample is taken within a few milliseconds. If the circuit does not trigger, the sample will run indefinitely. For this reason, an ABORT button is also provided to enable the current sample to be cancelled. Once a sample has been completed, the software automatical­ ly displays the results of the sample on the screen. Several tools are provided by the software to help analyse the resulting data. First, the display timebase can be modified to any one of four settings (x1, x2, x4 or x8). The sample data is made up of 1024 individual samples and so it is not possible to display all the results on the screen at the same time. The timebase feature allows the user to select the amount of data that is to be displayed. For example, a x8 timebase will display eight times as much data on the screen as a x1 timebase. But even with the multiple timebase feature, not all the data can be displayed at once. To cater for this, the software allows the user to scroll Fig.1: the opening screen displays the demonstration sample when the software is first booted up. You can vary the sampling frequency from 100kHz to 6.0MHz in 100kHz steps by clicking on the Up & Down arrows & choose from one of four timebase settings. Fig.2: clicking on Edit Trigger brings up the Trigger Selection dialog box. Triggering is controlled by the first four channels & these can be set to trigger on a high, low or don’t care state. This command can also be activated by double-clicking the left mouse button in the data display area. the display, thus allowing different sections of the sample data to be examined. A status bar shows the currently displayed sample number and also shows the hex value of the sample. To help locate a particular sample value, the software also provides a comprehensive search feature. It is possible to search for a specific value on any one of the eight channels or for combinations of values on any or all channels. It is also possible to measure the period and frequency of any two points shown on the display area. The actual frequency and period, as calculated by the software, are based on the sam­pling frequency. This results in June 1993  37 VCC 16 1 15 R1 1k R2 1k R3 1k R4 1k R5 1k R6 1k R7 1k GND GND GND BD7 BD6 BD5 BD4 BD3 BD2 BD1 BD0 IOR IOS IOU ALE BA7 BA6 BA5 BA4 BA3 BA2 BA1 BA0 TRO3 TRO4 CLOCK IO RDY AEN 2 2 S5 4 14 3 S3 6 13 4 S1 8 12 5 S0 11 11 6 S2 13 10 7 S4 15 9 8 S6 17 +12V VCC -12V -5V 3 A15 5 A13 7 A11 1 9 A9 20 12 A8 2 14 A10 21 16 A12 3 18 A14 22 1 AEN 4 14 2 P0 P=D P1 U2a 19 1 U3e 74LS04 11 14 10 IOR 3 P2 12 13 U2d P3 IOS 11 P4 5 P5 P6 74LS02 U2b 6 P7 U1 D0 74LS688 4 13 U3f 12 7 7 IOU IOU D1 D2 D3 D4 D5 D6 D7 G 23 10 5 ADDRESS DECODING 24 6 25 7 VCC VCC 26 20 8 27 D7 9 D6 28 D5 10 D4 29 D3 11 D2 30 D1 12 D0 31 IOS 13 IOR 32 14 2 3 4 5 6 7 8 9 19 1 20 A0 B0 A1 B1 A2 B2 A3 B3 A4 A5 U4 74LS245 B4 B5 A6 B6 A7 B7 18 17 16 15 14 13 12 11 BD7 2 A7 BD6 A5 BD5 A3 BD4 A1 BD3 A0 BD2 A2 BD1 A4 BD0 A6 E 4 6 8 1A1 1Y1 1A2 1Y2 1A3 1Y3 1Y4 U5 11 74LS244 2A1 2Y1 13 2Y2 2A2 15 2Y3 2A3 17 2Y4 2A4 1G 2G 1A4 1 DIR 18 16 14 12 9 7 6 3 BA7 BA5 BA3 BA1 BA0 BA2 BA4 BA6 19 10 10 BUS BUFFERING 33 15 34 16 35 RESET 20 S7 S1 SW-DIP8 GND IOR R8 1k 17 VCC C1 0.1 C2 0.1 36 C3 0.1 C4 0.1 C5 0.1 DECOUPLING 18 37 19 J2 DB37/F I/O PORT CONNECTIONS I/O BUS EXPANDER Fig.3: the circuit details for the internal I/O card. The location of the logic analyser in the I/O map is set by S1, with U1 performing partial address decoding on address lines A15-A8. Bus transceiver U4 provides data bus isolation for the D0-D7 data lines, while U5 buffers the A7-A0 lines. a very accurate measurement of both frequency and period. The display can also be configured 38  Silicon Chip in a number of different ways. First, it is possible to change the labels associated with any or all of the channel traces. Second, it is possible to temporarily hide any unwanted traces on the display. And third, the colour of the display can be configured to suit personal taste. Once a sample has been taken it is possible to save the results to file. A descriptive note can also be added to the saved results. The data can then easily be read back at a later date for further analysis or even further testing. Hardware – internal card The software controls two pieces of hardware: (1) an inter­nal XT bus card (or I/O Port Card); and (2) an external logic analyser board. The internal card will work in either an XT or AT bus slot. Its sole purpose is to provide a means of addressing the external logic analyser board. It provides basic I/O decoding and maps the I/O addressing signals to a 37-way D-type connector. Fig.3 shows the circuit details of the I/O Bus Card. Address decoding The internal card will work in either an XT or an AT bus slot. It provides basic I/) decoding & maps the addressing signals to a 37-way D-type connector. A point to note here is that because I/O address signals are only partially decoded (ie, A18-A15), the internal card reserves a full 256 consecutive I/O address lines. This may seem wasteful but the circuit was specifically designed this way to allow external boards to be cascaded (more on that later). To guarantee that the circuit works correctly, the I/O address must be configured so that it doesn’t clash with any existing I/O devices. This means the card must be addressed to a portion of the I/O map that contains 256 consecutive unused I/O address locations. The 8086 architecture provides over 65,000 I/O address locations from which to choose and, on most machines, I/O devices are located at the lower end of the I/O address space. So to ensure that the card functions correctly, it is best to use a high address space (an address that seems to work well is 0F30H). External logic analyser board The external logic analyser board performs all the actual processing required to sample eight digital input channels. The board can be divided into the following regions: address decod­ing, hardware control registers, clock generation, trigger pro­gramming and the RAM storage unit. Fig.4, Fig.5 & Fig.6 show the details. The external logic analyser board takes all its control signals from the DB37/M expansion port. It decodes the remaining A7-A0 I/O address lines using U100, a 4-bit comparator, and S100 (the 4-bit DIP switch) – see Fig.4. The result of the comparison is used to partially enable U101 and U102, the two 3-line-to-8-line decod­ers. By using the IOR-bar and IOU-bar signals to further enable U101 and U102 respectively, we end up with eight active low I/O write signals and eight active low I/O read signals. The logic analyser requires the use of 3 I/O write and 2 I/O read address lines which are configured as shown in Table 1. The output DB37/F expansion port is used to connect to a possible second external board. The two octal bus transceivers, U103 and U104, are used to provided additional line drive for the outgoing expansion port, while U103 also provides data bus isola­tion. The philosophy behind this is to allow external boards to be cascaded. ▲ The location of the logic analyser in the PC I/O map is controlled by a DIP switch (S1). The 8-bit DIP switch setting is compared with the A8-A15 high order address lines of the XT address bus using U1, an 8-bit comparator. The remaining lower order address lines (A7-A0) are passed to the external board through the D37 expansion port. This means that the internal card only partially decodes the address lines and relys on the external board to complete the full decoding process. The result of the address comparison is combined with the XT bus IOR and IOU signals by NOR gate U2 and hex inverter U3 to produce three active low I/O signals: IOS-bar, IOU-bar and IOR-bar. The IOS-bar signal is active low when the I/O address match­es the S1 DIP switch setting, thus indicating a valid I/O ad­dress. The IOR-bar and IOU-bar lines indicate that a valid I/O address is being sent to the D37 expansion port. These correspond to read and write cycles, respectively. The IOR-bar and IOS-bar lines also feed into U4, the bus transceiver, to provide proper data bus isolation whenever the board is not selected. U4 also provides additional data bus line drive and helps protect the PC data bus. The low order address lines (A7-A0) feed out through the D37 expansion port via U5, an octal buffer. This chip is there to provide extra address line drive and to protect the PC address bus. Fig.4: the external logic analyser circuit takes all its control signals from the DB37/M expansion port & decodes the remaining A7-A0 address lines. The result is then used with the IOR-bar & IOU-bar signals to enable U101 & U102 to derive the I/O write & read signals. IC13, IC20 & IC21 synthesise the sample clock signal. June 1993  39 40  Silicon Chip June 1993  41 VCC CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 IC1a 14 1 13 20 2 BCH7 IC1f 74LS14 12 BCH7 1 LA 11 LCLK BCH0 3 3 11 5 IC1b IC1e IC1c 4 BCH7 BCH1 18 BCH2 17 BCH3 10 BCH3 BCH4 BCH5 6 BCH4 BCH6 BCH7 9 13 1 IC1d IC2e OE OD0 D0 D0 CLK OD1 D1 D1 OD3 D2 D2 OD2 D3 D3 D0 D0 D1 D1 D2 D2 IC3 4 D3 74LS374 14 D4 7 D5 13 D6 8 D7 8 BCH5 12 BCH6 3 20 D3 D4 D5 D6 D7 2 19 16 5 15 6 12 9 CD0 CD1 CD2 CD3 CD4 CD5 CD6 OD5 IC4 D4 74LS374 D4 OD4 D5 D5 OD7 D6 D6 OD6 D7 D7 IOU2 CLK OE CD7 1 2 TA0 TA0 10 19 TA1 TA1 12 16 TA3 TA2 13 5 TA2 TA3 15 15 M1 6 TB0 9 M0 12 M3 9 M2 VCC M0 10 10 BCH0 BCH1 CHANNEL BUFFER BCH2 IC2a 74LS14 1 BCH7 BCH3 7 74LS08 1 14 IC5a M1 2 5 M2 4 9 M3 10 12 IC5b IC5c IC5d 13 3 TB0 6 TB1 8 TB2 TB1 11 TB2 14 TB3 1 A0 16 A=B A1 A2 A3 IC6 74LS85 B0 6 TRIG B1 B2 B3 A<B A>B 2 4 8 11 TB3 7 TRIGGER CIRCUIT Fig.5: the input data is buffered by Schmitt trigger stages IC1 & IC2 & clocked into IC3, an 8-bit latch. Once latched, the data byte is then written into RAM (IC10) by the write cycle. IC4, IC5 & IC6 form the trigger circuit. This means that multiple external boards can share a single internal card, provided they are mapped to a unique I/O address space. Hardware control registers The software can monitor the status of the hardware by reading the status byte located at IOR0. The status byte is defined as shown in Table 2. The DONE signal indicates when the sample is complete. The software monitors the DONE line to decide when to end the sample cycle and start the read cycle. The INT/EXT signal indicates if the board is currently using its internal or external sample clock, while the TRIG signal indicates if the trigger circuit is currently triggered. The software controls the logic analyser using two 8-bit latches (IC17 & 1C16). The software writes control information to either of these latches by addressing IOU0 or IOU1 respectively. The definition of the two control bytes is as shown in Table 3. The clock data allows the software to program the sample clock generation circuit. The 7-bit clock data makes up the clock divider count, as used by the phase lock loop (IC13) to synthesise the sample clock signal. The LA-bar bit (pin 2, IC16) controls access to the logic analyser data bus. Because the PC and the logic analyser both need to access the RAM, there exists a possibility of bus contention. To protect against this, the LA-bar signal mutually excludes the PC and the logic analyser from accessing the data bus. When LA-bar is low, the logic analyser has control of the bus, TABLE 2 Bit No. Name Description 0 DONE Active high indicating sample complete 1 TRIG Active high indicating circuit triggered 2 INT/EXT Clock source: 0 = internal clock, 1 = external clock 3-7 Not Used Spare TABLE 3 IOW0 Control Byte: TABLE 1 Bit No. Name 0-6 Clock Data Clock divider data byte 7 Not Used Spare I/O Line I/O Read I/O Write 0 Status Register Frequency Divider 1 RAM Data Control Register 2 Spare Trigger Control Bit No. 3 Spare Spare 0 LA 4 Spare Spare 1 RSET 5 Spare Spare 2-5 Not Used 6 Spare Spare 6 START 7 Spare Spare 7 ALWAYS 42  Silicon Chip Description IOW1 Control Byte: Name Description Bus control signal: 0 = logic analyser, 1 = PC Software controlled hardware reset signal Spare Enable sampling circuit Not currently used Conversely, when LA-bar is high, the PC has control of the bus. The RSET signal enables a software controlled hardware reset, while the the START signal is used to control the hardware sampling. To enable the hardware, the START signal must be high. The ALWAYS signal is not currently used. Clock generation The clock signal is produced by hex inverters IC15f & IC15e. The resulting 2MHz output is divided by 10 in IC19 to produce a 200kHz clock signal. This is then further divided by 2 in D-type flipflop IC12A to produce a 100kHz base clock. The base clock is used by the phase lock loop (IC13) to synthesise a programmable sample clock signal. The PLL takes the base clock as the input frequency and compares it to the feedback clock, produced by a clock divider circuit. This divid­ er circuit consists of IC20 and IC21, which are 4-bit up/down coun­ ters. The PLL works by locking the feedback clock signal (IC13, pin 3) to the input clock signal (IC13, pin 14). Once locked, both clocks run at the same frequency – in this case, the fre­ quency of the input clock. Thus, we can write the following equa­tion: Input clock frequency = feedback clock frequency. The feedback clock is derived from the sample clock (IC13, pin 4) by dividing the sample clock by a programmable value of N. Thus, we can also write: Feedback clock frequency = (sample clock frequency)/N, where N is the divisor programmed into the clock divider circuit via the control registers. By now combining the above two equations , we get the following equation: Input clock frequency = (sample clock frequency)/N. Finally, because the input clock is fixed at 100kHz, we can re-arrange this equation to obtain the following result: Sample clock = N x 100kHz The software allows a value of N = 1 to N = 60 to be pro­grammed into the clock divider circuit. This means it is possible to select a sample clock frequency anywhere in the range from 100kHz to 6MHz in 100kHz steps. As a final option, switch S1 provides selection between the internal clock and an external clock signal. However, the logic analyser circuit can only be guaranteed to work up to 1 1 the maximum sample clock rate GND GND 20 20 of 6.0MHz and so the external GND GND 2 2 clock should also be limited to GND GND 21 21 this value. GND GND 3 3 The external clock feature BD7 OD7 22 22 is basically provided for cases BD6 OD6 4 4 where a very slow clock speed BD5 OD5 23 23 BD4 OD4 is required. The external clock 5 5 BD3 OD3 must be a TTL signal and thus 24 24 BD2 OD2 must conform to TTL specifica6 6 BD1 OD1 tions in terms of maximum and 25 25 BD0 OD0 minimum voltage levels and rise 7 7 IOR IOR and fall times. 26 26 IOS IOS The selected clock signal 8 8 IOU IOU is fed through a clock timing 27 27 ALE ALE circuit made up of IC14, IC24 9 9 BA7 OA7 & IC2. These ICs generate cor28 28 BA6 OA6 rect clock timing and phase as 10 10 BA5 OA5 required by the RAM to ensure 29 29 BA4 OA4 that the data write cycle works 11 11 BA3 OA3 correctly. 30 30 BA2 OA2 A point of interest is the role 12 12 BA1 OA1 of IC18 (the tri-state gate) and 31 31 BA0 OA0 IC24d (the 2-input AND gate). 13 13 TRO3 TRO3 Because both the software and 32 32 TRO4 TRO4 the hardware access the RAM, 14 14 CLOCK CLOCK there is some possibility of 33 33 bus conflict. IC18 ensures that 15 15 IO RDY IO RDY the sample clock (and thus the 34 34 ADDE ADDE sample write cycle) is disabled 16 16 when the software is reading 35 35 the RAM. 17 17 RESET RESET IC24d provides a method for 36 36 +12V +12V reading the RAM via software. 18 18 VCC VCC When the software reads the 37 37 -12V -12V RAM, it uses the IOR1 line. By 19 19 -5V -5V feed­ing this signal into IC24d, a rising edge ACLK signal is genOUTPUT INPUT DB37/F DB37/M erated at the end of every IOR1 I/O CONNECTORS read. This rising edge causes the RAM address counter circuit Fig.6: the pin assignments for the DB37 (IC7, IC8 & IC9) to increment, input & output connectors on the external card. meaning that the RAM counter then addresses the next RAM location. it to the 4-bit OR mask to produce the Thus, the software can read all 1024 TRIG (trigger) signal. RAM locations by just using the RSET When the TRIG level goes high, this line to initially reset the RAM address indicates that the trigger criteria has counter circuit and by reading the been met and so a rising edge trigger IOR1 address line 1024 times. pulse is generated. This method of triggering means Trigger programming circuit that the trigger circuit can be proThe trigger circuit is made up of grammed to operate on any combinaIC4, IC5 & IC6 – see Fig.5. The soft­ tion of the first four input channels. ware latches the trigger data into For example, to get the circuit to IC4, an 8-bit octal latch, using the trigger on a high level for channel #1 IOU2 address line. The trigger data and on low levels for the remaining is made up of a 4-bit AND mask and three channels, the software would a 4-bit OR mask. IC5, a quad 2-input write out the following data to the trigger circuit: AND gate, gates the first four input channels and the 4-bit AND mask. Trigger Byte AND Mask OR Mask The 4-bit result is then fed into IC6, 11111000 (F8H) 1 1 1 1 1000 a 4-bit comparator, which compares It is also possible to program the June 1993  43 PARTS LIST 1 PC board for internal card 1 PC board for external card 1 DIP switch (DIP8) 1 DIP switch (DIP4) 1 DPDT toggle switch 1 RCA panel socket 1 2MHz crystal (XTAL) 1 plastic instrument case, 260 x 80 x 190mm 1 0.6-metre length of 40-way IDC ribbon cable 9 mini IC clips (8 red, 1 black) 1 software package D Type Connectors 1 DB37/F - long footprint, PCB mount (J2) 1 DB37/F - short footprint, PCB mount 1 DB37/M - short footprint, PCB mount 1 DB37/F IDC connector 1 DB37/M IDC connector 1 DB15/F IDC connector 1 DB15/M solder bucket with case Sockets 2 14-pin DIL 1 16-pin DIL 1 20-pin DIL 1 24-pin DIL 1 16-pin IDC Semiconductors 1 74LS688 (U1) 1 74LS02 (U2) 2 74LS04 (U3, IC15) 4 74LS245 (U4, U103-104, IC11) 1 74LS244 (U5) 2 74LS14 (IC1, IC2) 4 74LS374 (IC3, IC4, IC16, IC17) 3 74LS08 (IC5, IC23, IC24) 2 74LS85 (IC6, U100) 6 74LS193 (IC7, IC8, IC9, IC19, IC20, IC21) 1 6116 (IC10) 1 74LS74 (IC12) 1 74HCT4046 (IC13 – Philips) 1 74LS32 (IC14) 1 74LS125 (IC18) 1 74HCT4040 (IC22) 2 74LS138 (U101, U102) Capacitors 1 0.47µF 37 0.1µF monolithic 1 2200pF Resistors (0.25W, 5%) 2 10kΩ 1 100Ω 12 1kΩ 44  Silicon Chip trigger with a “don’t care” option. For example, if we want the circuit to trigger only when channel Ω1 goes high, the trigger would be programmed as follows: Trigger Byte AND Mask OR Mask 10001000 (88H) 1 0 0 0 1000 In this case, the AND mask will only allow channel #1 data to pass. The comparator will always match the three don’t care channels as they are always 0. Thus, the trigger signal will only go high when channel #1 goes high. Control of the trigger circuit is achieved via the software interface. This provides an easy-to-use dialog box interface to allow selection of any trigger combinations. The resulting TRIG signal is fed into IC12b, a D-type flip­flop. This signal clocks the START data to the flipflop output to give the TRIP signal. This must be high for the circuit to start sampling. Thus, sampling will only every occur if the circuit is triggered and the software has set the START signal high. This allows the software to control the sampling by controlling the level of the START signal. Once the trigger has been latched, the sampling cycle be­ gins. Ripple counter IC22 keeps track of the number of samples taken. Once 1024 samples have been taken, the DONE signal goes high. This signal is fed back to hex inverter IC2, which disables any further sampling. The software monitors the state of the sample by reading in the DONE signal via the status register and when this signal goes high, the software ends the sample cycle and initiates a read cycle. Ram storage circuit The input data is buffered by Schmitt trigger inverters IC1 and IC2 – see Fig.5. The input buffer not only squares up the input signal but also protects the remainder of the circuit from over-voltage. By buffering the input and installing these two ICs in sockets, any damage due to over-voltage can be repaired simply be replac­ ing the ICs. Note: this circuit is only designed for TTL voltage levels so care must be taken when sampling data, to ensure that excess voltages are not applied. IC3, the 8-bit latch, takes the buffered input channel data. This data is clocked in at the rate of the sample clock (LCLK). Once latched, the data byte is written into RAM by the write cycle. The latch is also used to protect the data bus from bus contention. If the bus is in use by the PC (ie, LA-bar is high), the latch drives its outputs to a high impedance state, thus allowing the PC to have uninterrupted access. The RAM address counter is made up using IC7, IC8 & IC9 which are cascaded to form a 12-bit UP-counter. This counter is driven by the sample clock signal ACLK. The least significant 10 bits of the 12-bit count make up the sample address and are fed into IC10, a 6116 RAM chip. Note that the counter reset pin is tied to the software controlled RSET line signal, thus allowing the counter to be reset by software. IC11, an octal bus transceiver, gives the PC access to the logic analyser data bus. The PC software uses the IOR1 read signal to enable IC11, which in turn allows the PC to read the RAM data bus. That’s all we have space for this month. Next month, we shall resume with the construction and installation details. As well, we’ll describe how the SC Digital Logic Analyser is used. Where to buy the kit The kit is offered in three formats: (1). A complete kit consisting of all the parts as listed – price $215.00 plus $10.00 for postage and handling. (2). A complete kit of all parts except for the instrument case – price $185.00 plus $5.00 for postage and handling. (3). Two double-sided PC boards (with screened overlays) plus software – price $90.00 plus $5.00 postage and handling. To order, send cheque or money order to Jussi Jumppanen, PO Box 697, Lane Cove 2066, NSW. Phone (02) 428 3927. Please specify whether a 5¼-inch or 3½-inch disc is required. Note: copyright of the two PC boards for this project is retained by the author. 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 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 AMATEUR RADIO BY GARRY CRATT, VK2YBX The Smith Chart – what it is & how you use it Possibly one of the most useful graphic tools available today to the RF engineer is the Smith Chart. This chart, named after its inventor, Mr Phillip Smith, an engineer at Bell Labora­tories during the 1930s, first appeared in “Electronics” magazine in the USA in January 1939. problems, the precise reason for its creation. In fact, the Smith Chart is really a special type of graph, having curved co-ordinate lines, instead of the rectangular lines encountered on standard graph paper. Quite complex mathematical reasons exist behind the construction of the chart but these do not need to be understood by the user. It is easy to be put off by the Smith Chart. At first glance, it looks like a nightmare, with all those apparently spiralling curves, but after you’ve read this article you should be quite at ease with it. It really is a very useful chart Different curves for the amateur radio operator. Essentially, the Smith Chart is used to graphically repre­ sent the reflection characteristics and impedance of an RF cir­cuit. It is ideally suited for the solution of transmission line To make the Smith Chart easy to understand, we’ll show its different curves separately and then bring them all together as a simplified composite chart. Fig.1 is the first set of curves 0 REACTANCE AXIS -0.2 +0.2 0 RESISTANCE AXIS 0.2 -0. 5 0.5 PRIME CENTRE .5 +0 RESISTANCE CIRCLES 1 -1 +1 2 h Fig.1: the first components of a Smith Chart are the resistance circles. The values are “normalised” to a value of 1.00, the prime centre of this plot. +5 50 +2 -2 -5 5 h Fig.2: the second component of the Smith Chart is the reactance plot. Again the reactance values are normalised. June 1993  53 tance lines plotted on the one graph. Note that this is a greatly simplified Smith Chart, as those normally pub­ lished have the circles at much closer intervals which is why they look so complicated at first glance. Now let’s see how you might plot a particular impedance on the chart. Consider an example where we have an impedance con­sisting of 50Ω resistive and 100Ω inductive reactance (50 + j100), and a prime centre value of 50Ω. This particular impedance can be plotted at the intersection of 1.0 on the resistive scale and 2.0 on the positive reactance circle. AMATEUR RADIO – CTD 0 + j0 (SHORT CIRCUIT) -0.2 +0.2 0 0.2 -0. 5 .5 +0 0.5 1 -1 +1 SWR circles 2 0.5 + j1 +2 -2 5 1 + j2 50 +5 -5 1 - j2 OPEN CIRCUIT Fig.3: this simplified Smith Chart shows the resistance and reactance circles plotted together. Note that the resistance axis coincides with the zero reactance line. which are resistance circles. Each resistance circle is assigned a particular value, shown where the circle cuts the vertical resistance axis. That value remains the same for all points along that circle. In fact, the values range from zero at the top of the axis to infinity at the bottom and represent a ratio with respect to the centre point of the chart which is mark­ ed “1”. By assigning the centre point or “prime centre” of the chart a particular value, each circle represents a value of resistance scaled in accordance with the ratio for that circle. For example, if you allocate a value of 100Ω to the centre point, any point lying on the 0.5 circle has a value of 100 x 0.5 = 50Ω. Similarly, any point on the 2.0 circle has a value of 200Ω. This also means that the resistance value of any point on the chart can be calculated by multiplying the ratio of the particular line with the value assigned to the prime centre. The value you would normally assign to the centre point is the same as the value of the characteristic impedance of the line being matched, typically 54  Silicon Chip 50Ω. In fact, special printed charts are available having a prime centre of 50Ω. All resistance and reac­ tance values can then be plotted directly, without having to “normalise” impedances. Reactance circles Fig.2 shows curves which are reactance circles. Note that these circles originate from the left and right hand sides of the vertical zero reactance line. The circumference of the circle is the reactance axis. Just as each resistance circle was assigned a particular value, so are the reactance lines. Any point along a reactance circle has the same value and these values can be multiplied (or normalised). Points located to the right of the zero reactance axis are positive (inductive) and values to the left are negative (capacitive). Note also that the vertical zero reactance line on Fig.2 coincides with the vertical resistance axis on Fig.1. That makes sense because any “pure” resistance will have zero reactance. Fig.3 is the composite Smith Chart, with the resistance circles and reac- Now we come to the nub of the matter, as far as most ama­teur radio operators will be concerned. A useful addition to the Smith chart is the standing wave circle. A series of these can be drawn on the chart using a draughting compass, centred on the prime centre. The point at which a circle for a given SWR crosses the resistance axis is the value of SWR. So the circle represent­ing an SWR of 2:1 has its centre at the prime centre and the radius crossing 2.0 on the resistance axis. Fig.4 shows a simplified Smith Chart with SWR circles added. If we wish to match a 50Ω transmission line, having a length of 2¼ wavelengths to a terminating im­pedance of 25Ω resistive and 25Ω inductive reactance (25 + j25), the following procedure should be used. First, we “normalise” the terminating impedance by dividing both components by 50. This equates to 0.5 +j0.5. We then plot this impedance at the inter­section of the 0.5Ω resistance line and the 0.5Ω reactance cir­cle. We know the reactance is positive (inductive), so it must be located on the right hand side of the resistance axis. By drawing a circle, whose centre is at the prime centre and whose radius is the distance from the prime centre to the impedance point, we have plotted (0.5 + j0.5). By noting where the circle intersects the resistance axis, it can be seen that a voltage ratio of 2.6:1 exists at that point. Wavelength scale A comprehensive Smith Chart, as distinct from the simpli­fied examples used here, also bears a wavelength 5.0 SWR CIRCLE -0.2 +0.2 0 2.0 SWR CIRCLE 0.2 -0. 5 .5 +0 0.5 1 -1 +1 2 GW QUALITY SCOPES 100MHz +2 -2 50 PLUS FREE DMM +5 -5 5 Fig.4: plotting SWR circles on a Smith Chart is a useful step in the process of matching a transmitter to an antenna, while avoiding the need for tedious mathematical calculations. scale around the perimeter of the chart. The scale is marked in fractions of a wavelength of a transmission line. One scale runs anticlockwise, starting at the “generator” end, which is normally the input end, and running towards the load. Another scale runs in the opposite direction from load to generator. The complete circumference equals one half wavelength. Using our matching example above, we could further progress towards a solution by drawing a line from the prime centre, through the plotted 0.5 + j0.5 point, and to the wavelength scale. As our plotted impedance point is looking from the load end of the network, we use the “towards generator” scale to read 0.088 wavelength at the point of intersection. We know that our 50-ohm cable has a length of 2.25 wave­lengths, and as the complete scale on the chart represents a half wavelength and any impedance reflections will be repeated every half wavelength, we need only use 0.25 as our transmission line length for this calculation. By adding 0.25 to the 0.088 indicated on the wavelength scale, we can locate the resultant 0.338 on the wavelength scale and draw a line from that point to the prime centre. The point where this line intersects our 2.6:1 SWR circle is the line input impedance, in this example 1.0 - j1.0. To find the line im­pedance, we simply multiply by 50, and this gives 50Ω resistive and 50Ω capacitive. This is the impedance that the transmitter must match. Line loss & multi-element matching The Smith Chart can be used to calculate line loss and also to facilitate the design of multi-element matching networks. A comprehensive guide to the use of Smith Charts can be found in the Sams publication “RF Circuit Design” by Chris Bo­wick. Good background material can also be SC found in the ARRL Antenna Handbook. 40MHz ESCORT EDM-1133 20MHz • • • • • • 3¾ Digits Autoranging 8 Functions DC V, AC V DC A, AC A Ohms Valued at $127! GOS-6100 GOS643 GOS622 4 Channels 2 Channels 2 Channels 100MHz BW 40MHz BW 20MHz BW 500uV - 5V/DIV 1mV - 5V/DIV 1mV - 5V/DIV Dual Timebase to 2ns/DIV Dual Timebase to 2ns/DIV Timebase to 2ns/DIV Dual Timebase Trig Audio Trigger Level Lock Audio Trigger Level Lock Variable Hold-Off Variable Hold-Off Variable Hold-Off 20kV Accel. Voltage 12kV Accel. Voltage 2.2kV Accel. Voltage EMONA INSTRUMENTS NSW (02) 519 3933 VIC (03) 889 0427 QLD (07) 397 7427 Also available from: WA (09) 244 2777 SA (08) 362 7548 TAS (003) 31 6533 June 1993  55 VINTAGE RADIO By JOHN HILL A look at high tension filtering Valve radios require a high tension DC power supply for the valve plates (anodes). This high tension supply is a frequent source of problems & must be carefully restored. Most mains-operated valve radios obtain high tension DC using a transformer and rectifier valve (usually fullwave). However, the DC output from such a setup has a high ripple cont­ent (at 100Hz from a full-wave rectifier) and must be filtered before it can be used to power a receiver. Inadequate filtering will produce a 100Hz hum in the audio output. While low levels of hum are tolerable, high levels are not and the hum must be suppressed as much as possible. High tension (HT) filtering can be achiev­ed in several ways and usually involves either chokes (inductors) or resistors, and electrolytic capacitors. Let’s take a look at some of the methods used. The most common high tension filtering arrangement used in prewar receivers is the filter choke type – see Fig.1. This filtering arrangement is very effective and leaves little to be desired. High tension supplies designed around a filter choke have quite low hum levels. The inductance of the filter choke opposes any change in current flow, whether this change be an increase or a decrease. High tension filter chokes come in two physical forms. Either the field coil of an electrodynamic loudspeaker can be used or it can be a separate unit This photo shows the field coil (inside metal housing) of an electrodynamic loudspeaker from the mid-1930s. The field coil played a dual role: (1) it was used as an electromagnet for the loudspeaker; & (2) it was used as a high tension filter choke. 56  Silicon Chip bolted to the chassis at some convenient place. This latter looks like a small transformer. In the first case, the cost of a choke is saved by making the field coil of the loudspeaker do double duty. A filter choke is nothing more than a large coil of fine copper wire wound on an iron core. In the case of a field coil, the iron core, when energised, becomes the speaker magnet. At the same time, the field coil filters the power supply current. Electrodynamic loudspeakers were used on most early AC receivers. Hum problems This arrangement does have one disadvantage, however. Be­cause the speaker field is being energised by only partially filtered current, a small amount of hum can be generated in the speaker itself. This was overcome by fitting the speaker with a “hum bucking coil” in series with the voice coil. It was magneti­cally coupled to the field coil and cancelled out most of the hum generated in this manner. Speakers using permanent magnets instead of a field coil were also available in pre-war sets. However, they required very large and expensive magnets, and were not very efficient. They were mainly used with batteryoperated sets. That situation changed after about 1948 when much more powerful magnets became available – as a result of wartime re­ search – and permanent magnet (permag) speakers were subsequently used in all types of receivers. Because a field coil was no longer used, these receivers required a separate high tension filter choke. Whether the filter choke is a speaker field coil or a separate unit, its function is much the same; it opposes any change in the current flowing through VINTAGE RADIO We are moving in February 1994 MORE SPACE! MORE STOCK! Radios, Valves, Books, Vintage Parts A selection of high tension filter chokes. These chokes perform the same function as a field coil in smoothing the high tension supply & are usually mounted at some convenient spot on the chas­sis. BOUGHT – SOLD – TRADED Send SSAE For Our Catalogue WANTED: Valves, Radios, etc. Purchased for CASH RESURRECTION RADIO Call in to our NEW showroom at: 242 Chapel Street (PO Box 2029), Prahran, Vic 3181. Phone: (03) 5104486; Fax (03) 529 5639 into a piece of equipment rather than added as an after­thought. Capacitor values Either a field coil, a choke or a resistor form the central com­ponent of most high tension filters. In conjunction with high voltage electrolytic capacitors, they provided adequate HT filter­ing for most valve radio receivers. it. Effective though it is in this role, it is not sufficient by itself. But when large electrolytic capacitors are connected from each end to ground, the result is a smooth DC current. Capacitors have the ability to store an electrical charge and this is their main role in a high tension filter. By taking on a charge when the rectifier voltage rises and giving up that charge when the voltage drops, capacitors supplement the filter choke constant-current action by tending to maintain a constant voltage. In some applications, where heavier DC currents are re­ quired, a second filter choke and an additional electrolytic capacitor can be added to produce an even smoother supply. As far as domestic radios of the four or five-valve Fig.1: a typical HT power supply for a valve radio receiver. In some circuits, a resistor is used instead of a choke or loudspeaker field coil. HT supplies are a common source of trouble. type are concerned, this extra filtering stage is unnecessary. It must be remembered that an additional choke will also lower the output voltage and thus needs to be de­signed The size of the electrolytics also has an effect on the effectiveness of the filter. Hum can often be reduced simply by installing larger capacitors, particularly on the output side. A larger output capacitor also gives better regulation. However, if one cares to check the valve specification manuals, recommended maximum capacitor values for the input side of the filter are usually listed for various rectifiers. It is inadvisable to fit larger than recommended capacitors in this position. The objection is the excessive peak current that these will draw through the rectifier. Large input capacitors should not normally be necessary for hum free results. If larger input capacitors do need to be fitted, limiting resistors should be added in series with the rectifier plates to protect the valve. The values of these resistors are usually listed in valve characteristics manuals. If a filter system incorporates a June 1993  57 These 20W wirewound resistors can dissipate quite a lot of heat and should be mounted well away from any heat-sensitive compon­ents. Note that the resistor on the left is adjustable. This receiver uses three parallel 1W resistors in its high tension filter. They are used in conjunction with two 24µF electrolytic capaci­tors to provide a wellfiltered HT rail for the valve anodes. speaker field coil, 8µF electrolytic filter capacitors would typically be used. Troubleshooting A distinct hum in an old receiver is very often the result of electrolytics losing their capacitance. Replacements will usually solve the problem. Another cause of hum could be the bypass capacitors across either of the grid bias (cathode) resis­tors. Electrolytics with electrical leakage problems are also a matter for concern, as they can have two effects on a high ten­sion filter. Leakage will not only lower the filter’s output voltage but will also overload the rectifier valve and shorten its life. However, the worst aspect of high tension leakage is the fact that it often overloads the 58  Silicon Chip choke itself and results in a burnt-out winding. By the 1950s, radio manufacture had become very competitive and more and more receivers where being made to a price rather than to specifications. As a result of this cost cutting, the overall number of parts in many receivers was reduced to a bare minimum. One of the components found to be dispensable, by care­ful circuit design, was the high tension filter choke. The choke was replaced with a resistor and larger electro­lytics used to keep hum at an acceptable level. Many of these sets have filter capacitors ranging from 16µF to 32µF. But the main trick with these designs was to take the high tension for the output valve directly from the input side of the filter. Since there is no amplification following this stage, the hum remained within acceptable limits. Only the current for the front end of the receiver passes through the remainder of the filter system. And, since this current is relatively small, it can be quite adequately filtered by the second electrolytic. The resistor is not a filter compon­ent as such but serves mainly to isolate the second electrolytic from the heavy current demands of the output stage, so that it serves only the front end. The resistor used in these filters is often made up of two or three carbon resistors connected in parallel, in order to provide an adequate wattage rating. Typically, the resistance varies from 1.5kΩ to 10kΩ and is rated at around 2-3W for small receivers. So while a high tension filter that uses a resistor may seem to be a crude alternative, it is reliable, effective and does have some good points. Filter systems employing resistors rarely gave trouble. Field coils and filter chokes, on the other hand, were common breakdown items and they could be costly to repair or replace. If a high tension short circuit causes a filter resistor to blow, it is both cheaper and easier to repair than a loudspeaker with a burnt out field coil. So its use makes a receiver a little more trouble-free over a long period. What’s more, most people would never know the difference when listening to it. Field coil substitution Using a resistor type filter system as a substitute for a choke system becomes a tempting proposition when a vintage radio repairer is faced with a serious loudspeaker problem. An open field coil is not the only thing that can go wrong with an old speaker, however. The speaker cone can be out of shape, split or completely in tatters. In such instances, the easiest way out is to fit a “permag” speaker. When doing so, a suitable substitute for the field coil/choke must be made and a resistor may be the logical way to go. Better still, a combination of choke and resistor can be used, provided they add up to the same DC resistance of whatever it is they are replacing. Some old radios draw a fair amount of current through the field coil and this needs to be taken into account when selecting a suitable resistor. A Possible faults If high tension current is excessive, it can be caused by a number of factors: (1) a faulty valve could be drawing too much current; (2) there could be electrical leakage through the high tension capacitor on the output side of the filter; or (3) the re­ceiver could have a grid bias problem whereby the output valve draws more plate current than it should. A defective coupling capacitor is a prime suspect with this particular problem. But whatever the cause, it needs to be corrected to avoid damaging expensive components. In summary, the high tension filter is an important part of any mains-powered valve receiver and it requires periodic maintenance to keep it in good working order. While the physical arrangement differs from set to set, they all serve the same func­tion –to produce a smooth DC supply. A ripple free high tension current is essential SC for hum free operation. SILICON CHIP BINDERS BUY A SUBSCRIPTION & GET A DISCOUNT ON THE BINDER (Aust. Only) These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers and are made from a dis­ tinctive 2-tone green vinyl that will look great on your bookshelf. ★ High quality. ★ Hold up to 14 issues (12 issues plus catalogs) ★ 80mm internal width. ★ SILICON CHIP logo printed in gold-coloured lettering on the    spine & cover. Yes! Please send me ________ SILICON CHIP binder(s) at $A14.95 each (incl. postage in Australia). NZ & PNG orders please add $5 each for postage. Not available elsewhere. Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date______/______ Name _____________________________________________________ Street _____________________________________________________ Suburb/town __________________________ Postcode______________ SILICON CHIP PUBLICATIONS PO Box 139, Collaroy, NSW 2097, Australia. Phone (02) 979 5644 Fax: (02) 979 6503. ✂ 1930’s set with six or seven valves can draw about 60mA of high tension current and this requires a high wattage wirewound resistor to handle the load. I prefer something with a 20W rating – one of those big hollow resistors with a brass core that can be bolted to the chassis. This convenient mounting method also helps the resistor to dissipate some of the heat, since the chassis can act as a heat­sink. Field coils and high tension chokes should not run hot. Their normal working temperature is moderately warm; hot is abnormal and indicates a fault somewhere. An average 5-valve receiver will draw approximately 50mA if it is operating correctly. If the current consumption exceeds that (eg, 60-65mA) there will be a considerable increase in the operating temperature of the central filter component, whether it be a choke, a field coil or a resistor. Overloads of this nature can eventually lead to the over-stressed component breaking down. Simply touching a field coil or choke after a half-hour operating period will give a reasonable indication of working temperature (but make sure that the receiver is unplugged first)! Connecting a milliammeter in the high tension line will give an accurate assessment without the half-hour wait. June 1993  59 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 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 Remote volume control for hifi systems; Pt.2 Remote volume controls are now common in commercial rack hifi systems but this design is far superior in its dynamic range, tracking and signal-to-noise ratio. This month, we describe the construction of the unit & show you to connect it to your hifi system. mitter is housed in a small plastic case which has a front panel label measuring 73 x 63mm. A PC board coded 01305933 and measuring 62 x 59mm clips inside this case. Five small plastic chrome buttons protrude through the front panel and are used to press down onto click action switches mounted on the PC board. Before starting construction, check all three PC boards for breaks in the copper tracks or shorts between tracks. Any defects should be repaired before proceeding further. Check that all holes have been correctly drilled also. links are straight to avoid shorts and note that the 27Ω 5W resistor must be mounted about 1mm above the board because it runs rather warm. The ICs can now be installed, taking care with the orienta­ tion of each device. We used a high quality machined pin socket for IC1 but we recommend you don’t use sockets for the remaining ICs as they will tend to prejudice the audio performance. Do not insert the microprocessor into its socket at this stage. Next, install the diodes, regulators and capacitors, taking care to ensure that all polarised components are correctly oriented. Note that the 4700µF and 330µF capacitors are mounted on their sides so that they don’t touch the lid of the case. Each 3-terminal regulator is bolted to the board with a screw and nut, while REG1 is also mounted on a small heatsink. The mating faces of the regulator and heatsink should be smear­ ed with heatsink compound during assembly. Finally mount the relay, switch S2, the ceramic resonator and the crystal. Main board assembly Display board Begin assembly of the main PC board (01305931) by install­ ing the PC stakes, wire links and resistors – see Fig.6. Make sure that all the wire You should follow the assembly details for the display board (01305932) carefully, since the method is unusual. Begin by installing the By JOHN CLARKE Building the Remote Volume Control involves the assembly of three PC boards, some metalwork and the internal wiring. To keep this article reasonably brief, we shall assume that you are building the project up from a kit which has a pre-punched case and screen printed panels. The Remote Volume Control receiver is housed in a 1-unit high rack mounting case. It uses two PC boards: a main board coded 01305931 and measuring 283 x 161mm; and a display board coded 01305932 and measuring 283 x 39mm. The screen printed front panel artwork measures 480 x 44mm, while the rear panel artwork measures 180 x 34mm. The front panel also incorporates a red Perspex window measuring 150 x 20mm, for the LED displays. The handheld remote control trans64  Silicon Chip Fig.6: install the parts on the main & display boards as shown here & use a socket for IC1. Note the two wire links (dotted) that run under the LED displays. IC1 is installed after the initial power supply checks have been made. June 1993  65 A 100pF 0.1 LED1 K 100pF X2 10uF .015 4.7k 27  5W K S5 6.8uF 47uF G 0.15 A 1 10uF 0.22 .0047 S3 10uF 22uF S4 D9 D10 270  10k 10k 0.1 REG1 7805 IC11 MV601 0.1 IC10 SL486 A 39pF X1 IC2 4511 1uF D11 D8 D7 D6 39pF 10k G IRD1 K 270  270  270  270  270  1 10k DISP1 270  270  10uF 1 IC3 4511 4.7M DISP2 1 270  DISP3 1 A 0.1 1 1 220pF 220pF DISP4 IC5 UCN2003 IC7 AD7112CN IC4 4511 IC1 MC68HC705C8P 270  4700uF 25VW 270  HEATSINK 47  0.1 270  270  270  270  270  REG2 7815 270  270  270  270  270  270  270  10uF 0.1 270  10uF 270  REG3 7915 270  10uF 270  330uF 25VW 270  D5 270W 470uF 1 1 0.1 1 0.1 IC9 OP27 0.1 0.1 IC8 OP27 IC6 ULN2003 270W 120  270W 120  270W D1-D4 K S2 RELAY 1 D12 10k 10k LED2 Fig.7 (left): this is the parts layout for the transmitter PC board. Be sure to orient the pushbutton switches exactly as shown & note that S1 & S4 face in the opposite direction to S3, S2 & S5. The two LEDs are mounted at full lead length – see text. LED1 K A K A Q1 2. 2  220uF 100pF 9V BATTERY 100pF 10  X1 1 LK1 LK2 S4 IC1 MV500 S5 10k S2 S3 Fig.8: the transmitter is encoded to match the receiver by installing links LK1 & LK2 on the copper side of the PC board. If necessary, the coding can be changed by installing different link options, as described in the text. S1 wire links on the board, then install three PC stakes from the copper side of the board at the A, K and GND locations adjacent to infrared diode IRD1. The three pushbutton switches (S3-S5) and the three 7-seg­ment LED displays mount onto pins to raise the level of these components by about 7mm. This is necessary so that the switches ultimately protrude through the front panel of the case, with the LED readouts just behind the Perspex window. We used machine pins from an IC socket for this job. They can be removed by pushing each one through from the underside of the socket using a pair of small pliers. Be sure to orient the switches correctly (ie, flat side of the switch to the left of the PC board, as shown in Fig.6). The infrared diode (IRD1) is mount­ ed with its leads at full length (don’t cut them short!) and bent at right angles so that its front face sits vertically. LED1 should be installed with just its anode lead soldered at present so that its height can be adjusted later – don’t cut its leads. Orient the 10-LED array (DISP4) with the anode leads (longer leads) to the left and set the array at the same height as the 7-segment displays. Mating the two boards The main board is butted to the back of the display board at right angles. It must be arranged so that its underside is 5mm above the bottom edge of the display board. How do you do this? First, support the main board upside down on a flat surface. The easiest way to do this is to fit long screws to the four mounting points on the board so that they become the supports. This done, stand the display board on its topside edge and butt it to the main board. Adjust their positions so that the display board has its edge 5mm above the copper side of the main board. When everything is correct, tack solder the two boards together at either end. Finally, check that the two boards are butted correctly and are at right angles before soldering the remaining tracks. Transmitter board The transmitter board should first be tested for fit into the base of the handheld case. Check that the clips hold the board correctly and that the alignment pin on the base of the case CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC code EIA code 0.22µF 220n 224 0.15µF 150n 154 0.1µF 100n 104 0.015µF   15n 153 .0047µF   4n7 472 220pF 220p 221 100pF 100p 101 39pF   39p   39 RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   7 ❏   1 ❏ 32 ❏   1 ❏   1 ❏   1 66  Silicon Chip Value 4.7MΩ 10kΩ 4.7k 330Ω 47Ω 10Ω 2.2Ω 4-Band (1%) Code yellow violet green brown brown black orange brown yellow violet red brown orange orange brown brown yellow violet black brown brown black black brown red red gold brown 5-Band Code (1%) yellow violet black orange brown brown black black red brown yellow violet black brown brown orange orange black black brown yellow violet black gold brown brown black black gold brown red red black silver brown The two PC boards in the receiver are soldered together at right angles & mounted on the base of the chassis on 5mm spacers. Check that the three momentary-contact switches operate smoothly when the front panel is bolted into position & adjust them if necessary. passes through the hole in the centre of the PC board. If the PC board is too long, it will need to be filed down to size. Once the PC board clips properly into the case, snip off the top of the plastic alignment pin with a pair of sidecutters so that it is flush with the top of the PC board. This will allow the IC to sit over the alignment pin. Begin the assembly by installing the IC, the link and the resistors – see Fig.7. This done, install PC stakes for the battery connections, then install the two 100pF capacitors and the ceramic resonator. The 220µF electrolytic capacitor must be mounted on its side as shown in Fig.7. Each pushbutton switch S1-S5 should be mounted with its flat side oriented as shown on the layout diagram. Transistor Q1 is mounted with its leads bent at right angles and is bolted to the PC board using a screw and nut. The two LEDs are mounted without shortening their leads, so that they can sit on the plastic cup rests at the front of the case. Finally, you need to install links LK1 and LK2. These set the data rate of the transmitter to match the data rate set for IC11 in the receiver circuit. LK1 and LK2 tie pins 14 & 15 of IC1 high and are installed on the copper side of the PC board – see Fig.8 (note: this coding can be changed if necessary, as described later). When the assembly is completed, clip the board into the case and bend the LED leads so that they sit on the plastic cup rests. This done, pass the battery clip leads through from the battery compartment and connect them The transmitter switches are activated by chromed plastic buttons which pass through the front panel of the case. Each button is modified by gluing it to a second chrome button mounted side on. June 1993  67 the top. Finally, check that the buttons activate the switches properly. Receiver chassis The three pushbutton switches (S3-S5) and the 7-seg­ment LED displays are mounted on IC socket pins so that they sit about 7mm above the board surface. This is necessary so that the switches ultimately protrude through the front panel of the case, with the LED readouts just behind the Perspex window. Although optional, a black cardboard mask can be fitted to prevent light leakage around the LED displays. The viewing window for the 7-segment readouts is fitted with a plastic filter to improve display contrast. to the PC board, taking care to ensure correct polarity. Check that switch S3 clears the side of a plastic bush in the base of the case. If necessary, this bush can be shaved down with a sharp knife. As mentioned previously, the switches on the PC board are activated by chromed plastic buttons which pass through the front panel of the case. To prevent excessive play between the base of the chrome buttons and the top of the switches 68  Silicon Chip on the board, the base of each button is shimmed up with a second chrome button mounted side on. Use super­ glue to glue the buttons together (see photo) and file down the side lobes on the shim piece. The front panel label can now be affixed to the transmitter case and a sharp knife used to make the rectangular cutouts for the chrome buttons. This done, load the five chrome buttons through the back of the case lid, then clip the lower case assem­bly over Work can now begin on the receiver chassis. Assuming that the chassis holes are pre-drilled, you can secure the side and rear panels to the base­ plate but leave the front panel off at this stage. Next, mount the RCA sockets, switch S6, solder lug and fuseholder F1 on the rear panel and install the mains cable. The transformer, earth lug, terminal block and PC board assembly can then be mounted on the baseplate (mount the board assembly on 5mm spacers). The front panel can now be secured to the baseplate and the power switch installed. Check that the Mute, Down, Up and Tape Monitor switches operate smoothly in the front panel cutouts. If the click action switches foul the front panel they can be ad­justed by removing the panel and pushing the switches to one side. To simplify the wiring procedure, we have produced a sepa­rate diagram of the whole chassis – see Fig.9. Be sure to use 250VAC-rated cable for the wiring to the mains switch (S1), mains terminal block and the transformer primary. Insulating sleev­ ing (eg, heatshrink tubing) should be used to cover the bare terminals of the fuse and mains switch, to prevent accidental contact. Don’t forget to solder the .0047µF 250VAC capacitor across the mains switch. The green/yellow earth wire is connected to an earth lug terminal on the base of the chassis. Make sure that this terminal is properly connected to chassis by scraping away the paint or anodising from the surrounding area of the hole. Once this termi­nal is secured with a screw, nut and spring washer, measure the resistance between the chassis and earth terminal to ensure that it is indeed a good connection – the meter should read 0Ω. Similarly, the earth terminal at the ▲ Fig.9 (right): be sure to use mainsrated cable for all the mains wiring & sleeve all exposed wiring with heatshrink tubing to eliminate the possibility of electric shock. The remainder of the wiring (except to S6) is run using shielded cable. June 1993  69 The transmitter case was sprayed black to match the receiver chassis. Check that the acknowledge LED on the receiver comes on each time one of the buttons on the remote control is pressed. Now check the operation of the remote control. The ACK (acknowledge) LED on the receiver should light when one of the remote control switches is pressed. Check that the Up, Down and Mute switches operate the receiver displays correctly. Note that you can control the balance only when the receiver is unmuted. Note also that the balance display can show two LEDs lit at the same time. If the balance setting is 0dB, 3dB, 6dB or 9dB, only one LED will be lit but for in-between settings, such as 4.5dB or 7.5dB, two LEDs will be lit. Connecting it to your hifi rear of the chassis should make a 0Ω connection to the rear panel. Check also that the rear panel is electrically connected to the chassis by again measuring the resistance between them with your multimeter. If not, you may need to remove paint from around some of the screw holes for the various panels. The mains wiring should be neatly anchored with plastic cable ties. This not only makes it look tidy but also stops the wiring from coming adrift. All of the signal wiring is run using shielded cable. Use a short length of twin shielded cable for the wiring from the infrared detector (IRD1) on the display board to IC10 on the main board. Twin shielded cable is also used between the INPUT sockets and the TAPE OUT sockets. Use single shielded cable for the remaining audio wiring and use plastic ties to anchor the wires in place. Testing Before applying power to the unit, check your wiring care­fully. Note that the microprocessor, IC1, should not be installed just yet. Now apply power and check that the +5V supply rail is between +4.75 and +5.25V. If not, switch off the power and locate the problem before switching on again. Check that +15V is present at pin 7 of IC8 & IC9 and that -15V is present 70  Silicon Chip at pin 4 of IC8 & IC9. Check that +5V is present at pins 1, 3, 37 & 40 of IC1’s socket; at pins 3, 4, & 16 of ICs 2, 3 & 4; at pin 7 of IC7; at pins 4 & 7 of IC10; and at pins 5 & 16 of IC11. If everything is correct, switch off and install IC1. Make sure that IC1 is correctly oriented, then apply power. The LED display should show 48.0 and the balance LEDs should all be lit. If so, press the Mute control to check that all the balance LEDs except the 0dB LED extinguish. If everything is working correctly, pressing the Up and Down switches should alter the attenuation display in 1.5dB steps. Note that pressing the Up switch will decrease the atten­uation reading while pressing the Down switch will increase the attenuation reading. Where to buy the microprocessor The coded 68HC705C8P microprocessor will be available only from SILICON CHIP magazine and is priced at $45 including sales tax. For postage and packing to anywhere within Australia, please add $6.00. Payment may be made via cheque, postal money order or credit card authorisation (Bank­ card, Visa and Mastercard). When all checks are done, you are ready to connect the unit to your hifi system. If you have a separate preamplifier and power amplifier, the Remote Volume Control is connected between the two. If you have an integrated amplifier, the Remote Volume Control is wired into the Tape Monitor loop. The Remote Volume Control has its own tape monitor loop to replicate the loop on the amplifier. Switch on your hifi system and check that the volume and balance are adjustable via the handheld remote control. You will need to turn up the volume control on your integrated amplifier or preamplifier to the maximum to obtain the full volume range from the remote control. With the volume setting advanced and no signal present, check the noise level from your loudspeakers. It should be no more than the noise level from your system without the remote control in circuit. If you have a low level hum, try the “earth” or “float” settings of the rear panel switch (S6). This has been included to cope with systems which are earthed or double insu­lated. Finally, we should comment on the transmitter and receiver coding. We have presented only one coding option and we do not anticipate that it will be necessary to change it. However, if you do encounter interference from other IR remote controls, try changing the coding using different link options. For example, you could install either LK1 or LK2 (but not both) on the receiver board (see Fig.4) and change the transmitter coding to match (eg, if LK1 is installed in the receiver, install LK2 & LK3 on the SC transmitter (see Fig.5). COMPUTER BITS BY DARREN YATES Double your disc space with DOS 6 Microsoft has just released its new DOS 6 upgrade pack­age. We take a look at some of its major features which include anti-virus & disc defragmenting utilities, plus a utility to double disc capacity. By now, most readers will have heard about the recent launch of Microsoft’s new DOS 6. If you talk to the average computer store assistant, they’ll quickly tell you that “it doubles your hard disc space”. And they’re right too but it’s much more versatile than just a glorified copy of PKZIP or LHARC. The odds are that you’re probably hanging back from buying the DOS 6 upgrade because it isn’t that long ago that DOS 5 appeared. You’d be right but these days the average life expectancy of any software package is only around 18 months or so. So to sweeten the pot, Microsoft is selling the new DOS 6 upgrade for only $99 until June 30th. From then on, you’ll have to pay $199. Either way, you will get your money’s worth. There are many features in this new version of DOS which take care of some of the little quirky jobs that use to take forever to do, as well as some major additions. For example, have you ever tried deleting a program stored on multiple sub-directories on a hard disc? In short, it’s pain­ful! You have to clear File backups can now be made from within Windows, with easy-to-follow menus to guide you every step of the way. In addition to doing complete backups, you can now also do incremental & differential backups to save time. each subdirectory before you can delete it and if you have sub-directories within sub-directories, it’s enough to make you keel over with boredom. In DOS 6, this problem has been solved with DELTREE, a simple command which deletes all files and sub-directories from a specified point. You can now also move files around your hard discs and floppies much easier as well, instead of having to copy and then delete. The MOVE command works in a similar way to the COPY command except that the files no longer exist in the origi­nal position. And for something different, DOS 6 has three utilities which can be run from either DOS or in Windows – a virus checker, a backup utility and the highly useful undelete utility. Anti-virus The risk of a virus affecting a computer system or network is now all too real. At best, a virus will be of nuisance value only. At worst, it can destroy valuable data and cost many thou­sands of dollars. Microsoft has addressed this problem by including a utility called Anti-Virus, which detects and removes over 800 different viruses. What’s more, you can run it either from the DOS prompt or from within Windows. This is a handy feature because if you’re running Windows applications, you don’t want to have to exit right out of Windows just to scan a floppy disc and then have to go all the way back in again. The same applies for DOS applications. Who wants to wait for Windows to boot up just to scan a drive? The anti-virus utility used by Micro­ soft is licensed from Central Point Software and uses dialog boxes to make it easy to follow. You can get two anti-virus updates for $67.80 by June 1993  71 some added protection to greatly improve the likelihood of recovery. It contains two extra levels of delete protection called Delete Sentry and Delete Tracker. Delete Sentry, the highest level of protection, is able to retrieve just about any file without difficulty by preventing other files from being written over the top of it. This requires some memory and hard disc space to run. Delete Tracker, the next level down, can retrieve most files but there may be the possibility that some data in the file may be lost, if you do accidentally delete it. Disc Defragmenting The front & back covers of the DOS 6 Upgrade manual feature a “road map” that illustrates many of the program’s new features. You can use the program to automatically free up memory, recover files, detect viruses, defragment the disc, double disc capacity & to easily back up data. filling in and mailing a coupon at the back of the manual. Backup Remember the less-than-helpful BACKUP command? Well, it’s now been updated it into a far more friendly utility with more features and includes both Windows and DOS versions. Instead of having to backup either the entire hard disc or just the odd-subdirectory, you can now also do incremental and differential backups. An incremental backup backs up only those files that were changed since the last full or incremental backup. This makes it a quick and easy option to save important data. A differential backup, on the other hand, saves those files that have been 72  Silicon Chip changed since your last full backup. The BACKUP utility supports any drive you can copy files to, including removable drives and “flopticals”. It also features, at last, a complete online help system to get you going in the shortest possible time. Undelete There are few feelings worse than the one you get two seconds after you’ve wiped out the last three weeks’ work. Thank­fully, DOS 5 had the life-saving UNDELETE command which made it possible to retrieve just about any file – but it wasn’t perfect. On the odd occasion, some data in files could be lost due to the fragmented nature of the file. The new UNDELETE utility contains DEFRAG is another useful utility and is based on Norton Utilities’ Speedisk program. It’s reorganises files on your hard disc so that they are no longer fragmented (ie, stored as frag­ments at different locations on the disc). This can significantly increase the speed at which your computer loads files from your hard disc since it doesn’t have to spend half its time going from one location to another to find the next section of the file. While running, the program provides an on-screen display of what is happening to your hard disc, as files are shuffled from one place to another. It’s quite fascinating to watch as frag­ments of the hard disc are removed at random and shifted to sequentially fill the disc space, leaving an unfilled block as the remainder. And even if it doesn’t make a big difference to the speed at which your system works, it’s a nice feeling to know that your hard disc is “all neat and tidy”. DoubleSpace By far the most interesting feature of DOS 6 is its ability to double your disc storage space. But it doesn’t just work with hard discs – you can also use it with floppy discs (not 360Kb). DoubleSpace is a feature-packed program which can not only double the size of your entire disc drive but can be also create logical compressed drives from the space you have left. For example, say you have 30Mb of space left on your hard drive. You can select the program to create a new drive and leave you 10Mb of space on that drive. It will then create a drive I: As with Backup, the Undelete utility can be run from within Windows to make file recovery a convenient point & click operation. This utility has also been upgraded to greatly improve the likelihood of data recovery by including two extra levels of delete protection. from the 20Mb remaining and this will have 40Mb of storage space. It can also compress an entire drive, even if it already has files on it. The beauty of the system is that once compression has taken place, you can use the drive as normal. You don’t have to go through the DoubleSpace program each time you wish to access the drive. Once installed, DoubleSpace becomes part of the AUTOEXEC.BAT file and automatically loads each time you boot up. You can then copy to and take files from the compressed drive as normal – it all takes place in the background. A custom set-up procedure allows you to set up DoubleSpace as you wish, including changing the compression ratio of a disc. You can go from 1:1 up to a compression ratio of 16 times. DoubleSpace will try to compress all files at your desired ratio but will ultimately compress files at its own maximum rate. The only trick is that the space available on a compressed drive is only an estimate. DoubleSpace cannot detect how much memory a file takes until it compresses it and since all files compress differently, it cannot really know the exact amount of space remaining. On-line help If you’re not used to computers at all, the worst thing is sitting in front of a PC with the cursor madly blinking at the DOS prompt. The first instinctive action many people try to take is to frantically bash out “HELP” on the keyboard. In earlier versions of DOS, all you would end up with is the old “Bad command or file name”. By contrast DOS 6 comes with an on-line help system which gives clues and information on over 120 related DOS commands. So even if you’re not exactly sure what it is you’re looking for, you’ll probably find it without too much effort. You can also find help on any topic by just typing “HELP <command>”. For example, if you want to know more about DELTREE, you just type HELP DELTREE <enter> at the DOS prompt. What could be easier? Laptops With the ever-growing laptop computer market, DOS 6 also provides a couple of useful and unusual utilities to benefit these machines. First, Inter­ link provides a simple and effective way of transferring data from one computer to another. You no longer need floppy discs to transfer files (many of which won’t fit on one floppy disc anyway). You can use either parallel or serial ports to transfer data, but they must be the same on each comp­ut­er. You can even run a program on one machine and access data on the other. Using a client-server technique, a “client” laptop computer can be configured so that it can look not only at its own drives but instantly access those of the “server” desktop machine as well. The other useful utility is called POWER. This unusual program can actually save you up to 25% in power usage when applications and hardware devices are in idle mode, by closing then down. The only catch is that the hardware devices must match the Advanced Power Management (APM) specifications. If they don’t, you can still get about a 5% benefit out of it. The program is loaded as part of your CONFIG.SYS file as a driver which can be loaded into either high or low memory. MemMaker If you’re finding that you’re running out of conventional memory space for some of your programs, then MemMaker will be a welcome utility. It checks through your system and determines what device drivers can be loaded into the high memory area. It does everything automatically without you having to know any technical details at all. After it’s completed, it automatically sets up your machine to boot up with these new settings. We tried it on a workhorse 386 and it managed to boost the free conventional memory space from 601Kb to 626Kb. This may not sound like much but many programs fail to run because of a lack of conventional memory and anything that helps to create more space is worthwhile. At the end, it even gives you a table to show what the memory situation was before and after you ran MemMaker. If you’re not happy with what it’s done, you can easily abandon any changes made and return to your old configuration. Conclusion Well, there are still more features such as enhanced SMART­drive drivers and diagnostic programs but we may look at these another time. DOS 6 is well worth getting and at the bargain price of only $99, you would be silly to wait until after June 30th. You can buy it at virtually any softSC ware supplier. June 1993  73 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 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 REMOTE CONTROL BY BOB YOUNG Unmanned aircraf t – the early developments As discussed last month, the development of unmanned aircraft goes as far back as the 1890s but the first really serious attempts were made by the British in 1917 in designing aerial targets (ATs). These early attempts were monu­mentally unsuccessful. In America, the Army and Navy undertook “Aerial Torpedo” programs, both using the principle of the Sperry Gyroscope to control the UMA (unmanned aircraft) by autopilot rath­er than remote piloting by radio. This early development of the autopilot technique was to stay with UMAs and in most cases the radio control inputs are fed to the controls via the what little data is sent to the UMA does arrive safely. Such techniques as frequency hopping, high speed transmission of data, digital encoded transmissions and many more exotic techniques are employed in an effort to make the control link secure. As we have already noted, these techniques are very effective, as the sur­vival rate of these little vehicles is RAE (Royal Aircraft Establishment) achieved the launch and stability breakthrough that led to the decision to develop the Larynx (Long-Range Gun with Lynx Engine). This UMA, though its warhead trials were a failure, was way ahead of anything flown elsewhere. The modern miniature warheads developed for missiles and RPVs are a real work of art (if killing people can be considered an art form) and show the absolute genius humans can bring to bear on the development of systems of destruction. Some of these warheads are quite tiny in terms of explosive force and one to five kilograms of explosives is quite typical. The trick is to make this charge do the work of a much bigger bomb. The spring technique “The concept of the attack drone resurfaced at the outbreak of World War II. The best remembered examples were perhaps the German V1 and the Misteln, a piggy-back composite aircraft” autopilot, with the autopilot remaining the primary means of stability and con­trol. There are many reasons for this, the most important being that the UMA then becomes an autonomous vehicle and is relatively immune to jamming. If a radio link were required for stability via the pilot back at base, interference could easily bring the bird down. As it is, radio designers go to incredible lengths to make sure that 80  Silicon Chip now very high. However, when flown in 1918, the Navy-Curtiss autopilot controlled design was no more successful than the British ATs. Only one of the 12 built worked properly. The Army “BUG”, de­signed and built by Dayton-Wright, was more successful but the need for such weapons evaporated with the ending of hostilities in 1918. Development work was recommenced in the early 1920s and the One very effective technique is to place the charge inside a tightly compressed spring. When the charge explodes, this spring opens out into many broken, but quite long pieces which are capable of cutting the wing off an aircraft or doing equally serious damage to other parts of the airframe. It must be remem­bered here that modern aircraft are so fully packed that it is almost impossible to put a piece of shrapnel through them without damaging something, thus rendering the aircraft unserviceable even if it does get home. A friend of mine once saw the results of an accidental missile strike on a warship. He told me that one of these spring fragments went through the side of the steel super­structure and left a zig-zag cut as clean as a whistle. Aircraft are not made of steel plate. Obviously much progress has been made in warhead design since 1925. AUSTRALIAN MADE TV TEST EQUIPMENT Battleship vulnerability 12 Months Warranty on Parts & Labour The real impetus for UMA development came as a result of General “Billy” Mitchell’s demonstration of the vulnerability of battleships to aerial bombardment. Nav­ ies around the world sat bolt upright at the news that a single aircraft had sunk a bat­tleship. This was shape the Pacific war, with the Japanese whole­heartedly adopting the methods advocated by Mitchell and develop­ing carrier-based bombers and torpedo aircraft. As a result of the Mitchell trials and the success of the Larynx system, the RAE modified three Fairy IIIF floatplanes into Fairy Queen radio controlled targets, to test the ability of Royal Navy gunners. Off Gibralter in January 1933, one of these flew for two hours through concentrated AA fire from the Home Fleet which failed to register a single hit. Without further ado, the Air Ministry issued Specification 18/33 for a dedicated radio-controlled target, which resulted in the de Havilland Queen Bee. Thus, the UMA came of age. More than 400 of this Moth Major/Tiger Moth hybrid, the world’s first mass produced target drone, were eventually built. SHORTED TURNS TESTER “Other UMA experiments involved aircraft as large as the B-17 (Flying Fortress) and PB4Y 4-engined bombers, primarily as explosiveladen, expendable UMAs” Built-in meter to check EHT transformers including split diode type, yokes and drive transformers. $95.00 + $4.00 p&p HIGH-VOLTAGE PROBE Built-in meter reads positive or negative 0-50kV. For checking EHT & focus as well as many other high tension voltages. $120.00 + $5.00 p&p DEGAUSSING WAND Great for computer mon­­­it­ors. Strong magnetic field. Double insulated, momentary switch operation. Demagnetises colour picture tubes, colour computer monitors, poker machines video and audio tapes. 240V AC 2.2 amps, 7700AT. $85.00 + $10.00 p&p TUNER REPAIRS From $22. Repair or exchange plus p&p. Cheque, Money Order, Visa, Bankcard or Mastercard TUNERS 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone for free product list Phone (02) 774 1154 Fax (02) 774 1154 The USN tested its own version of an aerial target with similar dismal results (for the gunners). However the first US targets were not ordered in quantity by the Army Air Force until 1940 and by the Navy in 1942. Interestingly enough, these were provided by Radioplane, a small company founded in 1939 by the Hollywood actor, Reginald Denny. Denny began experimenting with radio-controlled model aircraft in 1935 and Radioplane was estab­lished to commercially develop R/C models. Radioplane ultimately became the Ventura division of North­rop, the world’s largest producer of target aircraft. The concept of the attack drone resurfaced at the outbreak of World War II. The best remembered examples were perhaps the German V1 and the Misteln, a piggy-back composite aircraft. Misteln was comprised of a bomber carrying a radio-controlled fighter to the target. The fighter was launched and guided to the target from the bomber. Less well known was the American Interstate TDR-1, an ex­pendable UMA with a 2,000lb (907kg) warhead which was used with some success, albeit briefly, in the Russell Islands campaign in Autumn 1944. It was guided by a Grumman Avenger mothership and of the 46 launched, 29 reached the target and 21 scored direct hits or near misses. Other UMA experiments involved aircraft as large as June 1993  81 REMOTE CONTROL – CTD the B-17 (Flying Fortress) and PB4Y 4-engined bombers, primarily as explosive-laden, expendable UMAs. The above aircraft, whilst strictly defined as unmanned aircraft, fall more towards the definition of primitive guided weapons or missiles and serve to illustrate the fine distinction between what constitutes a guided missile and an expendable UMA. Post-war, the acquisition of German control and guidance technology was channelled with enthusiasm into the development of guided missiles. A residual of this enthusiasm trickled down into the UMA area, mainly in Wagner’s “Lightning Bugs and other Reconnaissance Drones”. As pointed out in last month’s story, the recovery rate of these vehicles was remarkable and from the 3,435 sorties undertaken in Vietnam during the years 1964-1975, the bird re­turned home in more than 83% of cases. This was to improve with the development of more sophisticated technology to a final figure of well over 90% in the last four years of that war. Nor was this recovery rate the result of ineffective AA fire or missile firings by the North Vietnamese. From the early 1960s to 1971, the Ryan “The real hub of activity in the RPV field has proven to be the Middle East, with the Israelis being the leading exponents in the design & development of such vehicles” the belief in the UMA as a target with perhaps a grudging acknowledgement of their potential as reconnaissance aircraft. Thus we saw a very limited use of radio controlled F6F Hellcats during the Korean War and a reversion to the belief that the only real role for the UMA was in the target field. Then suddenly, the Cuban Missile crisis changed all of that. In 1962, a Cuban SAM (Surface to Air Missile) brought down an American U-2 reconnaissance aircraft with the loss of its pilot and interest was suddenly focused on the UMA as a reconnaissance vehicle. The result was the development of the Teledyne Ryan 147 (alias AQM-34). Vietnam The story of how this “Son of Firebee” eventually grew from the original BQM-34 target drone into a huge family of multi-capable un-manned aircraft is a part of UMA folk-lore. They were used for high, low and medium-altitude photographic and video reconnaissance, ECM (electronic countermeasures), decoy, leaflet-dropping and damage assessment missions during the Vietnam War. This was brilliantly told in William 82  Silicon Chip 147s were also used for reconnaissance flights over mainland China and it was unofficially reported that up to 20 MIG fighters made between 30 to 50 passes at the first of these before bringing it down. China’s own Chang Hong 1 began life as a reverse engineered Ryan 147 and is still in service today. With the ending of the Vietnamese War, the Ryan 147 had demonstrated conclusively that RPVs (the new “in” term for UMAs) could deliver the goods, were eminently survivable, put no human crew at risk and were an order of magnitude cheaper than manned vehicles. Despite that, the interest in RPVs dropped back to an almost non-existent level in the USA, despite a plethora of hopeful new designs from a defence industry which believed it had a discovered a new bandwagon on which to climb. The one notorious exception was the US Army’s Aquila project which developed into a textbook example of how not to procure a cheap and effective operational system. Thus, the Aquila grew from a small 54.4kg vehicle capable of carrying a 13.6kg payload for 1.5 hours into a vehicle capable of tasks which includ- ed communications relay, weath­ er reconnais­ sance and electronic warfare, as well as a myriad of other func­ tions. Weight grew to 120kg (gross) with a 25kg payload and an endurance of well over 3 hours. Added to this was a stealth exterior. The final cost of this project blew out from an original estimate of US$250,000 per unit to over US$1,000,000 per unit, hardly a low cost, throw away item. Still, it is considerably cheaper than a $40,000,000 manned aircraft and the life of the pilot is not at risk. Sadly, the project was cancelled in 1989 as being too expensive after some 15 years of development and test­ing. In fairness to the above project, much of the confusion which was to result in the high final cost was brought about by a constant moving of the goal posts. This problem of constantly changing the final aims of any project is the bane of the engineer’s life and goes on in all fields of technological endeavour. Once the top brass issue the latest decree, they tend to forget all that has gone on before and the engineering department carries the can when the cost and time overruns come in. Middle East activity The real hub of activity in the PRV field has proven to be the Middle East, with the Israelis being far and away the leading exponents in the deployment of such vehicles. The first RPVs to appear there were about a dozen Ryan 124-Is acquired by Israel in 1972-73 as decoy drones and high altitude photographic reconnaissance vehicles. A number of Northrop BQM-74 Chukar targets were also converted by Israel for decoy use, both types proving their worth during the Yom Kippur War. From that point on, Israel was sold on the value of RPVs, to the point where that country is now demonstrably this leader in the field. Yet the beginnings of the home-grown Israeli RPV industry could hardly have been more modest. It is said that the most expensive single item in the first domestic RPV prototype was a $600 Sony TV camera, whilst the launching platform was the roof rack on the designer’s car. Next month, we’ll look at the role of the RPV in the Middle Eastern wars of SC the past 20 years. PRODUCT SHOWCASE Philips radio test generator The new PM 5330 radio test generator from Philips Test & Measurements can meet a wide range of testing requirements at frequencies from 100kHz to 180MHz. It offers a sweep facility together with programmable AM and FM, variable output levels and optional RDS/ARI functions and FM stereo modulation. An FM stereo option provides both stereo multiplex and RF-modulated signals. In the FM stereo mode, both internal and external modulation can be applied over a 20Hz to 15kHz frequency range, with selectable 50µs or 75µs pre-emphasis and a choice of stereo and left or right channel only signals. Both internal AM and FM modulation are programmable between 20Hz and 20kHz, or can be applied from external sources. The sweep function is ideal for checking filters, and offers ten calibrated sweep widths from 10kHz to 10MHz, with a clear indication of the centre frequency by a dot marker on the display. The lower sweep width of 10kHz and slow sweep are intended for narrow bandpass testing such as in SSB applications. The PM 5330 has been designed for very simple operation. A large backlit LCD display shows all parameter and function settings while conventional multiple pushbuttons are replaced by a large multifunction rotary control, with a limited number of keys for mode 0-30V power supply has adjustable current In the past if you wanted an economically priced power supply with a reasonable voltage range, there was only one solution – you built it yourself. That option is still available and indeed is still often the only way for more powerful units. However, this solidly built power supply is available at quite an attractive. It has fine and coarse voltage adjustment controls to give zero to 30V DC output as well as adjusta- ble output current limit anywhere from zero to 3 amps. A green LED shows when the supply is in "constant voltage" mode and when the and parameter selections. Setting of parameters can be done by direct entry of the desired values at the numeric keypad, incrementing/decrementing a displayed value using the rotary control, or using the variable-resolution up/down step adjustment function, which allows increments as small as 10Hz for frequency and 0.1dB for output level. The optional RS232 or IEEE-488 interfaces allow the PM 5330 to be used in remote-controlled test systems. The IEEE-488 interface allows the generator to be integrated into automated GPIB measurement systems, while the RS232 interface provides a cost-effective solution for "standalone" automation. Both interfaces allow full remote programming, with facilities for downloading of user-defined test and test routines. The PM unit also has a built-in frequency counter with a range of 10Hz to 200MHz with a 5½-digit display. For further information, contact Philips Test & Measurement, 34 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 8222. AM486 microprocessors now available Advanced Micro Devices has announced it has begun shipments of current limit cuts in, the green LED goes out and a red LED comes on to indicate "constant current" mode. Load regulation is quite good at around 2% or better and hum and noise output is typically less than 1mV peak-peak at all settings. Overall dimensions of the supply are 178mm wide, 148mm high and 310mm deep, including knobs and rear heatsink. Mass is 5.5kg and unit comes with a detachable 3-core flex and IEC female plug. Priced at just $279, the power supply is available from all Jaycar Electronics stores (Cat No MP-3090). June 1993  83 Neat & nifty tool kit This neat little tool wallet has been made up to meet the needs of students doing electronics courses, after consultation with TAFE colleges. It comprises a pair of side-cutters, long-nose pliers, adjustable wire strippers, tweezers, Phillips and straight bladed screw drivers, utility knife and a pair of jewellers screwdrivers with 2mm Phillips and straight blades. The whole lot is housed in a well made zippered vinyl case. The price is attractive too, just $30 including sales tax. The toolkit its AM486 microprocessors. These include 33MHz, 40MHz, and clock-doubled 50MHz 486 DX devices. Developed using the same design methodology as the AM386 microprocessor family, AM486 devices announced are compatible, plug-in replacements for 486DX products currently used in IBM-compatible personal computers. The AM486 microprocessor family also is compatible with the existing base of software applications used in millions of PCs in service worldwide. Initial members of the AM486 microprocessor family incorporate Intel microcode. AMD will continue development of its "clean room" microcode in order to achieve technological independence. Volume production of the AM486DXLV microprocessor, designed to offer the rapidly growing mobile computing market high performance and low power consumption of longer is on sale from All Electronic Components, 118-122 Lonsdale Street, Melbourne, Vic 3000. Phone (03) 662 3506. battery life, will begin in July. The 3.3V AM486DXLV device will be offered at no price premium over the standard 5V product. For further information, contact VSI Promark Electronics, 16 Dickson Ave, Artarmon, NSW 2064. Phone (02) 439 4655. New monitors from Mitsubishi Electric Mitsubishi Electric has announced a range of new high performance computer monitors that exceed world health and safety standards and are backed by a 3-year warranty. The company has also announced a $1000 trade-in on any computer monitor against a new Mitsubishi Electric Diamond 17-inch or 20-inch monitor. The new Mitsubishi 17-inch and 20-inch colour models incorporate dynamic beam focusing for crisp edge- VIDEO & TV SERVICE PERSONNEL TV & VIDEO FAULT LIBRARIES AVAILABLE AS PRINTED MANUALS $90 EACH + $10 DELIVERY BOTH MANUALS VIDEO & TV $155 + $15 DELIVERY OR AS A PROGRAM FOR IBM COMPATIBLES $155 + $10 DELIVERY FOR MORE INFORMATION CONTACT TECHNICAL APPLICATIONS FAX / PHONE (07) 378 1064 PO BOX 137 KENMORE 4069 84  Silicon Chip to-edge displays, anti-glare screen coating and a wide auto-scanning horizontal frequency range. The new monitors also incorporate high refresh rate capabilities for flicker-free displays and a Mitsubishi Diamond Match Colour Calibration System that enables users to set up, on screen, colour parameters to precisely match hard copy output or Pantone colours for desktop publishing applications. For further information, contact Richard Allen, Mitsubishi Electric Australia, 348 Victoria Rd, Rydalmere, NSW 2116. Phone (02) 684 7200. Complete stereo preamp with midrange control This well made PC board assembly has all the circuitry for a simple stereo control unit. It includes a phono preamplifier with RIAA compensation for a magnetic cartridge and a tone control stage with treble, midrange and bass controls. There is provision for a loudness switch and a tone defeat switch. Phono sensitivity is quoted as 2.5mV at 1kHz for 1V output while line sensitivity is 100mV for 1V output. Harmonic distortion is quoted as .005% at rated output. Bass and treble Prizes awarded for birthday celebration On March 17th, some of the NSW prize winners and sponsors gathered for a presentation at the Pasadena Restaurant on Sydney's Pittwater. The Ford Festiva was awarded along with prizes from Jaycar Electronics, Philips Test & Measurement, A-One Electronics. Av- Wim Jonganeelen and his wife came down from Bargo to be presented with their new Ford Festiva hatchback. (car courtesy of Titan Ford, Brookvale.) boost is ±10dB at 50Hz and 15kHz respectively while midrange boost and cut is ±5dB at 1kHz. The assembled board comes with a single instruction sheet with a circuit diagram showing how the unit would be wired to provide input selection, tape monitor switch and a suitable power supply. The circuit shows the quad op amps as being TL084s or 074s but the sample board was fitted with TL074s which are preferable because of their lower noise figure. Neatly packaged in clear plastic, the complete board (Cat S0307) is available from A-One Electronics Pty Ltd, 432-434 Kent St, Sydney, NSW 2000. Phone (02) 267 4829. Tektronix TDS 820 scope now with FFT Tektronix has announced the addition of Fast Fourier Transform (FFT) and a new high-performance active probe for the TDS 820 Digitising Oscilloscope. The FFT is part of an advanced maths option for the TDS 820 that includes integration and differentiation. Comm Electronics and Emona Instruments. All other prizes have since been despatched directly, to the prize winners announced in the April 1993 issue. Discussing the Av-Comm satellite receiver prize are, from left to right, Bruce Routley of Jaycar, prize winner R. Coleman and Garry Cratt of Av-Comm. The combination of the TDS 820's 8GHz (6GHz with delay lines) acquisition bandwidth, 0.4 picosecond timing resolution, and simultaneous time domain and FFT displays makes it ideal for oscillator characterisation, Telecom installation and maintenance and high-speed digital design and characterisation applications. With the advanced maths option, basic spectral magnitude, frequency, and phase measurements can be made using on-screen cursors. Results can be displayed linearly in volts RMS, logarithmically in dB RMS, in degrees or in radians. Users can select from four FFT windowing functions: Rectangular, Hamming, Hanning, and Blackman-Harris, depending on measurement requirements. The proprietary TriStar digital signal processor gives the TDS 820 very fast update rate for live display of all waveform processing functions, including FFT, integration, and differentiation. The TDS 820 now comes standard with two of the new P6207 high-impedance active probes. When combined with a TDS 820, the P6207 offers 3.5GHz (typical) system bandwidth, 100kW input resistance and less than 400 femtofarads (0.4 pF) input capacitance. Using the TDS 820's built-in trigger pickoff, users can now acquire highspeed signals without an external trigger and make precision timing measurements without concern for changing the circuit's behaviour due to probe loading. For further information, contact Tektronix Australia Pty Ltd, 80 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 7066 or Fax (02) 888 0125. June 1993  85 Silicon Chip Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). 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. Graphic Equaliser, Pt.1; Stereo Compressor For CD Players; Amateur VHF FM Monitor, Pt.2; Signetics NE572 Compandor IC Data; Map reader For Trip Calculations; Electronics For Everyone –Resistors. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone; How To Quieten The Fan In Your Computer; Screws & Screwdrivers, What You Need To Know; Diesel Electric Locomotives. April 1989: Auxiliary Brake Light Flasher; Electronics For Everyone: What You Need to Know About Capacitors; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor For Shortwave Receivers; Why Diesel Electrics Killed Off Steam; Index to Volume 1. January 1989: Line Filter For Computers; Ultrasonic Proximity Detector For Cars; 120W PA Amplifier (With Balanced Inputs) Pt.1; How To Service Car Cassette Players; Massive Diesel Electrics In The USA; Marantz LD50 Loudspeakers. February 1989: Transistor Beta Tester; Minstrel 2-30 Loudspeaker System; LED Flasher For Model Railways; Build A Simple VHF FM Monitor (uses MC3362), Pt.1; Lightning & Electronic Appliances; Using Comparators to Detect & Measure. March 1989: LED Message Board, Pt.1; 32-Band May 1989: Electronic Pools/Lotto Selector; 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. October 1989: Introducing Remote Control; 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); Sensitive FM Wireless Microphone; 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. 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. 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; PC Program Calculates Great Circle Bearings. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. 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. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Please send me a back issue for: ❏ January 1989 ❏ February 1989 ❏ June 1989 ❏ July 1989 ❏ December 1989 ❏ January 1990 ❏ May 1990 ❏ June 1990 ❏ October 1990 ❏ November 1990 ❏ March 1991 ❏ April 1991 1991 ❏ September 1991 ❏ January 1992 ❏ February 1992 ❏ June 1992 ❏ July 1992 ❏ November 1992 ❏ December 1992 ❏ April 1993 ❏ May 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 March 1989 September 1989 February 1990 July 1990 December 1990 May 1991 October 1991 March 1992 August 1992 January 1993 June 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ November 1988 April 1989 October 1989 March 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 February 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ➦ Use this handy form to order your back issues December 1988 May 1989 November 1989 April 1990 September 1990 February 1991 July 1991 ❏ August December 1991 May 1992 October 1992 March 1993 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /_____ Name ________________________________________________________ Street ________________________________________________________ Suburb/town ______________________________ Postcode _____________ $A6.00 each (includes p&p). Overseas orders add $A1 each for postage. NZ orders are sent air mail. Detach and mail to: SILICON CHIP PUBLICATIONS PO BOX 139 COLLAROY BEACH NSW 2097 Or call (02) 979 5644 & quote your credit card details. Fax (02) 979 6503. PLEASE ALLOW TWO WEEKS FOR DELIVERY 86  Silicon Chip ✂ Card No. Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. May 1990: Build A 4-Digit Capacitance Meter; High Energy Ignition For Cars With Reluctor Distributors; The Mozzie CW Transceiver; Waveform Generation Using A PC, Pt.3; 16-Channel Mixing Desk, Pt.4. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise 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. 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 Telephone; 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 Converter 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; The Fruit Machine; Two-Tone Alarm Module; Laser Power Supply; 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; LowCost 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 PC-Compatibles; 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; Playing With The Ansi.Sys File; FSK Indicator For HF Transmissions. May 1991: Build A DTMF Decoder; 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1; Setting Screen Colours On Your PC. 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; Electric Vehicle Transmission Options; 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; PEP Monitor For Transceivers. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Installing Windows On Your PC; 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. 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; Getting To Know The Windows PIF Editor. 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; Error Analyser For CD Players Pt.3; Modifying The Windows INI Files. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Windows 3 & The Dreaded Un­ recov­erable Application Error; Index To Volume 4. 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. February 1992: Compact Digital Voice Recorder; 50-Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. 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 Direct­ ories; 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 Memory; Switching Frequencies in Model Speed Controllers; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; LowCost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; A Look At Large Screen High Resolution Monitors; OS2 Is Really Here; 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; What’s New In Oscilloscopes?; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Off-Hook Timer For Tele­phones; Multi-Station Headset Intercom, Pt.2; Understanding The World Of CB Radio. 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; The Interphone Digital Telephone Exchange, Pt.2; 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 Battery Charger (Charges 6V, 12V & 24V Lead-Acid Batteries). November 1992: MAL-4 Microcontroller Board, Pt.1; Simple FM Radio Receiver; Infrared Night Viewer; Speed Controller For Electric Models, Pt.1; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.2; Automatic Nicad Battery Discharger; Modifications To The Drill Speed Controller. December 1992: Diesel Sound Simulator For Model Railroads; Easy-To-Build UHF Remote Switch; MAL-4 Microcontroller Board, Pt.2; Speed Controller For Electric Models, Pt.2; 2kW 24VDC To 240VAC Sine­ wave Inverter, Pt.3; Index To Volume 5. 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; Restoring A 1920s Kit Radio February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Your Car; 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; File Backups With LHA & PKZIP. 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. 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. 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. June 1993: Windows-Based Digital Logic Analyser; Build An AM Radio Trainer; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2; Double Your Disc Space With DOS 6. PLEASE NOTE: all issues from November 1987 to August 1988, plus the October 1988 & August 1989 issues, are now sold out. All other issues are presently in stock, although stocks are low for older issues. For readers wanting articles from sold-out issues, we can supply photostat copies (or tearsheets) at $6.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. June 1993  87 The Story Of Electrical Energy, Pt.24 The electrolytic smelting of alumina to pure aluminium is the most electricity intensive industry known to man. In fact, so much electric energy is required in the process that some commentators have referred to aluminium as “congealed electrici­ty”. By BRYAN MAHER Aluminium metal is electrolytically smelt­­ ed by the Hall-Heroult reduction process developed in 1886 and is now the metal of a thousand uses. Before this process was invented, the prohibitive cost of production made aluminium a rare substance. 88  Silicon Chip Today, well over a million tonnes of aluminium are produced in Australia each year. Aluminium is the sixth lightest of all metals and is exten­sively used in structural, decorative and functional applica­tions. When alloyed with other metals, aluminium is a major component in aircraft and transport vehicle construction. Being the fourth best electrical conductor (after silver, copper and gold), aluminium finds extensive use today in electric power lines at all levels from 240V street mains to 1.2MV DC systems. A critical property of any metal chosen for very large trunk power lines is its weight-resistance product. Although copper has the second lowest resistance, its high weight poses mechanical problems in the design of towers and hanging insulators. Compared with copper, aluminium has only two thirds the conductivity but on the credit side, it has only ▲ This overview of the Boyne Island aluminium smelter shows the two potline buildings, each almost 1km long. about one third the weight. To put it another way, if we have two equal conductor lengths of equal weight, one aluminium and the other copper, the aluminium could carry twice the current. Therefore, this metal is chosen for virtually all high voltage power lines, usually with a steel core for added strength. (For more on this subject, see Pt.4 of this series in the October 1990 issue). Major Australian smelters The three major aluminium smelters in Australia are Tomago Alumin­ ium’s plant near Newcastle, Alcoa’s Portland installation in Victoria, and the Boyne Island smelter in Queensland. They produce aluminium for Australian consumption as well as for export to Japan, the USA, Europe and other countries. Our story this month is based on the Boyne Island smelter. This island is at the mouth of the Boyne River, near Glad­stone, and is a joint venture managed on behalf of the partici­pating parties by Comalco Limited. In order of share holding, the participants are Comalco Limited, Austria Metal AG, Sumitomo Light Metal Industries, Kobe Steel, Mit­ subishi, Yoshida Kogyo, and Sumi­ tomo Chemical Corporation of Japan. These participants take the total production of the plant in proportion to their shareholding. The plant uses Comalco-modified Sumitomo Aluminium Ltd potroom technology. Almost 80% of the aluminium produced is in the form of 22kg ingots for overseas markets, for which the smelter earns Australia $240 million annually. The remainder of the product is in the form of cast billets or blocks for further processing by Comalco plants in Queensland, New South Wales and Victoria. The Boyne smelter is responsible for 18% of Australia’s aluminium production and 2% of the world’s total. The Hall-Heroult process During the smelting process, alumina is electrolytically reduced to pure This side view of one of the smelting pots shows nine of the 18 anode support rods. The workman is adjusting a gas collec­tion hood. Most of the aluminium produced at Boyne Island is produced in the form of 22kg ingots for export. The Boyne smelter is responsible for 18% of Australia’s aluminium production and 2% of the world’s total. aluminium in large rectangular carbon lined baths called pots. Because the oxide alumina is in a low energy state, vast quantities of electrical energy must be injected to achieve the high energy state of the pure metal. Each pot has a steel shell lined with a very thick layer of carbon, which is used as the bottom cathode and as the contain­ment for the molten contents. Alumina dissolved in molten cry­ olite (sodium aluminium fluoride, Na 3 AlF 6 ) forms the conducting electrolyte lying within the pot. A number of very large carbon blocks, used as the anodes, are immersed in the electrolyte. Enormous direct currents from a transformer and rectifier system are passed through the pot from the upper anode carbon blocks, through the molten electrolyte, and then out via the carbon lining at the bottom. Each pot has a voltage drop of 4V across it June 1993  89 This photo shows a pot being tapped. The molten aluminium is sy­phoned into the vacuum tank at right, after which is taken to a holding furnace prior to casting. Note the huge con­ductors in the foreground. Total current is 180,000 amps. gen is oxygen just formed from the breakdown of alumina and is in a very reac­tive state, probably in the atomic form). Each pot produces approximately 1.25 tonnes of aluminium per day. To keep the contents of the pots up to temperature, the process must be continuously maintained, 24 hours of the day, every day of the year. A hopper feeds dry granular alumina into the pot and the molten aluminium lies at the bottom. Floating on this is a layer of molten alumina dissolved in cryolite, while on top of this a cake of unmelted cryolite forms. Approximately every two minutes, hydraulic rams punch four 150mm diameter holes down through the cryolite crust and these pass a charge of 1.5kg of alumina into the melt below. Periodically, a pipe is pushed down through the cryolite cake into the molten aluminium at the bottom of the pot. This allows the molten aluminium to be syphoned up into a vacuum vessel. This is then carried by cranes to a holding furnace before being cast into ingots, rods or blocks for shipment. Up to 20% of Comalco’s share of the aluminium produced is alloyed with other metals to enhance properties such as hardness, strength and toughness. Various metals such as magnesium, sili­con, manganese and copper may be added to the melt to produce special product characteristics. Alumina supply The carbon anode blocks are continually burnt away by the reduc­tion process in the smelting pots & so they need to be replaced at frequent intervals. Here a new anode is being swung into place. from anode to cathode when 180,000 amps DC is passed through it. As well as providing the energy necessary to reduce the alumina to pure aluminium, this huge electric current also heats the contents of the pot, keeping the cryolite, alumina and pro­duced aluminium all in a molten state. Electrochemical reduction The passage of electric current through molten aluminium oxide 90  Silicon Chip releases the pure aluminium from the compound. This is the crux of the Hall-Heroult electrochemical reduction process. The simple equation is: 2Al2O3 + 3C + electrical energy ➝ 4Al + CO2 Molten aluminium appears from the electrolyte at the bottom cathode, while oxygen is produced at the anodes. At the operating temperature of 965°C, the evolved nascent oxygen burns the carbon anodes, forming carbon dioxide. (Note: nascent oxy- Granular alumina is carried to the Boyne smelter by a 9km overland conveyor belt from the Queensland Alumina refinery at Gladstone. For each tonne of aluminium produced, the Boyne smelt­ er consumes two tonnes of alumina. Each pot is electrically a very low impedance device (4V drop at 180,000 amps is equivalent to a pot resistance of 22 micro-ohms). To make this a more manageable load, a large num­ber of pots are connected into series groups. Thus, the Boyne smelter consists of two separate potlines. Each consists of 240 pots in two rows, all connected in series. Gigantic aluminium conductors, 600 x 600mm in cross sec­ tion, are used to carry the huge current through all the pots in one line. The circuit K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic These are connecting rods for the carbon anode blocks. They are attached to the carbon blocks using cast iron as the joining medium.The manufacture of new anodes is a never-ending process length for these 180,000 amp currents is almost 2km! Because all pots are part of the electrical circuit, they are insulated by their concrete foundations from each other and the building. As well, care must be taken when overhead travell­ ing cranes service the pots. Crane runway support columns and girders must be kept electrically isolated from the potline. The overall dimensions of each potline are enormous. They are 870 metres (almost a kilometre) in length, reputedly the longest in the world. During the construction phase in 1980, the company was spending $1 million dollars per day, 80% of which went to Australian industries and subcontractors. Total cost of the plant was more than $750 million. Power supply The total voltage applied across one whole potline is ap­proximately 1000V DC. This is obtained from “recti­ formers”; ie, transformers incorporating banks of huge silicon rectifiers mounted within an oil-filled tank. The primary supply is via twin 132kV 3-phase AC lines plus one 275kV line from Gladstone power station 18km away to the northeast. Because of the proximity of the plant to the sea, the entire 132kV switchgear is enclosed within gas (sulphur hexafluo­ ride (SF6) filled pipes and vessels. This gas acts as both an excellent insulator and a flame retardant for the circuit breaker contacts. The smelter consumes 385MW from the state grid continuously on a “take or pay” basis, making it the power station’s largest single load. Control of the current through the pots is achieved in two stages. The 132kV/1kV transformers for each potline are equipped with off-load tap changing switches. Regulation of the high voltage supply is by a 275kV/132kV on-load tap-changing auto­trans­­former in the main supply. This huge 500MVA oil-immersed transformer weighs close to 300 tonnes and has a separate fan-cooled heat exchanger and breathing tank. ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 Silicon Chip Binders Carbon electrodes Each of the 480 pots in the two pot lines contains 18 carbon anodes. These anode blocks, each weighing 1.4 tonnes, are consumed by the burning effect of the hot oxygen gases released in the smelting reduction process, as noted above. Therefore, a vital function of the plant is the continuous production of new carbon blocks for the periodic replacement of the 8640 anodes in service. The carbon section of the Boyne plant produces 130,000 tonnes of anodes annually. Petroleum coke imported from the USA, coal tar pitch from Newcastle, and recycled anode butts from the These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A14.95 (incl. postage in Australia). NZ & PNG orders add $5 each for postage. Not available elsewhere. 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. June 1993  91 This view of one of the pot lines shows the huge scale of the plant. Note that since each smelting pot is connected in series with 239 others in the plant, they must each be insulated from each other & from the building. potrooms form the ingredients of the anodes. The coke and butts are crush­ed and ground and mixed with coal tar pitch, and then heated to 160°C. The resulting hot paste is vibrated into the shape of the anode blocks. These are then immersed in 4.9-metre deep refractory lined baking pits and progressively heated to 1150°C over a period of 18 days. Oxygen is excluded to prevent burning and the volatile gases given off are used as supplementary fuels in the heating process. This baking imbues the anodes with the necessary elec­trical conductivity and mechanical strength. After baking, the anode blocks have large aluminium rods attached. These provide both mechanical support and electrical connection for the anodes while in the pots. The metal rods are bonded to the carbon blocks using molten cast iron as the joining med­ium. The manufacture of new anodes is a never-ending process, with thousands of units in various stages of assembly 92  Silicon Chip on the overhead conveyors at any one time. Before use in the potlines, each new anode is sprayed with aluminium to establish initial conductivity. precipitators. Total emissions from the plant are monitored by both the company and the Department of Environment and Conservation. Measuring equipment is installed within the plant, in the surrounding buffer zone and out in the community. Environmental protection Future developments Being electrically powered, aluminium smelting is basically a clean operation. However the exhaust carbon dioxide from the pots also contains traces of fluorides due to reactions with the cryolite. To keep these toxic gasses from the atmosphere, the potline exhausts are drawn off and the fluorides are absorbed by a process known as dry scrubbing. In this process, the exhausts are passed over hanging alumina-coated bag filters to catch the fluoride emissions, either in gaseous or solid particle form. Residues collected by the filters are ultimately returned to the pots for reprocessing. The four giant dry scrubbing plants operate at better than 99.7% efficiency. Emissions from the carbon baking furnace are cleaned by electrostatic A feasibility study is presently being carried out to investigate the possible building of a third potline to almost double the present plant capacity. This would make Boyne Island the largest smelter in Australia and possibly in the world. Such a plant enlargement also depends on the proposed purchase by the consortium of the existing Gladstone power station from the Queensland SC Government. Acknowledgements Special thanks to Trudy Habner and the engineering staff of Boyne Smelters for photos and data; also thanks to ABB (Aust), IE (Aust) and Alcoa. 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. Phased out generator question I am referring to the topic “3-Phase Power Supply From A Single Phase Supply”, raised by B. J. from Hahn­dorf, SA (SILICON CHIP, Jan. 1993) and by P. L. from Forster, NSW (Oct. 1992). Years ago I read something along that line and was lead to understand that a 3-phase motor – when driven through couplings or vee-belts from a separate power source to a speed around the synchronous limit (but not necessarily so) – could be coaxed to act as an asynchronous AC generator, either single or 3-phase, depending on the external connections to its terminal box/strip. The (theoretical) sketch showing the connections, and the even sketchier description of its operation, did not contemplate any connection whatsoever to the power distribution grid (power lines, that is!), either single or 3-phase. The sketch showed a number of capacitors symmetrically connected across the original leads of the motor, now used as an AC generator. It also showed a system of switches which allowed these capacitors – temporarily disconnected from the motor-gen­ erator windings – to be charged to a voltage equal to or somewhat higher How to stop the drill speed controller Recently, I built the Drill Speed Controller as described in the Nov­ember 1992 issue. I have very thorough­ly checked all the resistor values and the placement of all the component values but it refuses to work at all. Can you suggest what the problem might be? (W. S., Kingswood, NSW). • The most likely cause of any no-go fault such as this is an open circuit component somewhere in the circuit. Since all com­ponents than the RMS value of the AC voltage to be then generated by the mechanically driven motor/generator. While the capacitors were charging up, the driven motor-generator would be already rotating at the prescribed speed and the capacitors once charged would then be connected (switched, that is!) in the previously described configuration directly across the motor-generator windings. According to the theory, this action would create the original “field” of the generator and it would then be self-sustaining after that instant for as long as the driven motor-generator is kept in motion. I’ll leave it to your technical expertise to sort out and comment on such rather weird con­ trap­tion. Anyway, on a related question, how do you run a 3-phase motor and get some mechanical power out of it by connecting it to a single phase AC power supply? The motor should still be self-starting and able to run for indeterminate periods of time with­ o ut eventually burning out. I do not need to be told that it is a very inefficient arrangement and that the shaft delivered power will be less than one third that of a normal 3-phase arrangement. Years ago, I remember seeing a diagram showing how to achieve such a will be new, the most likely reason for an open circuit is a poor or unsoldered joint. However, recently we saw a kit-built drill speed controller which was also no-go. The fault turned out to be that the constructor had swapped the 100Ω and 1kΩ resistors in the gate circuit. The resulting voltage division of the gate signal meant that the Triac could never turn on. We strongly suggest that constructors use their multimeters to check all resistor values before they are installed on the PC board, as it’s easy to confuse the colours. goal and I can recall that again capacitors were involved in the process. (E. M., Alyangula, NT). • To our knowledge, the only way that a 3-phase motor can be made to operate as an alternator is for it to have slip rings and a means to separately excite its field windings with DC. Of course, after making a similar blanket statement in the magazine regarding the impracticality of 3-phase motor operation from single phase supplies, it is possible that some readers will come forward with a scheme for doing just what you want. DIY high voltage probe too dangerous I would be very interested in a circuit which would allow my Fluke 77 multimeter to read up to 35kV; ie, a probe type arrangement with an interface that produces a corresponding voltage that will read on a low volts range. I’m sure there would be many others who would be interested in this as most commercial HV probes are very costly. (S. W., Hamilton, NZ). • A 35kV probe would not be easy to design or build. In fact, following a recent death in Victoria involving the use of a high-voltage probe (see the December 1992 issue of SILICON CHIP), we will not even consider such a project. The risks of injury or death due to faulty workmanship are too high. Discharger doesn’t discharge enough I have recently obtained a kit of your Nicad Battery Dis­charger as described in the July 1992 issue and built it up. However, I find that there is a problem in that the cut-off discharge voltages are somewhat higher than the designer speci­fies. The 12V cut-off stands at about 11.5V and the 6V range (which is my main interest) cuts off at around 5.75V. I have the trimpot screwed over hard left to get that. I did try a higher value June 1993  93 94  Silicon Chip In the January 1992 issue of SILICON CHIP, you described a “Baby Room Monitor and FM Transmitter” based on a BA1404 IC, made by the Rohm Corporation, Japan. I have been unable to find any information on this IC, or the address of the Australian agent. Could you please help me with the following questions? Would you have a data sheet available for this IC? If not, could you please advise me as to where I can obtain one, or give me the address of the Australian agent? Could you also tell me if it is possible to crystal-lock the IC at radio frequencies? If so, how can it be done? (W. W., Beresfield, NSW). • The Australian distributors for Rohm Co Ltd are: Fairmont Marketing, 57 St. Hellier Street, Heidelberg Heights, Vic 3081. Phone (03) 457 7300 or fax (03) 457 7339. They can supply data on the BA1404 although we published most of the relevant data in the October 1989 issue (no longer available but we can supply photo­ copies at the standard $6 fee). The circuit could be crystal locked but there is very little point since the D2 D1 In my model railway control system I am using a number of NE555 timer ICs as switches. Also incorporated is the Traffic Lights Simulator (again using NE555) and the Points Controller published in the February 1993 issue. Separately, they work fine; together, the Points Controller triggers all others, while the Traffic Lights Simulator triggers the NE555 switches. I already have 0.1µF capacitors as suppressors on all DC plus AC power inputs of the modules. Can you suggest a cure please? (M. W., Surfers Paradise, Qld). • When ever there is a problem of false triggering in 555 circuits, the standard cure is to install a 0.1µF capacitor in the positive supply line to the chip and, more importantly, con­ nect a 0.1µF or larger capacitor from pin 5 of each 555 to the 0V line. This capacitor is already present in the traffic light circuit. Notes & errata Woofer Stopper, May 1993: unfortunately, the uncorrected wiring diagram (Fig.2) found its way into the article. This contains several errors: (1) Q2 is shown upside down; (2) the 100kΩ resistor to the right of IC5 should be deleted; and (3) the 100kΩ resistor below D2 should be 220Ω. The correct overlay pattern is shown below as Fig.1. The published PC pattern is correct. SC 22k 22k 0.1 220  1000uF IC1 4060 Q2 IC5 4013 Q6 Q7 1 10M Q8 33pF  1 Q4 Q1 D3 100k 10uF 0.1 Q5 100k 78L05 IC2 4518 100k 1 33pF Q3 IC4 4024 IC3 4020 1 1k Fig.1: corrected parts overlay pattern for the Woofer Stopper. Mutual interference in model railway circuits 1k 1k I have built the Digital Capacitance Meter as published in the May 1990 of SILICON CHIP. It functions reasonably well, except that it has the annoying habit of stepping back and forth around the actual readout; that is, with the standard 0.1µF capacitor supplied, the nF scale reads back and forth from 97 to 102. I have replaced all the ICs one by one but still the trou­ble persists. I would Questions on the BA1404 transmitter is very stable, provided that the specified NPO capacitors are used. X1 Fixing jitter in the capacitance meter appreciate your assistance to help me fix this trouble. I enjoy your magazine and think it is very good value. (D. M., North Balwyn, Vic). • The reason for jitter in the display is possibly caused by the transformer not being correctly earthed. Check for continuity between the transformer metalwork and ground. You may need to scrape away the coating on the mounting feet of the transformer for a reliable earth contact. 2.2k trimpot (20kΩ) but it doesn’t seem to make much, if any, difference. I use a fairly new Jaycar model QM-1400 digital multimeter to take readings which should be fairly accurate. In point of fact, I would like to be able to bring the cut-off battery voltage nearer to 1V per cell, which seems to be a popular figure. The batteries I use are Optronics OP-3S 6V for a Sony AU-230 video camera. The unit as a whole is very satisfactory and easily trans­ported on a trip but I would like to be able to reduce the dis­charge battery voltage a little lower if possible. (J. L., Big­ genden, Qld) • We are concerned about your difficulty in getting a suffi­ ciently low end-point voltage and while we hesitate to suggest it, wonder about the accuracy of your digital multimeter. Check the voltage across the LM3362.5 reference. The tolerance range is 2.39-2.59V and the range of adjustment with the trimpot is ±70mV. The range of adjustment can be increased to ±120mV by omitting diodes D1 and D2 and connecting the trimpot directly across the LM336. If your multimeter gives a reading outside the tolerance range for the LM336-2.5, we would be inclined to doubt its accu­racy and, by extension, the accuracy of all your voltage read­ ings. If you want to reduce the endpoint voltage of the circuit to 1V per cell, you will have to recalculate the voltage divider string across switch S1. Note that you can also reduce the end-point voltage of the circuit simply by omitting protection diode D4. However, this will mean that you have no reverse polarity protection for the circuit and the reduction in end-point voltage will be propor­tionately greater for 12V batteries. 1 22k D6 D4 D5 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. ANTIQUE RADIO ANTIQUE RADIO RESTORATIONS: specialist restoration service provided for vintage radios, test equipment & sales. Service includes chassis rewiring, recondensering, valve testing & mechanical refurbishment. Rejuvena- tion of wooden, bakelite & metal cabinets. Plenty of parts – require details for mail order. About 1200 radios within 16,000 square feet. Two-year warranty on full restoration. Open Saturday 10am-4.30pm; Sunday 12.30-4.30pm. 109 Cann St, Bass Hill, NSW 2197 Phone (02) 645 3173 BH or (02) 726 1613 AH. CLASSIFIED ADVERTISING RATES 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): $20 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 & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy Beach, NSW 2097. Or fax the details to (02) 979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ FOR SALE WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high resolution, shortwave fax, Morse & RTTY receiving program. Suitable for CGA, EGA, VGA and Hercules cards (state which). 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. THE HOMEBUILT DYNAMO: (plans) brushless, 1000 watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. _____________ _____________ _____________ _____________ _____________ AN INTERFACE to control the outside world from a PC paral­lel port. 32 bits in. 32 bits out. Units can be cascaded. _____________ _____________ _____________ _____________ _____________ TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS _____________ _____________ _____________ _____________ _____________ TRANSFORMER REWINDS Reply Paid No.2, PO Box 438, Singleton, NSW 2330. Ph: (065) 76 1291. Fax: (065) 76 1003. ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 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 June 1993  95 Short form kit includes software examples. $35 or send $2 for my 3.5-inch promo disk. Don McKenzie, 29 Elles­mere Crescent, Tullamarine 3043. Phone (03) 338 6286. PAY TV & SATELLITE Scrambling News Monthly, with the latest on descrambling techniques & addresses, where to buy SURPLUS COMPONENT SALE STOCK QTYS LIMITED, NO BACK ORDERS 2N3055 $1.20 RESISTORS TIP30C $0.50 MOST VALUES AVAIL. TIP122 $1.20 1/4W M/FILM $3/100 2N7000 $1.50 1/3W CARBON $2/100 2SC2240 $0.60 1/2W CARBON $4/100 VN88 $2.00 1W CARBON $5/100 3N170 $1.50 2W CARBON $8/100 2N5954 $1.50 5W WIREWOUND $0.30 2N3440 $1.20 10W RESISTORS $0.60 CONNER 120MB IDE HARD DISKS $525.00 KEYTRONICS KB 3270PC KEYBOARDS $220.00 HEWLETT PACKARD 545A LOGIC PROBE $55 HEWLETT PACKARD 546A LOGIC PULSER $75 ONE ONLY H.P. CURRENT TRACER 547A $75 ONE BWD 245A DUAL POWER SUPPLY $450 VALVES 1.44MB FDD $95.00 3A4 $8.00 1MB SVGA $125.00 417A $8.00 CHECKIT PRO $179.00 5651 $8.00 MOC3020 OPTO $2.00 5R4GY $8.00 MOC8050 OPTO $1.50 EL32 $8.00 74C161 $2.00 ONE ONLY TBL12/30 TRANSMIT TUBE $2700.00 PHONE OR MAIL ORDERS, CREDIT CARDS ACCEPTED FOR ORDERS $20 & OVER, DISCOUNTS FOR QUANTITY ORDERS SECONTRONICS PO BOX 2215, BROOKSIDE, QLD 4053, PHONE (07) 355 1314 143 GRAYS RD, ENOGGERA, QLD 4051, FAX (07) 855 1014 SHOP OPEN SATURDAY 9AM - 4PM AH (07) 855 1880 MEMORY & DRIVES PRICES AT APRIL 12th, 1993 SIMM 1Mb x 9 1Mb x 3 4Mb (1M x 36) 4Mb x 9 4Mb x 8 8Mb (2M x 36) DRAM DIP 1 x 1Mb 256 x 4 41256 1Mb x 4 70ns 70ns 70ns 70ns 80ns 70ns $53 $49 $210 $215 $195 $450 70ns $6.00 70ns $6.25 80ns $2.50 Z or D $24.00 DRIVES SEAG 42Mb SEAG 89Mb SEAG 107Mb SEAG 130Mb SEAG 245Mb 28ms 14ms 15ms 16ms 12ms $210 $292 $310 $340 $530 IBM PS.2 50/55/70 70/35 90/95 2Mb 4Mb 4Mb $130 $220 $220 TOSHIBA T3200SX T44/6400 T5200 T5200 4Mb 4Mb 2Mb 8Mb $270 $240 $150 $500 MAC 1Mb x 8 - 100 4Mb P’Book 27C 4Mb15 $16 Sales tax 20%. Overnight delivery. Credit cards welcome. Ring for Latest Prices 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 VINTAGE RADIO PARTS: numerous new and used valves, knobs and sundry parts. For price list, write to: Airwave Radio Restora­tion, PO Box 333, North Hobart, Tas. 7002. Bargains All in one board with two serial, printer, IBM keyboard, high density floppy & IDE mono video interface. Up to 4Mb RAM, 80286-16cpu, MS-DOS compatible, 130 page manual, small size 170mm x 255mm. Laptop power supply 240V 5V/3A 12V/3A $89 Taped components by the metre app 200pcs, tants, caps, zeners, diodes, resistors $5.95/metre $299 Infrared sets, 1 each IR LED, diode & IDC header $1 Ampro little PC Audio IC hybrids STK043-25 or STK058-40W $9.95 Fujitsu 40Mb hard disks $269 Microbyte-PC230 v30 CPU board, 1Mb RAM installed, 2 serial, print­er, 720Kb floppy, SCS1 hard disk, EGA video, IBM kb interface, made in Australia, surplus $185 ea 720Kb Floppy Drives $55 1.44Mb Floppy Drives $89 We buy surplus computer & electronic products, bankrupt stock and components. P.C. Computers PELHAM 600-600 ohm audio output transformers PCB mount 18Hz38kHz. $9.95 Antique Radio Restorations.........95 A-One Electronics.......................8,9 Av-Comm.....................................21 Cebus Australia...........................35 David Reid Electronics ................3 EEM Electronics..........................96 Emona.........................................55 Harbuch Electronics....................81 Hycal Electronics.........................96 Jaycar ................................... 45-52 JV Tuners.....................................81 Kalex............................................91 Kits Max I/O kit for PCs, 7 relays, ADC, DAC, stepper driver, TTL inputs, with software $169 PC I/O card with 8255 chip 24 I/O lines programmable as inputs or outputs $69 Oatley Electronics...................17,23 PC Computers.............................96 Pelham........................................96 Peter C. Lacey Services..............30 1.5 watt AM broadcast transmitter XTAL locked $49 Philips Test & Measurement....OBC 2.5 watt FM broadcast transmitter 88-108MHz. $49 RCS Radio ..................................95 Digi-125 audio power amp (over 19,000 sold since 1987) 50 watt/8 $14 125 watt/4 $19 New 200 watt/2 version $29 Resurrection Radio......................57 Infrared relay kit $9 Secontronics................................96 Remote control tester $4 36 Regent St, Kensington, SA. Phone (08) 332 6513. Rod Irving Electronics .......... 74-79 Silicon Chip Back Issues........86,87 Silicon Chip Binders....................59 FIX-A-KIT Technical Applications.................84 KIT REPAIR & CONSTRUCTION Tektronix....................................IBC 3 MONTHS WARRANTY ON REPAIRS 12 MONTHS WARRANTY ON CONSTRUCTION TECHNICAL ASSISTANCE HYCAL ELECTRONICS Design, Manufacture & Repair of Electronic Equipment (02) 633 5477 T. A. Mowles EEM Electronics Printed circuit boards for the hobbyist. For service & enquiries contact: Printed circuit board assembly, switchmode power supplies repaired. Design work from start to finish. Ring anytime 9am-9pm Mon-Sun. (08) 3265590 (03) 4011393 96  Silicon Chip Altronics ..........................IFC,60-63 Clarke & Severn..........................35 ICL 286 Board All in one NEC V40 CPU board, MS-DOS compatible, high density floppy. SCSI hard disk, 2 serial, printer, solid state hard disk, IBM keyboard interface, (4W), CMOS single +5V rail, up to 768Kb RAM, 384Kb ROM, 145mm x 250mm, 98page manual. $299 Advertising Index T. A. Mowles.................................96 $41 $270 CO-PROCESSORS 387SX 20/25 IIT $110 387DX All Intel $110 EPROMS the latest descramblers. Send stamp for info. John Papp, Box 37885 Winnel­lie, N.T. 0821. Transformer Rewinds...................95 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • Jemal Products, 5 Forge St, Welshpool, WA 6106. Phone (09) 350 5555. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491.