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Vol.7, No.1; January 1994 FEATURES FEATURES   4 The World Solar Challenge by Brian Woodward Honda wins at a record pace THIS 1.23-40V 3A VARIABLE power supply features a highefficiency switching regulator, preset current limiting, full overload protection & an LCD panel meter. Construction starts on page 16.   7 What’s New In Car Electronics? by Julian Edgar Mazda’s Collision Avoidance System   8 Electronic Engine Management, Pt.4 by Julian Edgar Changing the system 30 Luxman A-371 Amplifier & D-351 CD Player by Leo Simpson High quality equipment with no gimmicks 37 Active Filter Design For Beginners by Elmo Jansz A quick primer to get you started 88 Review: Kenwood’s DCS-9120 Oscilloscope by John Clarke Features both digital & analog modes of operation PROJECTS PROJECTS TO TO BUILD BUILD 16 Build A 40V 3A Variable Power Supply by John Clarke Full overload protection, an LCD panel meter & a switching regulator 40 A Switching Regulator For Solar Panels by Otto Priboj Can be used to charge 12V or 24V battery banks IF YOU USE SOLAR PANELS, you need an efficient regulator to ensure that any associated batteries are correctly charged. This unit can be built in two versions (10A or 20A) and can charge a 12V or 24V battery band – see page 40. 44 Printer Status Indicator For PCs by Darren Yates An alphanumeric display indicates printing problems 50 Simple Low-Voltage Speed Controller by Darren Yates Will control 12V DC motors or lights 80 Control Stepper Motors With Your PC by Marque Crozman You build an interface circuit & buy the software SPECIAL SPECIAL COLUMNS COLUMNS 52 Vintage Radio by John Hill Realism Realized – the Precedent console receiver 56 Serviceman’s Log by the TV Serviceman It was all a long time ago ARE YOU OFTEN frustrated by files which disappear down your printer cable but don’t print out? This printer status indicator uses an alphanumeric display panel to indicate problems as they occur. Details page 44. 65 Computer Bits by Darren Yates Even more experiments for your games card 70 Remote Control by Bob Young More on servicing your R/C transmitter DEPARTMENTS DEPARTMENTS   2 24 29 68 Publisher’s Letter Circuit Notebook Order Form Back Issues 90 93 95 96 Product Showcase Ask Silicon Chip Market Centre Advertising Index THE LUXMAN company in Japan has a reputation for high quality audio equipment with no unnecessary frills or gimmicks. This month, we review their A-371 stereo amplifier & D-351 CD player. Turn to page 30. January 1994  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald 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 SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 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. PUBLISHER'S LETTER Some Australian companies still do not give good service Talk to almost anyone these days who has recently purchased some product or service and you’re bound to hear a sorry story about botched deliveries, return calls to fix installations, repeat calls for warranty service and, in general, a high level of frustration. Two examples from our own staff serve as illustrations. Staff member No.1 arranged for a new garage door with UHF remote control to be installed. Within a few days, the door arrived and the installation team attempted to install it. They found that the door had been damaged and subsequently left after having also damaged the original door. One month and many phone calls later, a replacement door was finally installed but the remote control did not work properly – it had obviously never been tested. This required more phone calls and another visit from the installation team to put right. Staff member No.2 purchased a new double wall oven with microprocessor control and all the latest whiz-bang features. It was installed but subsequently it was found that one element in one of the ovens did not work. It took four visits by different service personnel to solve a wiring error that was compounded by errors on the badly drawn circuit diagram. I am sure that there are many thousands of such occurrences every year in Australia. Clearly, all these unnecessary repeat calls cost heaps of money to the companies concerned and it does nothing to build customer confidence in their ability to give good service. Apart from that, every time someone has to arrange to be at home for installation or service personnel to call means either a loss of income, or at the very least, quite a lot of inconvenience. And then when we come to getting warranty service on pro­ducts, the whole story repeats itself. You often have to take the product concerned to some outof-the-way suburb where the people concerned are obviously poorly motivated and are probably think­ing “not another one of these (censored) units!”. So the poor customer has to make at least two visits to the service company and there is no guarantee that the unit will be fixed when it is returned. None of this has to be. Electronic products these days are very reliable and once they are properly installed they should give many years of trouble-free service. But many companies clearly do not bother to check that the products they supply are properly assembled and that all functions work properly. Nor do they ensure that their products are correctly installed and that when they do ultimately need servicing, that servicing staff have the correct manuals and that they are polite and courteous to the customer. That’s all fairly straightforward isn’t it? It’s about time these companies got their act together! Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer’s Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A January 1994  3 Darwin to Adelaide: a new speed record of 85km/h The 1993 World Solar Challenge was won by Honda, slicing almost nine hours off the time of the last race & achieving an average speed of 85km/h for the 3003km race. By BRIAN WOODWARD Honda’s win came about due to progress in solar cells, power management, electric motor and tyre design and is represen­ tative of the great strides forward since the 1990 race. Professor Martin Green of the University of New South Wales is 4  Silicon Chip acknowledged to make the best solar cells on earth but a relative newcomer, Richard Swanson of SunPower Corporation, can be confirmed as the maker of the best silicon cells for solar race cars. It was Richard Swanson’s cells which helped win the third World Solar Challenge for Honda. The secret to the cells’ design was hidden in a simple sentence or two on the specifications sheet published by Honda shortly before the race. Rumours abounded that Honda had bought a complete set of race cells (more than 20% efficient) from Professor Martin Green in Sydney at a cost of more than $1.2 million. The price may be subject to doubt but the fact isn’t. Honda did buy the cells but used them for a ‘mule’ (a mule is a test-and-discover race car built for trials before the real car turns a wheel in anger). The cells used on the race car which appeared for scruti­neering a few days before the November 7th race day were RIGHT: HONDA’S winning Dream car sliced nearly nine hours off the record & recorded an average speed of 85km/h over the 3003km distance. The second placegetter, the Spirit of Biel, is shown on the facing page at left. Both cars used brushless hub motors. sourced from a relatively new US company, SunPower Corporation, which was not named at the time. They were described as “intrinsic mono­crys­tall­ ine silicon cells with back surface contacts . . . laminat­ed with a silicon poly­­mer and covered with a textured acrylic sheet. This sheet is fabricated with parallel angled grooves to enhance energy collection at low angles of solar incidence.” Fresnel lens What the description didn’t explain was that the ‘parallel angled grooves’ actually comprised an elaborate Fres­nel lens of varying angle. This meant that in the early morning and late afternoon, the sun’s rays were diverted by the lens to hit the cells at the optimum angle. For best output, solar arrays are turned until they are perpendicular to the sun’s rays. This isn’t practical with a solar race car because of poor aerodynamics, but this factor has been ignored by cell makers, up till now. SunPower made a solar array for the 1993 World Solar Chal­lenge and Honda’s claim of more than 1500 watts from eight square metres was beaten on several days when ideal conditions saw almost 1700 watts generated. The array weighs only 19.5kg. The array used by the Engineering School of Biel was devel­ oped by Deutsche Aerospace and proved to be almost as effective as in the Honda Dream. The car’s better aerodynamics were offset by the compromise angle of the array facing the sun. Naturally, it was best during the middle of the day. Inoue and Michelin both developed tyres which reduced roll­ing resistance by 30%. At low speeds, a solar race car spends almost one third of its power simply rolling along the road. A 30% reduction is significant. Getting the most efficient array’s power to an efficient motor in the most THIS CLOSE-UP VIEW shows the brushless DC hub motor used in the Northern Territory University’s Desert Rose. The motor is controlled by a power management computer & has a claimed efficiency of 96%. January 1994  5 LEFT: THE Spirit Of Biel with its solar array raised to recharge its batteries at the end of a day’s run. Below: the cramped cockpit in the University of Michigan’s car. efficient manner has been the bane of solar race car designers since the first race in 1987. With arrays at 20% and motors usually at 83-85%, losses in the tracking and motor management systems are to be avoided. The big breakthrough The big breakthrough for 1993 was the brushless DC motor-in-hub. Three cars, the Spirit of Biel, the Honda Dream and the Northern Territory University’s Desert Rose all used a hub motor designed to run at 900-1100 RPM with every individual winding addressed by a very busy power management computer. The Honda Dream’s motor had a claimed efficiency of 95%, the Desert Rose’s 96% and the Spirit of Biel’s 97%. All lost about 1.5-2.5% The Honda Dream motor had a claimed efficiency of 95%, the Desert Rose 96% & the Spirit of Biel 97%. All lost about 1.5-2.5% in the tracking & motor con­trolling computers. in the tracking and motor con­trolling computers. Compare this with a best of around 83% from the 1990 race winner and you can see why so much excitement was generated. It is highly likely that this motor design will become the electric car motor of the future. The effectiveness of power management in solar race cars is such that, at the Speed and Stability test day in Darwin, Biel claimed the Spirit of Biel would achieve 130km/h. It managed 129.9km/h. Honda claimed that its energy balancing computer system predicted an average speed of 86km/h. Over 3003km (even allowing time for flat tyres), Honda’s car achiev­ ed 84.96km/h. As it turned out, both estimates were amazingly close. SC 6  Silicon Chip What’s New In Car Electronics? Mazda’s Collision Avoidance System Japanese car manufacturer Mazda has developed a laser-based collision avoidance system for use in passenger vehicles. Using a laser which scans ahead of the vehicle across a 23° range, the system indicates objects potentially in the collision zone. The system can detect vehicles from approximately 140 metres away and pedestrians from 35-60 metres, depending on their cloth­ ing colour and material. It basically detects object move­­ment and from this determines the speed and direction of the object. When the system detects an object in the “caution zone” a warning buzzer sounds. Should the driver not respond and the object subsequently enters a “danger zone”, the vehicle’s brakes are applied. For example, the system would indicate a potential collision with a pedestrian when 30 metres from the person and would apply the brakes when the car was 20 metres away. At this stage the system is not available in any Mazda car currently on sale, although it is envisaged that the system will be fitted to production SC cars in the future. January 1994  7 Electronic Engine Management Pt.4: Changing The System – by Julian Edgar There is a widespread perception that a modern engine man­aged car is not open to engine modifications; that this type of system is signed, sealed and delivered. To some extent, this is true. Manufacturers leave little adjustment capability in an electronic engine management system, with often only the idle mixture and ignition timing open to change. In some cars, even these – ostensibly, at least – are non-adjustable. In a standard car, there are good rea- sons for this ap­proach. With exhaust gas oxygen feedback loops in operation, immediate ECM recognition of sensor failure, and limp-home modes of operation, the last thing that the manufacturer wants is someone armed with a screwdriver and a hammer deciding that the car needs a tuneup! A modern car might not need the mixture adjusted even once in 150,000 kilometres, for example. For those who like to tinker with their cars – to gain more power by fitting twin carbies, for example – the old days seem to be over. However, as with previous automotive technologies, there are ways of getting an electronic system to do as you want. Basically, there are four different approaches which can be taken: (1). The engine management system can have new inputs fed into it, thus giving changed outputs. (2). The system can have mechanical, electrical or electronic additions made to it. (3). The original manufacturer’s software can be changed – ie, the chip can be rewritten. (4). The original ECM can be removed and replaced with an after-market, fully programmable engine management computer. In this feature, we’ll look at the first two methods – crude, often effective and always cheap! The need for modification The engine coolant temperature sensor is just one of several sensors that provide information to the ECM. This ECM input is one of the easiest to fool. 8  Silicon Chip But why would you want to modify the engine management system, anyway? A turbocharged car is probably easiest to under­stand in this context, because the power produced by the engine is so easily increased. A naturally aspirated engine has air pushed into it by atmospheric pressure – through the air filter, past the throttle butterfly, into the plenum chamber, down the cylinder runner, EXTERNAL CONNECTIONS SEAL WATER (COOLANT) CONTACT ZONE THERMISTOR Fig.1: basic construction of a typical coolant temperature sensor. A thermistor is used as the sensing element. past the inlet valve and then (finally) into the cylinder. As the piston sinks on its intake stroke, a partial vacuum is created within the cylinder, and one bar of atmospheric air pressure does the pushing. The amount of air that the engine inhales depends on its size, on how much flow loss is experienced by the air on its torturous path into the cylinder, and how quickly the engine is rotating (its rpm). However, if the air If data showing the sensor’s temperature/resistance relation­ship is not available, then some testing with hot water, a thermometer & a multimeter will soon reveal its characteristics. pressure is raised above atmospheric by a turbocharger or supercharger, then greater flows will occur. With extra fuel added, more power will be produced. The induction pressure above atmospheric which the turbo produces (called turbo boost pressure) greatly influences the air mass passing into COEFFICIENT OF ENRICHMENT 1.0 the engine. Manufacturers are often conserva­tive in their boost pressure, generally using around 0.5 bar (about 7 psi). However, most turbo engines will happily cope with 0.7-0.8 bar without mechanical modification. The problem comes when the volume of air passing into the engine is much greater than the manufacturer designed the EFI (electronic fuel injection) system to cope with. To some extent, the system will self-compensate for changes. The airflow meter will signal the greater air mass flowing to the ECM and this in turn will control the injector pulse width to give CONTACT TEMPERATURE Above: this close-up view shows a typical coolant temperature sensor. It is usually mounted close to the thermostat. Fig.2: the enrichment pattern as a function of engine temperature in a VL Holden Commodore. January 1994  9 A resistor or potentiometer wired in series with the coolant temperature sensor will cause the ECM to provide more fuel – a very cheap modification. the appro­ priate mixture. However, if the airflow is increased too far, the stage will be reached where the mixture starts to become lean – with not enough petrol being mixed with the air. In this situa­tion, the injectors may be held open continuously but their flow rate may be insufficient. Other causes of increased induction flow which may cause leaning-out include traditional “hotting-up” methods like larger exhaust systems, head modification by bigger valves, and so on. Fooling the ECM The ECM computes injector pulse width on the basis of its inputs and on its internal base fuel figures. If the coolant temperature sensor indicates that the engine is cold, then more fuel will be injected – the equivalent of a choke in a car with a carburet- A microswitch can be used to cause full-throttle enrichment to occur at an earlier throttle opening than normal. tor. Similarly, if the throttle position switch (TPS) indicates that your foot is hard down, then the mixture will be slightly enriched to give maximum engine power. If any conditions which would cause the ECM to enrich the mixture are artificially created, then the fuel flow into the engine will be increased, assuming that maximum fuel flow isn’t already occurring. Probably the easiest sensor input to fool is the coolant temperature sensor. This sensor consists of a thermistor located in the engine cooling system, usually close to the thermostat. Fig.1 shows an example of a coolant temperature sensor. In Fig.2, the pattern of enrichment which the ECM carries out in response to low engine temperature is shown for a VL Holden Commodore. As the coolant temperature rises, the FULL THROTTLE CONTACT THROTTLE SHAFT CONTACT PATH (CAM) IDLE CONTACT (MICROSWITCH) ELECTRICAL HARNESS PLUG 10  Silicon Chip Fig.3: basic layout of a typical throttle position switch (TPS). The idle contact microswitch is normally closed at idle & opens as the throttle moves off its stop. The full throttle contacts are normally open but close at full throttle settings to provide extra fuel enrichment. resistance of the sensor decreases. A typical coolant temperature sensor has the follow­ing characteristics:    0°C 6000 ohms 20°C 2500 ohms 30°C 1800 ohms 40°C 1200 ohms 70°C   450 ohms 90°C   250 ohms 100°C   190 ohms 110°C   110 ohms If a 5kΩ pot is placed in series with the sensor, then the ECM can be easily persuaded that the engine coolant temperature is anything from 0°C to its real value! Feeding information to the ECM which understates the actual temperature of the coolant will cause the mixture to become richer than it otherwise would be. More fuel will be injected as the ECM program tries to overcome the expected cold-engine affects of poorer fuel atomization, thicker oil, and so on. However, while enrichment may be quite substantial at some rpm settings, it’s unlikely that the ECM was designed with the idea that the engine will be revved at 6000rpm with the coolant temperature at 5°C! Cold-start enrichment usually declines with increasing load and/or rpm. On the other hand, if the engine runs slightly lean throughout its rev range (because of engine modifi­cations), then a potent­ iometer in series with the cold-start sensor can be a very good starting point in overcoming it. If full throttle enrichment is wanted earlier in the throt­ tle opening, then a microswitch operated by the rotation of the throttle shaft can be used to trigger this input – a func- tion usually provided by the throttle position switch (TPS). Fig.3 shows a typical TPS. The correction coefficient used with the base fuel figures increases with increasing rpm – and the final correction step is inducted by the throttle position switch. Other sensors with the potential for deliberate misuse include the knock sensor (to retard timing), the airflow sensor (to change mixtures), the vehicle speed sensor (remove speed limiter), the MAP sensor (remove turbo over-boost fuel cutoff), and the induction air temperature sensor (change mixtures). Extra Injectors If the injection system provides insufficient fuel flow at full load, then extra fuel injectors can be added. The most so­phisticated way of doing this is to control the extra injector by the use of a commercially-made supplementary injection computer, which has various inputs to monitor load and rpm. However, be­cause full load usually coincides with maximum airflow, the accuracy with which fuel mixtures must be held for good performance is fairly low. An extra injector can be mounted prior to the plenum cham­ber to promote good fuel mixing and can be wired in series with one of the normal injectors. To prevent it from enriching the mixture constantly, it needs to be switched on and off. In a turbocharged car, the simplest way of achieving this is to use a pressure switch which is mounted on the plenum chamber. Adjust­ able pressure switches – under the Hobbs brand name – are avail­able from automotive instrument suppliers. However, switch-on of the injector can be triggered in a more sophisticated manner by monitoring one or more of the stan­ dard engine management sensors. By using voltage comparators, the airflow meter and throttle position switch could be monitored, with the extra injection occurring only at high gas flows and wide throttle openings. Of course, the extra injector does not come on stream gradually with this system. Instead, the mixture undergoes a sudden enrich­ ment by 10-20% (depending on the supple­ ment­ary injector size). To overcome this, a circuit can be made up which duplicates the commercially availa- Ancillary injectors can be used to provide more fuel if the original injectors prove to be inadequate after engine modifica­tions. The injector on the left is a cold-start injector, while at right is an injector from a 4-cylinder Nissan engine. The typical cost from a wrecker would be $10 each. This Holden VL Turbo Nissan engine has been fitted with extra fuel injectors which, along with other modifications, provide a 50% power boost. The additional injectors are triggered by mani­fold pressure switches & are pulsed by the standard computer. ble injection computer by increasing supplementary injector pulse width in response to greater gas flow, etc. In prtactice though, this is not always needed. Another approach is to use two sequentially-operated low-capacity supplementary injectors. The extra injector load placed on the output transistors of the ECM doesn’t appear to cause problems, although the supplemen­tary injectors should be of the same resistance as the original injectors. The power capability of the ECM output tran- sistors may also vary from computer to computer. With extra injectors available cheap­ ly from wreckers of Japanese engines (about $10 each), a supplemen­ tary in­jection system can be added for very low cost. The final mixtures should always be checked. The best way to do this is to use a chassis dyn­a­mometer in conjunction with a four-gas exhaust analyser. Another (cheaper) method is to build an oxygen sensor output meter and closely monitor the mixtures in SC real driving conditions. January 1994  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Build a 40V 3A variable power supply This 1.23-40V adjustable power supply is designed for heavy-duty work. It uses a highefficiency switching regulator circuit & features preset current limiting, full overload protection & an LCD panel meter for precise voltage & current readouts. By JOHN CLARKE By far the biggest advantage that this elegant new power supply has over other designs is its high-efficiency switching regulator circuitry. In this type of circuit, the regulator is either fully on or fully off at any given instant and so it dissipates very little power, even when delivering high current at low output voltage. In practical terms, this means that the regulator generates very little heat and so we don’t need to use large and 16  Silicon Chip expensive heatsinks. And that in turn means that we can greatly simplify the construction and pack the required circuitry into a much smaller case than would otherwise be required for a conventional design employing a linear regulator. In fact, by employing switchmode operation, the regulator in this circuit generates less than 10W under worst case condi­tions. By contrast, a linear regulator in an equivalent 40V supply would need to dissipate around 120W when delivering 1.23V at 3A! This is an enormous amount of heat to extract and would require a large finned heatsink to keep the regulator temperature within specification. This is one power supply that can continuously supply a high output current without suffering from thermal overload problems. By contrast, a linear regulator has inherently high dissipation, especially at very low output voltages (due to the high voltage across the regulator), and this severely limits its output current capability. Another very commendable feature of the circuit is the low level of ripple and hash in the output. Achieving this is not always easy in a switchmode design but we’ve done it using a combination of extra filtering and careful circuit layout. As shown in the specifications panel, the output noise and ripple is just 5mV p-p at 24V, reducing to a minuscule 1mV p-p at 3V. 4 Main Features • Output voltage continuously adjustable from 1.23V to 40V • Greater than 3A output current capability from 1.23-28V • Digital readout of voltage, current or current limit setting • 10-turn pot for precise voltage adjustment • Adjustable current limit setting • Current overload indication • Regulation dropout indication • Output fully floating with respect to earth • Load switch • Low output ripple • Short circuit & thermal overload protection • Minimal heatsinking AMPERES 3 1 0 0 5 10 15 20 VOLTS 25 30 35 40 Fig.1: the voltage vs. current characteristics of the supply. It is capable of supplying a hefty 3.8A over the range from 1.23V to 28V. Beyond that, the available output current decreases due to the transformer regulation. These are excellent figures for a switching design and are comparable to those achieved by linear circuits. The switching hash is also very low. It is far less than in previous designs and, in fact, is below the ripple level. Digital readout Do you need to precisely monitor the output voltage or current, or accurately set the current limit? Well, with this power supply you can because it uses an LCD panel meter to give a digital readout of voltage or current. A single toggle switch selects the measure­ment mode. A 10-turn pot makes it easy to set INPUT VOLTS 2 the output voltage to the exact value required, while the current limit is set by first pressing the Set button and then adjusting the Current Limit pot until the LCD shows the required value. In addition, there are two LEDs on the front panel and these provide current overload and regulation dropout indication. There’s one other control on the front panel that we have­n’t yet mentioned – the Load switch. This simply connects or disconnects the load (ie, the device being powered) from the supply rail and eliminates the need to switch the supply off when making connections to the output terminals. It also allows the output voltage and current limit values to be set before power is applied to the load. Output capabilities Fig.1 plots the performance of the supply. As shown, it is capable of Fig.2: how a switching regulator operates. When S1 is closed & S2 is open, current flows to the load via L1 which stores energy. When S1 subsequently opens & S2 closes, the energy stored in the inductor maintains the load current until S1 closes again. supplying a hefty 3.8A over the range from 1.23V to 28V. Beyond that, the available output current decreases due to the transformer regulation. However, there is still 2.2A avail­able at 30V, 1.4A at 35V and 600mA at 40V. The load regulation is excellent at the higher voltages but is not as good LM2576-ADJ 1 Cin REGULATOR 4 DRIVER 1.23V REF L1 2 OSCILLATOR RESET ON/OFF 5 3A SW THERMAL SHUTDOWN, CURRENT LIMIT D1 Vout C1 R2 3 Vout = 1.23(1 + R2/R1) R1 Fig.3: a basic switchmode voltage regulator based on the LM2576 IC. In this circuit, an internal 3A switching transistor takes the place of S1 in Fig.2, while diode D1 takes the place of S2. The output voltage is set by the ratio of R2 & R1, which feed a sample of the output voltage back to an internal comparator. January 1994  17 REGULATOR DROPOUT INDICATOR IC3c 240VAC INPUT TRANSFORMER T1 AC RECTIFIER AND FILTER 42V SWITCHING REGULATOR IC1 ON/ OFF FILTER L2 R1 CURRENT SENSE The circuit is based on the National Semiconductor LM2576HVT high voltage adjustable switchmode voltage regulator. Fig.2 shows how a switching regulator operates. In operation, S1 and S2 operate at high speed and are alternately closed and opened. These two switches control the current flowing in inductor L1. When S1 is closed and S2 is open, the current flows to the load via inductor L1 which stores up energy. When S1 subsequently opens and S2 closes, the energy stored in the inductor maintains the load current until S1 closes again. The output voltage is set by adjusting the switch duty cycle and is equal to the input voltage multiplied by the ratio of S1’s on time to its off time. Capacitor C1 is used to filter the resulting output voltage before it is applied to the load. Fig.3 shows a complete voltage regulator based on the LM2576 IC. It is a 5-pin device which requires just five extra components to produce a basic working circuit. Its mode of opera­tion 18  Silicon Chip 0V SIGNAL CONDITIONER IC4 DPM-02 LCD VOLTMETER MODULE RANGE AND DECIMAL POINT SWITCH IC3d, IC5 GND Fig.4: this diagram shows all the relevant circuit sections. Switching regulator IC1 forms the heart of the circuit & adjusts its output according to the setting of VR1. IC2 amplifies the voltage across current sense resistor R1 & the amplified voltage is then fed to IC3a where it is compared with the output from VR2 to derive the current limit setting. A 3½-digit LCD panel meter provides precise readout of the voltage & current settings. Basic principle VOLTS OR AMPS S3 OUTPUT VOLTAGE ADJUST VR1 at lower voltages. This is because of higher losses in the circuit due to the higher pulse currents involved at low voltage settings. The line regulation is less than 0.1% for a 10% change in mains voltage – see specifications panel. 0V CURRENT LIMIT VR2 IC2 x200 CURRENT LIMIT INDICATOR IC3b COMPARATOR IC3a SET CURRENT S4 is the same as that described in Fig.2 except that here a 3A switching transistor is used for S1, while an external diode (D1) is used for S2. What happens in this case is that when the transistor is on, the current flows to the load via inductor L1 as before and D1 is reverse biased. When the transistor subsequently turns off, the input to the inductor swings negative (ie, below ground). D1 is now forward biased and so the current now flows via L1, the load and back through D1. The output voltage is set by the ratio of R2 and R1, which form a voltage divider across the output (Vout). The sampled voltage from the divider is fed to pin 4 of the switcher IC and thence to an internal comparator where it is compared with a 1.23V reference. This sets Vout so that the voltage produced by the divider is the same as the reference voltage (ie, 1.23V). Apart from the comparator and the switching transistor, the regulator IC also contains an oscillator, a reset circuit, an on/off circuit and a driver stage with thermal shutdown & current limiting circuitry. The incoming supply rail is applied to pin 1 of the IC and connects to the collector of the 3A switching transistor. It also supplies an internal regulator stage which then supplies power to the rest of the regulator circuit. Basically, the LM2576 uses pulse width modulation (PWM) control to set the output voltage. If the output voltage rises above the preset level, the duty cycle from the driver stage decreases and throttles back the switching transistor to bring the output voltage back to the correct level. Conversely, if the output voltage falls, the duty cycle is increased and the switch­ i ng transistor conducts for longer periods. The internal oscillator operates at 52kHz ±10% and this sets the switching frequency. This frequency is well beyond the limit of audibility although, in practice, a faint ticking noise will occasionally be audible from the unit due to magnetostric­tive effects in the cores of the external inductors. One very useful feature of the LM2576 that we haven’t yet mentioned is the On/Off control input at pin 5. As its name implies, this allows the regula­tor to be switched on or off using an external voltage signal. This feature is put to good use in this circuit to provide the adjustable current limiting feature, as we shall see later on. Block diagram Although the LM2576-ADJ forms the heart of the circuit, quite a few other parts are required to produce a practical working variable supply. Fig.4 shows the full block diagram of the unit. Power for the circuit comes from the 240VAC mains. This feeds power transformer T1 and its output is rectified and fil­tered to provide a 42V DC supply which is then fed to the input of the switching regulator (IC1). VR1 sets the output voltage from the regulator and essentially forms one half of the voltage divider shown in Fig.3. IC3c monitors the input and output voltages from the regu­lator and lights a LED when the difference between them is less than 3.3V. This indicates that the circuit is no longer regulat­ ing correctly. Following the regulator, the current in the nega­tive rail flows through the sensing resistor R1. The voltage across this resistor is then amplified by IC2 and applied to comparator stage IC3a. R1 has a value of just .005Ω, while IC2 operates with a gain of 200. This means that IC2’s output voltage is numerically equivalent to the current (in amps) flowing through R1 (ie, IC2’s output increases by 1V per amp). So, in addition to driving IC3a, IC2 is also used to drive the LCD digital voltmeter (via S4, S3 & IC4) to obtain current readings. IC3a and potentiometer VR2 provide the current limiting feature. In operation, IC3a compares the voltage from IC2 with the voltage set by VR2. This voltage can be anywhere in the range from 0-4V, corresponding to current set limits of 0-4A. The circuit works as follows. If IC2’s output rises above the voltage set by VR2 (ie, the current through R1 rises above the set limit), IC3a’s output goes high and turns off the switching regulator via the On/ Off con­trol. The current through R1 now falls until IC2’s output falls below the voltage from VR2, at which point IC3a’s output goes low and switches the regulator (IC1) back on again. The current now rises until the regulator is switch­ed off again and so the cycle is repeated indefinitely. By this means, IC3a switches the regulator on and off at a rapid rate to limit the current to the value set by VR2. IC3a also drives comparator stage IC3b and this lights an indicator LED when ever current limiting takes place. Switch S4 selects between the outputs of IC2 and VR2, so that either the load current or the current Specifications Minimum no load output voltage ......................................... 1.23V ±13mV Maximum no load output voltage ....................................................... 40V Output current ...........................................................................see graph Current limit range .................................................................. 10mA to 4A Current limit resolution .................................................................... 10mA Line regulation ........................<0.1% for a 10% change in mains voltage Voltmeter resolution........................ 10mV from 1.23V to 16.5V (approx); 100mV from 16.5V to 40V Current meter resolution ................................................................. 10mA Meter accuracy .................................................................1% plus 2 digits Load regulation no load to 3A <at> 24V ......................................................................1.5% no load to 3A <at> 12V .........................................................................2% no load to 3A <at> 6V ........................................................................2.8% no load to 3A <at> 3V ........................................................................4.2% Output ripple and noise 3A <at> 24V ................................................................................ 5mV p-p 3A <at> 12V ................................................................................ 2mV p-p 3A <at> 6V .................................................................................. 1mV p-p 3A <at> 3V .................................................................................. 1mV p-p limit setting is displayed on the LCD panel meter. This makes it easy to set the current limit. All you have to do is press S4 and rotate VR2 (the Current Limit control) until the required value appears on the digital readout. Immediately following R1 is a filter stage which is based mainly on inductor L2. This filter removes most of the ripple and high frequency noise from the positive and negative supply rails. The two supply rails are then applied to the load via S2. Finally, the 3½-digit LCD panel meter is used to display either the output voltage, the output current or the current limit setting, depending on the positions of switches S3 and S4. The selected signal voltage is applied to the panel meter via signal conditioning amplifier IC4, which provides the required level shifting and attenuation. For voltages up to about 18V, the display resolution is 10mV. It is then switched to a higher range with 100mV resolution to prevent over-range for output voltages above 20V. This task is performed using IC3d and IC5. Circuit details Refer now to Fig.5 for the full circuit details. It con­tains all the elements shown in the block diagram of Fig.4. We’ll go through each of the major sections in turn. Transformer T1 is supplied with mains power via fuse F1 and power switch S1. Its 30VAC secondary is full-wave rectified using diodes D1-D4 and filtered using two parallel 4700µF 50VW electrolytic capacitors. The resulting 42V DC supply is applied to the switching regulator (IC1). Note the 100µF capacitor connected between pins 1 & 3 of IC1. This capacitor is necessary to prevent circuit instabili­ty and is mounted as close to the IC as possible. D5, L1, the two parallel 1000µF capacitors and VR1 form the basic switchmode power supply block (see Fig.3). D5 is a Schottky diode which is rated at 10A and 60V. It has been specified in preference to a conventional fast recovery diode because of its low forward voltage drop. As a result, there is very little heat dissipation within the diode and this leads to increased effi­ciency. The output from IC1 feeds directly into L1, a 300µH induc­ tor. This is wound on a Philips ETD29 ferrite core assembly with a 1mm air-gap to prevent core saturation, as can occur when DC currents flow in ungapped core windings. January 1994  19 The 3A-40V Adjustable Power Supply is easy to build since most of the parts are mounted on a single PC board & the LCD panel meter is supplied ready made. No large heatsinks are required in the design because the switching regulator (IC1) dissipates very little power, even at low-voltage high-current settings. VR1 and its associated 1.5kΩ resistor provide voltage feed­back to pin 4 of IC1, to set the output level. When VR1’s resist­ance is at 0Ω, the output from the regulator (pin 2) is equal to 1.23V. This output voltage increases as the resistance of the pot increases. The 680Ω 5W resistor connected across the regulator output discharges the two 1000µF capacitors to the required level when a lower output voltage is selected. Filter circuit 20  Silicon Chip Regulator dropout Comparator IC3c and its associated parts form the regulator dropout indicator depicted on the block diagram. In this circuit, a sample of the output voltage is applied to pin 8 of IC3c and compared with a sample of the regulator input voltage at pin 9. Zener diode ZD2 provides an offset, so that IC3c only switches its output (pin 14) low when the voltage across the regulator drops below 3.3V. In this situation, IC1 is no longer Fig.5 (right): the main switching regulator circuit is based on IC1, L1 & D5, while IC2, IC3a & VR2 control the ON/OFF input of IC1 to provide the current limit feature. IC4 provides signal conditioning for the DVM02 panel meter, with IC3d & IC5 providing automatic range switching. ▲ Inductor L2 and its associated 100µF and 0.1µF capacitors make up the filter circuit shown in the block diagram (Fig.4). This LC network effectively attenuates the switching frequency ripple by a factor of 10. In practice, L2 consists of two separate windings (L2a, L2b) on the same toroidal core. These two windings are phased so that the flux developed by L2a is cancelled by the flux developed by L2b. This type of winding arrangement provides what is known as DC compensation and is done to prevent core saturation. As shown in Fig.5, L2a is used to decouple the positive supply rail, while L2b decouples the negative rail. The inductor thus effectively filters any common mode signals, while the 100µF and 0.1µF capacitors across the output attenuate any remaining spikes. The resulting filtered voltage is then applied to the output terminals via load switch S2. Additional filtering is applied at this point using a 0.33µF capacitor across the termi­nals and a 0.1µF capacitor between the negative terminal and mains ground. Note that this 0.1µF capacitor must be rated at 250VAC to comply with safety standards. January 1994  21 E N ZD1 9V 1W A A 12345 K A K ADJ 100 16VW POWER S1 K VIEWED FROM BELOW 680  5W CASE 240VAC A F1 500mA 10k 47k D 10 8 VR4 5k 3 IC6 LMC7660 0V 15V 0V 15V 6.8k 1k 5 100k 10 D1-D4 4x1N5404 2 3 7 X 1k 4 IC4 OP77GP -9V +9V 4700 50VW +42V 6 0.1 100  100  4700 50VW 2 3 7 100 63VW 10k 22k +9V S4b 11 10 2 4 1 K 1 100k IC3d S3 1 OUT 13 10 MONITOR VOLTAGE 2.2k 4 5 A K IC3a LM339 9 10 11 C B A 680  5W L1 300uH S4: 1: MEASURE CURRENT 2: SET CURRENT LIMIT D5 MBR1060 2 MONITOR CURRENT S4a 2 CURRENT LIMIT VR2 1k 220  680  ON/ GND OFF 3 5 FB IN IC1 LM2576HVT-ADJ REF1 LM336-5 A -9V 1.5k 6 0.1 CURRENT CAL VR3 10k -9V 4 IC2 OP77GP 15k +42V OUTPUT ADJUST VR1 50k 10T 3A-40V CURRENT LIMITED POWER SUPPLY 91k 4 2 T1 M2170 5 cx 3 1000 63VW 4 c 6 1M D6 1N4148 IC5 4053 16 cy 2 2.2k 1000 63VW 7 1 2 2V 200mV +9V 6 7 L2b 8 b 15 RANGE by bx 14 330pF 0.1 R1 . 005  L2a IC3b K  A 0.1 63V +42V 1k 1 X I/P- 10k 47k DP COM DP2 9 8 ~2. 8V COMMON DVM-02 I/P+ 1k 4.7k 0.5W ZD2 3.3V 400mW 12 3 CURRENT LIMIT LED1 100 63VW 0.33 63V DP1 +BAT +9V IC3c REGULATOR DROPOUT LED2 0.1 250VAC LOAD S2 -BAT 14 1k K  A +9V GND OUTPUT 1.23-40V 3A PARTS LIST 1 PC board, code 04202941, 222 x 160mm 1 front panel label, 250 x 75mm 1 plastic instrument case, 260 x 190 x 80mm 2 aluminium front & rear panels for above case 1 M-2170 30V 100VA mains transformer (Altronics) 1 LCD voltmeter module (Altronics Cat. Q-0560) 3 captive head binding posts (1 red, 1 black, 1 green) 1 2AG panel-mount fuseholder 1 500mA 2AG fuse 1 TO-220 heatsink, 26 x 30 x 15mm (Jaycar Cat. HH-8504) 1 SPDT mains rocker switch with neon indicator (S1) 1 DPDT paddle switch (S2) (DSE Cat. P-7693 or equiv.) 1 SPDT toggle switch (S3) 1 DPDT momentary pushbutton switch with common terminal at side (S4) (Altronics S-1394) 1 ETD29 transformer assembly with 3C85 core (Philips: 2 cores 4312 020 3750 2; 1 former 4322 021 3438 1; 2 clips 4322 021 3437 1) 1 RCC32.6/10.7, 2P90 ring core (Philips 4330 030 6035) 2 15mm diameter knobs 1 mains cord & plug 1 cord grip grommet 2 5mm LED bezels 26 PC stakes 5 self-tapping screws to mount PC board 2 4mm screws nuts & washers 4 3mm screws, nuts & star washers 1 3mm countersunk screw, nut & star washer (use a dress screw if the front panel is screen printed) 6 crimp lug eyelets for 3mm screw 2 solder lugs for 9mm thread 1 TO-220 insulating bush & washer 12 cable ties 1 50kΩ 10-turn pot (VR1) 1 1kΩ linear pot (VR2) 1 10kΩ horizontal trimpot (VR3) 1 5kΩ horizontal trimpot (VR4) regulating and IC3c lights LED 2 to provide a warning that the supply has dropped out of regulation. low input offset voltage and input bias current specifications. This is necessary to ensure that IC2’s output will be at 0V when no current is flowing through R1. The OP77GP used here typically has an input offset voltage of just 50µV and an input bias current of just 1.2nA. Because its inputs operate at close to ground potential, IC2 must be powered from both positive and negative supply rails. The positive supply rail for IC2 (and for the remaining ICs) is derived from the output of the bridge Current limiting The current sense resistor (R1) is wired into the negative supply rail before L2b and consists of a short length of 0.4mm enamelled copper wire. As explained previously, the voltage across it is multiplied by 200 using IC2, so that IC2’s output delivers 1V per amp of load current. In this application, IC2 must have 22  Silicon Chip Wire & cable 1 2-metre length of 1.5mm enamelled copper wire 1 3.5-metre length of 0.8mm enamelled copper wire 1 60mm length of 0.4mm enamelled copper wire 1 200mm length of 0.8mm tinned copper wire 1 25mm length of 1.0mm enamelled wire (for use as a feeler gauge) 1 600mm length green/yellow mains wire 1 1.5-metre length of red hook-up wire 1 1.5-metre length of black hookup wire 1 1.5-metre length of green hookup wire 1 1.5-metre length of blue hookup wire 1 200mm length of 3-way rainbow cable 1 200mm length of red 32 x 0.20mm hook-up wire 1 200mm length of black 32 x 0.20mm hook-up wire Semiconductors 1 LM2576HVT-ADJ high voltage adjustable switchmode voltage regulator (IC1) (NSD) 2 OP77GP op amps (IC2,IC4) 1 LM339 quad comparator (IC3) 1 4053 CMOS switch (IC5) 1 LMC7660 switched capacitor voltage converter (IC6) 4 1N5404 3A 400V diodes (D1-D4) 1 MBR1060 Schottky diode (D5) 1 1N4148 signal diode (D6) 1 9V 1W zener diode (ZD1) 1 3.3V 400mW zener diode (ZD2) 1 LM336-5 5V reference (REF1) 2 5mm red LEDs (LED1,LED2) Capacitors 2 4700µF 50VW electrolytic 2 1000µF 63VW electrolytic 2 100µF 63VW electrolytic 1 100µF 16VW electrolytic 3 10µF 16VW electrolytic 1 0.33µF 63VW MKT polyester 4 0.1µF 63VW MKT polyester 1 0.1µF 250VAC polyester 1 330pF MKT polyester Resistors (0.25W, 1%) 1 1MΩ 1 4.7kΩ 0.5W 2 100kΩ 2 2.2kΩ 1 91kΩ 1 1.5kΩ 2 47kΩ 5 1kΩ 1 22kΩ 1 680Ω 1 15kΩ 2 680Ω 5W 3 10kΩ 1 220Ω 1 6.8kΩ 2 100Ω Miscellaneous Insulating tape, solder, heatshrink tubing, heatsink compound, 4.7Ω 5W resistor (for load testing). rectifier via a 680Ω resis­tor and 9V zener diode ZD1. IC6, an LMC7660 switched capacitor voltage converter, generates the -9V rail for IC2. In operation, IC6 first charges the 10µF capacitor between pins 2 & 4 to 9V. It then reverses the connections of the ca­pacitor so that it can charge a second 10µF capacitor at pin 5 with negative polarity. This process is repeated continuously at a rate of about 10kHz so that the resulting output is a relatively smooth DC voltage. Comparator stage IC3a monitors the output voltage from IC2 and compares this with the voltage on its inverting input, as set by current limit control VR2. This potentiometer and its asso­ciated 220Ω resistor form a voltage divider network which is connected across 5V reference REF1. In operation, VR2 sets the voltage on pin 4 of IC2 at between 0V and 4V, corre­ sponding to current limit settings of 0-4A. Because IC3a is an open collector device, its output at pin 2 is connected to the positive supply rail via a 2.2kΩ pull-up resistor. If the voltage at the output of IC2 is greater than that set by VR2, pin 2 of IC3a is pulled high by this resistor. This also pulls pin 5 of IC1 high and switches off the regulator to provide current limiting. At the same time, pin 6 of IC3b is pulled high via D6, and so pin 1 switch­es low and LED 1 lights to indicate current limiting. When the current subsequently falls below the preset limit, pin 2 of IC3a switches low again and the regulator turns back on. Thus, IC3a switches the regulator on and off at a rapid rate to provide current limiting, as described previously. The 1MΩ resistor and 330pF capacitor at pin 6 of IC3b provide a small time delay so that LED 1 is powered continuously during current limiting. Fig.6: this scope photograph shows 100Hz ripple at the output terminals of the power supply when driving a 3A load at 12V. Fig.7: this is the 100Hz ripple for a 3A at 24V. Note the increase in ripple with the higher voltage. Digital panel meter IC4 forms the basis of the signal condi­tioning circuit. This op amp is wired in differential mode and operates with a gain of 0.01, as set by the resistor feedback networks on pins 2 and 3. Its output appears at pin 6 and is applied to the I/P+ input of the digital voltmeter (DVM-02). The DVM-02 is a standard panel meter with differential inputs (I/P+ and I/P-) and requires a 9V power supply between its BAT + and BAT- terminals. Its I/P- input is fixed at 6.2V (ie, 2.8V below the positive supply) and this reference voltage is used to bias pin 3 of IC4 via a 1kΩ resistor. This bias produces an offset at the output of IC4 and ensures that the voltage fed to the digital voltmeter is within its operating range. This signal conditioning is necessary because the DVM-02 cannot be used to directly measure voltages within 1V of either supply rail. The voltage range of the DVM-02 is selected by bridging pads on the volt- Fig.8: this is the high frequency switching noise as seen on a 100MHz oscilloscope using a 10:1 probe. meter PC board. In this case, only the 200mV and 2V ranges are used. The decimal point is selected in a similar manner (ie, by bridging DP1 or DP2 to DP COM). In operation, switch S3 selects either the positive output rail or the output of IC2 to provide voltage or current measure­ ment, respectively. The resulting voltage signal on the wiper of S4b is then applied to pin 3 of IC4 via VR4 and its associated series resistors. Alternatively, pressing S4 applies the voltage on the wiper of VR2, so that the current limit reading will be displayed on the DVM-02. This occurs regardless of the setting of S3. In summary then, IC4 divides the voltage at point D by 100 and adds this to the 6.2V reference signal. Thus, if we are measuring an output voltage of 20V for example, IC4’s output will be at 6.2 + 20/100 = 6.4V. This is 200mV great­er than the reference voltage at I/P- which means that the meter will display 20.0 – assuming suitable range and decimal point switching. Range switching IC3d and IC5 provide the range and decimal point switching, so that this operation is completely automatic. IC3d is wired as a Schmitt trigger and monitors the voltage between point D and the negative output rail (point X) via a voltage divider (47kΩ and 10kΩ). IC3d’s output drives the A, B and C inputs of IC5, a 3-pole 2-way CMOS analog switch. In this application, one switch pole (pole ‘b’) is used for range selection and another (pole ‘c’) for decimal point selection. The third switch pole is left unused. When the voltage at D is less than 18V, IC3d’s output is pulled high and pole ‘b’ connects to the ‘by’ position so that the 200mV range is selected. At the same time, pole ‘c’ connects to the ‘cy’ position so that decimal point DP2 is selected. This allows the display to read from 0.00 to 18.00 volts (approx.) with 10mV resolution. However, if the voltage at point D rises above 18V, the output of IC3d switches low and so the A, B & C inputs of IC5 also go low. Pole ‘b’ now connects to the ‘bx’ position and pole ‘c’ to the ‘cx’ position, so that the 2V range and decimal point DP1 are now selected. The display can now read from 18.0 to 40.0 volts with 100mV resolution (note: the most significant digit is not used in this mode). Because Schmitt trigger IC3d operates with about 3V of hysteresis (as set by the 100kΩ feedback resistor), the voltage at point D must now drop below about 15V before pin 13 switch­ es high again to select the 200mV range on the DVM-02. The voltage at point D must then be increased above 18V again to select the 2V range. This small amount of hysteresis prevents display jitter at settings close to the range changeover point. That completes the circuit description. Next month, we will describe the SC construction. January 1994  23 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Amended pulsar probe D1 OA90 5-15VDC This circuit was published in the July 1993 issue but incorporated a number of drafting errors. For completeness, we are re-publishing the circuit, together with a brief description of how it works. Depending on how long pushbutton S1 is pressed, the circuit will generate a single pulse or pulse stream. IC1 is a 4093 quad NAND Schmitt trigger with IC1c connected as a free-running oscil­ lator which is enabled whenever pin 8 is pulled low. This happens whenever S2 is pressed long enough to allow C1 to charge and thus take pin 8 high. If S1 is pressed only briefly, the resulting low to high transition at pin 4 1.2k IC 4093 1 82k 3.3 25VW TANT 14 IC1a 3 1k Q1 BC558 2 S1 Q3 BC558 1.2k 0.1 68pF 82k 5 6 OUTPUT 12 4 IC1b IC1d D2 OA90 7 13 11 68pF 22k Q2 BC548 1.2k Q4 BC548 120k 1.8k 8 IC1c C1 4.7 25VW 10 1k 1k 9 3.3k C2 1 25VW 600Hz OSCILLATOR of IC1b is coupled though IC1d which sets its output at pin 11 high. Pin 11 is capacitively coupled to an output stage compris­ ing transistors Q1-Q4. If pin 11 goes high, Q2 and Q3 turn on while Q1 and Q4 turn off. Conversely, if pin 11 goes low, Q1 and Q4 turn on while Q2 and Q3 turn off. Greg Freeman, Nairne, SA.  0.7V Beta measurements with an analog multimeter By using a simple setup, you can make a direct measurement of hFE (Beta) for conventional and Darlington transistors at high currents. Most digital multimeters make Beta measurements at very low currents and do not give an indication of the gain at high currents. To do the test, you need a variable DC supply and an analog multimeter. First, adjust the power supply output to read 10V DC on the meter, then connect the transistor to be tested. The emitter resistor RE sets the maximum current drawn by the transistor while the base bias resistor RB is used to set the base current. For this method, we set the voltage from the power supply using the 10V range of the multimeter and then, without changing the range or mode, the Beta value is read directly off the “Ohms” scale. Typically, the method involves selecting a suitable value for RE to set the midscale current while RB determines the base current at midscale which then determines the Beta multiplier. For example, to obtain 100mA at midscale (5V = 0.1A x RE), RE should be 50Ω. Most meters would have the “Ohms” scale reading 10 at centre scale, so if we want 24  Silicon Chip 1k 5V AT CENTRE SCALE VARIABLE DC SUPPLY Rb ANALOG DVM ON 10VDC RANGE  0. 7V 5V AT CENTRE SCALE Re Beta to read 1000 at centre scale, the desired multiplier is 100. To calculate RB we use the formulas RB = 5V/iB and iB = iE/hFE = 100mA/1000 = 0.1A/1000. Therefore RB = 5/(0.1/1000) = 50kΩ. The Ohms scale will indicate the hFE directly between 100 to 10,000 with reasonable accuracy and can be used for matching transistors. Victor Erdstein, Highett, Vic. ($25) N 33k 33k 12 13 7 SPEED VR3 47k LIN 4 6 3 14 IC1 LM324 M1 240VAC 10k 4 .022 250VAC 11 VR1 1M LOG 33k D1 1N4148 1 SAWTOOTH GENERATOR 2 VR2 100k LOG 47k 10 16VW Induction motor speed controller Capacitor run or split-phase squirrel cage induction motors have come into common use because they have no centrifugal switch and have medium torque from zero to full speed. However, they cannot normally be run at low speeds unless a variable frequency supply is used. This circuit gets around that problem by using a burst fire method which also features zero voltage crossing triggering instead of phase angle firing of the Triac. The circuit is used to control the speed of a set of five split phase motors for a light industry application. Due to the pulsing nature of the supplied power, the motors turn noisily but that is not a problem in comparison to the satisfaction of achieving quite good low speed control. The motors are 8-pole types with a normal operating Single-pot Wien bridge oscillator This circuit is an interesting variation of the well-known Wien bridge oscillator in that it provides a frequency range of more than 15:1 using only a single potentiometer. As presented, the oscillator covers the range from 82Hz to 1.25kHz. By con­trast, a standard Wien bridge circuit requires a dual-ganged pot and would usually cover a range of only 10:1. Op amps IC1a and IC1b form the oscillator circuit with a 2.7kΩ resistor and .047µF capacitor in series in the positive feedback loop from the output at pin 1 to pin 3 of IC1a. 1 G IC2 UAA1061B 0.1 TRIAC1 BT136 2 240VAC 8 TRIAC2 BTA26/600B 5 8.2k 10W 220k 1W 220 16VW 18k 2W D2 1N4007 speed of 725 RPM and this circuit is used to run them at about one tenth of that speed but only for 10 minutes at a time. The heart of the circuit is IC2, a Motorola UAA1016B. Its features include an on-chip sawtooth generator for proportional control, plus even switching of positive and nega­tive power cycles to keep the supply authorities happy (no DC line current). The UAA1016B is designed to trigger Triacs which are switching high-current resistive loads like heater elements. In order to drive the highly inductive load of split-phase motors, the BT136 and the 100W lamp act to lock on gate drive to the main Triac (TRIAC2). This Triac also has a snubber network consisting of the 100Ω 2W resistor and .022µF capacitor to ensure reliable commutation. The 0.1µF capacitor at pin 2 of IC2 sets the sawtooth pro­ portional This op amp also has a negative feedback path to its pin 2, 2.7k with diodes D1 and D2 acting the stabilise the amplitude of 500k VR1 oscillation. Op amp IC1b acts to feed an inverted portion of the signal at pin 3 to pin 2 and hence it controls the frequency of osc­­ill­ation via potentiometer VR1 and the output amplitude via trim­pot VR2. Harmonic distortion is approximately 0.065% over the speci­fied frequency range and the output signal is just over 3V RMS. The envelope stability is within ±0.4dB over the entire range. Darren Yates, SILICON CHIP M2 240VAC G 2 1 100 2W N/C 1 0.1 1kV 240V 100W 12G TRIAC1 12G TRIAC2 A control frequency, while the speed control setting is determined by IC1. IC2 derives its DC supply from the mains via an 18kΩ 2W resistor and diode D2. IC2 then provides the DC rail to the LM324. IC1 is connected as a Schmitt trigger oscillator with fre­ quency and duty cycle set by VR1 and VR2 respectively. The pulse output at pin 14 is high for 0.5 seconds and low for 5 seconds. Unused inputs on the LM324 should be tied low. Note that the whole circuit floats at mains potential. Do not touch any part of the circuit while power is applied and use a pot with a plastic shaft for VR3. If you have trouble finding the UAA1016B, Worldwide Elec­ tronics in Perth stock them – phone (09) 367 6330. G. Host, Doubleview, WA. ($25) .047 2.7k +12V .047 3 200  VR2 2.7k 2.7k 2 .0022 1 2.7k 6 5 8 IC1a TL072 120k 2x1N914 D1 7 IC1b 4 -12V D2 .0022 The circuit is a variation of the Wien bridge configuration. VR1 sets the oscillator frequency, while VR2 sets the amplitude. January 1994  25 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) 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) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $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 January 1994  29 Luxman A-371 amplifier & D-351 CD player Luxman is a hifi brand which will be wellknown to many older enthusiasts but perhaps not so well known to younger read­ers. Produced by one of the smaller Japanese hifi companies, Luxman has a reputation for high quality equipment with no unne­cessary frills or gimmicks. We recently had the chance to review two models from Lux­man’s recently released range, the A-371 stereo amplifier and the D-351 compact disc player. Now while these units have a wealth of features, their front panels are certainly clean and well laid out and not at all daunting to the user. In addition, they have one other feature which will be most attractive to many users – front panels in champagne finish. These are a welcome alternative to black finished front panels. Talking about the A-371 amplifier first, this is an attrac­tive unit which at the same time is quite subdued in its styling. It measures 437mm wide, 125mm high and 363mm deep, including knobs and rear projections. It weighs 9.5kg. 30  Silicon Chip The control layout is fairly simple with a large volume control knob on the right hand side and then three small knobs for bass, treble and balance controls. There are eight large pushbuttons, for power and source selection: VCR, LD (laser disc player), AV (audio visual source), phono, tuner, tape, DAT and CD. As well, there are three smaller pushbuttons for selection of two pairs of loudspeakers, mono mode and two modes called “CD synchro” and “CD straight”. We’ll talk about these a little later. All source selection and control of the volume level can be done via the infrared remote control, a feature which is becoming standard with a lot of hifi equipment these days. On the rear panel, there is the usual plethora of RCA phono sockets, including those for video input and output signals. There are eight shrouded binding post terminals for connection of loudspeakers and a pair of jack sockets marked “bus line” which enables other Luxman equipment to be controlled via the ampli­fier’s remote control handpiece. Inside, the amplifier is packed with a surprising amount of circuitry. Apart from that which you would expect in a normal amplifier in the way of preamp, tone control and power amplifier boards, there are boards associated with the pushbutton source selection and the infrared remote control, all of which is overseen by a custom microprocessor. There are two power transformers, one small and one quite large. We assume that the small one is energised all the time so that the amplifier’s remote control circuitry can respond to the remote handpiece or front panel power button and “wake up” the main power supply when required. The amplifier is double insulated and comes with a twin-core mains flex. The internal wiring does appear to conform to double insulation standards but we do regard it as dangerous in one aspect. If the cover of the amplifier (or the matching CD player) is removed, the 240VAC wiring connections are completely unshrouded and it would be easy to touch them inadvertently. Granted, the rear of the chassis has a warning notice saying “Caution: risk of electric shock. Do not open” but we would like to see those 240VAC connections made much safer for the person who will inevitably open the case at some stage in its life. To provide the remote volume control facility, the volume control is powered by a small DC motor via a clutch which lets the user adjust the control manually if desired. For the purists, the A-371 has its “CD straight” feature. By pushing this button, most of the switching, tone control and other ancillary circuitry is bypassed by the input signals from the CD player and they go straight from the volume control to the power amplifier circuitry. D-351 CD player The other piece of equipment in this review is the Luxman D-351 CD player which has an overall width and styling to match the A-371 amplifier. Note however that it could be unwise to stack equipment on top of the A-371 amplifier as this would possibly cause problems with ventilation in FACING PAGE: the A-371 integrated stereo amplifier comes complete with IR remote control & delivers 70W RMS per channel. Below is the D-351 CD player which also features IR remote control. The interior of the A-371 stereo amplifier has quite a few PC boards, with additional boards being required for the front-panel pushbutton controls & the video switching inputs & outputs on the rear panel. Note the generously proportioned power transformer which is fitted with a copper strap. the amplifier and it might also cause hum induction into the CD player. If the equip­ment is to be stacked, the amplifier should at the top, for best ventilation. Dimensions of the Luxman D-351 CD player are 438mm wide, 90mm high and 346mm deep. It is a conventional front-drawer loading machine with the usual range of playing facilities, includ­ing random play and programmed play. If used with Luxman’s system bus, it can also provide “CD synchro” recording to a cassette deck, as mentioned above. In addition, the D-351 has “Edit Play”, a playback feature not found on most machines. You can use “Edit Play” when program­ming the machine for recording on to tapes. For example, you can set a play time of 45 minutes and then program in tracks to be recorded. This avoids the common problem when taping CDs to cassettes and finding that the tape ends mid-way through a track. It also has infrared remote control via its own RD-351 handpiece or via the comprehensive RA-371 remote control supplied with the amplifier. Funnily enough, as with most CD players having remote control, you can January 1994  31 The interior of the D-351 CD player has an uncluttered layout. Note the optical fibre socket & system bus sockets on the rear panel. The rear panel also carries a level switch which sets the maximum output signal to 2V or 1V RMS. even open or close the drawer remotely although you still have to load the disc in or take it out, by hand. You might think there is not much use in being able to open or close the drawer remotely and in the case of this player, even to turn on the power, but it does make sense to do so. Why? Because it stops you from putting your fingers on the front panel and thus preserves the finish as long as possible. If you don’t think that is relevant, take a look at the most used buttons on your present gear or home appliances. After a few years, the wear and tear can become quite obvious. Interestingly, if you are using the D-351 together with the A-371 amplifier and have them interconnected via the system bus, you get an extra level of playing convenience. Not only do you not have to turn each piece of equipment on or off separately, but if you select CD as the source, it will immediately start playing a disc or, if no disc is present, it will open the drawer ready to receive one. The D-351 CD player has its own stereo headphone socket and volume control, a worthwhile feature, particularly if you want to use the CD player on its own. And if you want to use the CD player with a DAT recorder, you can link the two together via the D-351’s optical fibre output. A large easy-to-read digital display is a feature of the front panel and you can program it to play up to 24 tracks. 32  Silicon Chip Natu­rally, you can do all this from the remote control for the A-371 amplifier so you don’t need more than one remote handpiece. Two small switches on the rear panel of the D-351 provide facilities not found on other players. One switch allows the maximum output signal voltage to be reduced from 2V to 1V. This is useful because it is a closer match to the output signals from other program (line) sources such as tuners and tape decks. Thus there will be less change in volume level when switching between sources. The second switch allows for timer operation. With the switch in the ON position, playback operation starts automatical­ly when power is applied, if a disc is inside the machine. Taken as a pair, the Luxman A-371 amplifier and D-351 CD player work very well together, as you would expect. They are quiet at all times and subjectively, they produce very good quality sound. And the measurements back up that impression. Test results Rated power for the A-371 stereo amplifier is 70 watts per channel for a total harmonic distortion of .01% over the frequen­cy range of 20Hz to 20kHz into 8Ω loads. Our tests showed that the amplifier met this specification easily and with plenty to spare, as far as power output was concerned. We measured maximum power at 85 watts per channel at 1kHz with both channels driven and 96 watts with one channel driven, into an 8Ω load. Power into 4Ω loads was somewhat higher, at just over 130 watts, and this also confirmed the Luxman specification. The signal-to-noise ratio was 82dB A-weighted with respect to 5mV and 1kHz for the phono inputs which was exactly as specified, while the S/N ratio for the line inputs (CD etc) was slightly over 101dB, a little better than the spec. Maximum boost and cut for the bass and treble controls was a little over ±8dB. This is somewhat less than is typical for mainstream stereo amplifiers and receivers but we think that this is probably good practice. After all, on most hifi systems the tone controls are rarely, if ever, used and if you are routinely using your system with lots of bass boost, there is something wrong with it (or, dare we say it, something wrong with you!). For its part, the D-351 CD player performed very well too, as you would expect from a system that claims dual D-A convert­ers, 8-times oversampling and 18-bit digital filters. Its fre­quency response was within ±0.6dB from 20Hz to 20kHz and its signal to noise ratio for the same bandwidth was 92.5dB and 104dB with A-weighting. We measured harmonic distortion at around .0035% for low frequencies but found that the figures rose quite considerably as the frequency was increased due to the presence of supersonic sampling artefacts at 44.1kHz. We were a little surprised by this in view of the fact that the D-351 is claimed to be an 8-times over­ sampling machine. Normally, 8-times over­sampling means that the residual sampling artefacts are at 352kHz (44.1kHz x 8) and at a very low level. Where the D-351 really does shine is with its linearity performance. This is measured with a compact disc with 1kHz signal levels that are progressively reduced, to an ultimate level of -90dB. By the time the level is reduced to -80dB most CD players have an error of around +2dB or so while at -90dB, the error can be as much as +5dB; ie, the actual measured signal level drops to -85dB instead of -90dB. At -80dB, the D-351 had an error of just +0.4dB while at -90dB the error was +2dB. This is very good. The separation between channels continued on page 92 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 r e t l i F e v i t Ac n g i s e D s r e n n i g e B r Fo RO UN DED GE 0 HB roughout h t d e s u y are widel le, we look at the s r e t l fi e Activ this artic lear away some n I . s c i n o electr y ers & c t l fi e v i t c g this ver a basics of ystery surroundin of the m nteresting topic. i By ELMO V. JANSZ A filter is one of the most common types of circuit used in electronic equipment. By definition, a filter passes some fre­quencies and suppresses or attenuates others. Filters can be active or passive, depending on their con­ struction. Passive filters use passive components such as resis­tors, capacitors and inductors, whereas active filters include an amplifying device, such as a transistor or operational ampli­fier, in addition to a number of passive components. The presence of the amplifier gives the filter very good isolation between its input and output and a certain amount of amplification as well. In this article, we shall learn how to design active filt­ers using simple calculations. Let us start by establishing a few basic ideas about active filters. Fig.1 shows the idealised amplitude response of a low-pass filter. A low-pass filter is one that passes all frequencies up to a point and heavily attenuates or suppresses Fig.1: idealised amplitude response of a low-pass filter. Fig.2: idealised amplitude response of a high-pass filter. frequencies beyond this point. The amplitude response is a plot of the gain of the filter against frequency. The gain is calculated by divid­ing the output voltage by the input voltage in the equation: G = 20 log10(Vo/Vi) where G is the gain expressed in decibels; Vo is the output voltage; and Vi is the input voltage. In Fig.1, the frequency fc is called the cut-off frequency while region AB in which the gain is constant is called the filter’s passband. Beyond fc, the gain drops rapidly and this region is called the stop-band. The rate at which the line BD falls is measured in dB/ octave or dB/decade. The is the “slope” of the filter. An octave is a doubling or halving of frequency; ie, for a frequency of 2kHz, octaves above are 4kHz, 8kHz and so on, while octaves below are 1kHz, 500Hz, etc. Decades are a ten-fold increase or decrease in frequency. For a January 1994  37 Fig.3: response characteristic of a practical lowpass filter. Fig.5: basic circuit for a first order low-pass Butterworth active filter. where G is the passband gain in decibels; W is the normalised angular frequency; and n is the order of the filter. The normalised frequency is given by W/Wc where W is the frequency in question and Wc is the cut off frequency Fig.4: a filter with ripples in the passband is called a Chebyshev filter. frequency of 2kHz, decades above are 20kHz, 200kHz and so on, while decades below are 200Hz, 20Hz, 2Hz, etc. We now come to another important definition, the “order” of a filter. This is the rate at which the line BD in Fig.1 falls off, or the filter’s ability to attenuate frequencies outside its passband. A “first order” filter has an attenuation outside its passband of 6dB/octave or 20dB/decade. The order of a filter is also referred to as its roll-off or fall-off. A “second order” filter has a roll-off of 12dB/octave or 40dB/decade; ie, twice that of the first order filter. A third order filter will have a roll-off of three times that of a first order filter and so on for higher order filters. A high-pass filter is the complement of a low-pass filter and will have an idealised response characteristic as shown in Fig.2. Notice that frequencies below fc are attenuated heavily. The roll-off has the same values as stated above but in this case will have the opposite sign. A practical low-pass filter will have the response charac­ teristic shown in Fig.3. The cut-off frequency in this case is not a sharp transition point as shown in Figs.1 & 2 but the frequency at which the gain is reduced by 3dB, from its passband value. A filter with a response as shown in Fig.3 – ie, one having a flat response in the passband – is called a Butterworth filter. A filter could also have a response as shown in Fig.4, with ripples in the passband. This is called a Chebyshev filter. The shape of the filter’s response is determined by a con­stant (alpha) called the Damping Factor. There are other filters called Cauer, Bessel and Thompson filters but in this article we shall confine ourselves to Butterworth filters, as they are the most popular due to their design simplicity. The general equation for a Butterworth low-pass filter of order n is given by: Gain = 20 log [G/(1 + W2n)½ ] 38  Silicon Chip Design of a first order filter Let us now design a first order low-pass Butterworth active filter. The basic circuit is shown in Fig.5. The portion within the dotted line is a low-pass passive filer. The operational amplifier is connected in the non-inverting mode. The cut-off frequency (fc) and passband gain (G) are given by the following formulas: fc = 1/(2πRC) G = 1 + RB/RA Suppose we wish to construct a low-pass filter with a cut-off frequency of 2kHz. We start by selecting a value for C. Let this be .022µF. By using the formula fc = 1/(2πRC), we arrive at: R = 1/(2π x 2 x 103 x 0.022 x 10-6) = 3.617kΩ This would be selected as 3.6kΩ, using the closest value in the E24 (5%) range. Let us set the passband gain required equal to 2. There­ fore, using the formula for gain: RB/RA = G - 1 = 2 - 1 = 1 Therefore, we can make RA equal to RB and set both at 10kΩ. A 741 could be used for the operational amplifier and then you have your basic first order low pass filter. By interchanging C and R, you can produce the corresponding high pass filter. Second order low-pass filter The basic circuit of a second order low-pass filter is shown in Fig.6. Here again a network of passive components is placed around an op amp. Second order active Fig.6: basic circuit of a second order low-pass filter. Fig.7: the circuit for a unity gain low-pass active filter. filters are also often referred to as Sallen-Key filters. This circuit has two RC networks, hence it is a second order filter. The cut-off frequency fc for this filter is given by: fc = 1/2π(R1.R2.C3.C4)½ and the mid-band gain is given by: G = 1 + RB/RA In practice, two versions of this circuit are possible: either a filter with a passband gain of unity, or a filter with equal components; ie, R1 = R2 and C3 = C4. Unity gain For this example, it is customary to make R1 = R2 and then C3 and C4 are fixed in the ratio C3 = 2C4, in order to satisfy the damping factor (alpha) requirements for a Butterworth re­sponse. The required circuit is shown in Fig.7. Note that the op amp has been configured for unity gain, as a voltage follower, by connecting its inverting input to its output. Using the formula fc = 1/2π(R1.R2.C3.C4)½ and remembering that R1 = R2 = R and C3 = 2C4 (ie, if C4 = C then C3 = 2C), the above equation can now be written as: fc = 1/2π(R x R x 2C x C)½ = 1/2πCR√2 If we select R = 10kΩ and if a cut-off frequency of 1kHz is desired, C can be calculated from the above equation to give: C = 1/(2π x 103 x 10 x 103 x √2) = 0.01µF. Therefore, we can select C3 = 0.02µF and C4 = 0.01µF. The final design is now R1 = R2 = 10kΩ; C3 = 0.02µF; C4 = 0.01µF. Fig.9: unity gain second order high-pass filter. The passband gain for a Butterworth filter is defined by the equation: G=3-α and since α = √2, G = 1.586. Unfortunately, this is the only gain that will permit the circuit to operate correctly. By selecting R = 5kΩ and a cut-off frequency of 1kHz, the above equation gives C = .032µF. A .033µF polyester capacitor would be suitable. The gain of G = 1.58 can be satisfied by making RB = 27kΩ and RA = 47kΩ (using preferred values). The final circuit is shown in Fig.8. Second order high pass filters High pass filters can be set up by interchanging the R and C components of the low-pass circuit. Two versions of this cir­cuit are possible, as for the low-pass configurations – ie, a unity gain circuit and an equal component circuit. These are shown in Figs. 9 & 10. For Fig.9, if C1 = C2, then R4 = 2R3 in order to satisfy the damping requirements for a Butterworth response. Equal component filter If R1 = R2 = R and C3 = C4 = C, then the equation fc = 1/2π(R1.R2.C3.C4)½ becomes fc = 1/2πRC Fig.10: equal component high-gain Butterworth filter. Fig.8: equal component low-pass Butterworth filter. For the equal components version of Fig.10, if R3 = R4 and C1 = C2, then the gain is fixed by the equation: G=3-α With alpha = √2, this again fixes the gain at 1.586. Higher order filters can be obtained by cascading appro­ priate filter sections. For example, a fifth order filter can be produced by cascading two second order and one first order sec­tions. Filters can also be set up to pass a band of frequencies and so are called band-pass filters. A band-pass filter can be obtained by cascad­ing an appropriate high-pass and SC low-pass section. January 1994  39 Are you interested in charging batteries from a solar panel? Here is a regulator designed especially for the job. It can be built in two versions (10-amp or 20-amp) & can be used to charge a 12V or 24V battery bank. I N THE SIMPLEST solar panel plus battery setup, all you need is a diode to isolate the panel from the battery. This prevents the battery from discharging via the solar panel when it is not illuminated by the Sun. This is OK for a temporary setup but unless the solar panel is only trickle charging the battery, you will eventually run up against the problem of over-charging. To avoid over-charging the battery you need a regulator circuit so that the panel can charge the battery at its maximum current output until it reaches full charge. At that point, the regulator disconnects the panel from the battery and no further charging takes place. That is the function of the circuit pre­sented here. As depicted in the photos in this article, this regulator is built up on a small PC board with a number of power semicon­ductors which need to be mounted on a heatsink. The board itself would normally be mounted inside a plastic case with the heatsink on the outside. How the circuit works In effect, this circuit works like a switch. If the battery voltage is below 13.6V, the solar panel is connected. Once the battery voltage rises above that point, the solar panel is dis­ connected. A Schottky power diode, used because of its low for­ward voltage loss, prevents the battery from discharging back via the panel when there is no sunlight. To see how the circuit works, have a look at the diagram of Fig.1. Switching regulator for solar panels Design by OTTO PRIBOJ The regulator circuit can be housed in a plastic case but note that the power devices must be mounted on a large finned heatsink to provide cooling. The two indicator LEDs protrude through the lid of the case near one corner of the heatsink. 40  Silicon Chip D1 1N4148 C 10k Q1 BC337 IC1 78L05/7805 OUT IN E GND 100k 22 B BC--B C E 0.1 K A 7805 78L05 OUT IN ZD1 15V GND VIEWED FROM BELOW I GO GDS K A D4 K A D5 LINK FOR 12V K 22 22k 1% 2 +6V 12V OR 24V 2xPBYR1645 ZD2 30V 39k 1% 3 VR1 5k +4V D2 1N4148 8 1 IC2a TLO62 6.8k Q2 BC557 B E D3 1N4148 C 4 4.7k 330k 1% 12k 1% 1k LED1 GREEN 1 8.2k  K A LED2 YELLOW 100k  220k SOLAR PANEL(S) Q3 STP60N05 S G 10k Q4 STP60N05 G S 4.7k A A D D K SOLAR PANEL REGULATOR Fig.1 (above): the circuit is based on comparator IC2a. When the battery voltage is below 13.6V, IC2a’s output is low & so Q2 turns on Q3 & Q4 to connect the solar panel. Conversely, when the battery voltage is above 13.6V, the output devices switch off & the solar panel is disconnected. While the circuit may look a little daunting, it is really quite simple in operation. Notice that the positive terminal of the solar panel connects via Schottky diode D4 (and D5 for a high current version – ie; greater than 10 amps) to the positive terminal of the battery. The negative terminal of the panel connects to the negative terminal of the battery via Mosfet Q3 (and Q4 for the high current version) and it is the Mosfet which is the switching element. It is turned on or off, depending on the charge state of the battery. Op amp IC2a is the heart of the circuit and it is connected as a comparator. It compares a reference voltage produced by a 5V 3-terminal regulator (IC1) at pin 2 with a proportion of the battery voltage at pin 3. When the voltage at pin 3 is above the reference voltage at pin 2, the output at pin 1 is high and transistor Q2 is off. Hence Mosfet Q3 (and Q4 if used) is also off and so the solar panel is effectively disconnected from the battery. Conversely, if the voltage at pin 3 is below the voltage on pin 2, the output The power devices (D4, D5, Q3 & Q4) are connected to the PC board via insulated flying leads. Use heatshrink tubing or plastic sleeving to insulate the leads of these devices, to prevent accidental shorts. January 1994  41 been designed around a TL062 dual low current Fet-input op amp but only one op amp, IC2a, is actually in use. The other op amp is disabled by tying its inputs (pins 5 & 6) low. 24V operation As noted above, the circuit can be used for 24V systems and for this you would need two 12V solar panels in series and a 24V battery (or two 12V batteries in series). When 24V operation is required, the input voltage divider from the battery is changed, to take account of the higher vol­tage. Note the 39kΩ resistor connected to the positive side of the battery. This is in circuit for 24V operation or replaced with a link for 12V operation. Finally, D1, Q1 and ZD1 form a nom­inal 15V regulator to supply op amp IC2a and transistor Q2. For 12V operation, this circuit can be omitted or left in place – the circuit will function either way. The voltage at the emitter of Q1 will be only about +10V for a 12V battery input. Current capacity The assembled PC board is mounted on the lid of the case on 10mm tapped standoffs. Note that a small slot must be cut in the base opposite the terminal block to provide entry for the leads to the battery & to the solar panel. at pin 1 is low and so Q2 turns on Q3 (and Q4 if used) so that the solar panel is now connected. The rest of the circuit really amounts to a few frills. LED 1, at the output of IC2a, indicates “float/full charge”. It turns on when the solar panel is disconnected. LED 2, driven by transistor Q2, is turned on while ever the solar panel is connected to the battery. It indicates “on charge”. We should note that the circuit has As noted above, the circuit can be configured to handle the output of panels rated up to 10 amps with one Mosfet (Q3) or increased to 20 amps with two Mosfets (Q3 & Q4). If two Mosfets, are used then two Schottky diodes will also be required. (D4 & D5). If more than one solar panel is used, then an alternative arrangement of one Schottky diode in series with each panel should be used. Construction All parts with the exception of Mos­ RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 2 1 1 1 2 1 1 2 1 42  Silicon Chip Value 330kΩ 220kΩ 100kΩ 39kΩ 22kΩ 12kΩ 10kΩ 8.2kΩ 6.8kΩ 4.7kΩ 1kΩ 4-Band Code (1%) orange orange yellow brown red red yellow brown brown black yellow brown orange white orange brown red red orange brown brown red orange brown brown black orange brown grey red red brown blue grey red brown yellow violet red brown brown black red brown 5-Band Code (1%) orange orange black orange brown red red black orange brown brown black black orange brown orange white black red brown red red black red brown brown red black red brown brown black black red brown grey red black brown brown blue grey black brown brown yellow violet black brown brown brown black black brown brown 8.2k 0.1 4.7k 1uF D3 100k 12k 6.8k 1 IC2 TLO62 VR1 330k 100k 39k PARTS LIST 4.7k 10k ZD1 ZD2 LED2 D2 22uF 22k 220k SOURCES Q3, Q4 SOLAR CELLS ANODES D4, D5 22uF Q1 D1 DRAINS Q3, Q4 BATTERY CATHODES D4, D5 LED1 IC1 1k Q2 GATES Q3, Q4 10k Fig.2: install the parts on the PC board as shown in this wiring diagram. The connections to the power devices (D4, D5, Q3 & Q4) are made via flying insulated leads which are soldered directly to the pins of the terminal block on the back of the PC board. 1 PC board, code OP-004 1 PC mount 4-way terminal block 1 heatsink (see text) 1 5kΩ multiturn trimpot (VR1) Semiconductors 1 78L05 3-terminal 5V regulator (IC1) 1 TL062 Fet-input op amp (IC2) 1 BC337 PNP transistor (Q1) 1 BC557 PNP transistor (Q2) 1 STP60N05 N-channel Mosfet (Q3; add Q4 for 10A version) 1 PBYR1645 Schottky diode (D4; add D5 for 10A version) 3 1N4148 diodes (D1,D2,D3) 1 BZX79C15 15V Zener diode (ZD1) 1 BZX79C30 30V Zener diode (ZD2) 1 green LED (LED1) 1 yellow LED (LED2) Capacitors 2 22µF 35VW PC electrolytic 1 1µF 35VW PC electrolytic 1 0.1µF monolithic Resistors (0.25W, 1%) 1 330kΩ 2 10kΩ 1 220kΩ 1 8.2kΩ 2 100kΩ 1 6.8kΩ 1 39kΩ 2 4.7kΩ 1 22kΩ 1 1kΩ 1 12kΩ The power devices must be insulated from the heatsink using suitable mica washers & insulating bushes. Smear all mating surfaces with thermal grease before bolting the assemblies together, then use your multimeter to confirm that each device is indeed correctly isolated. fets and Schottky diodes are mount­ed on a small PC board measuring 78 x 54mm. A 4-way insulated terminal black is mounted at one end for the four external connections to the battery and solar panel. Trimpot VR1 is a multi-turn top adjust type which gives easy and precise setting of the “end-of-charge” battery voltage. The 3-terminal 5V regulator may be a 7805 or a 78L05 type, although the latter is preferable since its current drain is lower which could be important in this application. Two prototypes are depicted in the photos accompanying this article. One is shown as a board only, with the power semiconduc­tors attached by flying leads. They will need to be mount­ed on a suitable heatsink with the usual insulating bushes, mica washers and thermal grease. The second prototype is shown with the PC board mounted in a plastic box and the two LEDs have been taken off the board and mounted so that they protrude through the lid of the case. Where to buy the parts Short form kits for this project are available only from the designer, Otto Priboj. The kit consists of the regulator PC board plus components and is priced at $54. Additional components to make a 20A version are priced as follows: STP60N05 $8; PBYR1645 Schottky diode $5.00; postage & packing, $4.00. Mail orders with a cheque or money orders should be sent to Otto Priboj, PO Box 362, Villawood, NSW 2163. Phone (02) 724 3801. Setting up To set the circuit up you will need a power supply to sub­stitute for a solar panel and a 12V battery (since the circuit will not work unless a battery is connected). Turn on the power supply and wind up the voltage. Note that no current will flow until the power supply exceeds the battery voltage. Turn up the supply voltage so that it is a few volts higher and measure the voltage across the battery. Adjust trimpot VR1 so that the battery vol­tage does not exceed 13.8V while on charge. For a 24V system, the approach is the same except that the cutoff voltage SC is adjusted to 27.6V. January 1994  43 A printer status indicator for PCs Have you ever been frustrated by files disappearing down your printer cable & not appearing at the other end? This Print­er Status Indicator uses an alphanumeric display to indicate any errors that occur during transmission. By DARREN YATES When it comes to printing, most programs leave you flat if something goes wrong while the file is being sent to the printer. And with many graphics print files exceeding 4Mb, it can be extremely annoying after sitting around for 10 minutes or so for the printer to compile the pages and then nothing happens! If you are using Windows, you will 44  Silicon Chip know that it does have a fairly good and reliable Print Manager to take care of these things. However, booting up Windows just to use the Print Manager is an exercise in time-wasting. If you’re running a small business with a number of PCs, the odds are that only one of the machines is connected to the printer. Those who need to print a file can then “Print to file” on their own machine, copy that file to a floppy disc and then trans­ fer the file to the PC that’s hooked to the printer. The problem arises when you use the DOS commands COPY <file­name. ext> LPT1 or PRINT <file­name.ext>. They give you little or no indication as to what’s going on. Try this for a test. Disconnect the printer from your PC and go into the root direc­ tory of your boot drive. Type “COPY AUTOEXEC.BAT LPT 1” and press <enter>. You should find that you get a message saying that the machine is now happily sending your file to the printer. You will have to wait quite a while to see it though – an eternity, in fact. Our Printer Status Indicator won’t prevent errors from occurring but it will notify you as soon as they happen. The basis of the project is a driver program called PRINTER.EXE and a 16-character x 2-line alphanumeric display. The Printer Status Indicator connects between your PC’s printer port and the printer (via DB-25 sockets) but becomes transparent to the printer port when a print file is being sent. Circuit diagram The circuit for the Printer Status Indicator in Fig.1 shows that very little additional electronic circuitry is involved. Putting it simply, the computer sends data to the printer via an 8-way Tri-state buffer. This is enabled via the SI line (pin 17) from the printer port. The SI (Select In), I (Initialise) and AF (auto-feed) control lines do not have to go directly from the computer to the printer socket for the printer to work correctly. As long as these lines are at the correct logic state, the print­ er will behave as normal. The only control line that must be fed straight through to the printer socket is the STROBE line. The SLCT, PE, BUSY, ACK and ERROR lines are outputs from the printer back to the PC and are used to indicate any problems the printer may experience during a print run. To enable us to run both the printer and the alphanumeric display from the same port, we have to stop the data from port A (data lines D0-D7) that is specifically meant for the display from going to the printer. This is accomplished by using IC1, the 74HC244 8-way Tri-state buffer. When SI pulls low, the buffers allow data to flow from the PC to the printer but when SI goes high, the outputs of IC1 go into a high-impedance state. Since IC1 is used to prevent confusion between data for the printer and data for the display, you may wonder how the display can function properly since it has the data lines connected to its inputs at all times. This is OK though because the display does not respond to the data until the AF and I lines are changed appropriately. In effect, pin 6 of the display must go high and then low (it’s a negative edge-triggered device) and pin 4 must either be high for data or low for a command (such as “clear display”). Power supply PRINTER PORT OUTPUT FROM PC (15) ERROR PRINTER PORT OUTPUT TO PRINTER ERROR (15) STR (1) (1) STR (13) SLCT SLCT (13) (12) PE PE (12) BUSY (11) (11) BUSY ACK (10) (10) ACK 1 1G 19 (17) SI 8 (2) D0 6 (3) D1 4 (4) D2 2 (5) D3 17 (6) D4 15 (7) D5 13 (8) D6 11 (9) D7 (14) AF (16) I IC1 74HC244 2G 1A4 1Y4 1A3 1Y3 1A2 1Y2 1A1 1Y1 2A4 2Y4 2A3 2Y3 2A2 2Y2 2A1 2Y1 10 6 4 7 8 9 12 D0 (2) 14 D1 (3) 16 D2 (4) 18 D3 (5) 3 D4 (6) 5 D5 (7) 7 D6 (8) 9 D7 (9) AF (14) 20 I (16) 10 11 12 13 14 2 ROW x16 CHARACTER ALPHANUMERIC DISPLAY VCC GND R/W 5 1 VO 2 3 SI (17) D1 1N4004 VR1 10k OUT 10 16VW 78L05 GND IN 9VDC 300mA PLUGPACK 10 16VW IN PRINTER STATUS INDICATOR OUT GND VIEWED FROM BELOW Fig.1: the circuit uses Tri-state buffer IC1 to prevent information intended for the alphanumeric display from corrupting the data intended for the printer. The alphanumeric display shows the current printer status & displays error messages under software control. dicator comes via a 9V DC 300mA plugpack. Diode D1 provides reverse polarity protection. A 78L05 low-power 5V regulator produces the 5V DC required to drive the display, as well as the two “dummy drive” lines to the print­er; ie the AF and I lines to the Centronics port connector. Trimpot VR1 allows you to optimise the contrast of the display to suit your viewing angle. Software As mentioned earlier, the Printer Status Indicator is driven via a software program called PRINTER. EXE. You can obtain a copy of this program from SILICON CHIP as set out PARTS LIST 1 PC board, code 07101941, 133 x 84mm 1 zippy case, 158 x 95 x 53mm 1 front panel label, 90 x 131mm 1 9VDC 300mA plugpack 1 DB25 male-to-male cable 2 DB25 PC-mount female sockets 1 2.1mm DC socket 1 16-pin 90-degree pin header 1 10kΩ horizontal 5mm trimpot 2 10µF 16VW electrolytic capacitors 4 10mm x 3mm spacers 2 5mm x 3mm spacers Semiconductors 1 16x2 row alphanumeric display (Altronics Z-7299; see note) 1 74HC244 Tri-state buffer (IC1) 1 78L05 5V 100mA regulator 1 1N4004 rectifier diode (D1) Miscellaneous Tinned copper wire, solder, screws, nuts & washers. Note: an alternative alpha­numeric display panel and matching PC board are available for this project from Oatley Electronics. For details, phone them on (02) 579 4985. Power for the Printer Status InJanuary 1994  45 FROM PC TO PRINTER ALPHANUMERIC DISPLAY IC1 74HC244 1 10uF 78L05 D1 VR1 10uF 9V FROM PLUGPACK Fig.2: install the wire links on the PC board before mounting the remaining parts. The alphanumeric display is installed by first soldering a right-angle pin header to the underside of the module & then soldering the pin header directly to the PC board. in the accompanying panel. We’ll be supplying both the EXE file and the source code for this project, so that those of you with the skill and incliBelow: the PC board assembly is secured to the lid of the case on 10mm stand-offs, with an extra nut on each stand-off to provide additional spacing. The trimpot sets the display contrast. 46  Silicon Chip nation can modify the program to suit an individual need. In operation, the software drives the alphanumeric display and sends the file byte by byte to the printer. It also provides a continuous on-screen display which shows the current status of the file in terms of the number of kilobytes sent and its status in bargraph form. This can be seen in the screen shots elsewhere in this article. Briefly, the program checks the printer’s status lines after each byte is sent to make sure that no errors have occurred during that transmission. If an error does occur, the printer changes the state of one of these status lines and the program then notifies you, both on-screen and on the LCD, that the error has occurred. To keep the speed up, the program uses one of the DOS interrupts, INT 21, in a machine-code routine to send each byte of data to the printer. The main benefit of this project is in the remote display. By having this sit next to your printer, you can instantly see when an error occurs and then rectify it. Construction The Printer Status Indicator is constructed on a small PC board coded 07101941 and measuring 133 x 84mm. Before you start installing components, check the PC board carefully against the published artwork – see Fig.7. Any defects should be fixed before proceeding further. You can start the board assembly by installing the wire links. Next up, take the alphanumeric display module and solder the 16-pin right-angle connector to the copper pads on the underside of its board. You should end up with a How To Buy The Software The program PRINTER.EXE and the source code PRINTER.BAS can be obtained by sending $6 plus $3 for postage and packing to SILICON CHIP, PO Box 139, Collaroy, NSW 2097 or by faxing your credit card authorisation to (02) 979 6503. Please nominate your choice of 3.5-inch or 5.25-inch floppy disc to suit IBM com­pat­ible computers. We accept credit card authorisations for Bank­­c ard, Visacard and Master­card. Fig.4: this is the opening on-screen display when PRINTER.EXE is executed. It gives the name of the file to be printed plus various file details & gives you the option of either printing or quitting back to the DOS prompt. row of pins which will then fit neatly into the associated holes on the main PC board. Don’t solder them to the main PC board just yet, though. The next task is to solder in the IC, followed by the capacitors, the diode, the regulator and the trimpot. After that, you can install the two right-angle DB25 female connectors on the board. Finally, mount the display module in position and secure it at the back using two 5mm spacers plus machine screws, nuts and washers. Drilling the case The next major job is to make the necessary cutouts in the specified plastic case which measures 158 x 95 x 53mm. You will need cutouts for the display bezel and for the two DB-25 sockets. The first step is to use the front panel label as a template to mark the cutout for the alphanumeric dis­play. The easiest way to make this cutout is to first drill a series of small holes around the inside perimeter of the display’s outline. The centre piece can then be knocked out and the job filed to a smooth finish. This done, the board can be temporarily positioned on the lid and its four mounting holes marked and drilled. The next step is to mark the cutouts for the two DB-25 sockets. Note that these cutouts must provide sufficient clearance for the cable connectors. As you can see from the photos, this requires holes to be cut in both the lid and the base. The cutouts in the lid are approximately 58 x 13mm at both ends, while the cutouts in the ends of the base are 58 x 14mm deep. Fig.5: this is the on-screen display that appears if problems are encountered in transferring the file. It suggests possible causes of the problem (eg, printer out of paper, printer cable not connected or printer off-line) & tells you what to check. Pressing ‘c’ will continue the file transfer to the printer once the problems have been cleared or you can press ‘q’ to quit. Fig.6: if printing is successful, the on-screen display completes the bargraph at top right & indicates that the file has been sent. Pressing any key then returns you to the DOS prompt. January 1994  47 TO PRINTER TO PC + 9VDC 300mA PRINTER STATUS INDICATOR Fig.7: it’s a good idea to check your PC board for etching defects by comparing it with this full-size pattern before installing any of the parts. The board is coded 07101941 & measures 133 x 84mm. Finally, you will have to drill a hole in one end of the case for the DC power socket. Applying power Before the unit is fully assembled into the case, it should be tested and the first step is check its current consumption. To do this, connect your multimeter in series with one of the supply leads (select the 400mA range), apply power and check that the current Fig.8: this artwork can be used as a drilling template for the display cutout. The cutout is made by drilling a series of small holes around the inside perimeter & then knocking out the centre piece & filing to a smooth finish. is less than 10mA. Any more than 20mA and you should switch off and check that you have installed all of the components correctly. If this is OK, you can hook up your printer and computer to the PC board via two DB25 cables. It is time to test the software and alphanumeric display. Copy the files on the program disc into a directory on your hard disc that’s in the path command (or modify your path command to include the These two photos show the read-out on the alphanumeric display when the printer is off-line & when the printer is switched off, respectively. Other messages are used to indicate that the printer is out of paper or that the file is being sent to the printer. 48  Silicon Chip relevant directory) and type: PRINTER C:\AUTO­EXEC.BAT <return>. You should obtain a screen display similar to those shown in this article. You are now asked to “Press [c] to start printing”. When you do so, the alphanumeric display should now show “Sending file:” on the top line and “AUTOEXEC.BAT_” on the bottom line. At the same time, your printer should also start to operate. If you’ve come this far without any problems, then it’s safe to say that the unit is working correctly. If the alpha­nu­meric display shows the correct information but the printer isn’t working, you should check that IC1 is working correctly and that you’ve installed it the correct way around. Finally, bolt the board to the lid and secure the lid to the case. Your Printer Status Indicator is now ready SC for action. If you need a low-cost speed control or low-voltage light dimmer then take a look at this little circuit. It uses just one IC & will control 12V DC motors or lights with rated currents of up to 1 amp. By DARREN YATES A simple low-voltage speed controller If you make your own PC boards, then no doubt you own one of those small PC board drills. These call for an external 12V DC supply capable of delivering at least 1A. With a supply of this rating, the drill will run at about 10,000 RPM. However, you don’t always want to run the drill at full speed and so ideally you need a variable power supply. This simple circuit will do the job efficiently and at low cost. It uses only a handful of components and will comfortably control DC motors rated up to 1A. It is a switching circuit which delivers bursts of current to the motor to provide an efficient means of varying the speed. The circuit can also be used to dim 12V lights and, in fact, its principle of operation is the same as used in the 50  Silicon Chip dimmers for automotive dashboard lamps. Circuit diagram As you can see in Fig.1, the Mini Drill Speed Controller uses very few components and only one IC – a CMOS 555 timer. The 10kΩ and 5.6kΩ resistors, along with the 0.1µF capacitor at pins 2 and 6, set the output frequency of the 555 to about 6.8kHz, although this will vary according to the speed setting. The duty cycle of the pulse output at pin 3 is set by VR1 which has its wiper connected to the control input (pin 5). The higher the control voltage to pin 5 of IC1, the higher the duty cycle and visa versa. The output signal is taken from pin 3 and drives Darlington transistor Q1 via a 1kΩ resistor. Q1 in turn drives the drill motor while diode D2 prevents Q1 from being damaged due to the back-EMF generated each time the motor switches off. The voltage supply to the 555 IC is regulated to 9.1V by zener diode ZD1 and its associated a 220Ω limiting resistor. While the 555 is fairly tolerant of supply variations, the zener diode and its accompanying 10µF filter capacitor are desirable to filter out hash and spikes which can be generated by the motor’s commutator. A 330µF capacitor at the supply input provides extra fil­tering, while diode D1 protects the circuit against incorrect supply polarity. Construction All of the components for the Mini Drill Speed Controller are installed D1 1N5404 220  10 16VW ZD1 9.1V 400mW MOTOR D2 1N4004 10k 4 8 7 5.6k 6 1k 3 IC1 LMC555 2 C B 1 Q1 BD679 E SPEED VR1 10k 5 12VDC 1A PLUG-PACK 330 25VW M D & K WILSON ELECTRONICS PLASTIC SIDE 0.1 E CB MINI PCB DRILL SPEED CONTROLLER Fig.1: the circuit uses 7555 timer IC1 to drive transistor Q1 & this pulses the motor on & off at a frequency of about 6.8kHz. VR1 controls the width of the output pulses on pin 3 of IC1 to set the speed of the motor. The circuit can control 12V DC motors rated up to 1A. on a small PC board measuring 61 x 43mm and coded 09111931. Before you begin any assembly work, check the board carefully for any shorts or breaks in the tracks by comparing it with Fig.3. If you do find any faults, fix them before proceeding further. Once the board has been checked, you can begin construction by installing the wire link, followed by the resistors, the diodes, capacitors and the IC. Follow the overlay wiring diagram to make sure that they are correctly located – see Fig.2. The transistor needs to be fitted with a small heatsink. The 10kΩ pot is a miniature 16mm type which solders directly to the board. If you prefer, you can use one of the larger types with some flying leads to the lid of a box for easier control. Before you hook up your 12V motor or lamp, apply power to the circuit and measure the current drain with your multimeter switched to amps. PARTS LIST 1 PC board, code 09111931, 61 x 43mm 1 miniature TO-126/220 heatsink 1 10kΩ 16mm potentiometer (VR1) Semiconductors 1 LMC555/7555 CMOS timer (IC1) 1 BD679 NPN Darlington transistor (Q1) 1 1N5404 3A diode (D1) 1 1N4004 rectifier diode (D2) 1 9.1V 400mW zener diode (ZD1) Capacitors 1 330µF 25VW PC electrolytic 1 10µF 16VW PC electrolytic 1 0.1µF 63VW MKT polyester Resistors (0.25W, 1%) 1 10kΩ 1 1kΩ 1 5.6kΩ 1 220Ω TO MOTOR 10uF IC1 LMC555 VR1 ZD1 1 2/87a Queen St, St Marys, NSW 2760. Phone (02) 833 1342 Fax (02) 673 4212 When switched on and with no load connected, the circuit should consume about 15mA or so. If this is OK, connected up a small 12VDC motor or lamp and adjust the control. You should see the motor speed or globe brightness vary as you turn the pot. The choice of case for the project is left up to you. You could install it inside a small zippy case or diecast SC box. 330uF D2 5.6k 10k 220  Have you found those components yet? We know that it can be difficult, frustrating and a waste of your valuable time. So why haven’t you contacted us? We specialise in hunting down and locating components – old, obsolete, leading edge, normally available but now scarce due to allocation by overseas manufacturers. Integrated circuits, resistors, capacitors, transistors, diodes, valves, varistors, etc. Any brands Let us save your valuable time Contact us now on 833 1342 We are also distributors for Electrolube lubricants and chemi­cals Hakko - desoldering & soldering irons; SMD tools; replacement parts NTE - replacements semiconductors 1k Q1 D1 12V PLUGPACK 0.1 Fig.2: install the parts on the PC board exactly as shown in this layout diagram. Fig.3: check your PC board against this fullsize pattern before mounting any parts. January 1994  51 VINTAGE RADIO By JOHN HILL Realism Realized – the Precedent console receiver A great deal of patience is sometimes needed if one is to restore an old radio to its former glory. My 1932 Prece­dent console was just one such set. This story started about five years ago in a junk shop in Castlemaine, Victoria. There it was in all its faded glory – a rather sad looking “Precedent” console radio cabinet with turned legs. The dial escutcheon bore the motto “Realism Realized”. Unfortunately, that’s all there was – it was just an empty cabinet and it was not in very good condition either. It had been wet many times and was quite shabby looking in appearance. However, those of us who collect old radios can picture in our mind’s eye what these wrecks looked like when they were new and, more importantly, what they can look like again when re­stored. As the old cabinet had fair prospects, I offered half the asking price and it was mine. No innards From that time on, the cabinet took up residence in my shed and nothing was done to it for the simple reason that there were no innards to put in it. I also realised that, because of its poor condition, the woodwork would require more professional refurbishing than I was able to give it. This home-made bearing (left) solved a troublesome dial problem. It was turned up on a metal-cutting lathe in the author’s workshop. Let’s face it: we can’t be good at everything and restoring dilapidated old radio cabinets is not my strongest point. To cut a long story short, I was able to locate a complete Precedent (a legless console) with the same dial and control positions. It took a few months to talk the owner into selling it but eventually I became the proud owner. Naturally, my intention was to fit the innards of the legless console into the old turned leg cabinet. I also hoped that I would be able to sort out the mess under the chassis for there appeared to be many modifica­tions to the original circuit. Incidentally, dates pencilled onto the underside of the chassis indicate that the set was made in October 1932. So we are talking about a 60-year old radio: one of those classics from the early 1930s. The background The Precedent’s dial escutcheon bears the motto “Realism Realized”. It is a typical half-moon dial from the early 1930s. 52  Silicon Chip We are going to do a bit of side tracking now but it is all part of the Precedent story. A friend by the name of Peter Hutton visits me occasionally and as Peter is a fellow radio collector, we have some rather lengthy conversations when he calls. Peter is more than a vintage radio enthusiast; he also runs a TV and video repair service and is a co-owner, with his brother David, of the Melbourne Wireless and Sound Museum at Peninsula Boulevard, Seaford, Victoria. One of the reasons Peter visits me is to see if I have anything interesting for sale and it’s not often that he goes away empty handed. He also offers a reasonable price for anything he wants – not like some collectors I know! On his last visit, I decided that it must be about time the money flowed the other way for a change, so I let him take away the old Precedent cabinet for restoration. Peter does refurbishing work and that old weather-beaten cabinet needed his profes­sional touch. Among other things, the top of the cabinet re­quired re-veneering, a rather specialised job to say the least. Apart from cabinet restoration work, The Wireless and Sound Museum offers a wide range of services to the vintage radio enthusiast, all of which are carried out on the premises. I will go into that aspect some other time. When the Precedent cabinet was returned, I was very pleased with the job. Looking closely, one can see that the original surface was a bit rough and weathered but the overall refurb­ ish­­ing is as good as could have been done considering the condition of the woodwork. It really did require the magic wand treatment and the old cabinet has responded well to many hours of diligent work. The “U” section chassis of the old Precedent was fitted with timber ends. Although the resulting set-up was not very rigid, such construction techniques helped keep production costs down – an important consideration in 1932! The restoration of the receiver itself was also far from simple and it needed considerably more time than is usually required. Perished rubber One of the biggest problems was the perished natural rubber-covered wiring that was used extensively through­ out the set. This insulation had broken away in many places, particularly where the wiring went through small holes in the coil cans, IF transformer cans and the chassis. All these leads had to be replaced in order to prevent short circuits and potentially dangerous situations. Considerable care must be taken when doing rewiring of this nature to make sure that everything goes back the way it was. Just one connection in the wrong place can cause a lot of trouble and inconvenience. Replacing one wire at a time is a good policy in this situation. One of the IF transformers had an open winding which was easily located. Green corrosion highlighted the trouble spot in one of the fine leads and it was repaired by bridging the Above: this close-up view shows the friction dial set-up. The small hole & its associated slit at the top of the disc allows light to shine through and illuminate the dial. At right is the dismantled resistor stack. These wirewound resistors are mounted one on top of the other, with insulating strips between them. January 1994  53 At least half of the original wiring had to be replaced because of perished insulation. The aerial, oscillator and bandpass coils all needed rewiring. gap with a piece of fuse wire. These old IF transformers were wound using single-strand copper wire on wood­­en bobbins. Litz wire had not come into general use in 1932. Valve line-up The Precedent’s valve complement was relatively common for that era and consisted of an 80 rectifier, 57 autodyne mixer, 58 IF amplifier, 57 detector and first audio, and a 47 output. The 47 output pentode is one of the few early AC valves that had a directly heated cathode. Many readers would know simply by the valves used that the old Precedent was an autodyne superhet with anode bend detection and no automatic gain control. This type of receiver was fairly standard in the early 1930s. However, the Precedent had a few oddities about it that were different to the norm. One of these peculiarities is the “resistor stack”. All the wirewound resistors in the set are wound on flat fibre formers with a solder tag at each end. These strip resis­tors are drilled at the ends and are mounted one on top of the other in a stack. There are four such wirewound resistors and they are separated from each other by an insulated strip. One of the photographs shows a dismantled resistor stack. This resistor stack caused just one of the many problems encountered with the restoration, as one of them had gone open cir­cuit. Fortunately, the break was at one end of the winding The tuning capacitor is a plain bearing type with two collars & set screws to control end float. Plain bearing tuners often require cleaning & lubrication if they are to work smoothly. 54  Silicon Chip and was easily repaired by reconnecting it to the solder tag. When restoring a receiver of this nature, it is advisable to measure and label such resistances. A known resistance is easier to replace than an unknown one should it break down at some time in the future. Another oddity was the 2µF paper capacitor that is used as a cathode bypass on the output valve. Normally, a low voltage electrolytic type is used in this situation. However, one must remember that this set was built way back in 1932 when “dry” electrolytics were in their infancy. Although they could have been around at the time, they may not have been reliable units – hence the large paper bypass capacitor. Dial problems Another problem was the friction drive dial mechanism. Although the drive had plenty of friction, the bearing that the control shaft turned in was very worn and allowed the control shaft to lift. This movement was sufficient to let the friction drive parts come out of engagement and lock up the works. Having a metal cutting lathe in my workshop helps to solve many worn dial problems and this occasion was no exception. A new bearing was turned up in hexagon brass (see photograph) and the dial drive now functions as it was meant to. Without the lathe, worn dial parts could present some really nasty problems that would be difficult to overcome. All the old paper capacitors, including the 2µF unit men­ t ioned The IF transformers required rewiring due to damaged insu­lation on the original wiring, particularly where this wiring passed through holes in the cans. All leads were replaced to prevent short circuits. 12 MONTHS WARRANTY ON PARTS & LABOUR THAT MAKE LIFE EASIER PRODUCTS YOU NEED AUSTRALIAN MADE TEST EQUIPMENT SHORTED TURNS TESTER Built-in meter to check EHT transformers, in­ clud­­­ing split diode type, yokes and drive trans­ formers. $95.00 + $3.00 p&p DEGAUSSING WAND This view shows the 80 rectifier valve (left) & the 47 output valve. The chassis cleaned up quite well for a 60-year old re­ceiver. The two terminals at bottom right are for a gramophone pick-up. earlier, were replaced with modern equiv­ alents. Likewise, the original chassis-mounted high-tension filter electro­ lytics. These were replaced with new 10µF 450V units. Another capacitor that needed attention was the tuning capacitor, an old 3-gang type with plain bearings. It was in really good condition for its age and only required cleaning and lubricating. The thrust bearings were also adjusted to prevent end float and to prevent the plates from touching each other. As luck would have it, there were no problems with the old loudspeaker. The cone was OK, as were the field coil and the output transformer. It's not unusual to strike trouble here, as open circuit field coils are a common problem. Worth the effort Now that the Precedent is back together and working again it looks rather good and was well worth the effort and expense. In reality, however, its performance is no better or worse than any other 5-valve auto­dyne receiver from the early 1930s. All these sets seem to have a slight amount of distortion (due to the anode bend detection) but most people would be unaware of this minor fault. By transistor radio standards, it sounds magnificent! Although some vintage radio collectors can boast about the beautiful original receivers in their collections, most of us have to make do Great for comput er mon­­­i t­o rs. 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 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 REMOTE CONTROL TESTER Designed to test infrared or ultrasonic remote con­ trol hand­pieces; eg, for TVs, VCRs, house alarms and car alarms. Supplied with extension infrared detector lead. Output is via a LED and piezo speaker. $97.00 + $4.00 p&p. SILICON CHIP COLOUR TV PATTERN GENERATOR Built-up kit comes with power plugpack, RF lead. $250.00 + $9.00 p&p. This view shows the finished receiver in its refurbish­ed cabinet. It’s quite a stylish outfit if you happen to like old console radios. by scrounging for what leftovers are still around today. Even so, by using skilful repair techniques, enlisting the services of experts and combining the best parts of several radios into one, the end result can be very pleasing. I believe my 1932 Precedent to be one such receiver. The Precedent may not really be “Realism Realized” by today’s standards but in 1932 it may well have been SC very close to it! TV & VCR (new) tuners – $47.00 each VCR converters – $49.00each TV, VCR TUNER REPAIRS FROM $22 REPAIR OR EXCHANGE Phone for free product list 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone (02) 774 1154 Fax (02) 774 1154 Cheque, Money Order, Visa, Bankcard or Mastercard January 1994  55 SERVICEMAN'S LOG It was all a long time ago I have two quite unusual stories this month. For how long & by what devious means can one keep a TV set working? And for how long should one keep customers’ records? The other story emphasises how lost we can feel when away from our own workbench. The first story really started over 11 years ago. It was little more than a routine job then and I certainly did not imagine that I would be resurrecting it after all this time. But I did make notes about it; not only in the normal way for my own benefit but also for a colleague who expressed some interest in it. So I was able to recall the events in reasonable detail. It was all brought back by a recent phone call. A lady at the other end of the line introduced herself – the name didn’t register immediately – and went on to remind me that I had fixed her TV set, an HMV, “some time ago”, and that it involved a problem with the green in the picture. My memory isn’t particularly good on some-time-ago jobs (one handles so many jobs) but the mention of the green problem rang a bell. I asked her if she was living at a particular address at the time – it’s funny the way one’s memory works at times. Yes, that was correct. And the whole story came flooding back. In particular, I remembered how accurately she had de­scribed the symptoms; far more so than most people. And I also registered that it was more than some time ago; it was long time ago. In fact, I had begun to link it with other events and was thinking in terms of six or eight years, which wasn’t that far out. But despite the fact that I remembered the set and its symptoms, I could not recall the fault itself or what I had done to fix it. Anyway, I regarded all that as being of little importance and asked what problem she had now. To my surprise, she replied that the HMV set was the problem. Was that set still going after all these years? Yes, it was but, on her own admission, apparently not very well. Her son, who works for the ABC in another state, had visit­ed her recently and commented that the picture – and particularly the colour – was rather poor. In short, he realised that gradual picture deterioration had crept up on Fig.1: the RGB driver stage in the HMV 12642. The green driver stage, X01, is at the top of the diagram & is direct coupled to the green gun cathode. Doctoring this stage restored performance. 56  Silicon Chip her over the years and suggested that it was time she bought a new set. And that was the purpose of the call; not to initiate any service to the set but to seek my advice regarding a new set. In particular, she needed to know which brands I handled on a war­ranty basis because she wanted to be sure I would be available to service the set. Such loyalty can be quite touching at times. So that was more or less it. I nominated the brands I handle on a warranty basis and left it to her to choose which ever one she fancied. She thanked me and we left it at that. How long ago was it? And that should have been the end of it. But I couldn’t get the set out of my mind. Just how long ago was it? So I began searching through my old files. It turned out to be quite a search but I eventually found the relevant file and a copy of the invoice, dated September 1st, 1982 – over 11 years ago at the time of writing. But that wasn’t the real surprise; that was only appreciated when I read my notes about the fault and its cure. The set was a 48cm HMV, model 12642 (which was also market­ed as a JVC 7765AU), and it was about five years old at the time. The fault, as described by the customer, was that the picture had lost its green content. And I had noted that this customer was more astute than most; her description was completely accurate. In greater detail, she explained how the set had turned on a display of multi-coloured fireworks on the screen. This display lasted for a few seconds and the set then behaved normally; except that there was no green. As recounted in my notes, there was initially some confusion on my part as to the exact cause. At first I suspected some kind of green gun failure but, in fact, I found I was able to produce a green image using various brute force tactics. This led me to suspect a circuit fault, whereby the tube was not receiving adequate green signals, and I spent some time following this lead, only to finally conclude that it was false; that the fault had to be in the tube. More specifically, I con­cluded that the fireworks display had been caused by a fragment – probably loose cathode material – causing a momentary internal short. And this had damaged the green cathode, reducing it’s emission to the point where it was virtually cut off at the normal bias level. So was it worthwhile fitting a new tube or was the set a write-off? It was a marginal situation and the lady was not very happy about spending a couple of hundred dollars on a replacement tube, much less the cost of a new set. Finally, I decided to take a punt on a mild form of butchery. As matters stood, the tube and – potentially – the set were both a write off. But suppose I were to doctor the bias voltage; could I brute force the green back to a normal level? And, if so, how long would such a trick last? The first question was easily answered. Reference to the circuit (see Fig.1) shows that the collector of the green driver transistor (X01) is directly coupled to the green gun cathode and sets it at about 142V. By shunting R01, a 1.2kΩ resistor in the emitter circuit of X01, the current through X01 would be in­creased, its collector voltage reduced, and the bias on the green gun reduced. And it worked. After some trial and error, I settled for a 5.6kΩ resistor across R01, which produced virtually normal green performance. The second question was another matter. I had no way of knowing how long it would last but I reckoned a minimum of 12 months would be a reasonable guess. Anything after that would be cream on the custard. And so, on that basis, I felt that this ap­ proach was justified. It would give the customer time to assess her financial situation and decide on a new tube or a new set. I was most careful to explain what I had done; that it was a short-term measure that could only be justified on a nothing-to-lose basis. Assuming she was happy, I would leave it like that. She said she was and so I did. As I recall, I checked the situation about a year later and the set was still going strong. And that was the last I heard of it – until now. But another 10 years? That’s a lot of cream! Curiosity killed the ... Having sorted out all those memories, another thought oc­curred to me. Would the lady let me borrow the set, to check it and satisfy my own curiosity as to just how well it had stood up over all those years? So, a week or so later, when making January 1994  57 a call in the area, I took a punt and knocked on the door. When the lady answered I explained that I was simply making a courtesy call in case she needed any more advice about a new set and to ask whether I could have a look at the old set out of curiosity. She greeted me warmly and invited me in to see her new set. It turned out to be a 48cm Samsung and she was very happy with it. Then a tray appeared carrying the inevitable cuppa accoutrements – teapot, cups and saucers, and chocolate biscuits. And so we sat and chatted for a while. Eventually, I raised the matter of the old set again. Yes, of course, it was in the back room. And I could have it if I wanted it; she was a loss to know what to do with it. I went through the motions of protesting but she was adamant; take it away. And so, after a pleasant interlude, I came away with the old set. I didn’t regard it as valuable in the financial sense but I valued it for what I might learn from it. Back at the shop, I lost no time in setting it up. In most respects, its performance was first class – a good sharp picture, excellent geometry, normal sound, no tuner problems and no noisy controls. It was quite remarkable for a 16-year old set, with only one service job in that time. But the colour – yes, that was crook. I fed in a colour bar pattern and, as 58  Silicon Chip in the original case, the green was very weak. Also, the red was flaring but the blue was about normal. Just for the heck of it, I went through the motions of grey scaling and this improved things a little. But it was still very poor. Picture tube rejuvenation So what now? Did I have any more tricks? Well, there was one other possibility but it was a Sydney-or-the-bush approach. What about a spot of picture tube rejuvenation? There are various devices for this but the basic principle is pretty much the same. Normally, the heater is run at its rated voltage, although some authorities recommend overrating it some­what. I prefer not to. After that, a voltage of between 600V and 700V is applied to the grid for about two seconds. This typically creates some brief fireworks around the cathode area and the idea is to keep applying short bursts until this activity ceases. It’s very much a gamble. Sometimes it works and sometimes it doesn’t. And even when it does, there is no guarantee as to how long the effect will last. But what did I have to lose? So I set up the booster and went over each gun in turn. Significantly, I needed to give the green gun about eight bursts before all the fireworks ceased. For the others, one or two bursts were sufficient. Next, I went through the grey scaling process again. It was much improved now; almost good enough, in fact. But there was one limitation which is common with weak tubes, whereby the grey scale tends to vary with the setting of the brightness control. In this case, turning the brightness down would increase the green level in the lowlights, while turning it up had tended to emphasise the red. The best that one can do is try to balance things at what would be regarded as a typical brightness viewing level. So this was what I did. I then let it run in the workshop for a couple of days to see how it would hold, this being the critical aspect of tube boosting. And it did shift, again involv­ing the green. I gave the green gun a second short boost and grey scaled it again, which again improved things a little. So that’s where it stands at the time of writing. I hope it might stabilise a little more with time but I know I’m being optimistic. So of what use is it now? Well, not much for serious bench work, although it could serve as a loan set in an emergency. But what I am really hoping is that I might score a suitable tube from a set written off for other reasons. If that should happen, I may have a set that’s good for a few more years – but not 11! Serviceman’s holiday And now for a complete change of scene – literally. After several months of planning, I recently set off on a leisurely trip up the New South Wales north coast on what was partly a holiday and partly a business trip. Among other things, I had been invited to stop over for a few days with a family I have known for many years but had not actually seen for quite some time, although we have kept in touch. And I had little doubt that they would have an array of electrical and electronic jobs lined up for me. And so I had packed as much gear as was practical – multi­meter, soldering equipment, small tools and an assortment of likely minor components. Outside of that, I could only hope. And so I found myself settled in and we spent some hours mulling over old times and catching up on all that had been happening. But then came the practical problems of the present, in the form of a video recorder which had begun to play up just a few days before I arrived. It was a Sharp model VC-505X, a model with which I have had very little experience and, without a man­ ual, I was starting behind scratch. The problem itself was that, at times, the ma­chine would go into the play – or record – mode briefly, then shut itself down. And it was similarly erratic in fast forward or rewind modes. Anyway, the recorder was taken out of its cabinet and set up on a small table. Since the problem was a mechanical one, there was no need for a TV set connection at that stage. I pulled the cover off, pushed in a tape, and set it running. It loaded and ran normally the first time and for the next several tries but then suddenly baulked. And the primary reason was immediately obvious; the take-up reel had stopped and the take-up reel sensor had shut the machine down. We then tried the fast forward and rewind functions, with the same results. Well, there was obviously a fault somewhere in the reel drive mech- anism and this was the first hurdle. As I mentioned earlier, I am not very familiar with this machine; all I knew was that it used an unusual reel drive system. Most machines use a rubber-tyred idler wheel and this is supported on the end of a short arm which toggles to one side or the other and engages the wheel with the appropriate reel drive. Instead of the tyred wheel, this machine has a gear wheel mounted on the end of the arm. This toggles from side to side in a similar manner and engages a matching gear in the reel drive train. But that’s not all; as well as moving from side to side, the arm carrying this gear also moves up and down. This movement is probably necessary to ensure smooth engagement of the gears. That much established, I took a breather. In addition to the main problem, I was also aware of several routine things that needed to be done. One was a general clean-up of the capstan, heads and guides, which were a trifle grotty. Another was to fit new belts. There are only three belts in this machine; one from the capstan motor Protect Your Valuable Issues Silicon Chip Binders These beautifully-made binders will protect your copies of SILICON CHIP. ★ Heavy board covers with 2-tone green vinyl covering ★ Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A11.95 plus $3 p&p each (NZ $6 p&p). Just fill in & mail the order form on page 101; or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. to the capstan drum and flywheel and two associated with the loading motor. They weren’t in bad nick but since it would probably be long time before I serviced the machine again, it seemed prudent to replace them if possible. Of course I didn’t have any such belts with me, or any cleaning alcohol. So, when the family announced a visit to the nearest large shopping centre, I jumped at the opportunity to try for what I needed. Medicinal alcohol Well, I was lucky. I found a TV service centre which had suitable belts and an obliging chemist who dispensed a small bottle of medicinal alcohol. Thus equipped, I completed the various routine tasks without incident but the mechanical problem remained a mystery. The problem was that the mechanism would not function at all unless there was a cassette in it and when there was a cassette in place, it was impossible to see the mechanism. The solution was crude but effective. My friend had several old tapes on hand which had been put aside due to wear or other faults. So I pulled one 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. January 1994  59 of these apart, removed the tape, and cut a small opening in the bottom. The result was a crude version of the commercial transparent dummy cassette I use in my workshop. With this in place, it all became clear. The reason the gear was not engaging was simply because the arm holding it was not lifting through the full distance. Well, that took me one step closer but the reason for this failure still had to be determined. In the event, this was the easy part. Closer examination revealed that the vertical shaft on which the gear arm moved up and down had become gummy due to some kind of lubricant, applied either during production or subsequently. A good swabbing down with alcohol cleaned this away and that was the answer. I chose not to lubricate it again; it was a plastic bearing moving up and down on a metal shaft and I seriously question the need to lubricate such a simple movement. Broken tape So that was that problem solved. But hardly had I heaved a mental sigh of relief than another one landed on my plate. It was a broken tape. More specifically, it was a recorded program 60  Silicon Chip which, while of no longterm value, was of considerable immediate interest. But they had seen only the first 15 minutes or so of it when the tape broke. As nearly as I could work out, the tape had been running for about 15 minutes when it became necessary to stop play for some reason. But then the recorder went cranky and would not start again. In the process, it had formed a small tape loop before the machine shut down. This loop then became tangled and the tape broke when the cassette was ejected from the machine. While not a common problem, it is not the first time a customer has turned up with a broken tape, begging for help. On my own bench it would be no problem. After the first couple of incidents, I invested in cheap tape splicer. It is a simple jig which holds the tape with the broken ends overlapping. An angled slot then guides a sharp blade to make a clean cut through both layers. The two ends now left butting together are joined with an adhesive patch. In spite of the jig’s low cost, it works quite well and has helped several customers. Prior to that, I had resorted to a more primitive approach. This involved making a simple overlap joint using an acetone-based adhesive, on the understanding that this joint would be used only to play the remainder of the tape and that it would not pass over the heads or capstan. Crude though it was, this idea worked too and it seemed that I would have to resort to a similar trick in this case. My friend’s workshop yielded a tube of clear acetone based adhesive and I went to work on the break, finishing up with reasonably neat joint. But I had no time to test it. It was time for me to leave and I wanted the joint to be left overnight to set properly. And so I departed, with an invitation to stop over again on my way back in about a week. I had an idea that there might be more jobs waiting for me then but I didn’t anticipate anything like what actually happened. It appeared that the jointing operation had been a complete success and the tape had been played to its conclusion. But when another tape was subsequently played, there was trouble. Although it was a 3-hour tape, at the end of two hours the take-up reel was chock-a-block full, to the point where excessive tape had fouled the bodywork, stopped the reel, and shut the machine down. Crinkled tape The basic reason was easy to see – the tape was crinkled, taking up much more space than normal. But why? I could only assume that something in the tape transport path was damaging it. So off came the cover and I went straight to guides, heads and capstan. And one glance at the capstan was enough. It looked as though it hadn’t been cleaned for years, even though I had cleaned it thoroughly only a few days before. More specifically, it displayed the two characteristic dark oxide rings (one tape width apart) that normally occur after prolonged use. Even more puzzling was the fact that attempts to clean it using alcohol and a tissue proved fruitless; it simply wouldn’t budge. Again, this is what one would expect from severe fouling over a long period – often requiring that the capstan be careful­ly scraped to remove the rubbish. But why after only 3-4 hours of playing? Anyway, I attacked it with the first thing handy – a fine screwdriver blade. I know that sounds drastic but it isn’t really, unless one is woefully heavy handed. And in this case only the lightest touch was necessary; all the fouling moved as one piece and came away as a tubular shell with the oxide rings at each end. The capstan was now as clean as I had left it. So what was it? The adhesive I had used to join the broken tape. And why? Because the tape had been rewound and, contrary to my advice, the join had passed over the capstan. How it happened I don’t know, and diplomacy dictated that I not stress the point. No real harm had been done apart from the damaged tape and nobody was upset about that. So it all ended happily in the long run. But I think the lesson is that trying to improvise away from one’s own workbench can be fraught with danger. It doesn’t always pay to be SC too clever. 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 COMPUTER BITS BY DARREN YATES Even more experiments for your games card In the November 1993 issue, we used some simple program­ming so that the games card could function as an analog inter­face. Now we take a look at how to obtain higher speed interfac­ing using some simple assembly language routines. If you read the last instalment of this series, you’ll probably think that using straight MS-DOS QBasic is just too slow and, in most cases, you’re right. Any language which is designat­ ed as an “interpreter” can usually be regarded as “slow”. However, one of the forgotten programming languages is Assembly Language which is faster than any compiler you could lay your hands on. What’s more, you have access to it through QBasic! Now most people, even competent programmers, seem to baulk at the idea of using assembler code as either being “old-fashioned” or “too hard to use”. But if you can program in BASIC, there’s no reason why, with a little care, you can’t do likewise with Assembler. Those of you who go back far enough will remember the DREAM 6800 and ETI-660 microcomputers which came onto the scene before the days of the TRS80s and Commodore 64s. Programming on the former was done by a form of machine code and by just following simple steps, even yours truly, as a 9-year old, could write simple software on them. By the way, if you still use a TRS80 or Commodore 64, then there’s no reason why you can’t keep using them for years to come. OK, so they may be pushing 20 years old, but if you’re a hobbyist who wants to interface your own projects with them, then they’re ideal. The main benefit the IBM PC compatible has in this area is just the sheer volume of information that is available on the internals - information which is hard to get on other machines. BIOS & DOS interrupts Getting back to machine code, Microsoft have taken most of the hard work out of writing assembler or “machine code” routines by supplying many routines as part of your machine’s disc operat­ing system (DOS). Other routines are supplied as part of the built-in operating system (BIOS) which comes in one or two ROMs on the motherboard. These two sets of routines allow you to get at the hardware of your machine without having to worry about the bulk of the programming. For example, you can set the time and date directly, check to see if your motherboard has a co-processor, check the number of printer ports or what’s on the printer ports, and so on. You can even display a message about the mother­board from its manufacturer. The list goes on and on. However, at this point, we’ll just look at those routines that pertain to the games card. Clock speed Back in the first article on using the games card (SILICON CHIP, January 1992), we looked at the circuitry of the games card to see how it was able to translate the joystick position into an 8-bit count. Recounting briefly, the games card contains a 558 quad timer IC which is wired as four monostables. Each x- and y-section of the joystick is a separate variable resistor which is connected up with one section of the 558 to form a monostable. To read back the digital count, the computer triggers the monostable and at the same time starts an 8-bit count. When the monostable falls low again, the count is stopped. Now this method is obviously going to be slow, particularly if it has to count to 256 on each scan and, as a result, the frequency of scanning is around 800Hz. When you couple this with QBasic’s relatively low speed, you can now see why the simple analog interface we built last time could only handle 40 samples per second. However, by using a small amount of machine code, we can increase this by about 10-fold. QBASIC & machine code Those of you who aren’t familiar with QBASIC will be sur­prised at its easy-to-use interface compared with GWBASIC. There have been a couple of small changes in the language, particularly with respect to using machine code. QBASIC gives the user direct control of the PC via a com­mand called CALL January 1994  65 Fig.1: Games Card Finder Program ‘ Games card finder program ‘ Copyright 1993 Silicon Chip Publications ‘ Written by Darren Yates B.Sc. ‘ This program prints a message indicating whether or not ‘ a games card is installed. ‘ It uses a machine-language program stored in an array ‘ to get the information from the operating system. DEFINT A-Z DIM Asmprog(1 TO 7) ‘ The machine-language program stored as data to read into ‘ the array. AsmBytes: DATA &H55 : ‘PUSH BP Save base pointer. DATA &H8B, &HEC : ‘MOV BP,SP Get our own. DATA &HCD, &H11 : ‘INT 11H Make the ROM-BIOS call. DATA &H8B, &H5E, &H06 : ‘MOV BX,[BP+6] Get argument address. DATA &H89, &H07 : ‘MOV [BX],AX Save list in argument. DATA &H5D : ‘POP BP Restore base pointer. DATA &HCA, &H02, &H00 : ‘RET 2 Pop argument off stack   ‘ and make far return. ‘ Get the starting offset of the array. start = VARPTR(Asmprog(1)) ‘ Poke the machine-language program into the array. DEF SEG = VARSEG(Asmprog(1))’ Change the segment. RESTORE AsmBytes FOR index = 0 TO 13   READ byte    POKE (start + index), byte NEXT index ‘ Execute the program. The program expects a single integer argument. start = VARPTR(Asmprog(1)) CALL ABSOLUTE(status%, start) DEF SEG ‘ Restore the segment. ‘ status% now contains bit-encoded equipment list returned by DOS. ‘ Mask off all but the games card bit (bit 12). game = status% AND &HC000 ‘ Print the appropriate message. IF game = 16384 THEN PRINT “Games Card present.” ELSE PRINT “No Games Card.” END IF END ABSOLUTE() which transfers control to machine code elsewhere in the program. A simple example of this is found in GAMECARD.BAS in Fig.1. This program checks the hardware of your computer to see whether it has a games card connected. If you’re writing your own programs to use a games card, you can use this routine to check if one exists in the computer before going further. This is a good idea because it saves the user 66  Silicon Chip the frustration of not knowing why the program won’t work. Looking at the program, the machine code is stored away in an integer array called ASMPROG. If you count through the data statements, there are 14 bytes of instructions but since an integer variable consists of two bytes, we only need seven to store away the program. Looking at the machine code bytes, each line contains the bytes required to execute that function – some require only one byte while others need three. The first line saves the current base pointer and puts it on the stack. The base pointer is a pointer to the current address of the last instruction and the reason we need to save this is that when we run or “call” this routine, we are effectively transferring control from one language to another. The base pointer performs the task of a “bookmark” – showing us where to go back to after we’ve finished. Next, we have to transfer our current base pointer of this program area, which is the array ASMPROG, into the BP register. This is to make sure that we use the correct area of memory. The next line performs an interrupt, which tells the com­puter to stop everything and run the routine which is designated 11 in the BIOS ROM. This returns a value to the AX register which contains the information shown in Table 1. The AX register is 16-bits wide and each bit is used to indicate which parts of the hardware are present or absent. Bit 0 shows whether or not there is a floppy drive. Few computers don’t have a floppy drive of some kind so this will invariably be ‘1’. Bit 1 shows if a co-processor is installed; bit 2 shows if you have a mouse installed; bits 4 and 5 show which video mode you’re in; bits 6 and 7 how many floppy drives you have minus one; bits 9-B how many RS-232 cards you have; bit C if you have a games card; and bits E and F how many printer ports you have. Now we want the machine code program to return this value of AX back to the variable STATUS%. To do this, we need to know the address of this variable and this is what the 4th line does. It uses “indirect addressing” to load into register BX not the value of BP+6 but the address of this position. The next line loads the contents of AX, not into BX but the address of the contents of BX, which in our case is the address of variable STATUS%. This sounds pretty long winded but it is a powerful way of using only a small number of registers to access a wide area of memory. Now that we’ve completed what we set out to do, we must restore everything and leave the stack the way we found it and that requires us to ‘pop’ the contents of the original Table 1: Bit Meanings F E D C B A 9 8 7 6 5 4 3 2 1 0 Meaning of bits x x x 0 1 x x x x 0 0 1 1 0 1 0 1 0 1 1 0 1 1 0 0 1 1 0 1 0 1 base pointer from the stack and put it back into register BP. The last line does what’s called a ‘far return’ which means that it re­ turns control from the machine code program back to the next instruction of the QBASIC program, wherever in the memory that may be. This machine code is loaded in via a FOR..NEXT loop using the POKE command. Before this happens, there are two commands carried out to make sure that these bytes go in exactly the right spot and these involve the commands VARPTR and VARSEG. Since the PC memory is divided Number of printers attached Not used Game adapter not installed Game adapter installed Number of serial cards attached Not used 1 disc drive attached (if bit 0 = 1) 2 disc drives attached (if bit 0 = 1) 3 disc drives attached (if bit 0 = 1) 4 disc drives attached (if bit 0 = 1) Initial video mode = 40 x 25 BW/colour card Initial video mode = 80 x 25 BW/colour card Initial video mode = 80 x 25 BW/mono card 16K system board RAM 48K system board RAM 32K system board RAM 64K system board RAM 1 Math coprocessor installed 0 No disc drives installed (bits 6-7 insignificant) 1 Disc drives installed (bits 6-7 significant) into 64Kb segments, we have to know which of these segments the array ASMPROG is sitting in. This is carried out by the VARSEG command which sets the current segment pointer to this segment. Next, we have to know where in that segment this array is and this is done by the VARPTR command which puts the location of the first array element of ASMPROG into the variable START. The command which calls the machine code is CALL ABSO­LUTE(STAT­ US%, START) with STATUS% the variable we want the infor­ mation returned in, while START tells the computer which memory address to begin the machine code program. Once it’s carried out, control is return to the next line of the program, which restores the segment back to the QBASIC program. Next up, variable GAME is used to store the single bit of information we need and we get this by ANDing the STATUS value with the hexadecimal number 8000. The end result of this is that if the computer has a games card, then GAME will equal ‘16384’ and ‘0’ otherwise. We simply use it in this case to print the appropriate message on screen. This program will run under QBASIC in either DOS 5 or DOS 6, as well as QuickBASIC 4.5. All of the programs mentioned so far in this games card series, including GAME­CARD.BAS and .EXE versions, are available from SILICON CHIP for $10 including postage and packaging. Please specify either a 5.25-inch 3.5-inch disc as required. You can call (02) 979 5644 with your credit card de­tails or send them via fax to (02) 979 6503. Next time, we’ll continue by looking at the games port address and how it can be used. References (1) Using Assembly Language; 2nd edition, Allen L. Wyatt, Que Corporation 1990. (2) The Programmer’s PC Source­ book; 2nd edition, Thom Hogan, SC Microsoft Press 1991. January 1994  67 Silicon Chip November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone; How To Quieten The Fan In Your Computer. 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. February 1989: Transistor Beta Tester, Cutec Z-2000 Stereo Power Amplifier, Using Comparators To Detect & Measure, Minstrel 2-30 Loudspeaker System, VHF FM Monitor Receiver, LED Flasher For Model Railways, Jump Start Your New Car March 1989: LED Message Board, Pt.1; 32-Band 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. April 1989: Auxiliary Brake Light Flasher; Electronics For Everyone: What You Need to Know 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. About Capacitors; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. 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. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). 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. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2; PC Program Calculates Great Circle Bearings. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. 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. Please send me a back issue for: ❏ February 1989 ❏ March 1989 ❏ July 1989 ❏ September 1989 ❏ January 1990 ❏ February 1990 ❏ July 1990 ❏ August 1990 ❏ December 1990 ❏ January 1991 ❏ May 1991 ❏ June 1991 ❏ October 1991 ❏ November 1991 ❏ March 1992 ❏ April 1992 ❏ August 1992 ❏ September 1992 ❏ March 1993 ❏ April 1993 ❏ August 1993 ❏ September 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 May 1993 October 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ November 1988 May 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 June 1992 January 1993 June 1993 November 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ➦ Use this handy form to order your back issues December 1988 June 1989 December 1989 June 1990 November 1990 April 1991 September 1991 February 1992 July 1992 February 1993 July 1993 December 1993 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 68  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. 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; 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. 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. 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. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With 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. 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. 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. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1; 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 Amateur 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. April 1992: Infrared Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; 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; 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. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. 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, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2; Double Your Disc Space With DOS 6. July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; Build An AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Low-Cost Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits; Unmanned Aircraft – Israel Leads The Way; Ghost Busting For TV Sets. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Electronic Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; FM Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Mini Disc Is Here; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier, Pt.3; Build A Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card; Preventing Damage To R/C Transmitters & Receivers. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock, although stocks are low for some older issues. For readers wanting articles from sold-out issues, we can supply photostat copies (or tearsheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. January 1994  69 REMOTE CONTROL BY BOB YOUNG More on servicing your R/C receiver Last month, we looked at the mechanical aspects of re­ceiver servicing. This month, we will be looking at the electron­ic aspects, with an emphasis on AM & FM sets. To begin, a circuit diagram of the receiver under discus­sion is a great help (as if you need to be told) and a component overlay is almost as important. There was a time not so long ago (before the popularity of FM) when a good knowledge of one re­ceiver was all you needed to service almost any receiver on the market. Technology has changed all that. FM brought into vogue the single IC receiver and PCM the in-house microprocessor. Surface mount technology has added a new complication in that most surface mount components are not marked with values (except resistors) and most components are hardly PERIOD OF NO CARRIER All receivers from PCM onwards are outside the scope of this article and must be left to the factory-trained and support­ed technician. I will be confining this discussion to AM and FM receivers using conventional components and some surface mount. Check the transmitter Servicing an AM receiver is a fairly straightforward busi­ness and, as usual, involves a strict discipline for the most efficient results. Adequate test equipment is a must and the home serviceman is at a disadvantage if his kit does not include an oscilloscope. I will attempt to include some tips for those with little equipment but you CARRIER MODULATED RF ENVELOPE Fig.1: a typical modulation pattern from an AM transmitter. Note that the modulation is completely blocked off for 350µs at regular intervals & this will result in an erroneous reading if you try to measure the carrier frequency using a DFM. recognisable. The new through-hole components will be even more horrendous in that they go into vias (ie, plated through holes in the board) and will be invisible. To cap this, knowing designers as I do, they will probably put them in vias which are located under ICs, so we are about to enter the true throwaway era. 70  Silicon Chip really are facing an uphill battle. To start with, and this applies for both AM and FM systems, check that the transmitter is working. For those with little equipment, placing the transmitter close to a TV receiver will usually result in a series of bars on the TV screen. This indi­cates that the transmitter modulation is OK and that the trans­mitter is radiating. Moving the controls will often result in a change in the bar pattern. A better test, is of course, to use a second receiver which can also be used for voltage comparisons. For those with an oscilloscope, testing an AM transmitter is fairly easy. First, clip the ground lead to the probe tip to make a sniffer loop, then hold the loop near the Tx antenna or, better still, slip it over the antenna. Now, turn up the scope’s sensitivity until a modulation pattern begins to appear on the screen. This will appear as a thick green line, blocked off into 100% modulated blocks – see Fig.1. The effectiveness of this test will depend upon many fac­tors, the prime one being the frequency response of the oscillo­scope. Often, even a poor scope will show some low level RF on the screen – enough to determine that the transmitter is working correctly. The FM transmitter presents more of a problem. The TV test may work and the second receiver certainly will. For those with test equipment, a scanning receiver, an RF test set or a modula­ tion meter will suffice to establish that RF and modulation are present and that the transmitter is working to some degree. Note that, for this series of articles, I am going to ignore the spectrum analyser on two counts. First, so few people have one of these devices that they may be discounted as far as most readers are concerned. And second, anyone with one of these devices probably has little need of instruction in how to use it. Having established that the transmitter is radiating, the next step is to establish the operating frequency. Most sets have plug-in crystals or modules these days and the number Fig.2: the circuit diagram of a typical FM receiver. Note the provision of a tuning point to aid the alignment process. +4.8V 120  3 2 .001 5.6M 36k 11 1 0.1 2 4 1 13 12 10 11 4 8 3 7 IC1 SO42P 14 2 3 5 0.1 27pF XTAL1 33pF RFC1 4.7uH 27pF 4 3 C1 3.3pF 33pF 2 1 L2 1 2 L1 ANTENNA is the correct one. Be aware that some modellers accidentally put the receiver crystal in the transmitter and vice-versa. This may result in a loss of range or a complete loss of signal if the receiver has another correct receiver crystal in it. A tricky problem here is that occasionally I have found crystals which have either gone off frequency or were incorrectly marked during manufacture. If in doubt, heavy some friend or acquaintance, or even the local serviceman, into checking the crystals for you. At Silvertone, I have a dedicated RF generator which we built many years ago. This is fitted with a 100dB stepped atten­ uator, switched crystals for all model bands, a crystal socket, an inbuilt 8-channel pulse width encoder complete with pot for operating the channel one servo, and a BNC connector and modula­tion kill switch for checking the crystal frequency. The output stage is fitted with a signal level meter which doubles as a crystal activity checker. Thus, for us the testing of an AM set begins with a voltage and field strength test on the transmitter, frequency count on the Tx crystal, modulation and purity checks of the RF sinewave on a 50MHz scope, T1 1 4101 4 5 47 CF1 270  “The number of times I have received transmitters with the wrong crystal in the socket is beyond my recall”. 2.2k 0.1 2 13 14 .01 47 270  3 If you have no equipment, then you are on your own and all I can suggest is that you check that the crystal 4 IC2 SO41P .0033 Check the crystal 5 8 12 6 7 9 1k 10 56pF 56pF TUNING POINT 100 36k 0.1 2.2 T2 4102 VR1 1M 1 IC3 LM111 VR2 6 10k 4.7k 5 4 8 7 10k S TB1 D1 1N4004 of times I have received transmitters with the wrong crystal in the socket is beyond my recall. Here, AM presents a real problem and FM is the easy one. Any frequency counter will just simply read off the carrier frequency if a sniffer probe is held in close proximity to the transmitter antenna. Be careful, though – move the transmitter just close enough to the test equipment to give a reliable read­ing. You can overload input stages and damage them if you stick the Tx antenna right down the poor thing’s throat. Because the carrier in an AM transmitter is blocked off for 350µs every 1-2ms, a frequency meter will give the incorrect frequency. The actual variation will depend on the counting period and the point at which the count started. Thus, unless the frequency counter can start and stop in less than 1ms, the chanc­es are that you will get an incorrect count. Counters such as this are not easy to come by and I have finally located one just recently after years of searching. So unless you have such a frequency counter, the best bet is a scanning receiver which shows the carrier frequency on the dis­play. If you have a scanning receiver, just tune for maximum RSSI (received signal strength indication) – or noise if your receiver has no signal strength meter – and read off the frequency from the display. January 1994  71 REMOTE CONTROL – Checking The Receiver and harmonic content checks on a spectrum analyser. The Tx crystal is then tested for activity if the Tx output appears to be on the low side. We then move onto a full visual inspection and more detailed work if required. For FM sets, a modulation meter is added to the above tests. This will give the frequency deviation and the demodulated audio waveform. I always check to see that the AM content of the modu­lation is within reasonable limits. Some FM sets have a very high AM content in their modulation. Receiver checks At long last we are ready to move on to receiver testing. Begin with the mechanical inspection and testing as outlined in the last two issues. Do a physical examination of the receiver battery and check the terminal voltage of each cell. All should be approximately equal. Next, test the receiver battery at the socket for no-load voltage. This should be about 5V. Some car sets are now running anything up to 7.2V for the higher-powered servos so be aware of this variation. Now plug the which gives approx­imately a 2-hour trace for a normal battery. A cycling battery charger is very handy for this type of testing and will give a very good indication of battery capacity. If you have only a voltmeter, get your friend to wriggle all of the transmitter controls briskly while you check the load voltage on the battery. The cells should not drop below 1.1V each under full load. Now measure the voltage at the point where the battery supply comes into the PC board. If you have voltage there and still no servo operation, then you really do have a problem. Fig.2 shows the circuit diagram of a typical FM receiver. At this point, I usually check the activity of the receiver crystal and its frequency, as it is easily and often broken in a crash and it is easy to remove and test. If this is OK, I then move on to a full voltage test on the PC board using the scope. Starting at the crystal oscillator, check that the oscilla­tor is running and giving a reasonable level of RF output. Next, check to see that all of the RF and IF coils are continuous, by using “I usually check the activity of the receiver crystal and its frequency, as it is easily and often broken in a crash. It is easy to remove and test”. whole system together and switch on. Check the battery voltage again under load – this should not be below about 1.1V per cell. If it is lower than this, then recharge the battery. If there are cells which are below 1.25V after charging, then dump the pack. The load should be all servos plugged in, Tx and Rx switched on and no servos operating. With all servos operating, the voltage may drop as low as 1.1V depending on a range of factors, including the servo current, number of servos and inter­nal condition of the batteries. At Silvertone, we use a cycling graphic analysis system and the batteries are placed under a 270mA load 72  Silicon Chip a voltage test where DC is applied or a continuity test where there is no DC as in the front-end RF coils. Coils are often broken in a crash and go open circuit. One point here is that when re-tuning the receiver, stay alert for signs of internal damage to coils and crystals. A large shift in the position of the slug in any tuning coil often indicates a broken coil. Replace the coil as a precaution. Remember always that the key element in servicing model aircraft equipment is prevention and any suspicion should be acted upon. If you have worked your way through the receiver to the detector and you finally have audio, you are past most of the fragile bits. From here on, it is generally routine servicing and the fault is usually visible crash damage. I have not gone into the complexity of every type of cir­cuit, as there are too many for the space allowed. Instead, I have briefly covered the spec­ial­­ised areas which are peculiar to R/C servicing. Receiver tuning Finally, just a word or two on tuning the receiver. Before doing this, unplug all servos and, if you are using the transmit­ter, remove its antenna (warning: do not let the Tx run for too long in this condition as the output transistor may overheat and suffer damage). In an AM Rx, there are two main types of detec­tors: (1) the simple diode detector; and (2) the transistorised version of the old “anode bend” detector. When tuning receivers with a diode detector, connect the negative lead of a voltmeter to the diode output and the positive lead of the meter to ground. When power is applied, the meter will read a small reverse voltage until the transmitter is turned on, at which point it will rise to about 0.6V or 0.7V, depending on the signal level and tuning. Reduce the signal level by moving the transmitter away or reducing the signal generator output until the voltmeter reads approximately 0V. In other words, tune at the lowest signal level you can read on the meter. Starting at the antenna coil, tune for maximum voltage and progress along the chain. When you get to the oscillator coil, this will tune to a peak and drop off slowly on one side and abruptly on the other. Tune into the abrupt side until the oscil­lation stops, then back out to the peak. When the oscillator starts again, continue in the peak direction for a full turn. That is the final setting. There is one problem with tuning the receiver this way, due to the fact that some receivers have a wave-trap in the input stage to suppress unwanted input signals. Unless you know the tuning specification and set-up procedure, there is little that can be done about tuning this wave-trap correctly. The main thing is to be aware of the situation. Tune the IF coils in the normal manner, firstly for peak voltage, then if a scope is available, for wave shape. SILICON CHIP BINDERS BUY A SUBSCRIPTION & GET A DISCOUNT ON THE BINDER (Aust. Only) Active detector Tuning an active detector is quite the opposite. In this case, the meter is hooked up with its negative lead to ground, while its positive lead goes to the tuning point (ie, the collec­tor of the detector transistor). In a well thought out receiver, such as Silver­tone, Futaba and some other Japanese receivers, the detector is clearly identified and a specially shaped resistor is provided to hook the meter or scope probe onto. In a really civilized receiver, the third pin on the bat­ tery connector will be arranged as the detector tuning point. Unfortunately, in the majority of cases, there is no thought given to the tuning and it is almost impossible to hang a lead on some receivers. When the receiver is switched on and the Tx is off, the active detector will read about 4V. This will drop to about 1.5-2V when the Tx is subsequently switched on. Tune for the maximum dip in voltage and trim the IF for wave shape (always at the lowest level of signal). FM receiver tuning FM receivers usually use a quad­ rature coil or ceramic filter as an audio detector. Hook the scope to a suitable point and tune for maximum audio, again trimming the IF coil(s) for wave shape. Again, keep that RF signal level to a minimum. One interesting point with an FM receiver is that if the quadrature coil is tuned to the wrong side of the carrier, the audio will appear in an inverted form. This is the reason why it is difficult to change some overseas FM sets which come in on 27-29MHz. The overseas 27MHz sets use a low side receiver crystal while in Australia, we use a high side receiver crystal. Thus, using a standard Australian crystal pair will invert the audio and the set will not work. The answer is an especially cut re­ceiver crystal on the low side of the carrier. That’s it for this month. Next month, SC we’ll look at servos. 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. ✂ Be sure to keep the signal level at the lowest level possible at all times, by constantly reducing the signal generator output or moving the Tx further away. Run through the complete set of coils again once the Rx is tuned to ensure that there is no interaction between coils. January 1994  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 Control stepper motors with your PC Ever wondered how stepper motors work & how you might control them using your PC? This article gives you the answers & presents a design for a stepper motor controller. By MARQUE CROZMAN Having a computer is one thing but haven’t you always wanted it to do something in the real world? Robots and computer controlled mechanical devices have always created intrigue for young and old alike but the problem has always remained: how can you easily control mechanical devices with your computer. A partial answer is sitting inside your very own PC at home. In each floppy and older hard disc drives sits a little stepper motor that accurately positions the heads over the sur­face of the disc. When hard discs and floppies die it 80  Silicon Chip usually is not the fault of the stepper. Normally it is either a case of the heads taking a nose dive into the disc or the spindle motor reaching the end of its life-span. This opens a rich supply of small stepper motors just waiting to be put to use in robots and toys, as well as more serious endeavours such as controlling antennas, plotters, servo systems and NC mach­ines; your imagina­tion is the only limit. Steppers are not like normal motors. When you apply power to them, they will only move through a small arc and stop, as op­posed to a regular motor that just keeps turning. They are thus highly suited to numerical positioning, where computers store positions as discrete numbers. Stepper motors can be used in an open loop system; ie, you can operate them without feedback. All other methods of accurate positioning require feedback to let the system know what the current position of the motor is and to correct it if there is an error. One common method used with steppers is to rotate the stepper until whatever is being moved reaches a limit switch. The controller then has a reference point to work against and therefore it knows where the stepper is. If you listen to a floppy drive power up, you will hear it find its reference point. The drive controller will then know how many steps to move the head to read a given track. With a more conventional motor, the magnetic attraction between the motor’s stator and rotor causes the rotor to turn in an attempt to make the poles align. By continually moving or advancing the field, by AC or brushes and split commutator, the rotor keeps turning. A stepper motor, on the other hand, lets the rotor’s magnet­ic field line up with the stator, as a compass does when you bring a magnet near to it. We can further this analogy by imagin­ ing a large number of magnets around the circumference of a compass. By switch­ing their magnetic attraction on and off, we could have the needle of the compass rotate, by energising each magnet in turn. Thus, we could stop the needle of the compass at any point by stopping the switching sequence. The magnets in the stator of a stepper motor consist of a ring with iron teeth. Each tooth has a coil wound on it, so that it becomes an electromagnet when it is energised. A coil on the opposite side of the stator is energised in opposition to create the other pole – see Fig.1(a). Increasing the number of teeth on the ring in­creases the resolution of the stepper; ie, the number of steps per revolution. We can also double the resolution if we switch on two adjacent magnets, making the rotor come to rest midway between two poles. This is called half stepping and also has the effect of increasing the available torque – see Fig.1(b). Steppers generally have quite a high number of poles or steps per revolution, with 100 to 400 being common. This is not to say that there are that many electromagnets in the stator. By placing teeth in the rotor as well, the number of poles will be effectively multiplied by the number of teeth in the rotor. So if there are 3 stator poles and 8 teeth in the rotor, the stepper will have 24 steps per revolution or a 15 degree step angle. Using a digital controller to energise the stator coils gives the sort of control you could expect from a normal DC servo but without feedback. All that has to be done is to calculate how many turns (or degrees) you want, then send that many steps to the motor. The rate at which you send the steps controls the speed or angular velocity of the shaft. Types of stepper motor Stepper motors can be divided into three basic classes: variable reluc- An assortment of stepper motors. The top middle motor is a variable reluctance type with a rotary encoder on the rear of the shaft, while at bottom left is a rare earth disc stepper. The rest are hybrid types. The motor at bottom right is typical of the steppers found in floppy & hard disc drives. S SHAFT STATOR S STATOR POLE SHAFT (a) STATOR POLE ROTOR ROTOR N STATOR N (b) Fig.1(a) at left shows a hybrid stepper motor with one stator pole energised. The nearest rotor pole moves to align itself with the energised pole (the other stator coils have been omitted for clarity). Fig.1(b) shows a hybrid stepper with two stator coils energised. In this case, the nearest rotor pole moves to align itself between the energised poles. tance, permanent magnet and hybrid. Variable reluctance motors have a soft iron multi-tooth rotor. You can recognise this type by rotating the shaft with your fingers. As the rotor has no magnetism, it rotates freely without poling, whereas permanent magnet and hybrid types have magnetic rotors and pole or “cog” when turned. Variable reluc­tance steppers are renowned for their high stepping rates and accuracy. Permanent magnet steppers have a toothless rotor which is radially magnetised, with alternating poles. The stator has two halves, each of which contains a coil. The rotor’s poles are attracted to the stator coils when energised. The rotor remains attracted to the closest stator pole even when no power is ap­plied, giving a “detent” torque. These steppers are economically competitive but suffer in terms of accuracy and speed in compari­son to other types. Hybrids are the most popular style of stepper and are the most common in computer equipment. The hybrid combines the stator of the variable reluctance type and the rotor of the permanent magnet stepper to produce a motor with high detent, holding and dynamic torque while retaining high stepping rates. The newest type of stepper motor is a variation on the permanent magnet type – the rare earth permanent magnet stepper – see Fig.2. These are also known as disc magnet steppers. The rotor is a thin disc which is axially January 1994  81 Table 1: Wave Stepping SHORT MAGNETIC CIRCUIT USING HIGH QUALITY IRON LAMINATIONS Step Phase 1 Phase 2 Phase 3 Phase 4 1 ON – – – 2 – ON – – 3 – – ON – 4 – – – ON NO MAGNETIC COUPLING BETWEEN PHASES Table 2: Two Phase Stepping Step Phase 1 Phase 2 Phase 3 Phase 4 1 ON ON – – 2 – ON ON – 3 – – ON ON 4 ON – – ON Table 3: Half Phase Stepping Step Phase 1 1 2 LOW INERTIA ROTOR Fig.2: layout of a permanent magnet stepper motor. This particular layout is for one of the new rare earth magnet disc steppers. Note that the magnets are axially aligned with the rotor. magnetised. This results in a motor with a very low moment of inertia, high acceleration and good dynamic behaviour. Disc magnet steppers outperform all other types. They are the most efficient and have by far the highest holding torque and power output per kilogram of motor, superior accuracy and high start/stop frequencies – see Fig.5. Identifying the sex of motors There are two methods of winding stepper motors – unipolar and bipolar, as shown in Fig.3. Bipolar steppers have one winding on each stator pole (monofilar wound). The magnetic polarity of the stator pole is changed by reversing the current in the coil. Reversing the current through the coil requires a circuit capable of switching polarity. Unipolar steppers have two coils per stator pole, one for each direction (bifilar wound). Changing the direction of move­ment involves switching the current from one coil to the other. Phase 2 Phase 3 Phase 4 ON – – – ON ON – – 3 – ON – – 4 – ON ON – 5 – – ON – 6 – – ON ON 7 – – – ON 8 ON – – ON Commonly, the two coils have a common connection to reduce the number of wires exiting the motor. The power supply can be much simpler than that for the bipolar, as you simply need single switches to turn different coil segments on and off. However, uni­ polar steppers have a lower torque than bipolars because only half of each winding is energised at a time – see Fig.4. Identifying steppers is easy. Bipolar steppers have four leads and unipolars have either five or six. Reading the V+ PHASE V+ PHASE OR FOUR LEADS 2 PHASE FIVE LEADS SIX LEADS 4 PHASE Fig.3: the diagram at left shows a bipolar winding arrangement, while at right are two unipolar winding arrangements. In the unipolar arrangement, only one half of the coil on each stator is energised at any given instant. 82  Silicon Chip (a) (b) Fig.4(a) at left shows a unipolar switch, while Fig.4(b) shows a bipolar (or H-bridge) switch. The unipolar drive arrangement only needs one switch per coil whereas the bipolar drive requires four switches per coil. The photo above shows the pole arrangement of a rare earth permanent magnet stepper motor. Its rotor is damaged but the axial rare earth magnet segments in the remaining thin disc section can still be clearly seen. At right is the view inside a hybrid stepper motor. Note that both the magnetic rotor & the stator have teeth. The stator coils can also easily be seen in this photo. It has the sequence of 1, 12, 2, 23, 3, 34, 4, 41, 1 or in the opposite direction, 1, 14, 4, 43, 3, 32, 2, 21, 1. The torque produced increases because the step length is reduced and each alternating step has two windings energised. The positional accuracy is also increased but it means that two steps have to be sent for every previous single full step. The power supply will also need to be of the same capacity as the two-phase drive – see Table 3. 12 9 LOSS (WATTS) name plate will also give an idea as to what type it is. To make the motor step, power is applied to each coil in turn. Steppers have three different stepping formats: wave, two-phase and half-step sequences. Each has its own advantages and disadvantages. Wave drive energises one coil at a time and the sequence is 1, 2, 3, 4, 1 or 1, 4, 3, 2, 1, depending on direction. Wave drive is the most economical as the power supply has only to provide enough current to drive one coil at a time, making it less expen­sive – see Table 1. Two-phase drive is similar to wave drive as far as step length is concerned but consists of energising two adjacent coils at the same time. The coils are energised in the order 12, 23, 34, 41, 12 or 14, 43, 32, 21, 14, depending on the direction. This increases the amount of torque produced over the wave-drive, as the rotor moves from the tug of two energised windings to the tug of the next two energised windings. The disadvantage is that the power supply requirements are increased – see Table 2. Half-stepping alternates between wave and two-phase step­ping to double the number of steps per sequence. HYBRID 200 STEPS/REV 6 DISC MAGNET 100 STEPS/REV 3 0 0 2500 5000 SPEED (STEPS/SECOND) 7500 10000 Fig.5: comparison of losses between hybrid & rare earth permanent magnet disc stepper motors operating at the same torque. The cheapest source of stepper motors is discarded floppy and older hard disc drives. Computer repair companies usually have a whole hoard of goodies from dead machines and will part with them for a token price. Ram Computers at Manly, NSW is one place that has a whole stock of steppers from printers, floppies, hard discs and other various bits of dead equipment. Stepper controller board This has been designed to be as flexible as possible and can be run from any parallel printer port. It will drive two steppers, either unipolar or bipolar types, or both. In the IBM PC compatible, the printer port is normally latched, in that once the data has been written to the port, it remains there until more data is written to it. This is not the case with some other computers though. Using a latch on the card fixes the problem with unlatched printer ports but there is another advantage. It allows us to implement selectable addressing. One parallel port can then drive up to four cards, each with its own address, giving control of up to eight motors simultaneously. January 1994  83 VCC IC6a 74HC04 14 2 16 11 1 10 13 12 IC6f IC2 74HC139 15 1 5 11 IC6e 10 IC4d 7406 9 +12V VCC 14 10k 8 1k B 8 C 6 DB25 MALE CONNECTOR STROBE AUTOFEED INIT SELECT D0 D1 D2 D3 D4 D5 D6 D7 IC6d 9 1k 8 B 7 14 2 1 1 14 2 16 3 Q1 BD682 C Q2 BD681 3 MOTOR 1 E 13 3 19 2 IC4c 16 5 10k 1k Q3 BD682 B D0 D1 D2 D3 11 2 18 3 3 4 17 5 4 6 14 7 7 12 8 13 1 9 8 1k 20 IC1 74HC374 Q4 BD681 B +12V Q5 BD682 E B +12V 4 17 E 4 E Q6 2 C BD681 B E RC SEE TEXT C D4 D5 D6 D7 20 15 6 22 14 2 10 11 IC7e 74HC04 14 10 11 5 6 13 3 IC7c IC3 74HC139 16 VCC 6 1 IC7a 2 VCC IC5a 10k 7406 14 2 1 5 1k B 13 IC7f 1k 12 B 7 15 7805 GND 560  1 VCC 1k 1k 1 16VW Q10 BD681 4 MOTOR 2 Q11 BD682 B E  B C 3 C Q14 1 C BD681 B 2 E C C I GO STEPPER MOTOR CONTROLLER 8 IC5d 9 1k +12V K B CE 10k 1k E C RC SEE TEXT A 84  Silicon Chip Q12 BD681 +12V Q13 BD682 E B E 0V LED1 13 C +12V +12V 1k IC4f Q9 BD682 E 10k IC5b 3 4 OUT Q8 BD681 B 12 E +12V IN 10k 1k +12V C 8 Q7 BD682 B RC SEE TEXT VCC 24 1k E 12 9 21 23 11 +12V C 19 IC4e E C E VCC 10 C 1 C 10k 1k E RC SEE TEXT Q15 BD682 B 10k 1k Q16 BD681 B 1k 6 IC5c 5 Q14 Fig.7: refer to this diagram for the lead colours & pin connections when connecting the stepper motor to the controller board. Note that the centre taps for a unipolar stepper are tied directly to the +12V supply rail. Warning – some steppers use a different colour coding & you may need a multimeter to sort out the windings. the printer port, viz, Strobe, Autofeed, INITialise or Select. These are by way of links on the PC board and are select­ ed when you build it. In this way, it is possible to build four separate controller boards and have them all running from the printer port simultaneously. The software does the selection for each controller; ie, the relevant line is toggled for the data sent to each controller. The four least significant bits (D0D3) are used to control motor 1 while the four most significant bits (D4-D7) control motor 2. Unipolar motors The circuit description above refers to bipolar stepper motors. If you propose to use unipolar motors, the H-bridges are not required. Instead, the buffered outputs from IC6 and IC7 directly drive the NPN Darlington Q6 Q8 1k 1k 1k 1k 10k 1k 10k PIN4 YEL Fig.8: install the parts on the PC board as shown here & note that those transistors & ICs marked with an asterisk can be omitted if the board is to control a unipolar stepper motor. Refer to the text for the linking options at top left. Q16 Q10 4 Q9  Q11  Q15 3 MOTOR 2 2 1  SE E TEXT 10k 10k 1k 10k 1k 10k 1k 1k 1k 1k Q12  Q13 RC 1uF PIN3 WHT 1 1k 1 PIN2 BLU PIN3 +12V PIN4 GRN WHT GRN/ WHT I C5 7406 1 RC 7805 Q4 I C4 7406 1 0V  Q1  Q5 1k 10k 1 1k 1 10k 1 IC2 74HC139 K Q7 IC6 74HC04 LED1 IC7 74HC04 +12V IC3 74HC139 4 3 2 1 560  MALE DB25 PIN2 RED/ WHT 1k MOTOR 1 1 2 3  Q3 4 Q2 RC The circuit of the controller board is shown in Fig.6. Essentially, the printer is connected to IC1, a 74HC374 octal D latch. This can be considered as eight D-type flipflops with one common latch enable or clock input, pin 11. Data can be loaded into the eight inputs and then when the latch enable pin goes high, that data appears at the eight outputs (pins 19, 2, 16 & 5 and pins 15, 6, 12 & 9). To send a byte of data to the controller, the computer writes a byte of data to the printer port and then toggles pin 11 high. This data then appears on the outputs of the latch, as noted above. The output lines drive a pair of PIN1 RED +12V BLK RC How it works PIN1 RED 1k Having a latch on the card is also useful if you are not using a printer port but perhaps driving the card from a micro­ controller such as the Southern Cross Z80 computer recently described in this magazine. In this case, the end section of the board that has the DB25 connector on it can be removed, leaving a header that ac­cepts 8 data lines and an enable line. However, we are getting ahead of ourselves. 74HC139s, which are dual two to four line decoders. Pins 5 and 6 of IC2 are the used outputs for the first decoder (two outputs are unused) and pins 10 and 11 are the used outputs for the second decoder. IC6 inverts the decoder outputs from active low to active high for the driver circuit. The driver circuit is an H-bridge comprising transistors Q1, Q2, Q3 and Q4. Q1 and Q2 are complementary switches so that when Q1 is on, Q2 is off and similarly when Q3 is on, Q4 is off. All four switches can be operated in such as way that the supply voltage is applied to the motor coil with one polarity or the other, or all four switches may be off so that no power is ap­plied to the coil. The state of the switches is controlled by decoder IC2 which only responds to valid data at its inputs. Note that IC6 only controls the NPN transistors in the H-bridge. The PNP transistors are driven by IC4, a 7406 hex invert­er with open collector outputs. IC4 is there for two purposes. First, it provides level translation from the 5V (TTL) outputs of IC6 to the 12V bridge circuit and second, it inverts the signals again to give the correct sense for the PNP transistors. IC2 controls two H-bridges, the second comprising Q5-Q8, and this acts in the same way, to control one motor (with two coils). IC3, its associated buffers (IC5 and IC7) and the H-bridge drive the second stepper motor. Note that pin 11 of IC1 is shown as connected to one of four lines from IC1 74HC374 ▲ Fig.6 (left): data from the printer board is latched into IC1 & decoded by IC2 & IC3 which each drive two H-bridges. Each pair of H-bridges then drives one stepper motor. Note that for unipolar stepper motors, the H-bridges are not required & therefore IC4, IC5 & the PNP transistors can be omitted (see text). January 1994  85 Table 2: Resistor Selection 5V stepper current rating Current limiting resistor 500mA 15R 800mA 8R2 1A 6R8 1.5A 4R7 Table 5: Motor Codes Phase Energised Motor 1 (HEX) Motor 2 (HEX) 1 01 10 2 02 20 3 04 40 4 08 80 Table 6: Debug To load a byte into the controller o 378 (mcode) Load motor code into port A o 37A 05 Assert card1’s latch enable low 0 37A 04 Pull the latch enable high to load the data into the latch q Quit from using debug Table 7: Motor Outputs Phase Motor 1 Motor 2 Output 1 D0 D4 1+ 2 D1 D5 3+ 4- 3 D2 D6 1- 2+ 4 D3 D7 3- 4+ 2- Table 8: Card Selection Card Selected Printed Signal Port C Value (HEX) No card selected – 04 Card 1 -STROBE 05 Card 2 -AUTOFEED 06 Card 3 +INIT 00 Card 4 -SELECT 0C transistors; ie, Q2, Q4, Q6 and Q8 for IC6 and Q10, Q12, Q14 and Q16 for IC7. IC4, the PNP tran­sistors and their resistors can be omitted. Similarly, for the second motor, IC5, the PNP transistors and their resistors can be omitted. Note that the centre taps of the motor winding are then connected to +12V – see Fig.7. Putting it together The stepper motor controller board 86  Silicon Chip measures 187 x 103mm and is coded 07201941. It has a DB-25 male socket at one end and two lines of plastic transistors at the other – see Fig.6. Start assembly by checking the board against the printed artwork for flaws such as bridges between tracks or broken tracks. These should be repaired with a utility knife or solder­ing iron if needed. Assuming all is well, construction can com­mence with the PC pins and wire links. If the board is being built for 12V steppers, install wire links in place of the current limiting resistors R1-R4. 5V steppers will require the current limiting resistors, as specified in Table 4. The resistors and the 1µF electrolytic capacitor can go in next, followed by the 4-way, 2-pin header for address selec­tion. This done, install the 5V regulator and LED, making sure they’re in the right way. If you desire, IC sockets can be used for all the integrat­ ed circuits. Otherwise, directly solder in all the ICs, taking care while handling them, as most are CMOS devices. As noted above, if the board is being constructed to cater for unipolar motors only, ICs 4 and 5 may be left out, as can all the PNP Darlingtons and associated resistors. All these components are marked with an asterisk on the component overlay diagram of Fig.8. Lastly, install the male DB25 plug. Be careful not to bridge any pins together whilst soldering it in, as it can be quite fiddly. Bridging could lead to some fairly weird problems later on. PARTS LIST 1 PC board, code 07201941, 187 x 103mm 1 DB25 right-angle male socket 1 4-way 2-pin header 1 header jumper 10 PC pins 1 1µF 50VW PC electrolytic capacitor 8 10kΩ 1% 0.25W resistors 17 1kΩ 1% 0.25W resistors Semiconductors 1 74HC374 octal D-latch (IC1) 2 74HC139 dual decoder (IC2,3) 2 74HC04 hex inverter (IC6,IC7) 2 7406 hex inverter (IC4,IC5) 8 BD681 NPN Darlington transistors (Q2,Q4,Q6,Q8, Q10,Q12,Q14,Q16) 8 BD682 PNP Darlington transistors (Q1,Q3,Q5,Q7, Q9,Q11,Q13,Q15) 1 7805 5V regulator 1 5mm red LED (LED1) How to buy the software The software for driving the stepper controller can be ob­tained by send­ing $6 plus $3 for postage and packing to SILICON CHIP, PO Box 139, Collaroy, NSW 2097 or by faxing your credit card authoris­ ation to (02) 979 6503. Please nominate your choice of 3.5-inch or 5.25-inch floppy disc to suit IBM compatible comput­ers. We accept credit card authoris­ ations for Bank­card, Visa­card and Master­card. Testing Apply 12V to the board and check that +5V is present at pin 14 of ICs 4, 5, 6 and 7, at pin 16 of IC2 and IC3, and at pin 20 of IC1. If any of the Darlington transistors gets hot, you have a problem. If so, power down and recheck the placement and orien­ta­tion of all components. When all is OK, connect the board to the printer port, then turn on the computer, power up again and run the test program on the stepper software disc which is available from SILICON CHIP – see parts list. If you don’t have this software, using debug, load the motor codes into the base address of the card, then write a 1 to the enable bit followed by a 0. These last two writes load the data into the latch – see Tables 5 and 6. After each step in the program or after manually writing each set of codes, check the voltage on the outputs of each phase where the motors connect to the board. There should be 12V across each phase that is on – see Table 7. All things being equal, it’s time to connect up a stepper motor and run the stepper software included on the stepper soft­ware disc. This contains example programs written in Qbasic and C, as well as the initial testing program. The C programs are more efficient and allow the motors to spin up to full speed. All programs are fully documented and the disc comes with a READ.ME file which provides 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 ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 AUDIOPHILES! Now high audiophile quality components & kits are available in Australia. Buy direct & save. *Kimber, Wonder, Solen & MIT Capacitors *Alps Pots *Holco resistors *High Volt. Cap. *Gold Terminals & RCA *WBT Connectors *Kimber Cables * Interconnect Cables *Output Transformers (standard or customised) *Power Transformers *Semiconductors *Audio Valves & Sockets *Wonder Solder *Welborne Labs Accessories Fig.9: this is the full-size etching pattern for the PC board. The board measures 187 x 103mm & carries the code number 07201941. other helpful information on stepper motors. Cascading controller boards If you want to use two or more controller boards from the printer port, they can be daisy-chained using a 25-way ribbon cable and IDC DB-25F plugs. You then need to set the linking via the DIP header to use one of the four enable lines – see Table 8. Acknowledgments Our thanks to RAM Computers at Manly, NSW for the supply of sample steppers from dead floppy disc drives. Thanks also to the University of Technology which supplied information on rare earth magnet stepper motors. Valve & Solid State Pre-Power Amplifier Kits *Contan Stereo 80 Valve Power Amp. (As per Elect. Aust. Sept. & Oct. ’92) *Welborne Labs Hybrid Preamp. & Solid State Power Amplifier Send $1.00 for Product Catalog PHONE & FAX: (03) 807 1263 CONTAN AUDIO 37 WADHAM PARADE MT. WAVERLEY, VICTORIA 3149. January 1994  87 Product Review Kenwood’s DCS-9120 100MHz digital oscilloscope Kenwood’s DCS-9120 programmable digital storage oscillo­scope provides both analog & digital modes of operation, with 4-channel 100MHz operation in the analog mode & two channels at up to 40 megasamples/second in storage mode. First impressions of the DCS-9120 are that it is a fairly compact unit with a front panel that has lots of knobs, buttons and control labelling. The knobs for vertical sensitivity and time­base do not have calibrations as their settings are displayed on the CRT screen, as is the triggering level and even the date and time if required. Most of the pushbuttons on the front panel are accompanied by backlit legends to indicate the selected setting. These are good because they give an unambiguous indication of the various settings. On the rear panel are ports for a pen recorder, plotter and an RS-232 serial interface. The DCS-9120 can also be controlled via a GP-IB interface so that it can be used for automated test­ing in production or other applications. Physical dimensions of the oscilloscope are 310 x 160 x 510mm, not including the tilting handle. Its mass is 10kg. When used in analog mode, the DCS-9120 functions as you would expect for a 4-channel 100MHz oscilloscope. Each of the four input channels has its own sensitivity adjustment from 5V/div down to 1mV/div and an uncalibrated variable knob can be used to vary the sensitivity within these ranges. In addition, the 100MHz bandwidth of the oscilloscope can be reduced to 20MHz to reduce noise on the display when signals below 20MHz are being measured. Signal coupling of the inputs can be 88  Silicon Chip DC, AC or grounded, while both the channel 2 and channel 4 inputs can be inverted as well. This feature can be used to provide a differential input mode by ADDing channel 1 to channel 2 or channel 3 to 4. Each input socket incorporates a detector which automati­cally adjusts the sensitivity (Volts/Div) reading on the screen whenever the supplied PC-31 probes are switched to 10:1. If other brands of probes are used, you will have to resort to mental arithmetic to multiply the sensitivity by 10 when 10:1 is selected on the probe. Sweep time is selectable from 20ns/ div to 0.5s/div in 23 ranges, with fine adjustment and x10 sweep magnification avail­able. Timebase modes are A, B or delayed trace, A intensified by B, A and B alternating or X-Y mode. The delay between the A and B timebases can be either a continuous delay, a trigger delay or a count delay. Triggering modes Triggering modes are Auto, Norm, Single and Fixed, with the usual CH1CH4 source selection or line frequency triggering. You can also select Vert triggering which automatically triggers on the lowest selected channel number. No external triggering input is provided. Coupling for the trigger signal can be DC, AC, High Frequency Rejection or TV (line or frame 1 or frame 2, NTSC or PAL). Horizontal or vertical cursors can be displayed on-screen to enable voltage, period and frequency measurements, a fairly standard feature of scopes with CRT readouts. Menus Apart from the front panel controls, there are many func­tions and operations that can be accessed via the menu options. The five menu subsets are Processing, Memory, Set, Output and Option. Some functions selected via the menus are only available with the storage facility. For example, if you select the average display from the processing menu, it will not operate in the analog mode. The averaging feature is very useful for improving the signal to noise ratio of the displayed signal since it filt­ers out random noise. Averaging can be selected from between 2 and 256 waveforms. Other functions available from the processing menu are interpolation (off, linear, sine and spline), calculation (+, -, x, /) between channels, and peak detection of maximum, minimum or both. Memory menu options allow you to select the display ad­dress, memory size and reference memory. The latter is a memory space into which a waveform can be stored, to be recalled at a later date and compared with another waveform on the screen. In the Set menu, you can change the delayed triggering options to be displayed in divisions or real time (seconds). You can also set the type of TV triggering, buzzer modes, display offset and time display modes and settings. The Option menu provides programming features so that on-panel settings can be stored, comments can be made on-screen and the present status displayed. A parameter sub menu provides selection of automatic calculations which can be done by the oscilloscope and then displayed on the DCS-9120 The DCS-9120 provides both analog & digital modes of operation. In analog mode, its bandwidth is 100MHz, while in digital mode it can operate at 40 megasamples/second. Many of the functions are accessed via menu options. screen. You can only select one per trace but each trace can have a different parame­ter displayed. The parameters selectable are period, frequency, pulse width, rise time, fall time, delay, overshoot, undershoot, peak to peak, RMS volts, top level, base level, amplitude and power. Digital storage Switching from analog to digital modes is as simple as pressing the Mode switch. The difference in the storage mode is clear, however, if you need to manipulate the display. You can magnify the stored waveform by up to 100 times or compress it to 1/ th of the original, depending on 10 how you want to observe the signal. You can also perform arithmetic operations between traces and set up peak hold for catching glitches as little as 50ns wide. Strangely enough, you can also observe the waveform before the triggering point. This is a feature only available on storage oscilloscopes and is possible since the storage of the waveform is continuous and the triggering point really only tells the scope what part of the waveform you want to observe. Conse­quently, you can observe the waveform before or after the trig­gering point, depending on whether post or pretriggering is selected. The other interesting feature is the way the storage memory can be set up. There are two separate 16K word waveform memories for channel 1 and channel 2. One is called the acquisition memory and the other the reference memory. Each word is eight bits wide. You can set up the memory to be 2K words long for eight screens of storage, or 16K words long for storing a large continuous waveform section. Storing waveforms As is the case with most storage oscilloscopes, it takes some time to become familiar with the operating features. A lot of the difficulty was due to the extraordinary number of options that are available in the storage mode. However, we found that digital storage was particularly useful for catching glitch­es and for observing non-repetitive waveforms such as the firing of a fluo­rescent tube – virtually impossible to observe on a normal analog scope. We had a minor complaint when using the Delta REF/DLY TIME rotary control to scan through the eight x 2K memory blocks. In operation, the delta V cursor switch was often accidentally bumped due to its close proximity to this control. The instruction manual for the oscilloscope is good although there are spelling mistakes and strange English in some parts. However, all the features of the oscilloscope are well explained and examples are given for both analog and digital storage modes. Overall, we liked the features of the DCS-9120. It provides the best of both types of scope; the fine detail waveforms in the analog mode and the facility to store and manipulate waveforms in the digital storage mode. The ability to print out waveforms and control the unit via the GP-IB interface also help make this oscilloscope a very versatile unit. It should appeal to a wide variety of users for laboratory, test bench and production use. The Kenwood DCS-9120 is priced at $9308 plus 20% sales tax if applicable and it comes with a 12-month warranty. For further information, contact the Australian distributor for Kenwood test equipment, Nilsen Instruments, 18 Hilly St, Mortlake, NSW 2137. Phone SC (02) 736 2888. (J.C.) January 1994  89 PRODUCT SHOWCASE automatic antenna tuner, AT-300 automatic antenna tuner for long wire and whip antennas, MB-13 mobile mount, PS-32 power supply, LF-30A low pass filter, TL-922 linear amplifier and SP50B mobile speaker. Kenwood's TS-50S is covered by a twelve month parts and labour warranty and it has a recommended retail price of $1589. For further information on the TS-50S or other Kenwood products, contact Kenwood on (02) 746 1888. Rugged clamp meter from Fluke World's smallest HF transceiver Kenwood Electronics has introduced the world's smallest HF Transceiver, the TS-50s. Designed for operation on the 160 to 10m amateur bands plus continuous coverage from 500kHz to 30MHz, the TS-50S also supports SSB, (LSB & USB), CW, AM and FM modes of operation. Measuring 179mm wide, 60mm high and 233mm deeps and weighing 2.9kg, the TS-50S is designed for the ham shack, office and mobile installation. Although small in size, the Low priced colour scanner Hewlett-Packard has introduced the lowest, priced, highest-performance colour and grayscale flatbed scanner it has ever produced, the HP ScanJet IIcx. With improved software and enhanced resolution, the new unit performs up to twice as fast as the previous model. The HP ScanJet IIcx has 1600 dpi enhanced resolution and 400 dpi optical resolution for both image and text scanning. Gray scale scanning takes eight seconds, compared with 15 seconds for the previous model. An optional transparency adapter allows the scanner to work with 90  Silicon Chip TS-50S delivers 100 watts in SSB, CW, FSK and FM modes and incorporates an automatic cooling fan. With 100 channels for transmit and receive frequencies, the TS-50S can hold both the A and B VFO, frequencies enabling FM split-frequency repeater operation. The split feature allows the user to transmit on one VFO and receive on another. Similarly, in TF-SET mode, the operator can `lock' the receiver frequency and then find the best frequency at which the DX station is located. Optional extras include an AT-50 a variety of hardcopy media, such as 35-mm slides, transparencies and paper. The adapter accepts transparencies ranging in size from 35mm to 8-1/2 x 11.7 inches. The scanner also accepts standard paper sizes up to 11 x 14 inches. An optional automatic document feeder provides unattended scanning for up to 50 pages. Recommended retail price is $2258 including sales tax, available from authorised HP dealers. The optional 50-page automatic document feeder is $1168. For further information on HP products and sevices, phone 131347 (no STD area-code required). Fluke Corporation has developed a new clamp meter which can measure AC current to 400A and AC volts to 600V. The new unit is intended for commercial, industrial and residential electricians as well as for HVAC/R (Heating Ventilation Air Conditioning Refrigeration) service technicians. Its tapered jaws, with centred opening, give easy access to conductors in crowded junction boxes. The Model 30 is more accurate and easier to use than analog meters. A HOLD button “freezes” the display so values can conveniently be read. It conforms to the safety standards of the IEC 1010 and has UL, CSA and TUV certifications. Accuracy is quoted as ±1.3%, specified for one year after calibration. Operating temperature range is from -10°C to +50°C. For further information, contact Philips Test and Measurement, 34 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 8222. Compact DC-DC converter Claimed to be the world's most advanced, high density single and triple output DC-DC converters, the MicroVerter uV series can deliver up to 250 watts. These miniature converters are available in three input voltage versions: 28 & 48V DC for the telecommunications industry and 300V DC for distributed power applications. Operating at a constant frequency, the Micro-Verter series is parallelable for current sharing, and is fault tolerant with a true n+1 redundancy, offering MTBF of over 1.1 million hours. The converters have non-shutdown over-voltage protection, thermal and input OVP protection, extremely low thermal resistance and an excellent transient response. As well as the single or triple voltage outputs, an "output good" signal is provided and there is an optional "sync" pin. For further information, contact Amtex Electronics, 13 Avon Road, North Ryde, NSW 2113. Phone (02) 805 0844. Central Coast annual field day The Central Coast Field Day is one of the longest running events in the Australian amateur radio calender. The next Central Coast field day will be held on Sunday 27th February 1994, at Wyong Racecourse and this will be the 37th year of this popular event. As usual, the large contingent of suppliers of electronic equipment, High capacity removable drive Southend Data Storage have announced a new removeable hard disc drive from Teac Corporation. The Drive, called TEAC-STOR consists of the drive, docking bay for a 5.25-inch slot and carrying case, and is available in capacities of 250 and 360 megabytes. Both the 250MB and 360MB models require only a single 5V DC power source, a first for 3.5 inch hard disc drives. Power consumption during read/write operation is only 2.5 watts, giving a significant power saving. Both drives are compatible with the industry standard IDE interface, components and books will be attending. These companies will have their latest products on display and many traders will have items on sale at very special Central Coast field day prices. Last year, the popular flea market attracted a large number of people who traded an enormous amount of surplus electronic equipment to eager buyers from trestles, trailers or from the boots of their cars. This year an even bigger program of interesting lectures and equipment displays has been arranged. More than two thousand people attended last year’s Central Coast Field Day and the next one at Wyong Racecourse will be bigger and better than ever, so mark the 27th February 1994 down in your calendar. Gates will open at 9:00 AM in wet or fine weather and making them suitable for almost any system. For further information on TEAC-STOR or other TEAC data storage product, Rick Stanford of Southend Data Storage, PO Box 25, Menai, NSW 2234. Phone (02) 541 1006. all displays are under cover. Compact R/C modules McLean Automation has introduced a series of `bricks’, being a range of portable radio control modules housed in Clipsal 265/5 (210 x 110 x 80mm) enclosures with carry bar. Similar in appearance to a house brick with a handle, these rugged units are affordable and Australian made. The brick series extends from simple single button transmitters to multi code transceivers capable of actuating 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 January 1994  91 Philips slashes DCC prices In a dramatic move to get DCC players and recorders moving in the marketplace, Philips has announced big price cuts. The fullhouse DCC900 recorder, previously priced at $1799, is now $999 while the DCC600, previously $1499, is multiple remote loads with separate on/off coding and receiving `loop back’ acknowledgement of switching function. All systems have a 2km range from a radio licence exempt HF transmitter with excellent long wavelength diffraction performance around obstacles in the propagation path. The transmissions are digitally encoded and the the dry batteries give 6-12 months’ service. For further information, contact McLean Automation, PO Box 70, Freemans Reach, NSW 2756. Phone (045) 796 365. now $799. And the recently released DC130, pictured here being used by Australian aerobics champion Sue Stanley, is now $699. Customers who have already purchased a DCC player or recorder at the old prices need only call Philips at (008) 80 3312 to receive a complimentary set of 25 pre-recorded DCCs. High-power subwoofer for cars Kenwood Electronics has announced a subwoofer and dedicated subwoofer amplifier guaranteed to rattle the windows. Called the Letterbox, it measures only 251mm wide, 266mm high and 400mm deep and can be mounted behind the seat, on the van floor or in the boot. The Letterbox is a bass reflex design employing what Kenwood call a spherical flow duct. This is a tapered port to enhance low frequency response down Luxman amplifier & CD player: continued from p.32 check­ed out at -93dB at 1kHz which is not quite as good as the claimed -100dB but the dif­ ference is largely academic since anything over -70dB is more than adequate. Measurements aside, we can state that both the A-371 stereo amplifier and D-351 compact disc player are very fine products. They work well and produce excellent sound quality and, as the final icing on the cake, 92  Silicon Chip they come with a 5-year full parts and labour warranty. Pricing is $1399 for the A-371 amplifier and $799 for the D-351 compact disc player. Luxman equipment is available from selected hifi retailers. For the name of your nearest dealer, contact the Australian distributor for Luxman, International Dynamics Pty Ltd, 78-80 Herald St, Cheltenham, Vic 3192. Phone (03) 585 0522. (L.D.S.) delow 40Hz. Combined with reasonably high efficiency (90dB), can deliver lots of bass. Designed to be used as a single unit or in a multi-subwoofer set up, the Letterbox can handle bass program material up to 200 watts. To drive the subwoofer, Kenwood market the KAC-714 mono power amplifier, rated at 100 watts but capable of delivering around 200 watts on peaks. Measuring only 280mm wide, 50mm high and 170mm deep the KAC-714 can fit snugly into most boots. A built-in crossover offers variable cut off from below 30Hz to 200Hz and an input gain control match the sound levels to other speakers. The Letterbox subwoofer is priced at $399 while the KAC-714 mono power amp is $349. Both units are covered by a twelve month parts and labour warranty. For further information on Kenwood car audio products and your nearest Kenwood car audio dealer, phone (008) 066 190. Digital DC power supplies The new Leader Digital Series regulated DC power supplies consist of five models: two 18V, two 36V and one 70V model. Intended for R & D, automated and educational applications, the series features optional GPIB for computer control. The power supplies can also be remotely controlled using the standard remote control connector. For stable output, voltage drops caused by test leads resistance and contact resistance at the output terminal are compensated for by using the sensor plug provided. For further information, contact AWA Distribution, 112-118 Talavera Road, North Ryde, NSW 2113. Phone (02) 888 9000. SC 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. More on pendulum clocks One of those few times when SILICON CHIP should be told instead of asked occurred in the October “Ask Silicon Chip” letter regarding electrical activation of a pendulum clock. It is true that the IR method would probably use more power but what was missed is the necessity to use two detectors with gating, so as to energise the electromagnet only as the pendulum passes in one direction. Otherwise, the results would be unpre­dictable. In fact, the clock action would be chaotic. (I hope we are all informed about chaos?). As for the alternative of driving the pendulum from a crys­tal clock IC, that too is doomed to failure because of chaos. Only a mathematical treatment (far too long for here) can proper­ly analyse the system but consider some of its elements. Start the pendulum swinging and the clock pulse will occur somewhere at random along its cycle of travel. Chances are that the pulse is wasted by the pendulum being out of range of the electromagnet at that time. If the clock and pendulum periods are closely matched (as would be expected for good timekeeping), it 24V version of fluoro inverter I am in the process of building the 16W version of the fluorescent light inverter as designed by Otto Priboj in the February 1991 of SILICON CHIP. I will be using it in my 12V solar powered house, however I have plans to upgrade my system to 24V. Can the inverter be easily modified to run on 24V? (K. A., Kangaroo Flat, Vic). • Although we have not tried it, it should be possible to run the inverter from 24V by changing the could take many swings before the pulse occurs while the pendulum is within range; so many that probably mechanical loses have damped the swing to the point where the magnet cannot build it up again. After all, if you build a crystal clock into the project, why not get the time from it instead? There is a way to get a self-synchronous electronic drive for the pendulum. First, the bob must incorporate a permanent magnet (mounted transverse to the arc) which swings past and above the pole faces of a central electromagnet. A small circuit involving one transistor is then used to sense the approach of the pendulum from the voltage transients induced in the electromag­net coil and to turn on a current pulse through the coil. Note that this happens twice per period; ie, at the bottom of each swing. The current pulse must terminate before the magnet moves appreciably past the pole faces or it would remove some of the kinetic energy imparted to the pendulum by its onset. In fact, this is the usual way to stabilise the swing amplitude – someth­ing which should be done to aid good timekeeping and which was at the heart of the mechanical contact arrangement. This sort of drive was used in some primary wind­ing from 6 turns to 12 turns. No other circuit changes should be necessary although a bigger heatsink may be needed. In the November 1993 issue, we also published a more complex inverter for fluorescent lights. It is suitable for 18 or 36 watt tubes, is more efficient and produces the same brightness from the tubes as if they were operated from the 50Hz mains supply. The design presented in February 1991 did not deliver full brightness from the fluorescent tube. The later design can be easily adapted to 24V. electric clocks for motor cars before ICs were available for crystal clocks. Such clocks used a balance wheel with a hairspring instead of a pendu­lum but the principle is unchanged. (E. W., Florey, ACT). Sick Teac needs adjustment I am writing about a problem I am having with an integrated amplifier (Teac BX-330). I have attempted to repair the system but unfortunately the problem goes beyond my 17-year old capabil­ities. The problem is as follows. Due to ignorance and careless­ness, the left speaker terminal was subjected to a fairly small (but fatal to the amplifier) external voltage. The system consequently shut down. Initial inspection of the unit revealed two ‘retired’ 4A fuses in the power supply’s secondaries. Thinking optimistically, I replaced these with new fuses of the same rating, only to murder them with a lethal burst of current when the system was once again powered up. Advancing from the simplicity of replacing fuses, I began the tiresome task of a resistance check on the majority of com­ponents in the amplifying circuit. The fuse-blowing problem was found in the heart of the power amplifier (left channel). Both main transistors (the heatsunk ones) were well and truly dead. On removing these offending pieces, I hit the power switch. Naturally the left channel would be dead (I didn’t even supply it with a signal), however the right channel presented me with the usual performance; ie, it still operated OK. The only complaint from this test was heating of two 5W resistors located within the power supply. Being impatient, I simply replaced the transistors and hoped the resistors would return to their normal operating temperature. With the transis­tors in place, the amplifier once again burst into action for about three minutes, January 1994  93 Near field studio monitors Could you please explain to me what is meant by the term “near field studio monitors” when applied to speakers suitable for use in a recording studio. How do these speakers differ from good quality hifi speakers? Has SILICON CHIP ever described a kit for near field studio monitors or a speaker kit that would be suitable for this application and if not, could this be done? From what I have read, these monitors may be suitable for use with a PC fitted with a sound card and amplifier, where high-quality, high-level sound is required. As these sorts of systems are becoming popular, it may be a good opportunity to produce or revisit a kit after which the transistors again died, taking the fuses with them. With a circuit diagram in front of me and limited access to an oscilloscope, I’m stuck – not willing to sacrifice another two transistors for three minutes of music. I have included a copy of the circuit diagram and indicated the offending components. If you have any suggestions, I’m listening. (J. D., Blackburn South, Vic). • There are a number of possible reasons as to why your ampli­fier’s output stage is not working as it should. The first ap­proach should be to measure the voltages marked on the circuit with no load attached. It is quite possible that the degree of heating in the 5W (marked 2W on the circuit) resistors is normal. If the associated volt­ages (+15.4V and -15.7V) are correct, then it should be OK. However, the most important thing to do when you have re­placed the output transistors in a power amplifier is to set the quiescent current using, in this case, trimpot R130. The relevant voltages for this are shown at the emitters of Q109 and Q110 (ie, +0.618V and -0.589V). Therefore, you should connect a digital multimeter across the 220Ω resistor between the emitters of Q109 and Q110 and adjust trimpot R130 until the voltage is 1.207V. Leave the amplifier operating for at least half an hour after doing this 94  Silicon Chip approach to this type of speaker system. I appreci­ ate your comments and look forward to hearing from you. (R. C., Stockport, SA). • In audio parlance, “near field” refers to the response of transducers at very close proximity, in the pressure region. Hence “near field” microphones are used by vocalists (where they almost swallow the microphone). We would assume that “near field studio monitors” are intended for use in the confined spaces of recording studios, at listening distances of less than one metre. If this is so, such speakers are unlikely to be suitable for use in domestic living rooms. We have contacted a number of audio equipment distributors on this question but none of them have been able to give any information. adjustment and redo it if the reading has increased. The equivalent quiescent current through the output tran­ sistors can be calculated by dividing the total voltage between the output transistors (+0.012V, -0.007V) by the total resistance (0.66 ohms). This gives a quiescent current setting of 28 mil­liamps. Wireless microphones need muting Over the years, the magazines have designed bucket loads of FM wireless microphones but they are not much good for singers because they usually don’t have enough dynamic range. They aren’t very good for announcements on PA systems either be­cause they must be on all the time, even when you aren’t speak­ing. If you turn them off, you get random radio noise coming out the speakers (unless you are using an expensive tuner). So why have we all built one of them? Probably because they are really “neat” gadgets. How many of us are still using them? Not very many, I suspect. I’ve heard that FM stereo is transmitted with a signal frequency to signify that it is stereo (around 16kHz). My sugges­tion is to add this frequency to one of your FM microphone cir­cuits and then get a tuner with a stereo LED and use the LED output to switch a relay which disconnects the speakers when the mic is off. This stops noise from coming out the speaker when the mic is off or there is no audio. The relay could also be used to switch on music when the mic is off. Can you make a project out of it? It just seems like a logical improvement for the old FM mic! (C. P., Coromandel Valley, SA). • It is true that quite a few such circuits have been pub­lished over the years and that some are much better than others. The design featured in the October issue of SILICON CHIP is quite good although it does not incorporate your idea of muting. FM stereo signals are transmitted with a pilot signal of 19kHz at ±7.5kHz deviation of the FM carrier (ie, 10% modula­tion). We would be reluctant to use this pilot signal as a mute control as you suggest because it would automatically switch the tuner into stereo whenever it was present. This is not a good idea for wireless microphone applications since tuners always have an inferior performance in stereo mode compared to mono mode. What you really need is a VOX circuit to switch off the microphone when it isn’t being used but which leaves the trans­mitter section operating to keep the tuner “quieted”. We shall see what we can do. Note & errata Solar-Powered Electric Fence, April 1993: C4 should be increased from 10µF to 470µF to improve the supply decoupling and prevent erratic operation of the inverter circuitry. UHF Remote Switch, December 1989 and August 1990: in some cases, the MC145028 decoder (IC2) may not operate correctly since the specified oscillator components cause it to operate at 770Hz which is outside its recommended frequency range of 1kHz to 400kHz. The solution is to change the timing components so that the oscillators operate at about 2kHz. For IC1 in the transmitter, replace the resistors at pins 11 & 13 with 220kΩ and 100kΩ resistors respectively and change the .01µF ceramic capacitor at pin 12 to a .0022µF polyester type. For IC2 in the receiver, change the resistors at pins 7 & 10 to 39kΩ and 180kΩ respectively. The capacitors at pins 7 & 10 are unchanged. MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. ANTIQUE RADIO 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, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ ANTIQUE RADIO RESTORATIONS: specialist restoration service provided for vintage radios, test equipment & sales. Service includes chassis rewiring, recon­ densering, valve testing & mechanical re­­furbishment. Rejuvenation 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 on 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. FOR SALE _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. WEATHER FAX programs for IBM XT/ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & RTTY receiving program. Suitable for CGA, EGA, VGA and Hercules cards (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) ❏ 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 January 1994  95 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. ELECTRONIC CAD FOR DOS Zeus 2000SCH: $150 Parts Database: $30 Zeus 2000PCB: $200 Micro PCB: $80 Payment by cheque/mo. Add $5 postage. G. A. GEORGOPOULOS 34 Scouller St, Marrickville, NSW 2204. 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. PAT TV & SATELLITE Scrambling News Monthly, with the latest on de­scrambling techniques & addresses, where to buy the latest descramblers. Send stamp for info. John Papp, Box 37885 Winnellie, NT 0821. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. CONTROL RELAYS, Robots, Radios or Railways from LPT1: of your XT to 486 PC. 64 bits. Fully expandible. Demo programs, flow charts, circuits, drivers in M.L. & Basic. Main PCB & software $35. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. MICROWAVE SYSTEM CATEL MWV2000 23GHz including baseband equipment; 2-channel expandible, never used; original value approx. $22,000 only $8000. SATELLITE DISH 1.5m AWA with Ku band LNC $220. PHASE­ TRACK LINIPLEX F1 PLL HF Rx 9 ch MEMORY & DRIVES PRICES AT DECEMBER 1ST, 1993 SIMM 1Mb x 3 70ns 1Mb x 9 70ns 4Mb (72-pin) 4Mb x 9 70ns 4Mb x 8 80ns $70 $82 $275 $250 $230 DRAM DIP 1 x 1Mb 256 x 4 1Mb x 4 70ns 70ns Z $8 $8 $35 IBM PS.2 50/55/70 70/35 90/95 2Mb 4Mb 4Mb $160 $275 $275 MAC 2Mb SI & LC 4Mb P’Book $130 $330 CO-PROCESSORS 387SX to 25 387DX to 33 $105 $105 LASER PRINTER HP with 4Mb $260 TOSHIBA T3200SX T44/6400 T5200 4Mb 4Mb 8Mb $360 $340 $680 SUN SPARC 10/20 16Mb $1100 DRIVES SEAG 42Mb 28ms $190 SEAG 130Mb 16ms $290 SEAG 452Mb 12ms $750 Sales tax 21%. 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 PELHAM ICL 286 Board Kits 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. 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 1.5 watt AM broadcast transmitter XTAL locked $49 2.5 watt FM broadcast transmitter 88-108MHz. $49 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 Infrared relay kit $9 Remote control tester $4 $299 Ampo little PC 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 P.C. Computers 36 Regent St, Kensington, SA. Phone (08) 332 6513. LSB-DSB-USB crystal locked $400. SHURE M615 Equalisation Analyser (unused) $600. 3 off NAKAMICHI 1000 stereo cassette decks (service man­ual included) $750. NAKAMICHI HiCOMM II Noise Reduction System (as new) $65, dBX 11 122 Noise Reduction Unit $30, dBX 119 Compresser Expander $30, QUAD 405 Power Amplifier $150. Offers considered. Ron Beckett, 10 Gwandalan St, Emu Plains, NSW. AH (047) 35 6883; BH (02) 287 4918. TEST EQUIPMENT – COMPANY CLOSING DOWN Trio CS2070 4-Chan CRO with probes ...............................................$1000.00 Philips PM6456 FM MPX Signal Generator ..........................................$500.00 Philips PM5326 AM/FM RF Sig Gen & Sweep Oscillator ...................$1000.00 Philips AM/SSB 201 CB Transceiver inc. mic ........................................$100.00 Leader LMV181A AC Millivoltmeter ......................................................$150.00 Heath IG18 Sine/Square Audio Generator ...........................................$100.00 Yaesu FT200 Transceiver, inc. Mic & Speaker ......................................$300.00 All in good condition & in working order. Service manuals available for most items. Contact Norm Hughes on (018) 38 2288 96  Silicon Chip Advertising Index All Electronic Components..........67 Altronics ................................ 26-28 Antique Radio Restorations.........95 A-One Electronics........................49 Cebus Australia...........................59 Contan Audio...............................87 David Reid Electronics ................7 Dick Smith Electronics........... 12-15 D & K Wilson Electronics.............51 Harbuch Electronics......................7 Jaycar ........................ 33-35, 61-64 JV Tuners.....................................55 Kalex............................................87 Kenwood Australia.....................IFC PC Computers.............................96 Pelham........................................96 Peter C. Lacey Services..............56 Philips Test & Measurement......IBC RCS Radio ..................................95 Rod Irving Electronics .......... 74-79 Silicon Chip Back Issues....... 68-69 Silicon Chip Binders....................73 Silicon Chip Book Club..................3 Technical Applications.................91 Tektronix..................................OBC Transformer Rewinds...................96 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590.