Fullscreen HTML5Med Res (??MB)HTML4

Vol.7, No.5; May 1994 FEATURES   4 Electronic Engine Management, Pt.8 by Julian Edgar Books & journals THIS FAST NICAD CHARGER will charge two or four cells in rapid time. It’s built around a special IC & automatically throttles back when the cells are fully charged – see page 18.   8 The Fingerscan ID System by Leo Simpson Just plunk your digit on the window 14 Passive Rebroadcasting For TV Signals by Mike Pinfold One way of overcoming TV reception problems PROJECTS TO BUILD 18 Fast Charger For Nicad Batteries by Darren Yates It charges four “AA” cells in 50 minutes 24 Two Simple Servo Driver Circuits by Nenad Stojadinovic Build them for servo testing or direct control 34 An Induction Balance Metal Locator by John Clarke Use it to find coins, watches & other valuables 54 Build A Dual Electronic Dice by Darren Yates BASED ON A SINGLE IC, this simple unit can be used to test servos or used to control a servo in applications where a radio link is not required. We show you how to build it starting page 24. VERTICAL POLARISATION HIGH SIGNAL AREA ANY POLARISATION Easy-to-build circuit has auto switch-off 64 Multi-Channel Infrared Remote Control by Brian Roberts 60dB PATH LOSS PASSIVE RE-BROADCAST SYSTEM LOW SIGNAL AREA Add remote control to your tuner, tape deck or other appliances SPECIAL COLUMNS 58 Serviceman’s Log by the TV Serviceman Always look on the grim side DO YOU HAVE A PROBLEM with weak TV reception. Our article on page 14 shows you how to deliver a TV signal from a remote antenna up to 1km away. 74 Computer Bits by Darren Yates What’s your free disc space? 80 Vintage Radio by John Hill Trash or treasure – recognising the good stuff 86 Amateur Radio by Garry Cratt The Rhombic: a high gain wire antenna for HF 88 Remote Control by Bob Young How to service servos & winches, Pt.2 DEPARTMENTS   2   3 32 53 70 79 Publisher’s Letter Mailbag Circuit Notebook Order Form Product Showcase Bookshelf 84 91 93 94 96 Back Issues Ask Silicon Chip Notes & Errata Market Centre Advertising Index ADD THE CONVENIENCE of remote control to your tuner, tape deck or to some other appliance with this easy-to-build project. A separate low-cost transmitter is used to program a universal remote control. Details page 64. Cover design: Marque Crozman May 1994  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Advertising Enquiries Leo Simpson Phone (02) 979 5644 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 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER We must reject any move to reduce our mains voltage to 230V. You may recall that month I discussed the move to reduce our mains voltage from a nominal 240V to 230VAC. The main advan­ tage to Australia is supposed to “improve the opportunities for the electrical equipment we produce, opening up the world to our industry”. I pointed out that Australians would pay a very high price for this in terms of higher electricity distribution costs and so on. Well this month, I felt I should return to the topic in case some people thought that it was an “April Fool” story or that it would not affect them directly. It certainly will. Con­sider, for example, that any heating appliance which you present­ly have will not get as hot on 230 volts and the difference will be quite noticeable. Your stove hotplates will be noticeably less hot and there will be a consequent increase in cooking times. The same applies to your microwave oven, convection oven, even your toaster, electric iron and so on. All of these heating appliances will either take longer to come up to a selected temperature or in the case of appliances which aren’t thermostatically con­trolled, they just won’t get as hot. Nor will your lights be as bright and you will find the need to replace all light bulbs with new ones rated for 230V AC if you want the same brilliance as you had before. That is bad enough but if you are using 12V halogen lamps which need to run at close to their rated voltage to work properly, then they will be noticeably dimmer - they will no longer sparkle at all. Again, the only solution may be to change all halogen lamps or worse, change the 12V transformers. If you have fluorescent lights, they will take noticeably longer to start, particularly on cold mornings - so you’ll have more of that annoying flick-flick-flickering each time you turn them on. And when they do come on, they won’t be as bright eith­er. Nor will your refrigerator and freezer work as well and they will cost more to run. Still not convinced? What about that old colour TV you’ve had for many years? It’s been working fine and you don’t have any real reason to update at this stage. Well, when you run it from 230 volts AC, you will no doubt find that its picture will shrink and that will certainly take the gloss off its performance. New TV sets will not be affected at all by this change because their power supplies can cope with a large range of mains voltages but people who can’t afford to update their equipment are going to be disadvantaged. No, the more I think about this proposal to reduce our mains voltage to 230 volts AC, the more I think it is harebrained. If you agree, don’t just nod your head and turn the page. Either write to us or write to the Minister for Energy in your state. It’s likely they haven’t heard of the proposal yet. Get them to nip it in the bud! Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG Solar regulator I read with interest the article on the solar panel regula­tor in the January 1994 issue. This is a step in the right direc­tion and I am sure that it will contribute to greater use of solar energy in the future. One small point disturbs me, however. At the end of the article, instructions are given to adjust for a battery voltage of 13.8V. Presumably this regulator will be used with lead-acid batteries of the automotive type, in which case the battery will never be charged to full capacity. Both car and battery manufacturers recommend that regula­tors be set at a minimum of 14.2V and not to exceed 14.5V. For long battery life and minimum water top-up requirements, it may be desirable to revert to 13.8V after a period of moderate gas­ sing and this would lead to a slightly more complex design for the regulator. Maybe there will be another article on the subject? M. Findlay, Badgerys Creek, NSW. Information on guitar amplifiers With reference to the “IF generator is nifty” letter from L.T. from Eagle­hawk, Victoria (Ask SC column, December 1993), he (?) asked for a course on antique musical instruments, specifically guitar amplifiers. In 1989, I purchased a paperback book from McGill’s bookshop in Melbourne, called “The Tube Amp Book II” by R. Aspen Pittman. As far as I can tell, it is published by Groove Tubes, 13994 Simshaw Avenue, Sylmar, California 91342, USA. My edition was published in 1988. There are 400 pages to this book and it has 32 pages of photos of various guitar amplifiers and a few other items. There is a considerable rundown on the history and technical details of many amplifiers, including 10 pages listing valve types used in various makes and models. There is a small cross reference list of US/industrial/European type equivalents, a list of Groove Tube com- panies and instrument manufacturers (worldwide list) and most importantly, 277 pages of circuits of all the big name guitar amplifiers. If this book is still available it should be just what is needed. As a regular reader, let me compliment you on your excel­lent magazine. I am a collector of early radio equipment and a technician by trade, so I read the Vintage Radio and Serviceman’s Log columns first, followed by the rest of the magazine articles. I am a member of the Historical Radio Society of Australia and a local vintage radio club (The North East Vintage Radio Club). About 17 of our (local) members went across to see John Hill’s museum in Maryborough a few weeks ago. How I wish I had as many of my radios restored and somewhere to display them like that! E. Irvine, Benalla, Vic. Adjustable compressor wanted I was interested to see a section in a sound mixing in­struction book devoted to compressors and limiters which are used in the music industry. They had adjustable attack and delay, adjustable levels, and even adjustable “knee” or cutoff (or percentage compression). I am told that these cost $400 yet they are ideal for setting up automatic sound control of individual music instruments and for public address. What strikes me is that we have endless amplifier kits yet I know of no kit that resembles this professional music industry device. I see big advantages in its use in pulpit microphone control and tried to use an opto-coupled FET in a home brew circuit but it needs heaps of redesigning. May I suggest this type of compressor for a project of in SILICON CHIP? Glen Host, Doubleview, WA. Easier calibration for the Digital Tachometer I recently built the Digital Tachometer from the August 1991 issue and it works well. SILICON CHIP, PO Box 139, Collaroy, NSW 2097. As I only had a 6V AC plugpack, I reduced the 4.7kΩ cali­bration resistor to 2.7kΩ and wired it permanently to a chassis mount socket on the inside of the case. When I adjusted the 50kΩ pot (VR1) to calibrate the unit, I found it difficult to obtain an exact 1000 rpm because of the “touchiness” of the adjuster. Here I might mention that I am using a 56kΩ resistor for RX to suit a 6-cylinder motor. The nearest adjustment which I could obtain was near the centre point of the 50kΩ pot and this subsequently measured approximately 35kΩ. The 35kΩ and 56kΩ resistances added up to 81kΩ and so I decided to substitute a 75kΩ resistor for RX and use a 10-turn 10kΩ trimpot for VR1 to make the adjustment much less critical. This trimpot was glued to the edge of the PC board using two-part epoxy and wired to VR1’s pads on the PC board via flying leads. Chris Potter, Kilsyth, Vic. Serviceman column is useful One of the most enjoyable features are the cartoons that appear in the Serviceman column every month. They certainly put some fun back into what can be a dry and serious profession. Additionally, I have used the information in this column to help assist me in repairing TVs and videos – even one annoying fault in my mother’s video! After having repaired several valve radios by reading the Vintage Radio column, I wonder how easy the current generation of electronic equipment will be to service in the next 20 years. About three months ago, I helped one of our apprentices repair an elderly colour TV that he found on the footpath during a council cleanup. The manufacturing date stamp was for 1975! After repairing several minor faults, it was as good as ever! Finally, I am eagerly awaiting the completion of the extra add-on for the colour video fader described last year. Mark Allen, Artarmon, NSW. May 1994  3 Electronic Engine Management Pt.8: Books & Journals – by Julian Edgar Finding appropriate texts and journals which deal with electronic engine management is difficult. Most material written on electronics in cars is either too simple (being directed at apprentice mechanics) or too generalised to be of help when dealing with a specific car. However, there are some references which are useful. Buying the books outright can be expensive but TAFE libraries will often respond to requests to buy specific books if they lack material in that area and if the college teaches automotive subjects. TAFE lib­raries are the best source of material of this whole subject area and they also allow free public membership. Generalised texts There are several books that give a good general treatment of electronics Gregory’s produce very useful references on various cars. In the foreground is a standard Gregory’s workshop manual, which has engine management fault diagnosis material in it. The background book (EFI & Engine Management) contains material on the engine management & EFI systems in all Australian cars from 1980-1990. 4  Silicon Chip in automotive applications. “Understanding Automo­ tive Electronics”, “Automotive Computers and Control Systems” and “Automotive Electronic Systems” (full details of the books cited are at the end of this feature) are just three examples. The first two are published in the United States while the latter book is British. All three books give an overview of both analog and digital automotive systems. The first book is probably more useful from purely an electronics perspective, with the second book also examining aspects such as diagnostics and the testing of systems in American vehicles. The latter book provides probably the best of both worlds! A very different type of book – but still useful – is pub­ lished by the Australian Government for use by apprentices. Called “Engine Petrol Injection”, it covers all aspects of elec­ tronic fuel injection (EFI) and is aimed at mechanics. Electronic engine management (which incorporates both fuel and ignition control) is not covered, however. Very clear diagrams are used throughout the book, especially on the mechanical aspects of EFI. The book is available from Commonwealth Government bookshops for about $15 and is a bargain. Bosch The next step is to look at material Above: these three generalised texts all provide excellent background material on the subject of electronic engine management & automo­tive computers. produced by the origi­nal manufacturers of the equipment. Bosch invented electronic fuel injection and engine management, and has published a series of books and booklets dealing with the topic. Their material is generally excellent. The Bosch “Automotive Handbook” is the Bible among car de­signers and serious amateur modifiers. Pocket size, it packs an incredible amount of information into its 700 pages. It’s written in a sort of technical shorthand, with each paragraph containing many points. The actual sections dealing with electronics in car applications form a relatively small component of the book but it is worth buying for these sections alone. It is available from the Society of Automotive Engineers in Canberra (02 449 6551) and costs around $45. Also produced by Bosch is a series of booklets dealing specifically with each of that company’s engine management and fuel injection systems. Booklets are available on L-Jetronic, Motronic, Engine Electronics, and so on. Each This book provides a good introduction to EFI, with very clear diagrams used throughout. It is pitched at the apprentice mechan­ic level & is excellent for beginners. booklet is about 40 pages long. They are very expensive but most TAFE colleges which deal in automotive electronics stock the booklets in their libra­ries. Specific car systems When you require information on specific car systems there are two sources. The first are books which have been writ­ten to cover a variety of manufacturers’ systems. Gregory’s have published “EFI and Engine Management”, a good book which covers most of the common cars sold in Australia in the period 1980-1990. It costs about $60. The information includes such material as accessing and reading fault codes, wiring diagrams, sensor types, and so on. Also provided is a 40-page summary of how EFI works, the common inputs and outputs, and how to test sensors. In all, it provides an excellent summary of the procedures used for maintenance and simple fault-finding. Gregorys’ indi­vidual car workshop manuals also contain this material on a specific-car basis but in an abbreviated form. Workshop manuals The other way of obtaining material on a specific car is to use the manufacturer-produced workshop manual. These vary sub­ stantially in quality and depth, both from manufacturer to manu­facturer and from model to model. The best manuals will devote a whole volume to engine man­agement. This generally includes a discussion on how each of the input sensors works, their response curves, and so on. Pin-outs of the ECM will be included and typical voltages and/or waveforms specified. Not all manufacturers go to this trouble though, with some giving just fault codes and simple testing procedures. Often, the first model to introduce a new management system will have an extensive discussion of it in the workshop manual, with subsequent models having only a brief coverage. May 1994  5 The Bosch Automotive Handbook has an incredible amount of infor­mation packed into it – some of which is on car electronics. It’s worth buying for this aspect alone. Examples of good manufacturer-developed workshop manuals include the Holden VL Commodore, Mazda RX-7 twin turbo, Subaru Liberty and Ford L-Jetronic Falcon. The manuals are available directly from the manu- More specific information on the various Bosch systems is avail­able in their Technical Instruction booklets. They’re expensive to buy, though. facturer – though some sweet-talking may be required before they will sell them to a private individual – and from TAFE libraries. The cost is usually quite reasonable – the Subaru Liberty manual, for example, comprises six Factory workshop manuals often provide an in-depth analysis of the engine management system used in that model. The Subaru Liberty manual, for example, comprises six volumes, one of which is devoted to engine management. 6  Silicon Chip volumes, each up to 300 pages long, and costs $140. This covers the whole of the car of course – not just the engine management. Modifications Books on the topic of fuel injection modification are very rare and those which are available also become quickly dated. There don’t seem the be any books which cover programmable injection, for example. “Tuning New Generation Engines for Power And Economy” (about $45) covers all aspects of modern engine modification – including a chapter on fuel injection. This book is already dated (it was first published in 1988) in that it deals solely with fooling the computer inputs in order to change the outputs. Fitting high-flow injectors and then using an air-bypass around the vane airflow meter so that over-fuelling at low loads doesn’t occur is dis­cussed in some detail, for example. However, some good points are made about fuel flow, injector capability, and so on. Bosch Fuel Injection and Engine Management is an American book which gives an excellent overview of both mechanical and electronic injection and management systems. Much of its material is drawn straight from the Bosch manuals and is therefore clear and accurate. A chapter on modification is included. This book is a good buy at about $60. Also available are some books which cover modifications to specific fuel injection systems. Published in the United States, some are relevant to use when Australian cars use the same engine management systems. Since both Ford and Holden are US-owned, books dealing with EEC (Ford) and GM-Delco (Holden) systems are useful. An example is How to Tune and Modify Ford Fuel Injection, which covers the EEC-IV system. Journals Various US, British and Australian engineering periodicals cover electronics in cars. The Australian journal “The Automotive Engineer” (published by the Australian Society of Automotive Engineers) is really aimed more at mechanics than engineers and tends to cover material at about the same level as the well-known “Gregory’s manuals. It provides coverage each time a new car is released, concentrating mainly on the technical aspects of the vehicle and its engine. The Society of Automotive Engineers in the United States also publishes material on electronics in cars. The best way to obtain this is in the collected papers which are published occa­sionally and which deal with one topic. “Engine Management and Driveline Controls”, for example, was published in 1989 and has a collection of engineering papers dealing with these topics. Other collections are also available. Once again, TAFE libraries sometimes carry these publications. This early Ford manual gives good background information & is applicable to all L-Jetronic EFI cars. Bibliography Here is a list of books containing good material on elec­ tronic engine management. There must be many others and I would welcome feedback from any reader who knows of other relevant references – especially in the area of modification. (1). Australian Automotive Industry Training Council, Engine Petrol Injection, Australian Government Publishing Service; Basic Training Manual 17-8, 1992. (2). Bell, A. G., Tuning New Generation Engines for Power and Economy; Haynes Publishing, 1988. (3). Bosch, Automotive Handbook; Robert Bosch GmbH, 1986 (4). Bosch, Technical Instruction – L-Jetronic; Robert Bosch GmbH, 198? (5). Bosch, Technical Instruction – Motronic; Robert Bosch GmbH, 1983. (6). EFI and Engine Management; Gregory’s Scientific Publications, 1990. (7). Mellard, T., Automotive Electronic Systems; Heinmann Newnes, 1987. (8). Probst, C. O., Bosch Fuel Injection and Engine Management; Robert Bentley, 1989. (9). Ribbens, W. & Mansour, N., Understanding Automotive Elec­tronics; Texas Instruments, 1984. (10). Watson, B., How To Tune and Modify For Fuel Injection; Motorbooks International, 1992. (11). Weathes, T. & Hunter, C., Automotive Computers SC and Control Systems; Prentice-Hall, 1984. This is one of the few books available which looks at modifica­tions to EFI systems. It is now getting a little dated but is still useful. May 1994  7 Fast & easy proof-positive identification The Fingerscan Personal ID System Fujitsu Australia has announced a marketing agreement with Bio Recognition Systems for the Fingerscan personal identi­fication system which was designed & developed in Australia. Fujitsu will market the system world-wide. By LEO SIMPSON Many readers will recall our report on the Fingerscan system which was featured in the May 1990 issue of SILICON CHIP. It has now been refined and repackaged and the software rewritten for Windows applications. The Fingerscan system has wide applica­tion in small or large businesses, anywhere where personal secur­ity is required, whether it is for entry into a carpark or build­ing, or for access to a computer system or to a restricted area. For those who are not familiar with the Fingerscan system, we shall provide an updated description. Finger­ scan is an elec­tronic finger scanning device which records and stores your finger image in computer memory. The photos accompanying this article show it used in two applications, one for access to a computer instead of the normal password system and the other, Fujitsu’s immediate application as a time and attendance clock for retail stores and factories. As shown in the photos, with both units you just place your finger over a small plastic window. The unit then scans your finger and shortly after you are either identified or asked to try again. According to the developers, Bio Recognition Systems, the Finger­ scan “is based on digital holography and involves an electro-optical scanner about the size of a thumb print which reads three-dimensional data from the finger such as skin undula­ Originally used in our May 1990 issue, this tions, ridges and valleys, photo shows Finger­scan being used instead of reflections and other living the more traditional password to control access charac­teristics. to a computer system. It makes unauthorised “One of the living characaccess virtually impossible. 8  Silicon Chip teristics is the blood flow pat­tern within the finger. Building on these various three-dimen­ s ional data, a unique personal pattern is built up. This pattern is not a fingerprint and does not rely on print data. A fingerprint is a two-dimensional pattern which relies upon certain key minutiae to identify one print from another. The heart of the system is a CCD (charge coupled camera) which takes three scans of the finger. For each separate scan, the finger is lit by different coloured LEDs: red for the first, orange for the second and green for the third. Each of the LEDs illuminates the finger from a slightly different angle so that the image detail recorded by the CCD camera is not the same. The analog picture information from the CCD camera is converted into digital data and processed in a module which employs a 68000 microprocessor and a large custom gate array. The data is compressed and stored as a 1242 byte template file. By comparison, a finger image file takes up about 150 kilobytes. A template file can only be compared with a newly presented finger image to provide identification. This has three results which are important for privacy implications: (1) a finger image cannot be recreated from a template file; (2) A template cannot be compared with any other template and therefore the system can only be used with the cooperation of users who must put their live finger on the scanner in order to be matched with a stored template; and (3) A person has a choice of 10 fingers to use, none of which is the same. Therefore, a person could use a different finger for dif­ferent applications where Fingerscan was in use. This is the new version of Fingerscan, developed in Australia as a Time & Attendance clock for Fujitsu. It uses a CCD camera to create and store a 3-dimensional record of a person’s finger. For example, a person could use the index finger for time and attendance at their place of work, the left thumb for a bank account and the ring finger for computer access. A person is therefore recognis­ able only within a closed system and only if they so choose. Users are enrolled in a Fingerscan system in about 25 sec­ onds. Each subsequent positive identifications takes less than half a second. The false acceptance rate is claimed to be .0001% (ie, one in a million), while the false rejection rate is less than 1%. The Fingerscan unit comes in various memory sizes. The base model has 512Kb of memory which can be increased up to 2Mb, allowing for storage of up to 1200 finger records as well as a transaction log. The unit can also retrieve finger records when networked from a remote PC or other host computer. There is therefore no real limit to the number of users that can be regis­tered on a system. The keyboard has 16 keys which includes six function keys that can be programmed to suit the application. The readout is a backlit 2-line by 16character alphanumeric display. Fingerscan comes with a variety of interfaces. It has four TTL alarm inputs and four TTL outputs, RS232 or RS485 serial outputs and an optional smart card interface. It can also operate a doorlock using the built-in doorlock relay driver. Mr John Parselle, managing director of Bio Recognition Systems, made the following comments on the agreement with Fujit­su: “Our new design came about because we had a major client with an offshore subsidiary who required a much more responsive bio­ metric device than our existing model. We successfully applied for a Federal Government Discretionary Grant to redesign Finger­scan to meet this export opportunity. The initial order is for 250 units but we have great expectations of increasing this to several thousand in the short term. We subsequently designed the second Finger­scan unit specifically as a Time and Attendance clock for Fujitsu Australia and signed the marketing agreement with Fujitsu Australia to jointly market both new Fingerscan products. For further information on the Fingerscan ID system contact Fujitsu Aust­ralia Ltd, 376 Lane Cove Road, North Ryde, NSW 2113. Phone (02) SC 887 9222. May 1994  9 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Passive rebroadcasting for TV signals Do you have a problem with weak TV reception & no pos­sibility of “line of sight” to the TV transmitter. If so, then this article on delivering a TV signal over a distance of up to 1km will be of interest. By MIKE PINFOLD A letter featured on page 93 of the August 1993 issue prompted me to put pen to paper. It referred to the possibility of passively re-broadcasting TV signals picked up in a high signal strength area by beaming them down into a low signal area. This was to be done by coupling two television antennas back to back with a length of low loss coaxial cable. At first thought, the idea seems a good one but with simple propagation theory and antenna maths it can be demonstrated that it has only limited potential. The letter also mentioned the use of a masthead amplifier and the matching of a long feedline from the high signal area down some distance to the TV set. But first, let’s address the problem of passive re-transmission of TV signals. There are a number of mathematical formulas that enable one to calculate field strength at a distance from a transmitter. The first of these is used to calculate the power density “P” at a point “r” metres from an isotropic radiator: P = Pt/4πr2 where P = received power in watts/square metre; Pt = transmitted power in watts; and r = distance in metres between transmitter and the reference point. This formula shows the in14  Silicon Chip This photo shows the author’s original open wire feeder system in use with a vertically polarised VHF antenna in a remote part of New Zealand. verse-square nature of radio waves. The energy level reduces in proportion to the square of the distance. Note that the frequency of the signal does not enter this equation. The electric field intensity “E” of a radio signal “r” metres from a point of “P” watts is given by the equation: E = √(30Pt)/r where E = the intensity in volts per metre; Pt = the transmit power in watts; and r = the distance in metres. The power density of a signal and the electric field in­tensity are related by the equation: Pr = E2/120π where Pr = received power density in watts per metre squared; E = intensity in volts per metre; and 120π = the resistance of free space. The above formulas are for theoretical signal strengths between isotropic sources in free space. However, there are other external influences that may times 20dB is 100 times. Thus, the formula to include gain arrays is: HIGH SIGNAL AREA Pr = 1.64Pt/4πr2 ANY POLARISATION Antennas have a performance factor known as “antenna aper­ ture” and it determines how 60dB PATH LOSS much of that potential signal the PASSIVE antenna extracts from free space. RE-BROADCAST LOW SIGNAL AREA The larger the receiving area, SYSTEM the more power is intercepted. Aperture is determined by the following equation: A = λ/4π For a gain array with a gain of “G” times over isotropic, the equation is: Fig.1: this diagram shows the general concept of pas­sive rebroadcasting as outlined in the article. The hilltop antenna picks up a strong signal which is re-radiated A = Gλ/4π downhill by another antenna to the receiving antenna at the bottom of where the hill. λ = wavelength of the signal in metres; G = gain of the antenna (not in VERTICAL POLARISATION +30dB dB format) over isotropic; and +30dB A = Aperture, as a decimal HORIZONTAL POLARISATION fraction. Remember that an isotropic antenna has a gain of unity and 60dB PATH AMPLIFIED LOSS RE-BROADCAST a dipole has a gain 1.64 times LOW SIGNAL AREA SYSTEM more. Thus, the amount of power available is derived by: ISOLATION: GEOGRAPHICAL Pa = PiA AND POLARISATION where Pi = power density in watts/ metre2; Pa = power available; and Fig.2: this is a variant of the passive rebroadcasting system with better isolation A = Antenna aperture as a decbetween antennas and a masthead amplifier interposed between the hilltop imal fraction antennas. By combining the above equations, one arrives at an equa­tion have a bearing on the outcome and of a halfwave dipole, broadside to the that can determine the received power signal strengths can be assumed to dipole, is: in an antenna of known gain: be slightly less than those calculated. Pr = 1.64Pt/4πr Pr = Pt.Gt.Gr.λ2/(4πr)2 An isotropic radiator is not exactly a or The situation of passive rebroad­ useful concept in the real world, alE = √(49.2 x Pt)/r casting (receiving signals on one though it is a base on which to place where antenna and feeding them down to firm theory. Pr = power density in w/m2; another for rebroadcast) can be shown There are different correction factors Pt = power transmitted in watts; to be something of a hopeless case and that are added to the equations to take r = distance in metres; and will only work if the received signal account of antenna performance and E = field intensity in volts/metre. strength is exceptionally strong and other configurations. For a half­wave The above equations give the pow- the rebroadcast distance is relatively dipole oriented for maximum radia­ er density at a point “r” metres from short; ie, a couple of hundred metres. tion, there is a correction factor of 1.64. the source. If you have a transmitting By using the above formulas, the This factor when converted to dB gives antenna with a gain of 10dBd (over received power level at the hilltop the apparent gain difference between a dipole), then this factor must be receiving site can be approximated if anten­nas referenced to a dipole and incorpo­rated into the equation. 10dB you know several important factors: those to the isotropic source. When is a power increase of 10 times, so the the radiated power of the transmitter, looking at manufacturers’ antenna gain input power in watts must be multi- the frequency of the signal, the gain figures, check to see if they are refer- plied by the apparent increase over the of your receive antenna, and the disenced to isotropic (dBi) or to a dipole original antenna (with its compensa- tance between the transmitter and the (dBd). Those referenced to isotropic tion factor present if required). receiving anten­na. appear to have 2.15dB more gain but This multiplication factor is its Let us put a few figures into the their real gains are the same. power gain not in dB form but linear equation and see how our theoretical The formula for the field intensity form; eg, 6dB is 4 times, 10dB is 10 system is going to perform. To get a VERTICAL POLARISATION May 1994  15 antenna is 6.16nW. Let’s assume the transmit antenna has a gain of 10dBi and that the receive antenna has a gain of 10dBi. The power received by the home TV antenna is found by uti­lising the same equation and a transmit power of 6.16nW (the original received signal). This results in a signal level of 5µV/m, a totally useless signal for any TV. 75mm 600mm BLACK POLYTHENE SPREADER Calculating the path loss 8-12 GAUGE FEEDLINE SPACER TAPERED MATCHING SECTION APPROX. 2m LONG 10mm SUPPORT ROPE CHOCOLATE BOX CONNECTORS PVC STRAINER BLOCK 300  RI BB ON Fig.3: this is the author’s open line feeder system which gives very low signal loss over a long path. The open line is matched to 300Ω ribbon with a 2-metre long tapering section and terminat­ed as shown. good quality signal at the TV set, you need a minimum of 250µV (assuming a modern sensitive TV set). For the purposes of this exercise, we’ll assume the following: • 100 watts of transmitter radiated power (Pt x Gt); • UHF channel 42; 640MHz approximately; wavelength = 0.468 me­tres; • Distance from transmitter to receiver = 30km; • Antenna receive gain = 6dBi (4 times relative to isotropic antenna). Pr = Pt.Gt.Gr.λ2/(4πr)2 = 1000 x 4(0.468)2/(4 x π x 30,000)2 16  Silicon Chip = 876.096/(1.42 x 1011) = 6.16 nanowatts This is a respectable received signal strength and can be converted into volts/metre by the following formula: E = √(Pr.R) where R is the impedance of the antenna in ohms. The result is a signal of 679µV into a 75Ω antenna, a good signal indeed. In our setup, the receive antenna is connected via a short length of low loss coax to the “transmit” antenna as shown in the diagram of Fig.1. The power delivered to the transmit In order to produce the required signal level at the home TV, a level of amplification equal to the path loss between the rebroadcasting antenna and home receive antenna has to be insert­ ed at the re-transmitting site. This is easily calculated. It is the difference between the re-transmitted power level of 6.16nW and the home television received signal: 6.16 x 10-9 - 3.4 x 10-15 = 60dB This is about 60dB of path loss and therefore the gain required is 60dB. This amplification should be provided between the hilltop receiving antenna and the rebroadcasting antenna. While it is relatively easy to provide 60dB of gain into the rebroad­ casting system connecting coax, one must maintain adequate RF isolation between the receive and transmit antennas. This is to prevent feedback and thus stop the system becoming an RF oscillator at the frequency of maximum feedback. The two antennas must not “see” each other. One antenna could be placed on one side of the hill and the other placed on the other side, “hidden” from view of its mate. Even more isolation can be obtained by having one antenna with vertical and the other with horizontal polarisation. This can amount to as much as 20dB. One also has to make sure that the coax between them is well and truly decoupled to prevent RF coupling along the outside of the coax. The other factor that helps in antenna isolation is the front-to-back ratio. An antenna with a very good front-to-back ratio will have little problem ignoring signals coming to it from behind, again improving antenna isolation. This setup is shown in Fig.2. The foregoing should give the reader an insight into anten­na concepts and propagation. While it is possible for passive re­broadcast systems to work, the received signals must be very CAPACITOR 75  75  300  300  GND GND CAPACITOR HERE OR HERE C 300  OR C 75  Fig.4: this diagram shows the modifications needed to a standard 4:1 balun to enable DC to be sent up the ribbon to the masthead amplifier. Two such baluns will be required. strong, the antenna gains high and the rebroadcast distances short. Masthead antenna The other comment in the letter relates to using a masthead amplifier to drive a long feedline to the home TV below a hill in a weak signal area. My experience is that this setup can work extremely well, contrary to the comments from the magazine. I once built such a system for my parents who lived in the country and whose TV reception left a lot to be desired. It used a standard TV antenna on a hilltop and a homebuilt masthead preamplifier (BFY90) with a gain of about 15dB. This preamplifier fed signals down about 1km of balanced open wire feeder. Power was fed to the preamplifier via the open wire feeder. This feeder was made from single-strand copper wire spaced at about 75mm and used spreaders made from 12mm black polythene tubing. Matching into and out of the open wire feedline was by a 2-metre long tapering section that brought the open wire feeder down to the spacing of 300Ω ribbon. The 75Ω coax was matched to a short piece of 300Ω ribbon by the usual 4:1 ferrite balun, modi­fied slightly to enable it to pass DC into the open-wire feedline from the 75Ω coax. Fig.3 shows the details of the polythene spreaders and the tapering match and termination to the 300Ω ribbon. Open wire feedline can also be made from single strand galvanised fencing wire. At UHF, open wire feeder can have a loss of less than 1.5dB/100 metres. Even good quality coax has a much greater loss than this and is much more expensive. That means that you could run a 15dB pre­amp­ lified signal down 1km of open wire feeder and still have the same signal level present that was available at the receiving antenna terminals ahead of the masthead preamp. On the other hand, open wire feeder is more “messy” to use than coax as it has to be supported on poles and must not come too close to metal objects; ie, no closer than 200mm. Matching to 75Ω is somewhat involved and you must use modi­fied baluns to pass DC and RF simultaneously. Power to the masthead amplifier is best fed as AC as this will reduce electrolytic corrosion at connections but you can use DC if you want to. To get DC through the 300Ω-to-75Ω balun re­quires it to be modified slightly. For this, you need a small low-value (eg, 470pF) ceramic capacitor. Look very carefully at the way the balun is wound. The windings you want to investigate are those that appear to crisscross. The capacitor is placed in series with one of those wires. Fig.4 shows how the balun is wired. You will have to dis­connect each wire, leaving the others connected, and test for a loss of continuity between the inner and outer of the 75Ω side. When this is achieved, test for continuity from the 300Ω side to the 75Ω side without any shorts between either side of the re­spective feedpoints. If all is well, solder the capacitor in series between the 300Ω terminal and the “disconnected” end of the winding. It goes without saying that you need to put this assembly into a water-tight container. Two of these baluns are required, one for each end of the open wire feeder. A good way of connecting the 300Ω ribbon to the thin end of the taper is to use the insides from a “chocolate block connector” (ie, the internal metal sections from plastic barrier terminal blocks), as shown in Fig.3. References (1). Hewlett Packard. Spectrum Analy­ zer series Application Note 150-10, 1979. (2). I.T.T Radio Reference Manual, 4th Edition (3). Introductory Topics in Electronics and Communications, Antennas, by F. R. Connor, 2nd edition. ISBN 0-71313680-4. (4). Radio Communication in Tunnels, by K. F. Treen, Wireless World, March SC 1979. CALLING ALL HOBBYISTS We provide the challenge and money for you to design and build as many simple, useful, economical and original kit sets as possible. We will only consider kits using lots of ICs and transistors. If you need assistance in getting samples and technical specifications while building your kits, let us know. YUGA ENTERPRISE 705 SIMS DRIVE #03-09 SHUN LI INDUSTRIAL COMPLEX SINGAPORE 1438 TEL: 65 741 0300    Fax: 65 749 1048 May 1994  17 Charge your nicad cells in rapid time with this ... By DARREN YATES FAST CHARGER FOR NICAD BATTERIES Tired of waiting for the 16 hours it takes to charge your nicad cells? This low-cost project uses a single Philips IC & will charge four “AA” cells in 50 minutes. It runs from a 12V 1A plugpack supply or from a car battery. Nicad batteries are now one of life’s necessary evils. They can make running battery-operated gear much cheaper than using ordinary dry cells but they do have one big disadvantage – when the batteries go flat, it usually takes about 16 hours to re­charge them. Another disadvantage is their lower output voltage compared to standard dry cells (1.2V vs 1.5V). 18  Silicon Chip We can’t do much about the voltage difference between the two types of batteries but we can do something about the time it takes to recharge nicads. The answer is to build this Fast Nicad Charger. It can charge either two or four “AA”, “C” or “D” cells in rapid time – 50 minutes for “AA” 600mAh cells and 100 minutes for “C” and “D” 1.2Ah cells. The circuit is based on a new Philips chip – the TEA1100. This is a dedicated nicad charger IC with inbuilt switching controllers. This switching technique provides much higher efficiency than the more conventional linear techniques. We’ve used the switching controller feature and several other features of the chip to make one of the simplest yet most comprehensive nicad chargers currently available. It provides automatic cutout when the batteries are fully charged, a timer override and two charging modes – fast and trickle. Preventing overcharging Standard nicad chargers use circuitry which applies a con­stant current Voltage sensing & timing The Fast Nicad Charger uses both current and voltage sens­ing to ensure correct charging, as well as an RC clock/timer which shuts down the circuit after a preset time if the sensing circuit fails to detect the full-charge condition. The charging current is sensed simply by using a low-value resistor in series with the battery but the voltage sensing is somewhat more complicated. Instead of checking the battery vol­ tage for an absolute value, the circuit V CHARGE CURRENT Fig.1: typical charging curve for a nicad cell. Note how the voltage falls slightly at the end of the charging cycle. This is detected by the circuit & used to switch the charging current to a low level to keep the battery topped up. BATTERY VOLTAGE to the battery over a preset period of time – usually about 16 hours for ordinary nicads and five hours for the fast-recharge types. The big disadvantage of this technique is that it doesn’t take into account the current charge state of the battery and this can lead to overcharging and possible damage to the battery pack. By contrast, the Fast Nicad Charger does take the current charge state of the battery into consideration and sets its charging current accordingly. This prevents overcharging and greatly increases battery life. Another problem with nicad batteries is the so-called “memory effect”. Often, batteries are placed into a charger with­ out having been completely discharged beforehand. In the short term, this doesn’t cause too much of a problem but problems do occur after repeated charge/discharge cycles. What happens is that the battery develops a memory for the point to which it is continuously discharged and this ends up becoming the end point for future use. In other words, the bat­ tery will only partially discharge before appearing to go “flat”. This can reduce the effective capacity of the battery by more than half in some cases. The only way to prevent this unwanted memory effect from occurring is to deep-cycle the battery. In practical terms, this means discharging the battery to its recommended end-point vol­tage before placing it in the charger. An automatic discharge circuit is not a feature of this project, however. If you want to correctly discharge nicad bat­teries, we recommend that you build either the Nicad Discharger described in the July 1992 issue of SILICON CHIP or the Automatic Nicad Discharger described in the November 1992 issue. TIME looks for a relative change of 1% from the maximum voltage – see Fig.1. Unlike SLA batteries, once nicads reach their full charge capacity, their output voltage drops. Because it is virtually impossible to predict the absolute maximum voltage, Philips has used an alternative method called “-dV sensing”. By looking for a 1% drop in the relative battery voltage, the new TEA1100 can accurately determine when a nicad pack is fully charged. This ensures that the battery is never overcharged, regardless of its initial capacity. The RC clock/timer utilises a counter block within the TEA1100 to set a maximum timeout period. Its job is to automati­cally switch off the charger if the battery voltage hasn’t dropped the required 1% during the set time period, or if the -dV sensing circuit misses the slight drop in output voltage when the cells are fully charged. Essentially, the timing circuit is included as cheap in­surance against the circuit not shutting down, as can occur if the cells are faulty or if the sensing circuit fails to detect the full charge condition. Some cells have only a very shallow voltage drop at the end of their charging cycle and this can sometimes be missed by the sensing circuitry. In most cases though, by the timer the timer operates, the circuit will have already shut down. Circuit diagram Fig.2 shows the complete circuit details of the Fast Nicad Charger. Power is derived from a 12V DC 1A source and applied to the circuit via on/off switch S1 and reverse-polarity protection diode D1. Since the TEA­ 1100 requires a supply of between 5.5V and 11V, ZD1, Q3 and their associated components form an 8.5V regula­tor which feeds pin 12 of IC1. The output from the regulator also drives charging indicator LED 1 via pin 15. The charging current flows to the batteries from D1 via transistor Q2, a TIP32C 3-amp PNP power device. Main Features • • • • Two charging modes – fast and trickle. • Timer override to ensure charger cuts off if cells are faulty or fully charged condition not detected. • • Can be powered from a 12V 1A plugpack supply or from a car battery. Charges two or four cells (600mAh or 1.2Ah capacity) at once. Charges “AA” cells in 50 minutes & “C” & “D” cells in 100 minutes. Automatically cuts off when cells are fully charged & switches to trickle charge mode. Has reverse polarity protection for power supply & is fully protected against short-circuit or open circuit nicad batteries May 1994  19 C Q3 BC337 S1 12V INPUT L1 : 60T,0.5mm DIA ENCU ON ALTRONICS L-5120 TOROID 10 16VW ZD1 9.1V 400mW Q2 TIP32C C E 470 16VW 470  B 3.3k D1 1N4004 E LED1 CHARGE  L1 10k D2 FR104 B 100  Q1 BC337 C 12 2.2k B E 100pF K A 15 S2 IC1 TEA1100 5 4 13 16 3 27k B CE 0.1  5W S3 470 16VW 600mAH 1.2AH .0018 10 680pF E C VIEWED FROM BELOW 4 CELLS 7 1 2.2k B 100k 2 CELLS 2 OR 4 CELL BATTERY Fig.2: the circuit is based on IC1. It samples the cell voltage via its pin 7 input & provides a pulse width modulated (PWM) output at pin 1. This PWM output drives Q1 and this in turn drives power transistor Q2 which switches current pulses through to the cells. 100k .0039 47k FAST NICAD/NIMH BATTERY CHARGER Along with fast-recovery diode D2 and inductor L1, these components form a step-down DC-DC converter which is pulse width modulated (PWM) con­ trolled by IC1. The pulse-width modulated waveform appears at pin 1 of IC1 and is inverted by transistor Q1. This in turn switches power transistor Q2 to control the current fed to the batteries. Voltage monitoring is achieved by applying a proportion of the output voltage to the Voltage Accumulator input (pin 7). This is done by using S2 to select between one of two voltage divider circuits which connect across the battery. The valid input range for pin 7 is between 0.385V and 3.85V. The maximum charging time is set by switch S3 and its two associ- ated timing capacitors: 0.0018µF for 600mAH batteries and 0.0039µF for 1.2AH batteries. The two capacitors determine the frequency of the timing oscillator; the higher the capacitor value, the lower the frequency and the longer the charging time. The .0018µF capacitor sets the timeout period to 50 minutes, while the .0039µF capacitor sets the period to 100 minutes. Charge LED The TEA1100 uses only a single LED to indicate one of two charging states. When the charger is first switched on, the charge LED is on continuously, indicating that the circuit has gone into the main “fastcharge” mode. Once the circuit has decided that the batteries are charged, the LED flashes. This not only indicates “endof-charge” but also the rate at which the current pulses are being fed to the battery to maintain a “trickle” charge. This trickle charge will maintain the batteries in top condition after the main charging cycle has been completed. The charging current is regulated by the IC and the 2.2kΩ resistor between pin 5 and ground. This, along with the 0.1Ω 5W current sensing resistor on pin 16, sets the main charging cur­rent to just on 960mA. The main internal reference current is determined by the 27kΩ resistor connected to pin 10 and is set to approximately 45µA. In order to main maintain loop sta- RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 2 1 1 1 1 2 1 1 1 20  Silicon Chip Value 100kΩ 47kΩ 27kΩ 10kΩ 3.3kΩ 2.2kΩ 470Ω 100Ω 0.1Ω 4-Band Code (1%) brown black yellow brown yellow violet orange brown red violet orange brown brown black orange brown orange orange red brown red red red brown yellow violet brown brown brown black brown brown not applicable 5-Band Code (1%) brown black black orange brown yellow violet black red brown red violet black red brown brown black black red brown orange orange black brown brown red red black brown brown yellow violet black black brown brown black black black brown not applicable S3 PARTS LIST S2 5 2 3 4 A 1 6 LED1 K 470uF Q3 .0039 .0018 47k 2.2k 27k 0.1  5W Q2 1 2 LED1 A K 100  470  3 IC1 TEA1100 L1 4 5 6 1 680pF 100pF D2 2.2k 10k 100k ZD1 12V Q1 10uF 100k D1 3.3k S1 470uF OUTPUT Fig.3: install the parts on the PC board as shown on this wiring diagram, making sure that all polarised parts are correctly oriented. L1 consists of 60 turns of 0.5mm-diameter copper wire on a Neosid toroidal core. Fig.4: check your PC board against this full-size artwork before installing any of the parts. bility, an RC network consisting of a 47kΩ resistor and a 680pF capacitor is connected between pin 4 and ground. This ensures that no oscillation or “motor-boating” occurs by reducing the bandwidth of the circuit while still maintaining an adequate level of error voltage feed­back information. Construction All the parts for the Fast Nicad Charger, except for the three switches and LED 1, are installed on a PC board coded 11102941. Fig.3 shows the assembly details. Before installing any of the parts, it’s a good idea to check the board carefully for any shorts or breaks in the tracks by comparing it with the published pattern (Fig.4). If you do find any, use a small artwork knife or a dash of solder to fix the problem as appropriate. Begin the assembly by installing PC stakes at the external wiring points, then install the wire link, the resistors and diodes. Be sure to use the correct diode type number at each location and make sure that they are all correctly oriented. After that, you can install the MKT capacitors, the elec­trolytics and the 0.1Ω 5W resistor. Next, install the three transistors and the IC, again taking care with the polarity. Once these parts are in, a small finned heatsink should be attached to transistor Q2 using a 3mm machine screw and nut. The last component to go on the board is inductor L1. This is wound on 1 PC board, code 11102941, 102 x 56mm 3 SPDT toggle switches 1 plastic case, 137 x 60 x 42mm 1 micro-U heatsink 1 large black crocodile clip 1 large red crocodile clip 1 small black crocodile clip 1 small red crocodile clip 4 PC stakes 1 5mm LED bezel 1 front panel label 1 33mm OD toroidal core 1 2-metre length of 0.5mm diameter enamelled copper wire Semiconductors 1 TEA1100 battery monitor for nicad chargers (IC1) 2 BC337 NPN transistors (Q1,Q3) 1 TIP32C PNP power transistor (Q2) 1 1N4004 silicon diode (D1) 1 FR104 fast-recovery diode (D2) 1 9.1V 400mW zener diode (ZD1) 1 5mm green LED (LED1) Capacitors 1 470µF 16VW electrolytic 1 100µF 16VW electrolytic 1 10µF 16VW electrolytic 1 .0039µF 63VW MKT polyester 1 .0018µF 63VW MKT polyester 1 680pF 63VW MKT polyester 1 100pF 63VW MKT polyester Resistors (0.25W, 1%) 2 100kΩ 2 2.2kΩ 1 47kΩ 1 470Ω 1 27kΩ 1 100Ω 1 10kΩ 1 0.1Ω 5W 1 3.3kΩ Miscellaneous Screws, nuts, washers, hook-up wire. a Neosid toroidal core (Altronics Cat. L-5120) using two metres of 0.5mm diameter enamelled copper wire. Feed about one half of the wire through the middle on the toroid, then wind on about 30 turns, keeping the windings tight and close together. The other half of the wire can then be used to complete the winding. May 1994  21 screws and nuts, with an additional nut under each corner to serve as a spacer. This done, complete the wiring to the front panel items as shown in Fig.3. Make sure that switches S2 and S3 are oriented with respect to the LED exactly as shown (ie, the switch terminals connecting to points 1 & 6 on the PC board must be nearest the LED). You will also have to connect the power supply and output leads. These can be fitted with crocodile clips or terminated in some other suitable manner, depending on your power supply and the terminals on your nicads or their holder. Testing Once everything is in position, connect your multimeter (set to the 2A Plastic cable ties are used to secure the wiring to the two switches & to anchor range) in series with the power supply the large toroidal inductor to the PC board. Take care to ensure that switches and switch on. You should find that S2 & S3 are correctly oriented on the front panel – see text & Fig.3. the quiescent current measures about 5-10mA and that the LED is off. The exact number of turns is not for the two switches and the indicator If this checks out, set S2 and S3 to critical but you should find that you LED. It’s best to use a 3mm drill to match your nicad bat­tery pack and get about 60 turns on in total. begin with and then slowly ream the check that the output voltage is close Finally, trim off the excess lead holes to the correct size with a tapered to the mark – for two cells, it should be lengths, clean the wire ends and sol- reamer. somewhere around 2.4V and for four der the inductor into position on the The power switch (S1) is mounted cells it should be about 4.8V. board. The inductor can be anchored on one end of the case and an addiAssuming that the open-circuit using a plastic cable tie which feeds tional hole is drilled adjacent to this output voltage is correct, connect through a hole in the PC board – see to provide access for the power leads. the nicad pack to the output. You photo. A hole drilled in the opposite end of should find that the current drain the case is used for the battery output is now either about 600mA or 1.2A, Final assembly leads. In addition, you will have to depending on the setting of S3, and The board and its associated com- drill four mounting holes in the base that the LED is lit. ponents are in­stalled in a small zippy of the case for the PC board. Depending on how much charge is The various items of hardware can in the battery and the setting of S3, box measuring 137 x 60 x 42mm. First, attach the adhesive label to the lid of now be mounted in posi­tion and the the LED should stay on for some time the case, then drill out mounting holes PC board secured using 3mm machine (it could be as long as 50 minutes for “AA” cells” or 100 minutes for “C” or “D” cells) and then begin to flash. When this flashing begins, the current should drop CHARGE to about 10mA between flashes and rise sharply each time the LED lights. If the LED fails to light, check that it has been oriented 2 600 correctly. Now you can attack that FAST NICAD drawer full of nicad cells and CHARGER charge them up in quick time! Don’t forget though – if you 1200 4 want maximum performance mAH CELLS from your nicad cells, you should also build a discharger to discharge the battery pack to its correct end-point voltage Fig.5: this full-size artwork can be used as a drilling template for the lid of the case. SC before charging. Drill small pilot holes first, then carefully ream these to size. 22  Silicon Chip Simple drivers for radio control servos Build one of these simple servo drivers & you can run the devil out of your servos. You can use them for testing servos or for direct control applications where a radio link is not required. The circuit parts are cheap and readily available. By NENAD STOJADINOVIC As anyone who has been reading Bob Young’s excellent radio control column in this magazine will know, servos are the muscle behind any radio control system. These devices are a minor elec­tronic miracle: small, powerful and cheap, but until now have always been lumbered with a radio control system to drive them. Think of how useful they would be if you could drive them direct­ly from a simple pot or pair of pots controlled by a joystick. These were my thoughts, one dark and stormy night, as I was casting about for a good way of remotely controlling a pair of mirrors to be used in a laser light show. A quick perusal of some modelling magazines and the current circuit was born. After fashioning some suitable metalwork I 24  Silicon Chip 2.1ms 30ms soon had laser beams flying about the lab with gay abandon. Lately, I’ve been using servos in place of mechanical link­ages in my car and at around $20 per servo there is little in­ centive to fiddle around with cables, rods and so on. What’s more, running controls into areas of very high or low pressure is made easy by the availability of watertight bulkhead electrical connectors from your friendly local marine chandler. Anyway, whatever our field of endeavour, that old worn-out cliche about the applications are only limited by your imagina­tion must surely apply. So without further ado, on with the circuit. How it works The standard servo has three input This photograph shows the author’s prototype of the circuit featured in Fig.2. Note that the final version differs from this prototype in terms of board layout. 0.7ms Fig.1: the control signal for a servo consists of a continuous fixedfrequency pulse stream. The pulse width controls the servo position. pins and these are +5V (power), 0V (GND) and control. The control signal is a continuous pulse stream which is shown in Fig.1. It is important to note that the frequency of these pulses does not intentionally vary (it is not critical) and a period of between 20 and 50ms will do the job with most servos. The movement information is contained in the width of the pulses, which is why this sort of control system is referred to as Pulse Width Modulation (PWM). A pulse width of 0.7ms will usually give fully coun­ terclockwise movement and 2.1ms will give fully clock­wise rotation. This alternative version is based on the circuit shown in Fig.5. Once again, the final version differs in layout from this prototype – see Fig.6. 82k 11 180k 2 4 14 IC1a NE556 6 5 3 7 VR1 10k LIN Q1 100k VN10KM D 0.1 .01 G S 2.7k +5V PARTS LIST VR3 100k Circuit One (Fig.2) VR2 5k 100 .01 .01 10 13 0.1 .01 9 IC1b 12 DG S VIEWED FROM BELOW 1 PC board, code 09105942 1 556 dual timer (IC1) 1 VN10KM Mosfet (Q1) 1 10kΩ linear potentiometer (VR1) 1 5kΩ trimpot (VR2) 1 100kΩ trimpot (VR3) OUTPUT 11 8 .01 .01 0.22 Fig.2: the pulse frequency for the servo driver is derived using astable oscillator IC1a. Its output at pin 5 is differentiated & then used to trigger monostable IC1b via buffer stage Q1. VR1 varies the pulse width produced by IC1b. The duration of this output pulse is set by potentiometer VR1 which is calculated to give the required 0.72.1ms range. Taming the duty cycle As presented, the free-running oscillator has a duty cycle of about 60%, meaning that its positive output pulses will be about 18ms long. This is much longer than can be used to trigger the 556 monostable (IC1b), so some means had to be used to obtain short negative pulses. My solution was to differentiate the oscillator output and this produces a series of positive and negative spikes about zero volts at every transition. These spikes don’t have much energy and so are buffered by a Mosfet (Q1) which has a very high input impedance. Being an N-channel device, it only conducts on the positive pulses and so produces negative-going pulses at its drain (D). These pulses are coupled to pin 8 to trigger the mono­stable. It produces 100k VR2 1 +5V 1 PC board, code 09105941 1 4011 or 4001 quad gate package (IC1) 1 1N914 signal diode (D1) 1 0.1µF MKT capacitor 1 10kΩ linear potentiometer (VR1) 1 10kΩ trimpot (VR2) Resistors (0.25W, 1%) 1 1.8MΩ 1 1kΩ 1 150kΩ short positive pulses which can be set to vary between 0.7 and 2.1ms long. Building the circuit A small PC board was designed to accommodate the components and this is shown in Fig.4. With only a handful of components, construction is very simple. You could use a small piece of Veroboard as an alternative to a PC board. OUTPUT 0.1 GND 180k .01 VR1 Circuit two (Fig.5) Q1 0.1 2.7k IC1 556 82k VR3 Resistors (0.25W, 1%) 1 180kΩ 1 82kΩ 1 100kΩ 1 2.7kΩ 0.22 .01 100  The circuit to achieve this uses a free-running oscilla­ t or coupled to a monostable or “one shot”, as shown in Fig.2. It is based on a 556 dual timer which can be regarded as two 555 timers in the one package. The free-running oscillator has its frequency determining components connected to pins 1, 2 and 6 and these give a frequency of around 34Hz, corresponding to a period of about 30 milliseconds. The oscillator output is taken from pin 5 and it is used to trigger the monostable section of the cir­cuit. The monostable or “one shot” is the second half of the 556 and its pulse length is determined by the components connected to pins 12 and 13; ie, trimpots VR2 & VR3, control pot VR1 and the 0.22µF capacitor. The output pulse stream appears at pin 9. A monostable produces an output pulse of programmable duration each time it is triggered, the only proviso being that the trigger pulse must be of shorter duration than the output pulse. Capacitors 1 0.22µF MKT capacitor 2 0.1µF MKT capacitor 2 .01µF MKT capacitor GND Fig.3: install the parts on the PC board as shown in this diagram, taking care to ensure that the IC is oriented correctly. Fig.4: the full-size etching pattern for the PC board. It is coded 09105942 & measures 51 x 40mm. May 1994  25 SATELLITE SUPPLIES Aussat systems from under $850 +5V 1 4001 IC1a 2 1.8M 1.8M ON CONTROL VR2 10k FEEDHORNS C.BAND FROM .........$95 150k 150k 4 IC1b 8 9 IC1c 10 12 13 14 IC1d 11 1k OUTPUT 7 0.1 .01 D1 1N914 LNB’s Ku FROM ..............................$229 FEEDHORNS Ku BAND FROM ......$45 6 VR1 10k SATELLITE RECEIVERS FROM .$280 LNB’s C FROM .................................$330 5 3 Fig.5: this alternative circuit from Bob Young was originally featured in the April 1993 issue. IC1a & IC1b form an astable oscillator, with pulse width set by VR1, VR2 and the 0.1µF capacitor. DISHES 60m to 3.7m FROM ...........$130 0V +5V 1k 1 OUTPUT 0.1 IC1 4001 150k 1.8M VR2 D1 VR1 Fig.6 (left): the circuit of Fig.5 is assembled as shown in this diagram. Note that the output frequency also varies with this unit but not enough to affect servo operation. Fig.7 at right shows the full-size etching pattern for the PC board. LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 553 1763; Fax (03) 532 2957 26  Silicon Chip The lead for your particular servo can usually be obtained from any good hobby shop. If not, just ask who repairs that particular brand and call them. While you’re at it, find out how the servo pins are arranged; the manual might have the informa­tion. If not, it’s simply a matter of checking the output voltag­es from the receiver with a multimeter. Ground and +5V should be fairly obvious and the lead with some small voltage will be the control output. Adjustment The servo travel limits are adjusted by VR2 and VR3. VR2 should be the anticlockwise limit and this is set by moving VR1 fully anticlockwise and then adjusting VR2 so that the servo is not stalled. It is important not to stall servos because they will draw high currents and get very hot, ultimately burning out the motor. The clockwise limit is then set in the same way using VR3. Second circuit Having designed the above circuit, I then came across a small circuit from Bob Young that does the same job as mine! It was featured in the April 1993 issue of SILICON CHIP. The obvious solution, of course, was to present his circuit as well, complete with a PC board and the addition of the suggested trimpot, VR2. Bob’s version is shown in Fig.5 while the PC component wiring diagram is shown in Fig.6. Take care to ensure that the IC and diode are correctly oriented during the PC board assembly. This workings of this circuit are less apparent than the circuit shown in Fig.2 but essentially IC1a and IC1b are connected as a free-running oscillator with an uneven duty cycle. The pulse duration is mainly a function of VR1, VR2 and the 0.1µF capacitor. There is also an essential difference in its operation in that when you change the settings of VR1 to set the pulse output, the frequency changes too, although not markedly. However, this does not affect the servo operation at all and so the circuit is quite valid SC for test purposes. 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 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. Battery voltage indicator for cars Prevention is always better than cure and less expensive. This simple battery voltage indicator was devised after the alternator in my car failed during a long trip and the alternator warning light did not light. The circuit uses six LEDs (one yellow, three green and one red). Each LED is wired in series with a zener diode and a 680Ω current limiting resistor, and connected across the supply line. In addition, each zener diode has a slightly higher voltage than the preceding zener diode. Thus, the LEDs progressively turn on as the battery voltage increases from about 9.6V up to 15V. The circuit can be powered via the ignition switch. Table 1 shows how to interpret the display. When building the circuit, arrange the LEDs in a straight line – yellow on Light meter adapter for a DMM This light meter adapter may appear primitive but it works very well. If you already own a multimeter, its cost would be insignificant compared to that of a dedicated instrument. It can measure from 1 lux to 200,000 lux, which is comparable in range to the light from a candle at one metre to the light from the midday sun at the equator. As shown on the circuit, a BPW21 silicon blue photocell is used as the sensing element. This has a logarithmic open circuit voltage response but a very linear current response for short circuit current versus light intensity. Its internal impedance varies from 20MΩ at 1 lux to a few megohms at 100,000 lux. By using a load resistor which is small with respect to the internal impedance, the cell acts as a cur­rent generator over a limited range and we accept a tolerance of a few percent. 32  Silicon Chip +12V FROM IGNITION SWITCH ZD1 7.5V LED1 YELLOW ZD2 10V  ZD3 11VV LED2 GREEN 680   680  LED3 GREEN 680  ZD4 12V LED4  GREEN 680  ZD5 13V  LED5 RED  680  TO CHASSIS TABLE 1 Yel Grn Grn Grn Red o o o o o o o o o o o o o o Volt. Battery Condition 9.6V Low (engine off); normal when cranking 12V Normal if engine off; undercharge if engine running 13V Undercharge if engine running 14V Normal (engine running) 15V Overcharge o the left, greens in the middle and red on the right. That way, you can tell the state of the battery at a glance. Best of all, there are no transistors, ICs or x1000 BPW21  R x100 10R 10R capacitors to fail, so reliability should not be a problem. B. Paynter, Narrogin, WA. ($20) S1 x1 x10 100R 100R 1000R (SEE TEXT) TO DIGITAL MULTIMETER ON 200mV RANGE The digital multimeter must be set to the 200mV range. If the reading is in excess of 200mV, the next load resistor is selected and a multiplier used, in this case a factor of 10. The multimeter used must also have an input impedance of 10MΩ, so as to simplify load resistor selection, especially on the lowest range. The resistor value R is chosen by using the Sun for cali­bration. To do this, wire a 200Ω variable resistor across the cell, then select a clear sky between 11am and 2pm and direct the cell towards the Sun. Now measure the voltage across the resistor and adjust the resistor value until the reading is 100mV in winter, or 120mV in spring and autumn, or 140mV in summer (Melbourne latitude). This simple light meter adapter plugs directly into a DMM to give a reading directly in lux on the 200mV range. This done, remove the resistor from the circuit and measure its value. This becomes the x1000 multiplier load. The other loads are now arrived at by multiplying this value by 10 (for 100R), 100 (for 10R) and 1000 (for R). Select series-parallel combinations to give values that are within 1% of the calculated values and adjust the 1000R value to take account of the meter impedance. The cell gives a nominal current output of 7nA per lux, is sealed, has a response to colour that’s similar to the eye and is very stable. The current has a temperature coefficient of -0.05% per degree C, which is negligible in this application. Victor Erdstein, Highett, Vic. ($20) RLY1 12V REED +12V TO COMPUTER POWER SUPPLY 47 16VW 14 1 2 10 10k 10k DELAY TIME VR1 500k C1 10 16VW IC1d 10k RESET TIME VR2 500k C2 4 3 IC1a 74C14 RESET LED1 13  IC1b 1 14 RESET OUT (TO RESET ON MOTHER BOARD) 12 IC1e 11 2 1 16VW 2.2k 5 9 6 10 IC1f RESET IN (FROM COMPUTER RESET SWITCH) 6 8 7 8 7 IC1c Delayed reset for PCs & compatibles For various reasons, some computers do not boot up correctly when power is first applied. The error message on the screen usually does not help since it is often unrelated to the fault. Often the fault is only a minor one related to a reset malfunc­tion on the VGA board. This can be cured simply by pressing the reset switch just after power is applied, after which the computer behaves faultlessly. This circuit was developed to provide a reset signal to the computer soon after power is first turned on. This provides the desired effect of a hard reset without having to reset manually. The extra time taken for the computer to boot up is minimal, since the delay between power on and resetting can be adjusted to a minimum of about one second. The circuit is powered by the +12V supply rail inside the computer. The reset lines from the circuit then con- nect in paral­lel with the lines to the reset switch on the computer’s front panel. A 10Ω resistor and 47µF capacitor isolate and decouple the +12V supply from the computer. Initially, capacitor C1 is dis­charged and the output of Schmitt trigger IC1a is high. The input of IC1b is also high and so its output is low. The paralleled inverters, IC1d-IC1f, have high outputs and the relay is off. The normally open relay contacts of RLY1 are connected in parallel with the reset line to the computer. When capacitor C1 charges up to the threshold voltage of IC1a, via VR1 and the 10kΩ resistor, the output of IC1a goes low. This pulls pin 1 of IC1b low via capacitor C2 and pin 2 goes high. The low outputs of IC1d-IC1f drive the coil of relay RLY1 and its contacts now close to provide a reset signal to the reset line. IC1c drives LED 1 to indicate the reset. Capacitor C2 now charges up to the positive supply via VR2 and the 10kΩ resistor, thus sending the output of Six-way decision maker uses two ICs This circuit will give a decision on just about anything. When S1 is pressed, its associated 4.7µF capacitor is charged to the positive supply rail and 555 timer IC1 starts. This in turn clocks IC2, a 4017 decade counter, so that, initially, the LEDs are rapidly cycled on and off. The 4.7µF capacitor now slowly discharges via its associat­ed 560kΩ resistor and pin 7 of IC1. As it does so, the 555 timer frequency decreases until eventually it stops and no further clock pulses are applied to IC2. This means that the LEDs gradu­ ally slow down Schmitt trigger IC1b low. RLY1 and LED 1 now switch off. Note that the relay is a reed type which only draws 12mA of coil current. Because the coil is internally clamped with a diode, the voltage polarity applied to the coil is important. Trimpots VR1 and VR2 set the delay time and reset time respectively. The delay time is adjusted so that the computer is reset a certain time after power is applied. This time must be long enough to ensure that the computer boots up successfully. The delay time is adjusted to be about 100ms or longer which should be sufficient time to reset the computer. Resetting times can be seen by observing LED 1. Note that if your computer does not have a spare power cable to obtain +12V for the circuit, you can buy a power split­ter cable from Dick Smith Electronics (Cat. X-2064). The relay is available from Jaycar Electronics (Cat. SY-4032). John Clarke, SILICON CHIP. +9V 100 S1 4.7 4.7M 560k 7 33k 4 8 IC1 555 6 2 6xLED 16 3 2 3 14 5 1 .047 .01 7    10 15 5 1 8 until only one remains lit, to give a decision. The LEDs can be marked in any way; eg, yes, no, maybe, perhaps, go  4 IC2 4017 13   1k and stop. Alternatively, the circuit could serve as an electronic die. S. Tsilomanis, Reservoir, Vic. ($15) May 1994  33 Build an induction balance metal locator res Main Featuerate. ild & op Easy to bu wet or r use over Suitable fo c lu d in g b e a c h d , in d ry gro u n . sand ground to exclude • Adjustment effects. control. • Sensitivity head­ ication via • Audible inlodudspeaker output phone or l detected. when meta uency ases in freq rch ea s • Sound incre r e d oves un as metal m head. le for nced hand • Counterba. la ease of use • • 34  Silicon Chip Most do-it-yourself metal locators are difficult to build & operate but not this one. This unit is a cinch to put together & is just the shot for finding coins, rings, watches & other valuable metallic items. By JOHN CLARKE Of course, as well as finding those more mundane items, a metal locator can also be used to locate the metal of our dreams – GOLD! But let’s be realistic; not many of us are ever going to strike it rich on the goldfields, although metal locators have detected large nuggets for a few lucky prospectors. No, a metal locator is more likely to be used for fun and any profits made from finding coins or jewellery are likely to be quite modest. Then again, you never know what might be hidden under the next few square metres of beach sand. The big advantage of a metal locator is that it saves lots of digging. One only has to dig in locations where the metal locator indicates the presence of metal. Of course, not all finds will be of any value except maybe for the recyclers of cans and scrap aluminium. To overcome this problem, some metal locators incorporate controls which discriminate against various types of metals (eg, ferrous metals) which are likely to be of little value. Taken to the extreme, the ultimate metal locator would find only things of value. As expected, metal locators which can discriminate against unwanted metals are usually expensive and can be extremely com­plicated to use. They are best left for experienced prospectors. The SILICON CHIP Induction Balance Metal Locator is not a discriminating type and is very easy to use. In fact, there are just three control knobs: Volume, Ground and Sensitivity. The first control sets the volume of the output from the loudspeaker or headphones. The second control (Ground) is the most frequently used – it adjusts the sound from the loudspeaker so that it produces a low frequency growl when the search head is positioned over the ground. The frequency will then increase sharply when metal is detected. The final control adjusts the sensitivity of the unit and sets the maximum depth at which an object will be detected. VR3 80kHz OSCILLATOR Q1 TRANSMIT COIL 3V BATTERY SUPPLY IC1b DC LEVEL (GROUND SET) RECEIVE COIL Q2 AMPLIFIER FILTER RECTIFIER VOLTAGE STEPUP IC3 +8.8V SUPPLY GAIN VR2 IC1a AMPLIFIER VCO IC2 AMPLFIER IC1d Q3,Q4 HEADPHONE OR LOUDSPEAKER Fig.1: this block diagram shows the main circuit elements of the Induction Balance Metal Locator. The output from the receive coil assembly is rectified, filtered & amplified by IC1a. IC1a in turn controls the output frequency from voltage controlled oscillator (VCO) IC2. IC1b & VR3 set the DC bias on IC1a to null out ground effects. The handle assembly for the prototype was made from 20mm-diameter electrical conduit, while the search coil assembly is fitted to a baseboard which is attached to a plastic dinner plate. Operating principle Most simple metal locators operate on the principle of beat frequency oscillation (BFO). In this type of design, the search coil is used as the inductive component of an oscillator. When a metallic object is brought near the coil, the frequency of the oscillator changes slightly due to the resulting change in the coil’s inductance. This frequency change is detected by mixing the oscillator frequency with a fixed frequency to produce an audible beat. It is often claimed that BFO metal locators are able to detect the difference between ferrous and non-ferrous metals. This is because the inductance of the search coil increases with ferrous metals and decreases with non-ferrous metals, correspond­ing to decreasing and increasing beat frequencies respectively. In practice, however, the audible beat can also increase for ferrous metals since eddy current flow in the iron often masks out the effect of increasing Typical Detection Distances $2 coin 170mm 10¢ coin 200mm Tin can 400mm Wedding ring 150mm May 1994  35 +8.8V L3 TP1 GND TP1 7 6 5 10 IC1c IC1a A B 22k .001 RECEIVE COIL L2 .0039 +7V 33k .015 22k B 1k E .0056 C Q1 BC547 100k L1, L2 : 50T, 0.6mm ENCU, 115mm DIAMETER L3 : 33T, 0.4mm ENCU ON NEOSID 17-732-22 TOROID 1k .022 B GROUND RANGE VR1 1k Q2 BC548 0.1 100  0.1 .01 D1 1N4148 12 GROUND VR3 10k LIN 100k 0.1 TRANSMIT COIL L1 36  Silicon Chip E C VIEWED FROM BELOW 330k D2 1N4148 IC1b LM324 13 4 14 0.1 K 390  9 SENSITIVITY VR2 100k LIN +7V 1 11 33k 8 9 VCO IN 3 5 IC2 4046 8 11 7 10k .068 6 VCO OUT 15 14 16 +7V ZENER 4 100 16VW VOLUME VR4 10k LOG 3V INDUCTION BALANCE METAL LOCATOR 220 16VW POWER S1 3 2 100  IC1d 1 330 16VW 100  2 6 7 IC3 TL496C 5 Q4 BC328 B B Q3 BC338 8 POWER LED1 C E E C 0.1 47 16VW 2.7k A K  8W SPEAKER +8.8V HEADPHONES ▲ Fig.2: the final circuit is built around just three ICs. The transmit coil forms a tuned collector load for oscillator stage IC1a & its output is coupled into receive coil L2 which is positioned for minimum pickup in the absence of metal. L2’s output is amplified by common emitter stage Q2 & rectified by D1 & D2 before being fed to amplifier stage IC1a which then drives the VCO. The output of the VCO appears at pin 4 & drives audio amplifier stage IC1d, Q3 & Q4. inductance. It is therefore impossible to discriminate between the two different types of metal. By far the biggest disadvantage of the BFO technique is that the search coil must be shielded with a metal screen to prevent reaction with the ground. This significantly reduces the sensitivity of the BFO type metal locator, which means that small objects buried in a few centimetres of soil can easily be missed. To eliminate this problem, the SILICON CHIP metal locator uses a completely different operating principle. Unlike the BFO type, it uses two coils in the search head, with one coil driven by an oscillator. The second coil is used to pick up signal from the first. During construction, the two coils are positioned in an overlapping fashion so that the second coil has minimum pick-up. When metal is introduced, however, the signal level in the second coil increases. This increased level is detected and the result­ing signal used to drive circuitry to provide an audible indica­tion that metal is present. This principle of operation is called “Induction Balance” (also known as “Transmit Receive) and it provides a far more sensitive metal detector than the BFO type. Its only disadvan­tage is that the two coils must be carefully aligned during construction. The depth to which the metal locator can detect metals under given conditions is set by the search head coil diameter. The larger the diameter, the deeper it will detect. However, large search coils suffer from lack of pinpoint accuracy in finding metals. We opted for a medium-sized search head which provides a good compromise between accuracy and depth. Of course, there’s nothing to stop you from experimenting with larger search heads if depth is important. Block diagram Fig.1 shows the block diagram of the Induction Balance Metal Locator. An oscillator operating at about 80kHz drives the transmit coil and signal from this is picked up by the receive coil. Amplifier stage Q2 boosts the signal output from the re­ ceive coil and the signal is then rectified and filtered to produce a smooth DC voltage. IC1a amplifies the DC voltage from the filter. Its output is offset by a DC voltage provided by IC1b and this, in turn, is set by potentiometer VR3 (the Ground control). In operation, VR3 is set so that the DC output from IC1b is equal to the DC voltage from the filter, so that IC1a’s output normally sits close to 0V (this is done to cancel out ground effects). When the search coils are brought near metal, the signal level in the receive coil increases. This results in a higher DC voltage at the output of the filter and this is then amplified by IC1a to produce a control voltage for the following VCO (voltage controlled oscillator stage). When IC1a’s output is at 0V (ie, no metal is present), the VCO is off and no signal is produced. Conversely, as the search coils are moved closer to metal, IC1a’s output rises and the VCO increases its output frequency from 0Hz to about 4kHz. This signal is fed to an amplifier stage (IC1d, Q3 & Q4) and the resulting output then fed to a loudspeaker or a pair of head­phones. Circuit details Refer now to Fig.2 for the circuit details. Q1 and its associated components form the transmit oscilla­tor. This stage oscillates by virtue of the tuned collector load provided by coil L1 and the .0056µF positive feedback capacitor between collector and emitter. The 1kΩ emitter degeneration resistor provides a small amount of DC negative feedback to reduce sinewave distortion and provide a stable bias point. The signal in L1 is coupled to receive coil L2. This latter coil is aligned with L1 so that the induced signal is normally at a minimum. The .0039µF capacitor across L2 forms a resonant circuit to ensure maximum pickup sensitivity. PARTS LIST 1 PC board, code 04305941, 159 x 83mm 1 front panel label, 90 x 180mm 1 plastic case, 190 x 100 x 40mm 1 2-metre length of 20mm-dia. electrical conduit 3 90-degree 20mm conduit elbows 3 20mm conduit U-clamps 1 20mm conduit joiner 1 50mm-long spring toggle bolt 1 180mm diameter plastic dinner plate (eg, Decor #459) 1 180mm diameter x 3mm Masonite sheet (or equivalent material) 1 37-metre length of 0.6mm enamelled copper wire 1 660mm length of 0.4mm enamelled copper wire 1 100mm length of 0.8mm tinned copper wire 1 1.5-metre length of dual shielded cable 1 miniature SPDT toggle switch (S1) 1 1kΩ miniature horizontal trimpot (VR1) 1 100kΩ linear pot (VR2) 1 10kΩ linear pot (VR3) 1 10kΩ log pot (VR4) 1 Neosid iron powder toroidal core 17-732-22 2 C-cell holders 2 1.5V C cells 1 6.5mm mono headphone panel socket with switch 1 27mm mini 8Ω Mylar loudspeaker 1 3mm red LED (LED1) 16 PC stakes 4 4BA x 25mm Nylon screws, nuts & washers The resulting signal from L2 is AC-coupled to the base of Q2 which is configured as a common emitter amplifier. Its DC bias is set by the 33kΩ and 22kΩ base resistors. The output from this stage is taken from the wiper of VR1 which allows the signal level to be adjusted from maximum (at the collector of Q2) down to full attenuation (ie, when the wiper is at the +7V rail). Following VR1, the level-adjusted 5 6BA x 25mm Nylon screws, nuts & washers 4 3mm x 5mm screws 8 2mm x 10mm screws & nuts 2 self-tapping screws 1 12mm OD rubber grommet 3 20mm OD knobs 1 75-gram tube of neutral cure silicone sealant (eg. Selleys Roof and Gutter Sealant) 1 container of conduit glue Semiconductors 1 LM324 quad op amp (IC1) 1 4046 phase lock loop (IC2) 1 TL496C 1.5V-9V converter (IC3) 2 BC548 NPN transistors (Q1,Q2) 1 BC338 NPN transistor (Q3) 1 BC328 PNP transistor (Q4) 2 1N4148, 1N914 diodes (D1,D2) Capacitors 1 330µF 16VW PC electrolytic 1 220µF 16VW PC electrolytic 1 100µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 5 0.1µF MKT polyester 1 .068µF MKT polyester 1 .022µF MKT polyester 1 .015µF MKT polyester 1 .01µF MKT polyester 1 .0056µF MKT polyester 1 .0039µF MKT polyester 1 .001µF MKT polyester Resistors (0.25W, 1%) 1 330kΩ 1 2.7kΩ 2 100kΩ 2 1kΩ 2 33kΩ 1 390Ω 2 22kΩ 3 100Ω 1 10kΩ signal is AC-coupled to the rectifier stage (diodes D1 and D2). The resulting DC output voltage from this stage is then filtered by the 0.1µF capacitor and applied to the non-inverting inputs of IC1c and IC1a (pins 5 & 10 respectively). The 330kΩ resistor provides a discharge path for the capacitor. IC1c functions as a unity gain buffer. Its output at pin 7 provides a convenient test point (TP1) for measuring May 1994  37 Fig.3: the PC board assembly is straightforward but make sure that all polarised parts are correctly oriented. Inductor L3 is made by winding 33 turns of 0.4mm enamelled copper wire on a small iron-powdered toroid. VR2 VR3 3 2 1 8 7 S1 VR4 Q3 330uF 100  2.7k 0.1 22k 100k 1 100uF 1k TP GND 0.1 100  D1 0.1 22k VR1 .022 8 .01 .001 33k 7 Q2 390  33k 330k 1k D2 0.1 A K LED1 10k .015 .0039 6 IC2 4046 1uF TO L2 38  Silicon Chip .068 IC1 LM324 .0056 the output of the rectifier during the setting-up procedure. IC1a is wired as a non-inverting amplifier with DC gain adjustable from 85 to about 340 using Sensitivity control VR2. The 1µF feedback capacitor between pins 8 & 9 rolls off the AC gain for frequencies above 5Hz at the low gain setting of VR2, and above 1Hz for the high gain setting. This roll-off reduces noise at the output of the amplifier. IC1b functions as a buffer stage for the DC voltage set by VR3 at its wiper. This pot sets the DC voltage offset for IC1a and functions as the Ground control. Note that its voltage range has been restricted by connecting a 100kΩ resistor in series with it, to make the setting less critical. The output from IC1a appears at 5 4 1 TP1 Q1 Q4 100  220uF 1.5V CELL 47uF L3 IC3 TL496 1.5V CELL SPEAKER 0.1 1 TO L1 6 5 4 100k pin 8 and drives the VCO input of IC2, a 4046 phase lock loop IC. In this circuit, we are only using the VCO section of the phase lock loop. The oscillator output appears at pin 4 and varies in frequency from 0Hz when pin 9 is at 0V to about 4kHz when pin 9 is at 7V. This upper frequen­cy is set by the 10kΩ resistor at pin 11 and the 0.068µF capaci­tor between the pins 6 & 7. The output signal from the VCO is fed to Volume control VR4 and thence to buffer stage IC1d. IC1d in turn drives complementary transistor pair Q3 and Q4, which act as high current drivers for the headphones or loudspeaker. Power for the circuit is derived from two 1.5V “C” cells connected in series to provide a 3V rail. This 3V rail is boosted to 8.8V using IC3, a TL496 1 2 3 HEADPHONE SOCKET low-voltage switchmode IC. LED 1 provides power on/off indication. IC2 has an internal 7V zener diode at pin 15 and this regu­lates the supply to 7V for the majority of the circuit. The audio amplifier output stage (Q1 & Q2) is powered directly from the 8.8V rail, however. Note that the 8.8V supply from IC3 is main­tained until the battery output drops below 2V. Construction A PC board coded 04305941 is used to accommodate most of the parts, including holders for the two 1.5V “C” cells. This board fits neatly into a plastic instrument case measuring 190 x 100 x 40mm and this is attached to the top of a long carrying handle. The coil assembly mounts at the other end of the handle – see photos. Fig.3 shows the board assembly details. The order of assem­bly is not critical but make sure that all polarised parts are correctly oriented. These parts include the ICs, transistors, diodes, LED and electrolytic capacitors. Note particularly that three different transistor types are used on the board, so be careful not to get them mixed up. LED 1 is mounted with its leads left untrimmed so that it can later be pushed into its mounting hole in the top end panel. Table 1 shows the resistor colour codes but it’s also a good idea to measure the resistor values on your DMM since some colours can be difficult to decipher. Once these parts are in, fit PC stakes to all external wiring points on the board. Coil L3 is made by winding 33 turns of 0.4mm enamelled copper wire onto a small iron-powdered toroid. Wind each turn adjacent to the previous turn and secure the completed toroid to the PC board using a Nylon screw, washer and nut through the centre hole. This done trim the leads to length and tin them with solder before connecting them to the board. Note: the wire is self-fluxing and requires heat from your soldering iron to melt back the enamel. The two “C” cell holders are secured to the PC board using 2mm screws and nuts at each corner. Use the battery holders as templates to mark out the holes on the PC board, then drill the holes and mount the holders in position. Make sure that the holders are oriented with the correct polarity and note that they face in opposite directions to each other – see Fig.3. The terminal ends of each holder are connected to the PC board using short lengths of 0.8mm tinned copper wire. The PC board can now be installed in the base of the case and secured using 3mm screws which tap into the integral corner standoffs in the case. This done, attach the label to the lid of the case and drill out the holes for the control pots and power switch. These parts can now be mounted in position and firmly secured using their lock nuts. The top end piece of the case must be drilled to accept the headphone socket and LED, and to make a speaker grill. This grill consists of a nine 3mm holes directly in front of the speaker COIL BASE-BOARD 180mm DIA. x 3mm THICK MASONITE OR SIMILAR RECEIVE COIL L2 TRANSMIT COIL L1 155mm DIA. SHIELDED LEADS Fig.4: this diagram shows how the two coils in the search head are mounted on the baseboard. Adjust L2 for a signal null in the absence of metal by following the procedure described in the test. This view shows the search head assembly after the two coils have been secured to the baseboard using neutral cure silicone sealant. May 1994  39 TOGGLE SCREW SPRING LOADED TOGGLE NUT JOINER END (SLIDE OVER TOGGLE WHEN SCREW IS STARTED) 11 MASONITE COIL CARRIER 185mm PLASTIC PLATE ANGLE BRACKETS, CONDUIT AND PLATE ASSEMBLED WITH 4BA NYLON SCREWS, NUTS AND WASHERS COMPRESS END OF CONDUIT TO 10mm ANGLE BRACKET FASHOINED FROM 'U' CLAMP 1280 10mm DIA. HOLE THROUGH CONDUIT ° 90ø ELBOW Fig.5: follow these mechanical details when making up the handle & search coil assemblies. Note that no metal parts can be used near the search coils (use plastic brackets & nylon screws & nuts instead). JOINER END 'U' CLAMPS CASE DIMENSIONS IN MILLIMETRES 19mm PLASTIC CONDUIT Search head 415 10 40  Silicon Chip cone. Deburr the holes using an oversize drill, then smear sili­cone sealant around the edge of the speaker and attach it to the panel. The hole for the LED should also be drilled to 3mm, so that the LED is a tight fit. The bottom end piece of the case is drilled with a single centre hole. This hole is fitted with a small rubber grommet and accepts the shielded cable that runs between the PC board and the two search coils. Use light-duty hookup wire when wiring up the potentiome­ters, head­ phone socket, loudspeaker and on/ off switch – see Fig.3. The figure-8 shield­ed cable that runs to L1 and L2 can also be connected to the PC board at this stage. It’s now time to do a couple of quick operational tests on the assembly so far. To do this, install the two “C” cells and switch on the power. Check that the LED lights (if it doesn’t, it’s probably wired incorrectly) and that pin 8 of IC3 measures 8.8V with respect to the TP GND pin. Check also that the voltage at pin 15 of IC2 measures about 7V. If these voltages are not within 10% of the nominated val­ues, check the circuit for faults and clear the problem before proceeding further. The search head, which consists of coils L1 and L2, is the critical part of the construction. As indicated previously, these two coils must be carefully aligned in order to ensure that the metal locator functions correctly. Fig.4 shows the mounting details for L1 and L2. Each coil is wound using 50 turns of 0.6mm enamelled copper wire on a 115mm diameter former. After winding, wrap each coil tightly with two layers of insulation tape (note: the wire ends should exit from the same position). The two coils are mounted on a sheet of Masonite which is cut to form a disc 180mm in diameter. Before mounting the coils, draw a 115mm-diameter circle on one side of the mounting sheet, then drill a hole in the centre to take a 4BA screw. The two coils can now be bent to shape and positioned as shown in Fig.4. The two coils must now be carefully aligned to ensure mini­ mum signal pickup in L2. This is done as follows: (1). Temporarily connect the shield­ The battery holders are each secured to the PC board using four small machine screws & nuts. Twist the leads to the front panel controls as shown & bind them with a cable tie to minimise the chances of a lead coming adrift. ed cable to the coils and make sure that the assembly is well away from any metal items. (2). Connect a voltmeter between TP1 and TP GND on the PC board and apply power. Rotate VR1 (Ground) fully clockwise and check for a high-frequency tone from the speaker if the volume control is wound up. If no tone is present, rotate the Ground and Sen­sitivity controls fully clockwise and adjust L1 and L2 until there is a tone. If no tone can be obtained, check the PC board for wiring faults. (3). Turn down the volume and adjust L2 relative to L1 for a minimum reading on the voltmeter. This should be somewhere bet­ween 0.8V and 1.2V. You will need to bend the coils at the L1 and L2 intersection in order to obtain the lowest DC voltage at TP1. Note that the coils should not go outside the 155mm diameter limit. (4). Check that the voltage at TP1 increases if a piece of metal is now brought close to where the coils intersect. If the voltage falls, move the coils together until the voltage rises when the metal object is introduced. (5). Turn up the Volume and adjust the Ground control for a low-frequency growl when no metal is near the coils. Now check that the tone frequency increases when metal is brought near the coils. Once you are satisfied with the coil locations, they can be secured in position with silicone sealant. This process will take time, so do not rush the job. First, unsolder the shielded cable and secure the transmit coil (L1) in position flat on the mounting plate. The receive coil (L2) can then be secured as well, but only around the 115mm diameter perimeter section. Do not apply any sealant to the overlapping May 1994  41 The case containing the electronic circuitry is mounted near the top of the handle as shown here. Note the holes drilled in the end panel to allow the sound to escape from the loudspeaker. section of L2 at this stage so that you can make fine adjustments later on when the rest of the sealant has dried. This means leaving the assembly for at least 24 hours. Mechanical details Fig.5 shows the general mechanical details of the entire metal locator assembly. It uses 20mm-dia. electrical conduit and 90° elbow sections for the handle assembly, while the search coil assembly baseplate is attached to a plastic dinner plate. Two plastic right-angle brackets are used to secure the plastic plate to the handle. These two brackets are made by cutting the curved section out of a U-clamp and then drilling holes in the brackets to accept 4BA Nylon screws. Note: metal parts must not be used anywhere near the search coil assembly. The next step is to compress the end of a 1280mm length of conduit in a vyce until it is 10mm thick. Once this has been done, the right angle brackets can be attached to the conduit using a 25mm-long Nylon screw and the brackets then used to mark out their mounting holes on the plastic plate – see Fig.5. Drill these holes to size, along with a further hole exactly in the centre of the plastic plate. You will also have to drill a couple of holes in the side of the plate (in line with the handle) to accept the leads from the shielded cable. The plastic plate can now be fastened to the right angle brackets using 4BA Nylon screws and nuts. Cut off Fig.6: this is the full-size etching pattern for the PC board. Check the board for defects before installing any of the parts. 42  Silicon Chip any excess screw lengths using a sharp knife or sidecutters. The other sections of conduit can now be cut to size and assembled as shown in Fig.5. Note that the bottom end of the top handle section is se­cured to the main section using a toggle screw (see detail). Shape the end with a round file so that it mates neatly with the main section, then drill the holes to accept the toggle screw and its spring-loaded nut. This done, cut a sleeve from one end of an elbow piece and slide this over the shaped end of the top handle section so that it clears the 10mm holes. The toggle screw can now be installed and the sleeve slid down over the 10mm holes after the nut is started. When the screw is tightened, the ends of the toggle should catch on the bottom edges of the 10mm holes to provide a secure assembly. Once the basic handle assembly is completed, the instrument case can be attached to it using two plastic U-clamps. Note that the bottom clamp goes over a sleeve which is cut from the other end of the elbow piece mentioned above. The top clamp goes over the sleeve on the end of the adjacent 90° elbow piece. Use the U-clamps to mark out the holes on the bottom of the case, then remove the PC board and drill the holes to accept 6BA Nylon screws. This done, mount the case in position, remove the excess screw lengths and remount the PC board. The U-clamps are secured to the handle using self-tapping screws. The next step is to drill a hole in the handle just below the instrument case and another in the bottom of the handle adja­cent to the search head. The bottom end of the handle is compressed to about 10mm thick by squeezing it in a vyce. It is then attached to the cover plate using two plastic right-angle brackets & Nylon screws & nuts. This photograph shows how the case assembly is secured to the handle using two U-clamps. The sleeve under the bottom U-clamp is obtained by cutting it from one end of a 90° elbow piece. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 2 2 2 1 1 2 1 3 Value 330kΩ 100kΩ 33kΩ 22kΩ 10kΩ 2.7kΩ 1kΩ 390Ω 100Ω 4-Band Code (1%) orange orange yellow brown brown black yellow brown orange orange orange brown red red orange brown brown black orange brown red violet red brown brown black red brown orange white brown brown brown black brown brown 5-Band Code (1%) orange orange black orange brown brown black black orange brown orange orange black red brown red red black red brown brown black black red brown red violet black brown brown brown black black brown brown orange white black black brown brown black black black brown May 1994  43 and adjust the Ground control for a low-frequency growl when no metal is near the coils. (2). Adjust the receive coil (L2) by bending it over the transmit coil (L1) until the voltage at TP1 is at a minimum (this gives the correct null point). (3). Disconnect the shielded cable again and fully secure L2 by applying additional silicone sealant. Wait until this sealant dries, then reconnect the shielded cable leads and cover the connections with insulation tape. Use a final coating of silicone sealant to secure the leads. (4). When the sealant has fully dried, attach the search coil assembly to the plastic cover plate lid using a 4BA Nylon screw and nut. Finally, run some silicone sealant around the edge of the plate to produce a watertight assembly. INDUCTION BALANCE METAL LOCATOR POWER SENSITIVITY Using the metal locator ON . . VOLUME . . . . . + . . . . . . . . POWER . . + . . . . . . + . . . . . HEADPHONES . . GROUND . . . + OFF SPEAKER Fig.7: this full-size artwork can be used as a drilling template for the front panel or used to make your own label. The shielded cable can now be fed down the inside of the conduit and out through the bottom hole, at which point it is separated and the leads connected to the coils. Make sure that each lead goes to its designated coil. If you get the leads transposed, the performance will be compromised. Finally, the conduit fittings can be 44  Silicon Chip glued with PVC adhe­sive and allowed to dry. Assuming that the silicone sealant on the search coils is dry, you are now ready for the final alignment procedure. The step-by step procedure is as follows: (1). Connect a voltmeter between TP1 and TPGND on the PC board and apply power. Turn up the Volume Once the sealant has fully cured, the metal locator is ready for use. You can hold the metal locator with one hand near the lower section of the handle, at the balanced position, and the other hand near the top end of the handle. The search head should be swivelled so that it is parallel to the ground. Adjust the Ground control so that the sound is just a low frequency growl and sweep the search head across the ground. When metal is located, the frequency will increase. Normally, the sensitivity control will be set at its maxi­mum. However, in some cases, the sensitivity may need to be reduced if, for example, the ground is mineralised or if you only want to find larger objects. VR1 is normally set to maximum (ie, fully clockwise). It should only be adjusted if the Ground control needs to be set almost fully anticlockwise to obtain a low-frequency tone (it’s just a case of adjusting VR1 to provide a reasonable range for the Ground control). Finally, note that the Ground control will have to be read­justed for changes in ground composition (eg, if you go from dry sand to wet sand), or if the distance between the search head and ground changes. For this reason, it’s best to keep the search head at a consistent height. That said, the unit is extremely easy to use and you’ll soon get the hang of it by practising SC on a few metal coins. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au 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 May 1994  53 If you’re always losing the Monopoly dice, then this could save you several hours of guests climbing the walls! It uses just four CMOS ICs, has auto power-off & even imitates the dice face! Build this Dual Electronic Dice By DARREN YATES There’s no doubt about it! Whenever you go looking for your favourite board game, the odds are that the dice have been pinched for use somewhere else or are just plain missing. There are few more ugly scenes in life than a room full of guests, a Monopoly board and NO dice! So before your guests start looking for a likely piece of rope, a roof beam and a chair, you can either somehow produce two dice or pull out your newly-built piece of electronics! Not only will you save your skin but you’ll be able to wow them with your skill and expertise. This electronic dice uses just four CMOS ICs, 14 LEDs and a handful of other components. It runs from a 9V battery and au­ tomatically switches itself off 30 seconds after use. You simply press the button and the dice start “rolling”. Once you let the button go, the dice then begin to slow down and finally come to rest on one of six “faces”. Both dice are inde­pendent of each other so there’s no chance of ending up with “doubles” all night. Circuit diagram Let’s take a look at the circuit dia- The button in the middle of the circuit board controls the roll of the dice. You can mount the LEDs on the circuit board as shown here, or mount them on the lid of a case & connect them to the PC board via flying leads. 54  Silicon Chip gram – see Fig.1. The four ICs are two CMOS 4015 dual 4-bit shift registers and two CMOS 4093 quad 2-input Schmitt-triggered NAND gates. If you look carefully, you’ll see that there are two identical halves to the circuit, both controlled by pushbutton switch S1. Starting off, when the ROLL button S1 is pressed, the 33µF capacitor is shorted while the 47µF capacitor is shorted via diode D3. Once S1 is released, both capacitors begin to charge via their associated resistors to the 0V rail. However, they do so independently. Because the time constant of the 33µF capacitor and its 68kΩ resistor is less than the 47µF capacitor and its 1MΩ resistor, the voltage at the anode of diode D3 will always be lower than that on its cathode. This is important, as we’ll explain later. Pressing switch S1 also allows the .01µF capacitors con­ nected to the inputs of IC1a and IC3a to be charged via their associated 1MΩ resistors. Looking at just IC1a for the moment, these components along with the 10kΩ resistor and diode D1 make up a Schmitt trigger oscillator with a difference. As the 33µF capacitor charges, it also supplies current through the 1MΩ resistor to charge the .01µF capacitor. This happens quite rapidly and once the capacitor voltage rises above IC1a’s threshold, its output at pin 4 goes low. Diode D1 now becomes forwardbiased and discharges the capacitor through the 10kΩ resistor. Once the D1 1N914 10k 1M 5 6 .01 .01 ROLL S1 33 14 7 470 16VW 4 9 IC1a 4093 7 IC2a C 4015 R 10k 8 6 47 1k 14 LED4 IC1c 13 1k A 11 .01 .01 D3 1N914 68k 5 Q0 D LED5 12 A  LED6  LED7 K IC1b 3   K YELLOW 10 1M 9V +9V 15 16 D 13 Q0 1 12 C IC2b Q1 11 Q2 R IC1d 1 2 9 8 1.5k 1.5k 1k A LED1 YELLOW A  K LED2 YELLOW  LED3 YELLOW  K +9V D2 1N914 10k 10k 1M 1 2 .01 .01 14 7 3 9 IC3a 4093 7 IC4a C 4015 5 Q0 D 15 16 D 13 Q0 1 12 C IC4b Q1 11 Q2 R R 10k 8 6 1k 14 4 .01 .01 IC3c 5 LED12 RED 6 K 10 11 IC3b 9 1.5k 1.5k K LED13 RED   LED14 RED  K 8 1k A LED8 RED A  K LED9 RED  LED10 LED10  RED DUAL LED DICE K Fig.1: the circuit uses two identical sections. IC1a & IC1b form free running oscillators & these clock 4-bit shift registers IC2a & IC2b respectively. These then clock IC2b & IC4b (via IC1b & IC3b) to drive the LEDs (LEDs 1-7 & LEDs 8-14). capacitor voltage falls below the lower threshold of the gate, its output swings high again, forcing the diode off and allowing the capacitor to once again charge via the 1MΩ resistor. While this all happens though, A  IC3d 13 12 A 1k A LED11 LED11 RED the voltage at the negative end of the 33µF capacitor is slowly dropping as it charges up. This means that there is less current flowing through the 1MΩ resistor to charge the .01µF capacitor so that it takes longer and longer to charge up. The end result is that the short negative-going pulses from the output of IC1a take longer and longer to appear so that its frequency gradually decreases until it eventually stops altogether. This is how we generate the “slowing down” effect of the dice rolling. At this point, some of you might be May 1994  55 LED7 LED4 A K A LED1 LED2 A K A LED11 K A A A K LED3 K LED14 LED9 K S1 A K LED10 A K A K K LED8 LED6 A LED13 K A K A LED12 A K K LED5 470uF 9V BATTERY .01 1k 1k 1.5k 1k 1k 1.5k 1k 1k 10k IC2 4015 IC4 4015 .01 10k D2 1M 1M 1M 1 1 47uF 68k .01 IC1 4093 D1 10k 33uF 10k 1 D3 IC3 4093 .01 1 Fig.2 (above): try to keep the LEDs at a consistent height when installing them on the PCB. You can do this by cutting a length of 5mm-wide cardboard & then using this as an alignment tool. Fig.3 (below) shows the full-size etching pattern for the PC board. wondering why we have chosen the same components for the two oscillator sections of IC1a and IC3a. Because of component tolerances, no two components will ever have exactly the same value so both oscillators will run at a different frequency. This ensures that we don’t always get the same number appearing on both dice repeatedly. Note that this is still possible by chance, of course. From here on, we’ll just discuss that part of the circuit which involves IC1 and IC2. The other half of the circuit works in exactly the same way. The pulses from IC1a are used to clock the rest of the circuit and simulate the roll of a real dice, whereby the LEDs cycle very rapidly at first and then slow down to a complete stop to give a static display. These clock pulses are fed to pin 9 of IC2a, a 4-bit shift register which is connected up as a D-type flipflop. IC2a is made to function as a flipflop by connecting its Q0 output at pin 5 to the D-input at pin 7 via inverter IC1b. The Q0 output of IC2a is also used to drive LED 1 which is on for all odd-numbered displays; ie, “1”, “3” and “5”. The output of IC1b is also used to clock the second 4-bit shift register, IC2b. The D-input of IC2b is tied to the positive rail so that on each clock pulse, a “high” is shifted to each output from Q0 to Q1 to Q2 (pins 13, 12 & 11 respectively). Pin 11 drives LEDs 2 & 3, pin 12 drives LEDs 4 & 5 and pin 13 drives LEDs 6 & 7. These LEDs combine to produce the even-numbered displays “2”, “4” & “6”. When Q0 of IC2b goes high, LEDs 6 & 7 come on to produce displays “2” and “3”. On the next clock pulse, Q1 also goes high to produce the “4” and “5” displays, as LEDs 4 and 5 are now also lit. On the third clock pulse, Q2 goes high as well, lighting LEDs 2 and 3 to produce the “6” display. Dice sequence Let’s now follow the dice sequence. When the first clock pulse from IC1a arrives, Q0 of IC2a goes high, producing the “1” display. The next pulse pulls it low again which sends the output of IC1b high. This clocks IC2b and sends its Q0 output high, turning on LEDs 6 and 7 to produce a “2”. The following pulse toggles IC2a again, sending Q0 high and lighting LED 1 to produce a “3”. The output of IC1b is a fall­ing edge this time so nothing happens to IC2b. The next clock pulse toggles IC2a again, turning off LED 1 but clocking IC2b so that 56  Silicon Chip Q1 of IC2b also comes on to produce the “4” display. The clock pulse after that toggles IC2a again, turning on LED 1 again to produce a “5”. The next clock pulse toggles IC2a off again and clocks IC2b so that the last of the LEDs now light (via IC2b’s Q2 output) to produce a “6”. This last high also pulls one of the inputs to IC1d high and when the next clock pulse arrives, Q0 of IC2a goes high. This pulls the output of IC1d low. This low output is fed to pin 12 of IC1c. The other input to the gate is controlled by the 47µF capacitor we mentioned right back at the start. While this continues to charge up, pin 13 is held at a logic high and so IC1c acts as an inverter. The low input that has just come from IC1d thus forces the output of IC1c high, which resets IC2b. Output Q2 of IC2b now goes low again and the reset condition is removed (ie, the reset pulse is quite narrow). The RC time constant on pin 6 of IC2a prevents this register from also being reset at this stage. This is because the .01µF capacitor doesn’t have sufficient time to charge. IC2a now toggles again so that its Q0 output goes high, lighting up LED 1 again, and so the cycle continues. While this is happening, the 47µF capacitor charges until the voltage at pin 13 of IC1c drops to a logic low. At this point, the output of IC1c is held high regardless of the pin 12 input level and thus both IC2a and IC2b are reset. All LEDs are now turned off and the current consumption is down to only a couple of microamps, allowing us to do away with a power switch. Once the ROLL button is pressed, the circuit comes alive and the whole process begins again. Power is supplied by either a 6V or 9V battery. The supply line is de­ coupled via a 470µF capacitor which also supplies the current surges re- quired by the circuit when the LEDs are being driven. Construction All of the components for the Dual LED Dice are installed on a PC board measuring 102 x 112mm and coded 08105941. Before you begin any soldering, check the board thoroughly for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. Once the board appears to be OK, you can begin by install­ing the wire links. Make sure that you follow the overlay wiring diagram so that they are installed in the correct place. Next up, continue on with the resistors and diodes, fol­lowed by the capacitors and ICs. As most of the components are polarised, be careful to make sure that they are installed cor­rectly. After that you can install the LEDs. This should be rela­tively straightforward since all of the LEDs face the same way. Finally, install the switch and the battery snap. You can use a 9V battery or a battery holder with four 1.5V AA cells (to give 6V). PARTS LIST 1 PC board, code 08105941, 102 x 112mm 1 snap-action PCB switch (S1) 1 9V battery snap 1 6V or 9V battery (see text) 4 10mm x 3mm tapped spacers Semiconductors 2 4093 Schmitt NAND gate ICs (IC1,IC3) 2 4015 dual 4-bit shift registers (IC2,IC4) 3 1N914 signal diodes (D1,D2,D3) 7 5mm yellow LEDs (LEDs 1-7) 7 5mm red LEDs (LEDs 8-14) Capacitors 1 470µF 16VW electrolytic 1 47µF 16VW electrolytic 1 33µF 16VW electrolytic 4 .01µF 63VW MKT polyester Resistors (0.25W, 5%) 3 1MΩ 2 1.5kΩ 1 68kΩ 6 1kΩ 4 10kΩ Miscellaneous Machine screws, solder, tinned copper wire. Testing Check your work carefully for any components which are incorrectly installed or for any solder splashes causing shorts between the tracks. Once everything looks good, connect up your battery and press the button. You should see the LEDs initially flashing quite quickly and then slow down to a complete stop. After about 30 seconds or so, the display should then turn off. You’ll need to do this a number of times to make sure that all the displays appear. If any LEDs fail to light up, check that you have them installed correctly. Note that for those LEDs which are in series with each other, you only need to have one installed incorrectly for both not to work. Cutting the board If you prefer, you can install this project in a plastic zippy box by cutting the board through the middle and then soldering wire links between the two boards to fold them over. This is best done before you start construction and will make the assembly that much smaller. OK, you’ve had your fun. Now you can get down to serious work with the SC board games. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ No. 3 1 4 2 6 Value 1MΩ 68kΩ 10kΩ 1.5kΩ 1kΩ 4-Band Code (1%) brown black green brown blue grey orange brown brown black orange brown brown green red brown brown black red brown 5-Band Code (1%) brown black black yellow brown blue grey black red brown brown black black red brown brown green black brown brown brown black black brown brown May 1994  57 SERVICEMAN'S LOG Always look on the grim side That heading describes the pessimistic service­ man. When he encounters a fault which looks easy, he automatically assumes it’s going to be hard. And when he encounters one that looks hard, he is quite certain it’s going to be hard. Of course, he’s often right – but not always. My first story this month concerns an HMV colour set, model B4803A, the “48” signifying 48cm and the “A” an Australian ver­sion. But more exactly, the chassis is actually made by JVC. This model has been around for about 15 years and I am fairly familiar with it. So, when the lady owner rang to say she had a problem, I assumed that it would be something I could handle without too much trouble. I asked her in what way the set was misbehaving and she replied that while there was a watchable picture on the screen, it was, in her words, “very red”. I pondered on this briefly, considered several possibili­ ties without reaching any conclusion, then simply advised her to bring the set in. Even then I didn’t anticipate anything 58  Silicon Chip unduly difficult. But then, one never does. Anyway, the set was duly delivered and I put it up on the bench and switched it on. The result was more or less as the customer had described it; the picture was complete and it was only the colour that was wrong. But it wasn’t red, as she had thought. It was magenta, a colour which is often mistaken for red, the difference being rather subtle. But it is an important difference, because it immediately pinpointed the real nature of the fault – loss of green, leaving red and blue which mix to make magenta. Well that seemed to simplify the situation; all I had to do was find out why there was no green. And, while there could be several reasons, failures of this kind are not normally difficult to track down. High voltage My first check was the voltage on the collector of the green drive transistor Fig.1: this diagram shows the colour decoder IC (IC302) and the neck-board circuitry for the HMV B4803. The picture tube driver transistors (X101-X103) are to the right, with the green driver transistor (X103) at the bottom. Pin 10 of IC302 connects to pin 7 of IC301 (not shown) via two resistors. (X103), which drives the picture tube green cathode. This normally sits at around 145V, with roughly similar values on the red and blue drives. However, this one measured around 180V which is the supply rail voltage, meaning that this transistor was not drawing any current. As well as suggesting a fault in the drive system generally, this also cleared the picture tube of suspicion. Further checking revealed that the voltage on the base of X103, normally around 7.4V, was only a fraction of this. And this in turn suggested two possibilities, both of which I had experi­ enced previously: (1) a fault in the drive transistor itself (they can develop some very funny faults); or (2) a more subtle fault around the colour matrix chip, IC302 (TA7622­AP), which provides the base voltages for the three driver transistors. It was toss up but the driver transistor is quite easy to change and I had one on hand, so I tried that first. But all that did was clear the transistor; replacing it made no difference. My next step was to take a look at the circuitry around IC302. The three pins involved are pin 2 (red), pin 4 (green) and pin 6 (blue). But there is a nasty trap here for unsuspecting players; not shown on the circuit is a modification consisting of three clamping diodes, one for each pin. These are designated on the board as D403, D404 and D405. In each case, the anode goes to the pin and the cathode to the 12V rail. These diodes have a nasty habit of going leaky. And when one does, it can produce symptoms very similar to these. Again it was a relatively simple job to clarify the point. I pulled the suspect diode out and, rather than waste time testing it (such tests are not always conclusive anyway), simply fitted a new one. But again, I drew a blank; the problem was still there. Which didn’t leave much, except the IC. I went over the circuit, seeking inspiration as to any other likely cause but without success; it just had to be the IC. Good news & bad Fortunately, I had this particular IC in stock and, with only 16 pins involved, it was a simple job to fit a new one. And I confidently expected that this would finally cure the fault. How naive can one be? All I had done was create a good news/bad news situation. The good news was that I had cured the original fault. There was now normal voltage on pin 4 of IC302 (and on the base of transis­tor X103) and all signs of the magenta cast had vanished. The bad news was that I now had a monochrome picture – there was no colour. By very carefully adjusting the fine tuning control, I eventually brought up some colour but it was still a long way from being right. There were several things wrong with the picture, some of them hard to describe. For example, there were patches where there was no colour, or where one particular colour was absent, to nominate a couple of minor faults. And I classified those faults as minor because the major one was a real beauty; the colour pattern was displaced by about 30mm to the right of the monochrome image to which it belonged. It produced a weird effect. The offair picture I was using happened to be coverage of a one-day cricket match, in which the fielding side was wearing bright yellow uniforms. Imagine, if you can, a fieldsman, portrayed in monochrome, chasing a ball across the screen from right to left, with the yellow of his uniform running several steps behind in what looked like a vain attempt to catch up. And then, when he turned and ran the other way, it looked as though he was trying to catch the colour! To the casual observer, it would probably have looked out­rageously funny. To me, faced with the task of May 1994  59 Fig.2: the power supply circuitry for the National TC-2658 colour TV set. The mains power enters on the left (blue & brown), while the bridge rectifier (D833-D836) is in the centre of the diagram. To the right of the bridge rectifier is switching transformer T801, while IC801 is at extreme right. Test point TPE1 is below IC801 & should normally measure 113V. finding out what was causing it, the humour of the display was somehow lost. More to the point, I didn’t have a clue as to where to even start looking for a fault like this. I had never seen, or even heard of, anything like it before. To add to my confusion, there was the question as to wheth­er there had been two faults in the set when it came to me: (1) the obvious loss of green; and (2) this “new” fault. It was quite possible that the second fault had originally been masked by the obvious loss of green but, to be truthful, I hadn’t taken all that much notice of the picture’s finer points. I had simply diagnosed loss of green and gone on from there. Alternatively, was there only one fault originally, meaning that I had created the second fault in curing the first one? It was all very disconcerting. Anyway, for want of any better ideas, I went around IC302 with the meter, checking the voltage on each pin. Everything tallied very closely with the circuit values until I came to pin 10. This is shown on the circuit as measuring a mere .08V but the meter was reading somewhere around 5V plus. I didn’t note it precisely; just 60  Silicon Chip that it was grossly wrong. Could the replacement for IC302 be faulty? It was hardly likely, seeing it was a brand new unit. But stranger things have happened and, as I had a second one on hand, I decided to make certain. So IC302 was changed for a second time. Result – exactly the same as before. That clinched it; it obviously wasn’t IC302. Next, I began tracing the circuit from pin 10 and, after running up a couple of blind alleys, I came to pin 7 of IC301, the chroma IC. This is marked with a similar value, in this case .09V, but the actual voltage was grossly high here too, being similar to that on pin 10 on IC302. I checked the circuit carefully for any other likely source of the spurious voltage and the only other possibility seemed to be diode D201, which might be leaky. To make sure, I disconnected it but that made no difference. So as far as I could see, IC301 was about the only possible place, apart from IC302 itself, from which the spurious voltage could originate. And IC302 had been replaced twice. The next logical step was to change IC301. The only snag was that I didn’t have one in stock and so one had to be ordered. I also ordered another IC302 while I was about it. In the back of my mind was the thought that a fault in IC301 might have damaged IC302, so it was best to be on the safe side. The two ICs arrived a couple of days later and, full of confidence, I lost no time in replacing IC301. It came as a nasty shock when this had no effect; the symptoms remained as weird as ever and the same spurious voltage was present. When I’d regained my composure, I did something which, in hindsight, I realised I should have done much earlier; I separated the two pins from each other. And so, at long last the truth was revealed; pin 7 of IC301 reverted to normal, while pin 10 of IC302 retained the spurious 5V. Initially, considering that IC302 had already been changed twice, I was loath to accept that the fault was actually in this IC. Instead, I tried to think of some external error which would cause it to produce this voltage. But I drew a mental blank; I could think of nothing that would do this. So there was only one thing left; change IC302 for the third time. I couldn’t believe that this was the answer but I didn’t know what I would do if it wasn’t. But it was the answer; the new IC cured the fault complete­ly. And that, from a practical point of view, was the end of the story. The set was returned to the owner and everyone was happy. Well, I was happy the problems had been solved but less happy and very puzzled about the IC situation. Statistically, ICs are very reliable and I cannot recall the last time that a new IC proved faulty. As for two new ICs being faulty – well, that would suggest lottery odds. But there was the evidence on the workbench. Granted, they had been in stock for a couple of years but that is hardly relevant. The only other point of note is that they both carried the same batch markings and, not surprisingly, these differed from those on the one I had just bought. So, if it was a batch problem, how many other unfortunate servicemen had been driven half way up the wall, as I had been? Strange symptoms My next story is not an especially profound one but is of interest because of an unusual fault in a particular component. But the fault was not only unusual; it also created some very strange symptoms. On the other hand, no great detective work was needed to track it down. In fact, this was one of those rare occasions when a job which looked as though it was going to be hard turned out to quite simple, rather than the other way round. The set was a National colour TV set, model TC-2658, which is fitted with an M14 chassis. This chassis, with minor varia­tions, has been used in a number of National models and I have dealt with it several times in the past. The customer’s complaint was simply that the set had failed completely and, when I put it up on the bench and turned it on, this appeared to be true enough, at least from his point view; there was no picture and no sound. But there were some signs of life. For starters, the power supply was giving forth a high pitched squeal of distress; the kind of sound usually associated with a gross overload. And this, initially, was what I suspected was happening. My first check was to measure the HT rail voltage, which is most conveniently done at test point TPE1 in the power supply section. The normal value at this point is 113V but, in this case, it was reading 163V. Apparently, the power supply was underloaded rather than overloaded and the sounds of distress were, somehow, due to the excessive voltage it was generating. My first reaction to the excessive voltage was to assume that some part of the circuit – most probably the horizontal output stage – was not drawing current. And, in turn, I suspected that the horizontal output transistor, Q501, might have gone open circuit. So this was pulled out and checked. No joy. It checked out perfectly and there was certainly no sign of an open circuit. So what now? As I have pointed out before when discussing this chassis, it is fitted with an elaborate protection circuit. This is designed to detect over-current and over-voltage situa­ tions in various parts of the circuit and to shut the set down to avoid more serious damage if a fault occurs. In this case, it was obvious that the excessive voltage had caused the protection circuit to shut the set down. Subscribe now to the largest faults & remedies library in Australia ✱ ✱ 1994 manuals are now available. Our database is regularly updated with information supplied by technicians such as yourself. ✱ Exclusive backup service by qualified technicians. ✱ ✱ Over 10,000 faults and remedies on file with flow charts and diagrams. Covers Colour TVs and VCRs of all brands sold in Australia EFIL Phone or fax now for your FREE information package ELECTRONIC FAULT INFORMATION Reply Paid 4 P.O. Box 969 AIRLIE BEACH 4802 Ph 079 465690 Fax 079 467038 May 1994  61 SERVICEMAN'S LOG – CTD tant point was that the set was work­ ing, with no obvious faults or signs of distress. This threw suspicion right back to the power supply; the HT voltage was not wrong because of any lack of loading in the set, so it had to be the power supply itself that was at fault. The heart of the power supply is an STR50113-M regulator chip (IC801). These devices are no stranger to me; while their failure rate is probably not excessive, I’ve had enough trouble with them to put me on alert. Except that I had never seen a fault like this before – usually, they develop an internal short to chassis, which takes out a 4.7Ω safety resistor (R841). Nevertheless, I could find nothing else in the power supply circuit which could possibly account for the excessive voltage. So out came IC801 – it has only five pins – and in went a new one. I switched the set on again – still on the Variac – and found that the HT voltage was now low. I then wound the input up to 240V, still on the alert for any signs of distress, but there were none. More importantly, I now had a HT rail that was spot on 113V and the set was running perfectly. One of the easy ones From a practical point of view, the existence of the pro­ tection circuit means that this has to be disabled in order to track down the fault. Only then will the set try to function normally and display the fault in its true colours. Disabling this circuit is simple enough. Resistor R536 (100Ω) connects to the emitter of transistor Q503, which forms part of the protection circuit, and removing this is all that is necessary. Risk of damage But there is more to it than that. If the fault is a poten­tially destructive one, disabling the protection circuit could cause additional damage. And that was exactly the situation here; with the power supply generating 163V on the HT rail, the risk of damage if the set was allowed to function with this voltage was quite high. Fortunately, the solution is fairly simple. In such circum­stances, I feed the set from a Variac. This is set initially at a suitable low voltage and then gradually wound up while the 62  Silicon Chip HT rail is monitored. There’s just one catch here – in many cases, the set’s kick start circuit will not function if the voltage is wound up from zero; it needs to switched on at a reasonable input level. I normally set the Variac to deliver about 100V, with the set switched off, then switch the set on. This is usually high enough to provide the required kick start but still low enough to avoid trouble in the event of a destructive fault. So that was the setup. The set started readily enough with an input of 100V and I wound the voltage up gradually until I had about 113V on the HT rail (note: this occurred at something consider­ably less than 240V input). And all seemed well – there was no smoke, flames, smells or other nasty symptoms and, more importantly, the set was functioning more or less normally, with a quite watchable picture on the screen. But I say “more or less” advisedly, because the HT rail voltage was quite unstable and the picture’s behaviour was some­what erratic. But the impor- So, relatively speaking, this was one of the easy ones. But I thought that it was worth recounting for several of reasons. My first reason was to restate the protection circuit situation. One must learn to recognise those sets which incorporate these circuits and know how to safely disable them without causing further damage. My second reason was simply to report the unusual fault in the regulator IC. It is a fault that I had not encountered or heard of before. And finally, I wanted to remind readers of what I had to do to finish the job – restore the protection circuit. Unfortunate­ly, I have encountered a disturbing number of sets which have had various protection circuits or safety features modified or disa­bled for one reason or another and not restored to original condition when the job was finished. It is important to always restore any protection circuits when the job is done, both from a safety aspect and to prevent unnecessary damage to the set if a fault occurs. After all, that’s what the protection circuit is there for in SC the first place. The receiver board at right is capable of 16 channels & you can build up to four to give 64 channels. In practice, one receiver board would be built to control each piece of equipment. A smart remote control with up to 64 channels Have you ever wanted to control a tuner, CD player, VCR or any other device that does not have its own remote control. If so, this project is for you. It was developed to control a tuner & a cassette deck but it could be made to control almost any­thing using the right interfaces. By BRIAN ROBERTS 64  Silicon Chip This project is extremely flexible and uses a universal infrared remote control. These “intelligent” or “learning” remote controls are readily available and can also replace the existing remote controls for your TV, VCR and other equipment. For my application, I required 12 channels for the tuner and eight for the tape deck. I did not want messy wires connect­ing between a remote control receiver and both of these units so the unit was designed to be address selectable which allows a receiver to be fitted inside each unit. This means, for example, that the tuner operates on channels 1-8 and 33-40 and the tape deck on say 9-16. If I needed to remote PARTS LIST Transmitter board The transmitter board (above) is used to teach codes to a learning remote control unit. Up to 64 codes are possible by changing the DIP switch settings & a single link. control another device, it would occupy addresses 17-24 and 49-56. Because the receiver units were fitted internally in my installations, they ran off the power rails in the controlled de­vice. The current drain is small, at approximately 25mA. Alterna­ tively, you could have external receivers which will require their own small power supplies and a multi-way cable to perform the control functions. Each receiver board is capable of handling 16 channels, so to provide a total of 64 channels you would need four separate receiver boards, each of which is programmed via linking options to decode its own 16 channels. The receiver board has two channels capable of either momentary or latched operation for switching relays that turn on and off high current loads. The two outputs per board can be configured for normally on or normally off operation and are capable of sinking 75mA from any rail up to and exceeding 16V. If this feature is used, there is a maximum of 56 channels available (14 per board). Circuit description The circuit of the transmitter board is shown in Fig.1. The transmitter is built up only to provide a source of codes which can be “learnt” by an intelligent remote control. After this is done, the transmitter board is not used. IC1 is an MV500 remote control 1 PC board, code 15105942, 47 x 36mm 1 MV500 remote control (IC1) 1 2N2222 NPN transistor (Q1) 1 CQY89A infrared LED (L1) 1 8-way DIP switch 1 4-way DIP switch 1 2-pin header 1 jumper shunt 1 Murata CSB500E 500kHz ceramic resonator (X1) 1 6V battery & snap connector 2 100pF ceramic capacitors 1 47kΩ 0.25W resistor 1 10kΩ 0.25W resistor 1 47Ω 0.25W resistor Receiver PC board (for 16 channels) 1 PC board, 80 x 86mm, code 15105941 8 4-way pin headers 1 8-way dual pin header 1 2-way dual pin header 4 jumper shunts Semiconductors 1 MV601 infrared decoder (IC1) 1 SL486 infrared preamplifier (IC2) 1 74HC138 3-to-8 line decoder (IC3) 2 4028 BCD to decimal decoders (IC4,5) 1 74HC74 dual D-type flipflop (IC6) 1 4071 quad 2-input OR gate (IC7) 4 4066 quad analog switches (IC8,9,10,11) transmitter IC. Pins 2-9 are the keypad row pins and pins 10-13 are the column pins. The keyboard is scanned in the conventional way and if a key is pressed, the transmitter will deliver a code relevant to that row/column combination. In this circuit, no keypad is used but DIP switches 1-8 and 9-12 provide all the combinations of a 32button keypad. Pins 14 and 15 control the output pulse frequency. SW13 is a link option which ties pin 14 high if inserted while resistor R3 ties this pin low if not. Therefore, two transmitting rates are possible. With the link present, the 1 LM358 dual FET-input op amp (IC12) 1 LM317T adjustable 3-terminal regulator (REG1) 2 BC549 NPN transistors (Q1, Q2) 1 red LED (LED1) 1 BPW50 infrared photodiode (IRD1) 1 1N914 diode (D1) Capacitors 1 68µF 16VW tantalum electrolytic 1 22µF 25VW electrolytic 1 10µF 16VW electrolytic 1 6.8µF 16VW tantalum electrolytic 1 4.7µF 16VW electrolytic 1 0.47µF monolithic 1 0.15µF metallised polyester (greencap) 3 0.1µF monolithic 1 .022µF metallised polyester (greencap) 1 .015µF metallised polyester (greencap) 2 .0047µF metallised polyester (greencap) 2 100pF ceramic Resistors (0.25W, 5%) 1 1MΩ 2 3.3kΩ 1 120kΩ 1 1kΩ 1 100kΩ 1 270Ω 1 27kΩ 1 240Ω 1 10kΩ 1 47Ω 1 4.7kΩ Note: PC boards for this project will be available from RCS Radio Pty Ltd. Phone (02) 587 3491. transmitted rate is 512 clock cycles (fast rate); otherwise it is 2048 clock cycles (slow rate). Pins 16 and 17 connect to ceramic resonator X1 and ca­pacitors C1 and C2 which form an oscillator circuit of 500kHz from which all timing is derived. Q1 is the output driver which is turned on and off by the current pulses from pin 1. L1 is the infrared LED and resistor R1 limits the current to a safe value. Now let’s have a look at the circuit of the receiver board – Fig.2. The signal from the remote control is May 1994  65 +3-6V SW9-12 SW-DIP4 R2 10k 8 1 7 2 6 3 5 4 13 VDD 12 C1 11 C2 SW13 (LINK) 15 RA RB 14 8 9 10 6 11 5 12 4 13 3 14 2 15 11 16 7 R2 6 R3 5 R4 4 R5 3 R6 2 R7 SW1-8 SW-DIP8 R1 47  R3 47k 10 C3 9 R0 8 R1 L1  CQY89A K B OUTPUT 1 7 A C E IC1 MV500 C2 100pF OSC 17 OSC Q1 2N2222 Fig.1: the circuit of the transmitter. IC1 generates a serial pulse code according to the settings of the DIP switches. 32 codes are possible and the total of 64 codes are obtained by varying the pulse rate low or high. X1 500kHz 16 C1 100pF VSS 18 B R C VIEWED FROM BELOW A K 66  Silicon Chip 6 (ie, pulses are fast), the output at pin 7 will switch high and this toggles the rate pin (pin 3) of IC1 so that it has the correct rate selected. We’ll come back to this factor in a moment. IR pulse decoder IC1, the MVA601 infrared pulse decoder, is really the heart of the circuit. Its timing is by the 500kHz ceramic resonator at its oscillator pins (6 & 7). IC1 decodes the pulses from IC2 and the decoded result is presented on five data lines D0-D4 which gives 32 possible channels (ie, 25). You will note that there is one extra data bus line (D5) on the circuit which comes from comparator IC12b. As the decoder chip can only provide 32 independent codes and the design called for 64 codes, we cheat by using the rate of the pulses to give the extra 32 codes. If the rate of the pulses is fast, then D5 is high. Conversely, if the rate is slow then D5 is low. We now have 32 combinations when the pulse rate is fast and 32 when the pulse rate is slow. Pin 10 of IC1 is the Data Ready pin and it goes low to light LED 1 when a valid code has been received. IC3, IC7, IC5 and IC4 convert the binary data (D0-D5) from IC1 to 16 decoded outputs. IC3 is a 74HC138 3-to-8 line decoder. Dependent on the data on its pins 1, 2 & 3, one of its eight outputs will go low. If the data was 00000 for D0-D5 and the links on PL1 & PL2 are as shown on the schematic, then the following Construction Let’s discuss construction of the transmitter first. It is built on a PC board measuring 47 x 36mm and coded 15105942 – see Fig.3 Mount all the Fig.2 (right): the circuit of the receiver board can decode up to 16 channels. Four receivers are required to give a total of 64 channels. IC1 is the heart of the circuit & it decodes the serial data from IC2 & presents it as parallel data on lines D0-D5. This parallel data is then decoded by IC3, IC4 & IC5 to drive the 4066 bilateral switches (IC8-11). ▲ received by infrared photodiode IRD1 and then processed by IC2 which is an SL486 infrared preamplifier chip with AGC. This IC has a number of features that ensure operation under a wide range of operating conditions. The chip has a differential input stage to minimise noise, while capacitors C2 and C3 are part of the gyrator circuitry to roll off the frequency response below 2kHz so that the attenua­ tion at 100Hz is approximately 20dB. C9 further reduces the gain below 2kHz in the first stage of the chip. The output signal from pin 9 is coupled back into the stretch input (pin 10) via capacitor C10 to lengthen the very narrow received pulses. This is done to make the rate detector formed by IC12 operate with wider margins. It also provides noise immunity as the stretch input has a threshold below which any noise spikes are ignored. The stretched pulses from pin 11 are fed via op amp IC12a and then to pin 1 of IC1, the infrared pulse decoder. The output of IC12a is also fed via diode D1 to a circuit that detects whether the pulse frequency is fast (output is high) or slow (output is low). Resistors R7 and R4 and capacitor C11 form a filter circuit for the rectified pulses from D1 and, depending on whether the pulse frequency is high or low, the filter voltage will be high or low. Op amp IC12b is connected as a comparator to monitor the filter voltage. If pin 5 is more positive than pin conditions occur. Pin 15 of IC3 would be low as a valid code (000) is being received which means that pin 8 of IC7c is also low. Pin 10 of IC1 (Data Ready) would also be low, so pins 9 and 2 of IC7 would also be low. Pin 10 of IC7c would then go low to drive the D input of IC4, a 4028 BCD-to-decimal decoder. This then turns on bilateral switch IC8 and channel 1 is enabled. The purpose of the dual 8-pin headers PL1 and PL2 is to allow link selection of a block of any 16 channels from 64. This ena­bles us to have multiple decoders which allow the flexibility talked about in the introduction – see Table 1. IC6a is a latch and channel 39 can be selected for latched operation by linking the pins of header SW1a, or for momentary operation by linking across SW1b. The same applies to IC6b and channel 40 (link SW2a for momentary operation and SW2b for latched). The time constant consisting of R12 and C1 ensures that latch IC6 has its pins 9 and 5 low at power up. The Q outputs of IC6 turn on transistors Q1 and Q2 which can sink more current than the bilateral switches. If the transistors are fitted, then IC11 is omitted and vice versa. The solder straps indicated by the dotted lines on the circuit diagram of Fig.2 allow the transistors to be normally off or normally on by se­lecting either the Q or Q-bar outputs from IC6. REG1 is an LM317 3-terminal adjustable regulator which is set to provide an output of +6.3V. This is a compromise supply between IC1’s maximum operating voltage of 7V and the desire to obtain a low on-resistance in the bilateral switches (IC8-11). VCC C7 .0047 R10 47  C6 .022 5 4 C2 6.8 2 C3 68 3 C5 10 IRD1 BPW41 C8 0.15 8 16 A 6 11 3 DEC4 OVCC DEC2 IVCC SOUT C1 IC2 SL486 DECA A C O/P 9 C10 .0047 DEC1 DEC1 1 IC12a 2 LM358 11 C2 R6 1M 8 D1 1N914 R3 4.7k  K R5 10k 7 C9 15 .015 C11 0.47 IC12b 10 B C 10 11 I/OA 6 CC 12 I/OA CD 5 I/OB CB 13 I/OB CA IC8 4066 I/OC I/OC I/OD 3 Q0 14 Q1 2 Q2 IC4 Q3 15 4028 1 Q4 6 Q5 7 Q6 4 Q7 VCC 14 14 16 D 7 I/OD 8 I/OA 6 CC 12 I/OA CD 5 I/OB CB 13 I/OB CA IC9 4066 I/OC I/OC I/OD I/OD VCC 16 1 10 A 13 B 12 C IC7a 11 3 2 +9-16V C4 22 IN IN REG1 REG1 LM317 LM317 ADJ R8 1k 11 D0 12 D1 OB 13 D2 OC A RB B C VCC OD OE OUT 7 R1 1k 14 D3 11 6 16 15 14 13 12 Y0 A E3 2 Y1 B 3 Y2 C IC3 Y3 74HC138 Y4 4 Y5 E1 5 Y6 E2 Y7 15 D4 D5 C13 100pF OUT R9 240  C12 4.7 CH1-8 CH9-16 1 2 3 1 2 3 CH17-24 CH25-32 CH33-40 4 11 5 6 7 D 4 5 CH41-48 6 CH49-56 7 8 8 CH57-64 PL1 PL2 1 2 3 4 E F 1 2 3 4 PL4 8 9 10 1 2 3 11 4 CH4 14 D 1 2 3 4 8 9 10 11 1 2 3 4 PL6 1 2 3 4 Q7 8 R12 100k C1 0.1 0.1 INTELLIGENT REMOTE CONTROL 1 PL7 2 CH36 6 CC 12 CD 5 IC10 CB 4066 8 13 I/OC CA 9 I/OC 10 I/OD 11 I/OD CH1 CH2 VCC PL5 VCC I/OA 1 2 I/OA 3 I/OB 4 I/OB CH3 CH5 13 CA 12 CD 6 CC 5 CB CH7 CH6 7 CH35 4 1 PL8 2 CH33 3 CH34 4 VCC 14 CH8 3 7 Q1, Q2, R13 AND R14 OPTIONAL. SEE TEXT 3 Q0 14 Q1 2 Q2 IC5 15 Q3 4028 1 Q4 6 Q5 Q6 7 VCC VCC PL3 7 14 E F 10 8 10 A 13 B 12 C 9  K VCC A D PPM C14 100pF SIN C15 100pF IC7c 4071 8 IC1 MV601 8 VSS 9 0/E OSC 6 X1 500kHz 7 4 R4 120k VDD DR 6 5 16 M/L C16 0.1 OA 3 R7 27k 5 RA RST C17 0.1 11 GND TP IVSS 14 13 OVSS 12 REG 4 2 R11 270  A LED1 RED 1 PL9 2 CH37 I/OA 1 2 I/OA 3 I/OB 4 I/OB IC11 8 4066 I/OC 9 I/OC 10 I/OD 11 I/OD 3 CH40 4 1PL10 2 CH39 3 CH38 4 7 Q1 R14 BC549 C 3.3k B E R13 3.3k B SW1b SW2a MOMENTARY 4 VCC 10 PR 9 12 Q CK IC6b 8 11 D Q CLR 13 MOMENTARY E SW1a LATCHED SW2b LATCHED C Q2 BC549 74HC74 VCC 14 2 3 5 Q CK IC6a 6 D Q CLR 1 7 A K A K B E C VIEWED FROM BELOW ADJ OUT IN May 1994  67 L1 3-6V Q1 47  A K 2x100pF 47k 10k SW-DIP4 IC1 MV500 SW-DIP8 X1 1 SW13 Fig.3: the component overlay for the transmitter. Note that you could substitute a 32-way keypad for the DIP switches if you wish. This would make coding much easier. Fig.4 at right shows the full size artwork for the receiver board. TABLE 1 Sw 1-8 Sw 9-12 Sw13 PL1,2 Channel Sw13 PL1,2 Channel 00000001 0001 out Pos 1 Ch1 in Pos 5 Ch33 00000001 0010 out Pos 1 Ch2 in Pos 5 Ch34 00000001 0100 out Pos 1 Ch3 in Pos 5 Ch35 00000001 1000 out Pos 1 Ch4 in Pos 5 Ch36 00000010 0001 out Pos 1 Ch5 in Pos 5 Ch37 00000010 0010 out Pos 1 Ch6 in Pos 5 Ch38 00000010 0100 out Pos 1 Ch7 in Pos 5 Ch39 00000010 1000 out Pos 1 Ch8 in Pos 5 Ch40 00000100 0001 out Pos 2 Ch9 in Pos 6 Ch41 00000100 0010 out Pos 2 Ch10 in Pos 6 Ch42 00000100 0100 out Pos 2 Ch11 in Pos 6 Ch43 00000100 1000 out Pos 2 Ch12 in Pos 6 Ch44 00001000 0001 out Pos 2 Ch13 in Pos 6 Ch45 00001000 0010 out Pos 2 Ch14 in Pos 6 Ch46 00001000 0100 out Pos 2 Ch15 in Pos 6 Ch47 00001000 1000 out Pos 2 Ch16 in Pos 6 Ch48 00010000 0001 out Pos 3 Ch17 in Pos 7 Ch49 00010000 0010 out Pos 3 Ch18 in Pos 7 Ch50 00010000 0100 out Pos 3 Ch19 in Pos 7 Ch51 00010000 1000 out Pos 3 Ch20 in Pos 7 Ch52 00100000 0001 out Pos 3 Ch21 in Pos 7 Ch53 00100000 0010 out Pos 3 Ch22 in Pos 7 Ch54 00100000 0100 out Pos 3 Ch23 in Pos 7 Ch55 00100000 1000 out Pos 3 Ch24 in Pos 7 Ch56 01000000 0001 out Pos 4 Ch25 in Pos 8 Ch57 01000000 0010 out Pos 4 Ch26 in Pos 8 Ch58 01000000 0100 out Pos 4 Ch27 in Pos 8 Ch59 01000000 1000 out Pos 4 Ch28 in Pos 8 Ch60 10000000 0001 out Pos 4 Ch29 in Pos 8 Ch61 10000000 0010 out Pos 4 Ch30 in Pos 8 Ch62 10000000 0100 out Pos 4 Ch31 in Pos 8 Ch63 10000000 1000 out Pos 4 Ch32 in Pos 8 Ch64 68  Silicon Chip small components first, leaving the MV500 IC till last. Watch the polarity of the IC, the transistor and infrared LED. Next, assemble the receiver. This is built on a board measuring 86 x 80mm and coded 15105941. Before you begin any soldering, check the board thoroughly for any shorts or breaks in the copper tracks. These should be repaired with a small artwork knife or a touch of the soldering iron where appropriate. If fitting the unit internally in a piece of audio equip­ment, you will need to look for a place to install the board and the infrared LED. You will also require a suitable relay which must be installed inside the equipment if you intend it to switch 240V AC. Naturally, you must follow standard wiring practice and take care with the isolation of all 240V AC wiring. You will need to make a number of choices during construc­tion and they are as follows: (1). Are you powering the receiver circuit from a regulated voltage of between 5V and 6.8V? If so, you will not need the LM317, R8 and R9. (2). Do you need to operate relays? If so, you are advised to delete IC11 and fit transistors Q1, Q2, R14 and R13. This enables you to drive two relays up to 16V and 75mA. Note that a reverse-biased diode should be connected across each relay coil. (3). If you are driving relays in the latched mode, do you want the transistor normally on or normally off? Using the solder links on the copper side of the board, short pin 8 of IC6b to pin 2 of SW2a for normally on and pin 9 of IC6b to pin 2 of SW2a for normally off (Q1); and pin 6 of IC6b to pin 2 of SW1a for normally on and pin 5 of IC6b to pin 2 of SW1a for normally off (Q2). Note: if you are using Q1 and Q2, it is advisable to con­nect any load to the unregulated positive voltage to avoid the need for a heatsink to be fitted to the LM317 regulator. With these decisions made, it is now a fairly straightfor­ ward matter of loading all the components onto the board, start­ing with small passive components and headers first and leaving the integrated circuits and other semiconductors till last. Take care with the polarity of semiconductors and electrolytic capacitors. Testing the transmitter There is not much to testing the 10uF .022 .0047 IC2 SL486 SW 2b 0.47 SW 1a 1 10k 1k X1 2x100pF 4.7uF +9-16V REG1 LM317 1M 1 IC3 74HC138 PL1/2 PL3 1 IC4 4028 IC9 4066 1k IC1 MV601 1 PL6 IC12 LM358 D1 1 1 IC6 74HC74 1 120k 4.7k IC8 4066 SW 1b 0.1 PL5 .0047 1 22uF .015 27k SW2a PL10 R13 Q2 M L IC5 4028 1Q1 R14 IC11 PL9 PL7 100pF 1 IRD1 1 0.15 GND TP IC10 4066 47  68uF 6.8uF PL8 240  0.1 100k transmitter until you have built the receiver circuitry. One simple go/ no-go test is to see if your intelligent remote control indicates that it has learnt a code when the two units are placed together. Another simple test is to replace the infrared LED with a visible LED and note if it is pulsing. Alternatively, use a logic probe on the collector of Q1. To set up a code, the transmitter must have one switch of SW1-8 on and one switch of SW9-12 on (see Table 1). The receiver must be powered up and tested before it is installed in the device to be controlled. You will also need to set the two shorting links on PL1 and PL2 to select the addresses so that you can set the transmitter code accordingly (again, see Table 1). Power up the receiver board and check that the current drain is around 30mA (with no relays operating). Select a code for a channel you would like to test and bring the transmitter close to the receiver’s infrared detector (IRD1). The Data Ready LED should light, until the transmitter is turned off. With a multimeter set to “ohms”, check the channel you have selected with the transmitter. Ensure that the transmitter is on and the Data Ready LED is on while checking the resistance between the two pins for the channel. When the channel is selected, the resistance should be less than 200Ω. If all is well, continue testing all channels. 1 PL4 IC7 4071 A 270  IC11 NOT FITTED WHEN Q1, Q2, R13 AND R14 ARE USED LINK ON REG1 FITTED WHEN OPERATING ON LESS THAN 6.5V LED1 Fig.5: the component overlay for the 16 channel receiver board. Take note of the settings in Table 1 when wiring up the board & refer to the text to select the pin header options. Troubleshooting If you have followed the testing procedure correctly and things are not working, here are some checks to make: (1). If the Data Ready LED does not light when the transmitter is sending a valid code, check that the supply voltage is correct for IC1 and IC2. Are you testing under direct sunlight or under very bright lights? Shade the infrared detector (IRD1) or bring the transmitter closer to the receiver. (2). If the Data Ready LED lights but the channels are not switching, try sending three or four different codes with the transmitter to see if it is an isolated problem. Check that PL1 and PL2 are set correctly; check the supply rails on ICs 3, 4 & 5; check the binary code from IC1 on pins 3, 11, 12, 13, 14 & 15; and check that it is the code that you expected the transmitter to send. Check that the Fig.6: full size artwork for the transmitter board. correct output for this code is enabled on IC3 (pins 7-15, excluding pin 8). Finally, check that the appropriate output of IC4 or IC5 is high to select its particular bilateral switch. (3). If channels 39 or 40 don’t latch or transistors Q1 or Q2 don’t turn on, check the solder straps on the copper side of the board associated with IC6. Check that SW1 and SW2 have short­ ing links in either the momentary or latched positions, as appropriate. SC May 1994  69 PRODUCT SHOWCASE Tektronix launches a new style of test instrument – the TekMeter Tektronix Australia has announced its TekTools product family which is aimed at the electronic measurement needs of the service professional. The first of the TekTools family, the TekMeter Series, is both an auto-ranging true RMS digital multimeter (DMM) and an autoranging oscilloscope in a rugged, battery-powered package. The TekMeter automates common electronic measurements in­ cluding power quality and line volt­age monitoring, and variable AC mo­tor drive measurements. Tektronix claim that the TekMeter series is half the price, size and weight of any other similarly featured product on the mar­ket. The DMM features auto-ranging DC and true RMS ranges from 400m V to 600VAC/850VDC and Ohms ranges from 400W to 40MW, as well as diode and audible continuity tests. The auto­ranging oscilloscope features Tek­tronix' proprietary signal tracking technology that automatically finds, scales and displays signals continuously for hands-free operation. DMM users will appreciate the TekMeter's familiar user interface. The TekMeter powers up in the DMM mode and with a single press of a button, it immediately displays the signal for verification, characterisation or analysis. "We've designed the TekMeter Series with the non-oscilloscope user in mind. The TekMeter takes advan­tage of advanced Tektronix technol­ogy so that users can have confidence that the signal it displays is accurate," noted Peter Roan, National Sales Man­ager. "With both the auto-ranging DMM and oscilloscope, users simply attach the lead to the test point and the TekMeter does the rest. We've in­cluded automatic measurements for power calculation, Transformer Har­ monic Derating Factor (THDF), variable 70  Silicon Chip speed AC motor control trigger­ ing and line aberration detection such as spikes, brown-outs and blackouts. We haven't compromised safety stand­ards either. The TekMeter is this in­dustry's first handheld DMM/oscillo­scope to receive UL and CSA safety certification" TekMeter's 600V RMS, 6kV surge rating provides ample protection in high-voltage environments. The TekMeter is compatible with commercially available DMM accessories in­cluding temperature and pressure transducers. Optional accessories for the TekMeter include current probes, a carrying case for hands-free opera­tion, a nicad battery pack with charger, and an AC/DC adapter with RS232 communication for hard copy print­outs and remote communications. Three models are available in the Tekmeter series: the THM 550 with single channel scope, the THM 560 with dual channel scope and the THM 565 deluxe model with advanced functions. The THM 565 can store up to 10 waveforms and instrument setups for data comparison or archival and rou­ tine measurements or calculations. A backlight and real-time clock are also available in the THM 565, allowing low-light viewing and date stamping of hardcopy printouts. DMM accuracy is ±0.5% + 5 counts on DC and ±2% + 5 counts on AC. Vertical bandwidth in scope mode is 5MHz and the maximum sampling rate is 25 megasamples/second/chan­ nel. Vertical resolution is eight bits and vertical sensitivity ranges from 5mV to 500V/division. Pricing is as follows: Tekmeter THM 550, $1659; THM 560, $1903 and THM 565, $2380. These prices include sales tax. All three units come with a 1-year warranty. For further information on the Tekmeter series, cQntact Tektronix Australia Pty Ltd on (02) 888 7066. Low noise block converters for satellite ground stations L&M Satellite Supplies have been appointed sole Australian distributor of Comtex microwave equipment for the reception of satellites. They have LNBs (low noise block converters) specifically manufactured for reception of the follow­ing satellites Aussat, Optus, Intelsat and Gori­zont. Their model CX 101 is a dual polarity LNB for use with Optus/ Aussat. It boasts a small size with exceptional electrical characteristics and unique dish illumination properties, being the only LNB that can be used with prime focus and or offset dishes. Some of its salient features are as follows: length 89mm, diameter 60mm, noise figure (total figure includ­ ing inbuilt feedhorn) 1dB typical, offset or prime focus reflector; inbuilt feedhorn, LO frequency 11.3 GHz for Optus/Aussat; and F/D ratio match 0.35 to 0.65. For further information, contact L&M Satellite Supplies, 33-35 Wickham Road, Moorabbin Vic 3199. Phone (03) 553 1763. Redback coaxial speakers for PA work These two loudspeakers are intended for wall or ceil­ing installation in PA applications. They represent a degree of refinement over the usual twincone speaker used in ceiling installations and will have a much better maintained upper frequency response. The coaxial model has a single dome tweeter with capacitor feed while the triaxial model has a cone midrange and dome tweeter, with both drivers fed by capacitors. Both drivers are rated at 50 watts RMS with a nominal impedance of 8W, a bass cone diameter of 200mm and a free-air resonance of 68Hz. Sensitivity is quoted as 92dB/1W/1m (quite high compared to hifi speakers) and both have a quoted frequency response May 1994  71 to 20kHz. As you might expect, the triaxial model has a somewhat smooth­ er frequency response than the co­axial unit. The triaxial unit is priced at $69.95 while the coaxial model is $59.95. See them at Altronics in Perth or any of their dealers. VGA to VCR/TV converter Boston Technology Pty Ltd has an­ nounced the release of the VID 701 Videoverter. The VID 701 Videoverter comes in a compact (50 x 89 x 25mm) box that fits in your pocket. Any PC that has a VGA graphics adaptor card can use the VID 701 Videoverter to produce low-cost custom videos on any standard video cassette recorder or display on a large screen TV The VID 701 Videoverter offers the following features: LCD/TV display toggling; TV auto blanking; display size and position adjustment; AVRCA or S-VHS outputs (NTSC & PAL versions available); interlaced/noninter­ laced display; 11 VGA display modes, up to 256 colours; compatible with Microsoft Windows, Lotus 1-2- 3, Ani­ mator, CAD and many more applica­tion programs due to its software in­dependence. The VID 701 Videoverter works with all major brands of VGA display cards including Paradise, Cirrus, IBM, Oak, ATI, Video 7 and Tseng Labs chip sets. For more information, contact Boston Technology, PO Box 1750, North Sydney 2059. Phone (02) 955 4765. TDK's new 30 minute videotape TDK has introduced an E-30 HS30 minute tape to complement its existing E-60, E- 120, E-180 and E-240 minute tapes in the popular HS formulation. Camcorder users favour a shorter tape time for dub­bing, rather than using E-120 and E-180 tapes. Until now, TDK had sup­plied E-30 only in its HDX-Pro grade, contending that the demand for this playing time was mainly for mastering and professional applications. The HS E-30 has a recommended retail price of $7.95 and is available at selected TDK dealers and department stores. For your nearest dealer, phone TDK on (02) 437 5100. HP introduces its fastest 486-based PC Hewlett-Packard has introduced its fastest 486-based PC, the HP Vectra VL2 4/100, which is based on the Intel DX4 100MHz microprocessor. The new PC delivers up to 50 percent more performance than PC systems based on previous Intel 486 technol­ogy at a recommended retail price of $4451, including sales tax. With the addition of the 100MHz Intel DX-4 based model, the HP Vectra VL2 series now offers a range of keenly priced systems designed to meet vir­tually any customer performance need. The HP Vectra VL2 series PCs are said to deliver more features, including accelerated local bus video, power management and plug-and-play features, than similarly priced mod­ els from other vendors. The new 100MHz Intel DX4 pro- Mini blow torch from Altronics This little blow torch has to be the nif­ tiest tool of its type that we have ever seen. All you do is slide back the little red lock and push the plunger to ignite a hot little flame that burns at 1300°C. It burns for as long as you hold down the plunger When you take your finger off, the flame goes out. The device is really easy to refuel too since it runs off a standard disposable gas lighter – you just click the case open, drop in the lighter and click the case together and you're in business. There are any number of soldering, brazing and heating applications for it and you will wonder why it wasn't on the market years ago. Called the Cadik Micro-Jet, the mini blow torch has a piezo­electric ignition system which is operated when you press the plunger. Operating time with a standard disposable lighter is about 20 minutes. The Cadik Micro-Jet is priced at $29.95 and is available from Altronics in Perth, or from their dealers. 72  Silicon Chip vides the highest performance of any 486 microproces­sor currently on the market. It has an iCOMP index rating of 435, SPEC int92 of 51.38 and SPECfg of 26.59. In addition to performance enhancements from the Intel DX4 microprocessor, the HP Vectra VL2 4/100 offers high performance through a Fast-IDE controller that provides a 10-15% system performance increase over PCs with standard IDE controllers. This system also features a video subsystem capable of displaying up to 1280 x 1024 pixels. A new power management feature, unavailable on competitively priced models, also has been implemented in the HP Vectra VL2 PC series. The HP power management system, which users can enable easily from the PC setup menu, has a standby mode and a sleep mode that reduce average power consumption to as low as 20 watts and 15 watts respectively. For further information on HP products and services, call 131347 (toll free Australia-wide). Otari cassette duplication system Otari's new DP-4050F series of cassette duplicators feature a 16-times duplication speed, enabling the pro­duction on C60 cassettes in one pass in under two minutes. The DP-4050 series comprises four models: the DP4050F-C2 which provides simultaneous duplication of two cassettes from one master; the Z3 cassette slave expander which provides three additional slave transports; the OM open reel master, for ¼-inch tapes; and the DP-4050E-Z buffer unit, a bias signal buffer unit for driving up to six Z3 slave units in a large system. Features of the DP-4050 series include switchable 8/16 times duplication speed, simultaneous stereo copying of both sides of a cassette, automatic rewind of master and slave transports at the program's end, microprocesor controlled 3-motor transports, 4-channel in-line fer­rite heads, fixed/variable master pitch control, inde­pendent and adjustable bias and level and EQ for each channel. For further information, contact Amber Technology Pty Ltd, Unit B/5 Skyline Place, Frenchs Forest, NSW SC 2086. Phone (02) 975 1211. May 1994  73 COMPUTER BITS BY DARREN YATES What’s your free disc space? This month, we begin a series of articles looking at BIOS & DOS interrupts. In this article, we take a look at a simple programming technique that enables us to find out the free space on any drive without having to use the DOS DIR command. If you’re writing programs that use up lots of disc space, particularly database files or any graphics programs, the odds are that you’ll need to keep track of how much space you have to work with on a disc drive, whether it be hard or floppy. A program that crashes when the disc drive is full is pretty useless but most programming languages don’t have a simple routine which returns the bytes free in a variable. An example of this related to electronics is if you’re writing code which allows the computer to sample incoming analog voltages via an A/D converter. At any time, and depending on your sampling speed, it would be quite easy for the system to run out of disc space. A crash at this point would be disastrous and would almost certainly necessitate a repeat performance of the sample. Thank­fully, we can get access to this information in the same way the DIR command does using a simple QuickBASIC routine. CALL INTERRUPT() In the past, we’ve used the CALL ABSOLUTE() routine built into both QBasic and QuickBASIC. This time, let’s try an even simpler routine which is built into QuickBASIC called CALL INTER­RUPT(). The original method consisted of writing assembly code which has to be 74  Silicon Chip stored into an array and then the base and offset address found for the first element of that array and so on. While it worked well, it was by no means an easy to remember process. When QuickBASIC was launched, the people at Microsoft realised the usefulness of the inbuilt BIOS and DOS routines and incorporated a simple interface function which allowed easy access to them. One of these routines happens to be “Find Disc Space”. In the DOS routines, it is designated INT 21h,3600h. When this routine is called, it returns various pieces of useful informa­tion and this can be seen in Table 1. Upon calling INT 21H, the AX register must be loaded with 3600 hex. As we mentioned a couple of months ago, you can think of the interrupt as TABLE 1 Get Disk Free Space (interrupt 21h, service 36h) Category: Disk services Registers on Entry: AH: 36h DL: Drive code Registers on Return: AX: Sectors per cluster BX: Available clusters CX Bytes per sector DX: clusters per drive the street name and the AX register as the house number. When the routine is completed, all four general purpose 16-bit registers AX to DX are called into play and return the sec­tors per cluster, number of free clusters, bytes per sector and clusters per drive, respectively. From these registers, we can gather the following about the drive: • bytes per sector; • number of sectors per cluster; • number of free clusters; • number of clusters per drive; • amount of drive space used; • drive space remaining; and • total drive size. In most normal programming cases, only the last three items are of any practical use. Sample program Right, let’s now take a look at the sample program in Fig.1. If you compare this to the other programs published so far, you’ll notice that it requires fewer lines of code. To start off, we first have to define a type variable which we’ll call REGTYPE. This consists of all the required registers for CALL INTERRUPT(). The initial values are not important at this stage so we don’t have to worry about clearing them. Next, we define two arrays – INARY and OUTARY – as copies of the type REGTYPE. After that, the AX field of INARY is set to 3600 hex. The following line takes advantage of QuickBASIC’s COMMAND$ string metacommand. When typing in the command line at the DOS prompt to start the program, you would normally type BYTEFREE C: or whatever drive letter you like. COMMAND$ then contains everything after the program name. Basic Listing For Disk Bytes Free Utility ‘Disk Bytes Free Utility ‘Written by DARREN YATES B.Sc. ‘Copyright 1994 Silicon Chip Publications Pty Ltd TYPE regtype AX AS INTEGER BX AS INTEGER CX AS INTEGER DX AS INTEGER BP AS INTEGER SI AS INTEGER DI AS INTEGER FLAGS AS INTEGER DS AS INTEGER ES AS INTEGER END TYPE DIM inary AS regtype DIM outary AS regtype inary.AX = &H3600 drive$ = UCASE$(MID$(COMMAND$, 1, 1)) inary.DX = ASC(drive$) - 64 CALL interrupt(&H21, inary, outary) bytespersector& = outary.CX sectorspercluster& = outary.AX freeclusters& = outary.BX clustersperdrive& = ABS(outary.DX) memfree& = bytespersector& * sectorspercluster& * freeclusters& drivesize& = bytespersector& * sectorspercluster& * clustersperdrive& PRINT : PRINT “Analysis of drive “; drive$ + “:” PRINT : PRINT “Bytes free:”; memfree&; “bytes”, , “Bytes per sector :”; bytespersector& PRINT “Drive size:”; drivesize&; “bytes”, , “Sectors per cluster:”; sectorspercluster& PRINT “Bytes used:”; drivesize& - memfree&; “bytes”, , “Clusters per drive :”; clustersperdrive& program can be converted to work in the same manner as BUTTON.BAS published previously by just substituting the new INT number and adding the appropriate bytes to the arguments being passed to the machine code program. For those using QuickBASIC, make sure that you load QB with the QB.QLB quick library. This library holds the CALL INTERRUPT and CALL ABSOLUTE routines. You can do this by typing in the following line at the C:\ QB45 does prompt: C:\QB45> QB/LQB.QLB The /L option allows you to load in an extra Quick library and automatically invokes QB.LIB when you compile the program. The program will also work with drives running Microsoft Double­ Space, recognising both the real and host drives. To run the EXE file, simply type: BYTEFREE <drive>, where <drive> is the drive letter. As usual, we are making copies of BYTEFREE.BAS/ OBJ/ EXE available for $7 plus $3 postage. You can either send your cheque to SILICON CHIP or call (02) 979 5644 and quote your SC credit card details. K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating So in this case, it would contain “C:”. Looking back at the program, this line takes the first character in the COMMAND$ string, converts it to upper case and then stores it in the DRIVE$ string. The interrupt we’re going to use also accepts a variable to allow us to select the drive we wish to analyse. This is stored in DX. However, the way it recognises the drives is 0 for A:, 1 for B:, 2 for C: and so on. Using the ASCII code we can simply take the drive letter, convert it to ASCII and then subtract 64 from it. This gives us the correct number for each drive. The following line then makes the call to the interrupt. Upon return, all four registers AX to DX contain our wanted informa- tion. These are then stored in long integers (four bytes wide), as denoted by the “&” symbol. The reason for using long integers is that it makes the following multiplication much easier to handle. Now all we have to do is to multiply the bytes per sector by the sectors per cluster and the number of free clusters to get our resulting free disc space. The drive size is found by multiplying the bytes per sector by the sectors per cluster and the number of clusters per drive. The number of bytes used is simply just the drive size minus the free disc space. The final four lines of code print this information on the screen. Now there are bound to be cries from people who only have QBasic. This 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 May 1994  75 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 BOOKSHELF QRP is alive & well! QRP Classics, edited by Bob Schetgen. Published 1990 by the American Radio Relay League, Newington, Connecticut, USA. 278 pages, soft covers, 276 x 211mm. ISBN 0 87259 316 9. Price $24.00. Over the last few years, it would seem that the art of experimenting in amateur radio was a dying one. The number of ready built Japanese “appliances” around these days would HF Antennas For All Locations HF Antennas For All Locations, by Les Moxon, G6XN. 2nd edition, published 1993 by the Radio Society of Great Britain. 322 pages, soft covers, 245 x 186mm. ISBN 1 872309 15 1. Price $45.00. Antenna theory has often been regarded as a black art and something that only a learned few understand in any depth. This book from respected British author and amateur Les Moxon combines much of the theory of HF antennas into one handy volume. It is full of diagrams, tables and examples of practical antennas suitable for just about all conditions and terrains. The book is divided into two parts. Chapters 1-9 explain the theory behind how antennas work, while chapters 10-20 put that the- seem to suggest that Amateur Radio is just an excuse to spend lots of money on the most powerful receivers and transmitters you can get. So it was a breath of fresh air when this book lobbed into the office and gave this writer hope that Amateur Radio isn’t dead yet. QRP Classics is a compilation of low-power (QRP) lowcost projects from QST magazine and the ARRL handbook. As you would expect, it is chock-full of practical circuits from oscilla­tors to receivers, transmitters and active audio filters. The good thing about many of these circuits is that they invite the reader to pull out the trusty soldering iron and start experimenting. What’s more, the writers encourage readers to substitute different components to see what happens – which is good to see! There are nine chapters, starting with an introduction to QRP ideas and then following on with Construction Practises, Receivers, Transmitters, Transceivers, Antennas, Accessories, Power Supplies and Design Hints. ory into practice. Some readers may find the theory a little heavy going but the author has kept the mathematics to a minimum and used lots of diagrams to illustrate the topics. The first nine chapter head­ings are: (1) Taking a New Look at HF Antennas; (2) Waves and Fields; (3) Gains and Losses; (4) Feeding the Antenna; (5) Close-Spaced Beams; (6) Arrays, Long Wires and Ground Reflections; (7) Multiband Antennas; (8) Bandwidth; and (9) Antennas for Recep­tion. The remaining 10 chapters are as follows: (10) The Antenna and Its Environment; (11) Single Element Antennas; (12) Horizon­tal Beams; (13) Vertical Beams; (14) Large Arrays; (15) Invisible Antennas; (16) Mobile and Portable Antennas; (17) Small Antennas; (18) Making the Antenna Work; (19) Antenna Con- The circuits in this book use clever design rather than brute force to get the most out of a signal and help dispel the myth that you need something the size of the Snowy Mountains Scheme to make big noises on the air. There are also theory articles scattered throughout the book which give the novice help on such topics as getting crystal oscillators going and how to get the best out of your antenna. The circuits range from a tiny 1-transistor CW oscilla­tor/transmitter up to a 3W PEP transceiver for six metres, so there is something for both beginners and experienced construc­ tors alike. Many of the transistors used are American 2N-series types but, for most circuits, it should be easy to substitute locally-available parts. Overall, this book is a mine of information and ideas to get even the most diehard appliance operator digging around for that soldering iron. Our review copy came from Daycom Pty Ltd, 44 Stafford St, Huntingdale Vic. Phone (03) 543 3733. (D.B.Y). struction and Erec­tion; (20) What Kind of Antenna. In summary, this text is one of the best and most complete sources on HF antennas available and deserves a space on any amateur radio shelf. Our copy came from Daycom Pty Ltd and you can contact them on (03) 543 3733. (D.B.Y). May 1994  79 VINTAGE RADIO By JOHN HILL Trash or treasure – or how to recognise the good stuff Scrounging old radios & the parts to restore them is all part of the vintage radio hobby. Much of what one finds is junk but every so often, one strikes it lucky. A few years ago, I was a most enthusiastic collector of old radio receivers. Countless hours were spent scrounging around secondhand shops, garage sales and auctions, looking for those elusive bargains. It was time-consuming work which located a lot of junk and very few real treasures. Those days have all but gone and scrounging is now someth­ing I mainly do when on holidays. My radio collecting has become so well known in the district in which I live that I no longer have to seek out old radios – they seek me out instead. Well, their owners do! In the past week I have been fortunate enough to have been offered a number of interesting items from various sources, some of them being of 1920s vintage. It is incredible that such anci­ent equipment still survives in any quantity. The old Apex receiver Perhaps the most interesting of these recently acquired items is a 1929 Apex, an 8-valve neutrodyne of American manufac­ture. This particular set is a mains-powered, steel-cased TRF receiver with a 3-gang tuning capacitor. The receiver’s 91-year old owner had This 1929 model 8-valve Apex is a TRF receiver of American manufacture. The pressed steel radio cabinet has about the same aesthetic appeal as a sardine tin. 80  Silicon Chip recently gone into a retirement village and I found myself in the right place at the right time, thus possibly saving the old set from going to the tip. While the receiver itself was in quite reasonable condition for its age, the same could not be said for the loudspeaker. Its open field coil and tattered speaker cone left little doubt as to its serviceability. When I first saw the old Apex, I thought that it would just have to be a 1929 model. Radios with pressed steel cabinets came in around the 1928-29 period and didn’t last much longer. The valve line-up also suggested a similar date. The valves include: a 280 rectifier, five 227 triodes and two 245s in the output. Whether the output valves are in push-pull or are parallel con­nected is not known at this stage. It is pleasing to note that Apex is mentioned in “Radio Manufactures of the 1920s”. The Apex chapter included an old advertisement for the 9-valve version of my particular set. The advertisement was dated June 1929 – not a bad guess! At this stage, I do not know whether the Apex is a 110V or a 240V model. The power transformer specification plate carries blank spaces where the vital information should have been stamped. In such a case, it would be prudent to plug the set into a 110V transformer for a preliminary try out. Because such a transformer is a permanent part of my workbench, that does not present a problem. Some of the better aspects of the old Apex are: the cabinet is undented, it still has its original knobs, the dial is OK, the friction drive works quite well and the on/off switch still functions. No doubt, the Apex will require a lot of work to restore it fully. There will probably be open-circuit audio transformers, crook paper capacitors and other nasties underneath the chassis, but such problems can usually be overcome one way or another. A quick check revealed that all but the output valves were in excellent condition. An unusual find In the same shed that the Apex was found there was also an old 5-valve chassis which is interesting in an unusual way. The chassis originally used 4V European side contact valves, as witnessed by the large valve socket holes and the 4V power transformer. Someone had gone to a lot of trouble in the past and removed the side contact valve sockets and replaced them with smaller octal sockets. Apparently, whoever did the conver­sion had not given any thought to the heater voltage of the replacement octal valves, as there was no provision made to supply 6.3V to the heaters. Instead, the octal replacements had been wired up to the 4V heater winding on the power transformer. It would appear as though the project was abandoned at that stage, with the new octal valves still in their sockets. Testing these valves in a valve tester revealed that they were indeed new for they all tested “GOOD”. There’s nothing like a bit of luck now and then! There was still another interesting item to come from that dusty shed and With the lid removed, the old Apex receiver looks a little more interesting. The pressed steel box at the right houses the power transformer & the large paper capacitors used in the high tension filter. These two ancient triode valves (both Ediswan PV5DE) are still in good working condition. One has the American UX base, while the other has the standard British 4-pin base. This old electrodynamic loudspeaker from the Apex receiver has not survived the past 60 plus years as well as the receiver & a suitable substitute will have to be found. This neutralising capacitor from the junkbox of parts is far sturdier than the much more common screwdriver adjusted variety. May 1994  81 With a bit of cleaning & repair work, this trio of matching dials, tuning capacitors & coils could be used to rebuild an early TRF receiver. This equipment would be of about 1926-7 vintage. This photo shows an old Igranic filament rheostat. It’s quite a sturdy & elaborate device for a variable resistor. that was a mid-1920s horn speaker. Although sadly neglected and shabby looking, the Sterling “Baby” was actually in working order and should restore quite well. The 1948 5-valve Healing hardly warrants a mention at this stage but it also came from the same shed. It was a good shed, that one, and it wouldn’t surprise me if something else old and interesting comes to light in the near future. There is still a lot of junk in there yet! A box of treasure I recently met Domonic, a new col82  Silicon Chip lector who has caught the valve radio “bug” really bad. He is collecting radios as though there will be none left by the end of the month. In the space of just a few weeks, he managed to track down about 20 old radios plus a box of miscellaneous radio parts. It was these odd bits and pieces that were offered to me; not for money but in return for a repair. It seemed like a good deal to me so I accepted it. Well, what was in the mystery box? All 1920s parts; that’s what! First, there were about eight old triode valves. A quick examination revealed that most had burnt-out filaments but two of them were still serviceable. And even though the others were no longer usable, they were still very acceptable as show pieces. A display of old valves only has to look the part; they do not have to be in working order. There was also a quantity of board mounted 4-pin valve sockets. These included the American UX type, as well as the British standard type. Two of the valve sockets were of the old porcelain variety which are fairly rare today. There are also five vernier dials which could come in handy although they would all require stripping, cleaning and new dial glasses before they could be considered usable. In addition, there are a few ancient grid leak capacitors of the type that have clips fitted to them to hold a grid leak resistor. And there were a couple of resistors to go with them. It is authentic old radio parts such as these that are so valuable when rebuilding an old 1920 receiver. Apparently someone had stripped an old 5 or 6-valve TRF at some stage and the three inclined coils and matching tuning capacitors have been saved. Three of the previously mentioned vernier dials were possibly part of the same receiver. Unfortunately, only one of the five audio transformers was still operative. This is not surprising as these particular items have a very high mortality rate. Most of them end up with open circuit primary windings due to the extremely fine wire used in their manufacture. Also included amongst the bits and pieces were a number of swinging coil sockets with their accompanying plug-in coils. There are several 2-coil models with a single swinging coil and a 3-coil unit with two swinging coils. Once again, these are fairly rare items these days! Bits & pieces Naturally, there are a lot of other incidentals: old mica capacitors, numbered dials, pieces of square section wire, odd vintage style control knobs, wire-wound rheostats, and a driver from an old Amplion horn speaker. The driver’s pole piece wind­ings are still intact, so that could be a handy item. The last items worth mentioning from my treasure chest are several variable grid leak resistors. There are four of them and they are all in working order with resistances averaging from about 0.5-10MΩ. It was the first time I had ever seen variable grid leak resistors; I had only read about them previously. Valuable items No doubt some readers may consider that what I have de­scribed in the last few paragraphs is little more than junk. Well perhaps it is to some people but not to me. As far as I’m con­cerned, there are a few really valuable items there although some may wonder what would I possibly use them for. I have quite a number of 1920s receivers with missing and damaged parts – sets with broken dials, open-circuit audio trans­ f ormers, missing knobs, burnt-out valves and numerous other problems. The restoration of old and incomplete receivers is an impossible task without a comprehensive supply of appropriate spare parts. In the January 1993 issue of SILICON CHIP, the Vintage Radio story for that month described the restoration of a mid-1920s 3-valve receiver. That particular restoration required the following old-style spares: an on/ off switch, a radio frequency choke, an audio transformer, a B605 valve, a couple of terminals and possibly a few other incidentals that have slipped my mind. All these parts were readily available from my own spare parts supply. Going back to the August 1989 issue, Vintage Radio gave details of a complete rebuild of a mid-1920s receiver. In this instance, what was little more than an empty radio cabi­ net was transformed into a working 3-valve receiver. This was done by using carefully selected vintage spare parts that were appropriate to that era. The finished receiver may not have been very original but it looked the part and is a whole lot more interesting than an empty cabinet. So there it is - old junked parts from valve radios of any age are useful to collectors and restorers of vintage receivers. One cannot operate without usable spares and one should not miss out on any opportunity to obtain them. No doubt many parts will never be used but others will be the essentials that restore an otherwise unrestorable SC receiver. This simple 2-unit swinging coil socket assembly (with spare coils) is one of several such coil assemblies found in the au­thor’s “treasure chest”. These old-style single-gang tuning capacitors always make a crystal set or 1-valve receiver a little more authentic looking. These variable grid leak resistors are real relics from the past. The one on the left has a carbon track & wiper arm, while the others are, presumably, carbon granule compression types. May 1994  83 Silicon Chip 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. 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. April 1989: Auxiliary Brake Light Flasher; What You Need to Know 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 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. 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. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car ORDER FORM Please send me a back issue for: ❏ May 1989 ❏ June 1989 ❏ November 1989 ❏ December 1989 ❏ April 1990 ❏ June 1990 ❏ October 1990 ❏ November 1990 ❏ March 1991 ❏ April 1991 ❏ August 1991 ❏ September 1991 ❏ January 1992 ❏ February 1992 ❏ June 1992 ❏ July 1992 ❏ January 1993 ❏ February 1993 ❏ June 1993 ❏ July 1993 ❏ November 1993 ❏ December 1993 ❏ April 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 July 1989 January 1990 July 1990 December 1990 May 1991 October 1991 March 1992 August 1992 March 1993 August 1993 January 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ November 1988 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 April 1993 September 1993 February 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 May 1993 October 1993 March 1994 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 84  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. 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. 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. 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. February 1992: Compact Digital Voice Recorder; 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; AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­controller – Lesson 1; Antenna Tuners – Why They Are Useful. 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. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4; Even More Experiments For Your Games Card. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags: More Than Just Bags Of Wind; Building A Simple 1-Valve Radio Receiver. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6; Switching Regulators Made Simple (Software Offer). April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7; Spectrum Analysis Using An Icom R7000 Communications Receiver. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, December 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from soldout 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. May 1994  85 AMATEUR RADIO BY GARRY CRATT, VK2YBX The Rhombic: a high gain wire antenna for HF reception Capable of providing significant performance at HF, the Rhombic is often overlooked because of space requirements. Where space is no object, this antenna can give excellent performance, particularly for HF point-to-point communications, on any single amateur band. Basically a variant of the long wire antenna, the Rhom­bic antenna is simple to construct, both electrically and mechan­ically. The antenna is used for skywave communications and adopts horizontal polarisation. When the length of each leg exceeds five wavelengths at the frequency of operations, the gain of a Rhombic compared with a half-wave dipole can exceed 12dB. There are two configurations of the Rhombic antenna: reso­nant and nonresonant. The non-resonant antenna, characterised by its resistive termination, has several advantages over the reso­nant configuration. A resonant Rhombic exhibits bidirectional characteristics, a disadvantage for maximum point to point commu­ nications. The non-resonant Rhombic is unidirectional, and pres­ ents a resistive match to the transmitter. Even though some energy is dissipated in the terminating resistor, that energy would have been radiated in the opposite direction in the reso­ l "A" "A" DIRECTIVITY "A" R "A" l Fig.1 (above): the layout of a typical Rhombic antenna. The diamond shape has four “legs” of equal length & the opposite angles are equal. The variation shown in Fig.2 at right uses several parallel elements. This helps reduce the characteristic impedance of the antenna & offers slightly improved gain. 86  Silicon Chip nant Rhombic antenna, so the energy dissipated does not equate to a loss of directivity. There is a theory amongst many HF amateurs that a long wire performs better than a Yagi of equivalent gain, due to the length of the actual receiving elements being able to overcome the diversity effects of ionospheric propagation. The Rhombic antenna, having multiple wavelength elements, goes a long way towards capitalising on this theory. Layout Fig.1 shows the layout of a typical Rhombic antenna. The characteristic diamond shape has four “legs” of equal length and the opposite angles are equal. Technically, the Rhombic is a large travelling wave antenna, which is terminated at the far end with a resistive load equal to the characteristic impedance of the antenna. Fig.3 (left): this diagram shows the gain of a Rhombic antenna compared to a dipole for various leg lengths. The optimum gain of a Rhombic antenna is realised when the side lengths, height & side angles are selected to give in-phase energy fields at the chosen operating band. 14 12 10 GAIN IN dB Ideally, the antenna should be fed with a transmission line having an impedance of 600-800Ω. However, this may not always be practical. Often, Rhombic antennas are fed using coaxial cable and a matching balun at the feedpoint. This termination suppresses reflections of the transmit power and the antenna behaves almost exactly as a matched trans­mission line, resulting in an almost constant impedance over a relatively wide bandwidth. As the gain and beamwidth are signifi­cantly affected by the operating frequency, the practical band­width limitation of the antenna is one octave (or about 2:1 in frequency terms). 8 6 4 2 0 1 2 3 4 LEG LENGTH IN WAVELENGTHS 5 75 Parallel elements Optimising gain A Rhombic antenna with sides equal to two wavelengths or less has relatively low efficiency but if the length of the sides is increased to seven or eight wavelengths, the gain becomes appreciable and the termination loss is reduced to around 20% due to improved radiation efficiency. Fig.3 shows the gain compared to a dipole for various leg lengths. Optimum gain of a Rhombic antenna is realised when the side lengths, height and side angles are selected to give in-phase energy fields at the chosen operating band. As is the case with all horizontal antennas, optimum point-to-point performance is achieved when the antenna is aligned to the calculated optimum wave angle. For amateur use, 70 OPTIMUM LENGTH 65 60 TILT ANGLE IN DEGREES A variant of the Rhombic uses either two or three parallel elements, similar in concept to the reflector and director used in resonant antennas. The use of multiple elements helps reduce the characteristic impedance of the antenna and offers slightly improved gain. The three wires should be separated by one metre or so and wired as shown in Fig.2. The terminating resistor needs to be non-inductive and 800Ω in value, rated at half the transmitter power being used. It should be mounted as close as possible to the ends of the three elements, in a suitable weatherproof hous­ing. This could be remotely mounted at the bottom of the mounting pole, via a length of 800Ω matching cable, for convenience of adjustment. WAVE ANGLE o 0 o 5 o 10 o 15 o 20 o 25 o 30 55 50 45 40 35 30 1 1.5 2 2.5 3 3.5 4 LEG LENGTH IN WAVELENGTHS 4.5 5 5.5 6 Fig.4: this diagram allows the required “tilt angle” to be determined for maximum radiation at the selected wave angle for a given leg length. The tilt angle is simply 90° minus the angle of maximum radia­tion. This is the angle formed between the two halves of an indi­vidual leg of the antenna. where the distance between stations is unpredictable, it is best to adjust the antenna for the lowest angle of radiation and place the elements as high as possible above the ground – normally at least 6-10 metres. Fig.4 allows the best “tilt angle” to be found to give maximum radiation at the selected wave angle, for a given leg length. The tilt angle is simply 90° minus the angle of maximum radia­ tion. This is the angle formed between the two halves of an indi­vidual leg of the antenna (see Fig.1 – shown as angle “A”). Further reading (1). Antenna Engineering Handbook, 2nd edition. Published 1961 & 1984 by McGraw Hill. (2). Antennas, by John D. Kraus, 2nd edition. Published by McGraw Hill. ISBN 0-07-100482-3 (3). The ARRL Antenna Book. Published 1983. ISBN 0-87259-414-9. SC (4). ITT Designers Handbook. May 1994  87 REMOTE CONTROL BY BOB YOUNG How to service servos & winches, Pt.2 Some servos must be regarded as throwaway items not able to be serviced but even defunct servos can be cannibalised to keep others going. This month, we continue with this topic & include an interesting if unusual description on how these cir­cuits work. The development of the modern integrated circuit servo goes back a long way. To my knowledge, Orbit Electronics in America commissioned the first IC amplifier in about 1969. I remember bringing back a bag full of them from the World Aerobatic Cham­pionships in 1971. They were a stunning innovation at the time, replacing an 11-transistor discrete amplifier which chewed up lots of space in the servo. As a result of this chip, Orbit introduced the PS-4 servo which rocked the R/C world at the time. We had never dreamed of servos so small. These days they still look small but the new miniature servos are an or- Fig.1: up until a few years ago, the Signetics NE544 was used in many servos but it is no longer available. 88  Silicon Chip der of magnitude down in size again and make them look very ordinary. However, in 1970 they were simply amazing. By modern standards the Orbit amplifier was not very good and it was prone to several shortcomings no longer encountered in the modern IC servo. They tended to dither around neutral due to the dead band being too small. This tended to raise servo current and made the neutralising a little less precise than it should have been. They also exhibited temperature drift which we ul­timately cured with the addition of a diode in the feedback path. They were also inclined to non linearity, a very serious fault in a servo. New ICs followed in quick succession as other manufacturers scrambled onto the bandwagon in order to maintain their position in the R/C marketplace. Each learned from the preceding and gradually the flaws disappeared. With the arrival of the NE544 IC (Fig.1), servo design came of age but not however without a struggle! The first two NE544 masks were duds. The “B” mask in particular was prone to latch up on the output bridge. This resulted in a short circuit through the bridge and the heat generated usually blew the top off the IC. With the arrival of the “C” mask, all difficulties and de­fects were overcome and I had a long and happy association with this amplifier. Linear, accurate and reliable, it was all we could ask for in a servo amplifier. Then they went and discontinued it. Why do manufacturers do these things? This is particularly upsetting when they offer no direct replacement and people with equipment designed around these devices are left stranded with no alternative. The Japanese in the meantime were pressing on with their own development and Futaba came up with a twochip solution, as shown in Fig.2. The logic was in one chip and the bridge in another. These were also prone to blowing out the side of the chip. (They were vertical mount). Manufacturers do tend to skimp on epoxy at times. They seem to forget that electronic devices are driven by smoke under pressure and that if the case ruptures and the smoke escapes, then the device will no longer function. (Editor’s note: we are indebted to Bob Young for this illuminating explanation of the workings of electronic components. Designing circuits will now be so much easier!) Futaba finally came up with a new single chip solution (with thicker epoxy?) and went on to produce some very popular and reliable servos. These days surface mount components have reduced the servo amplifier to a mere shadow of the old massive shoulder-to-shoulder discrete servo amplifiers. A couple of SM resistors and capacitors and a teensy IC, and that is it. Not like the good old days at all. From a servicing point of view, there have been some nasty techniques introduced by modern assembly methods which make servicing very tedious. Mounting the servo motor directly on the PCB is probably the nastiest. This means complete stripping of the servo to get inside to the amplifier. The completely sealed pot which has now become a throwaway item is another although the scales seem to have been balanced by the improved reliability of these pots. All in all, there is little that can be serviced in the modern servo and one must be careful not to be drawn into servic­ing something that is really a throwaway item. All you can do with cheap servos is to cannibalise them for parts. Fig.2: Futaba’s first integrated circuit servo used two ICs, one for the logic & the other for the motor drive bridge. the servo for crash damage, etc (see last issue) and then plug the opened servo into the analyser. Servo neutral and travel length are checked against the manufac­turer’s specs and a note taken of the servo motor current con­ sumption. Modern servo standards usually call for 1-2ms at extremes with a 1.5ms neutral. The old Futaba was 0.65-1.90ms and I have seen examples of sets swinging around 1.2-2.5ms although this was rare. If in doubt, check the manufacturer’s specifications – if you can get them, that is. with a lint free cloth and a smear of Vase­line will help minimise wear on the track. Check the wiper for tension and cleanliness. Servo motor current consumption is a bit of a headache as motors of various types draw widely differing current. Your best bet is to note the current on a new servo and use it as a guide. What you are looking for is a marked increase in motor current when the motor is free running. Typically, a new 11Ω permag motor will run free (unloaded) at around 80-100mA. As “All in all, there is little that can be serviced in the modern servo and one must be careful not to be drawn into servic­ing something that is really a throwaway item. All you can do with cheap servos is to cannibalise them for parts”. Routine chores That said, there are routine chores which should be carried out regularly and there are some not so routine techniques which may be helpful in unusual circumstances. At Silvertone, we use a servo analyser which consists of a pulse generator with variable rate auto-sweep, a pulse width meter with LED display and a current meter. We begin the service with a visual inspection of The servo is then checked for smoothness over the entire arc of travel. This will pick up any flaws in the potentiometer track. If the servo jumps or dithers around one spot this usually indicates a hole in the track or a dirty pot element. The pot is replaced or cleaned as appropriate and re-neutralised. Where it can be done, pots are cleaned routinely as part of a general service. Clean them they age, the current will creep up, sometimes to as high as 300mA. The causes are many and varied and include dry sintered bronze bearings, dirty commutator, bent shaft, broken brushes and sometimes pin­ions which have been pushed against the bearings. Lubrication Some motors can be stripped down for inspection and repair or cleaning, May 1994  89 REMOTE CONTROL – Servicing the servos and some cannot. A simple way to brighten up a tired motor is to start the motor running and spray CRC-226 onto the bearings (front and rear). This will soak into the bronze bushes and some will work its way into the commutator, cleaning it as well. Be sure to run the motor in both directions for about five minutes. I have seen motors respond well to this treatment, with current consumption falling from around 170mA to 100mA. In a model with four servos, this amounts to a significant reduction in battery load. Motor problems Motor problems are still a worry due to engine vibration pounding away at delicate brushes. One rule to remember in this regard is to never connect the case of the servo motor directly to ground. If the armature insulation breaks down then you have a dead short from motor drive positive to ground. Scratch one servo amplifier. The servo amplifier IC case will rupture immediately, fill the model with escaping smoke, blind whilst monitor­ing the detector output with an oscilloscope. Noisy servos will show up as noise bursts in the sync pause or even obliterated control pulses. If you lack a scope, then remove the Tx antenna and do a range check. With the model at the extreme of control­lable range, move each servo in turn. A noisy servo will kill the signal and control will be lost, whereas good servos will function normally. Once you are satisfied that all is well electronically, reassemble the servo and check for smooth operation and that the servo neutral and current draw have not changed. Sometimes tight­ening the screws in the servo case can distort the case or load the gears, causing increased current drain. Finally, before we close on the servo, servicemen are often asked routine questions or required to perform non-standard modifications on servos for special projects. Here are a few hints on these problems. Reversing servos One common inquiry is how do you reverse a servo. Virtually all transmit- poten­tiometer element. Do not touch the wiper wire. The tricky bit comes about because the wiper usually does not sit in the centre of the pot element. Therefore, after reversing, the wiper must be reset so that the angle/resistance (whichever is easier for you to meas­ure) is the same between the wiper and whichever of the two leads you used as a reference. Once the wiring has been swapped, reset the wiper so that the angle/resistance between the wiper and the reference end or colour is the same as the original. If you get this wrong, the servo will jam at one end of the track, possibly damaging the gears, amplifier or the motor. Plug the servo in and switch the Tx and Rx on. The servo should take up a position roughly around neutral and work in the reverse rotation. Reset neutral and seal up the servo. Stay alert during this procedure and take the phone off the hook. If you get interrupted, all hell can break loose. I have seen people come into my workshop with servos in pieces and unable to get normal operation in either direction. Usually they have reversed one pair of wires and not the other, forgotten to reset the wiper angle or moved the wiper wire by accident. Changing angle of rotation “One rule to remember is to never connect the case of the servo motor directly to ground. If the armature insulation breaks down then you have a dead short from motor drive positive to ground”. the pilot and almost certainly result in a crash. Checking for interference Finally, one last note on servo motors. One common cause of radio interference is servo noise getting into the receiver. This can be caused by a dirty commutator but is more usually caused by broken noise suppression capacitors on the servo motor. These sometimes get broken in a crash and can cause problems to the less experienced or alert serviceman. The best way to check for this is to reduce the Tx signal level to a minimum and run each servo separately 90  Silicon Chip ters these days are fitted with servo reversing switches and these are a good thing too. There are, however, many old transmitters still in use without this feature and the re­quest still comes at regular intervals. The change is tricky at times and some care is called for. Firstly, write down or draw the location of the original wiring before you disturb it. Next, before you touch the pot wiring, measure the angle/resistance between the wiper and one end of the pot element – this becomes your reference end or colour. Now reverse the two commutator leads on the motor and the two wires at the ends of the Another common request is for the angle of rotation of the servo to be changed. Some applications call for very small or very large angles of rotation. The request for 180° of travel for flaps, undercarriage, etc is still a common one. Again, modern transmitters can sometimes accommodate this or servos can be purchased with 180° of rotation as standard. If, however, you live on a desert island and need to doctor an existing stan­dard servo, the procedure is as follows. Most servo ICs have external components to set such parame­ters as travel length, minimum impulse and pulse stretching, so check the specifications for this information. Small varia­tions of rotation angle can be achieved by changing the value of the one-shot timing resistor. Large variations are best done by placing a resistor in series with the pot element. Done very carefully, rotation angles of up to 250° can be achieved. Do not forget to remove the output gear over-travel stops in SC the gearbox. 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. Binary confusion in programming I have read your Binary Clock article in your March 1994 issue with interest. As I am at the moment attending microproces­ sor classes, I saw this Binary Clock as a valuable practice for my binary reading. After typing the program into DOS 6.2 Dosshell Editor and double checking for any mistakes, I naturally wanted to run it. As I know nothing about PC programming, I saved the Binary Clock as Binary.exe and tried to run it through DOS. The computer was rebooted. I then tried through Windows and I got a message to the effect “violation of system integrity, reboot computer”. Could you please advise me how I could execute this pro­gram? (J. S., Portarlington, Vic). • As explained in the article, the published program runs under QBASIC and you have this if you are running DOS 6.2. If you do not have QBASIC set up to be accessed via the DOSSHELL, you can access it via your DOS directory by typing “QBASIC” and then “ENTER”. If you want to run the Binary Clock program as an execut­able file (ie, BINARY.EXE) you cannot save the listing with an .EXE extension. It will cause havoc as you have found. You can UHF antennas to build Could you please inform me as to whether any of the following items have appeared as construction projects in your magazine: (1) a UHF television antenna (channels 29-35), and (2) an infrared triggering device for 35mm SLR cameras, working on reflected beam. (R. P., Deloraine, Tas). • Two UHF antennas have been described in SILICON CHIP. They are the 4-Bay Bowtie Array described purchase the BINARY.EXE form of the program from SILICON CHIP for $7 plus $3 for postage and packing. Overloaded Discolight blows Triacs A while ago, I built two Discolight kits (SILICON CHIP, July & August 1988 & October 1990) with dimmer controls for a friend to be used as light controllers in bands. Since then, we have had occasional problems with the 8A Triacs blowing up which was not caused by overdriving them. As a result, we upgraded to 16A Triacs in the same package and they too are occasionally blowing. The problem is not just with the one chan­nel or the one kit and there is nothing wrong with the lights we are using. What we need is something that is going to be 100% reliable and not give up on us half-way through the gig. We were thinking of using 40A TO-3 Triacs mounted with their heatsinks in a sepa­rate metal box, with a cooling fan and a custom made PC board that has the optocouplers, capacitors, inductors and resistors mounted on it. This way, there will be a low voltage multicore cable between the main controller and the new “output” box. What I need to know is: (1) does the value of the 0.1µF 250VAC capacitor need to be changed?; (2) does the in the January 1988 issue and the UHF Corner Reflector described in the June 1991 issue. An infrared light beam relay which might be applicable to your camera application was published in the December 1991 issue. We also featured a PIR triggered motor driven camera in the March 1993 issue. The 1988 issue is now unavailable but we can supply a photostat copy of the article for $7 including postage. We can supply the other issues for $7 each, including postage. wattage of the 680Ω resistors need upgrading as two of these have burnt out before?; and (3) as the physical size of the inductor will need to be upgraded to handle more current, what should the wire size be, what are the number of turns required and what size/part number should now be used for the toroid formers? Each channel has to be rated at 15-20 amps continuous with­out anything getting too hot. We do need the interference sup­pression as we sometimes get RF switching noise coming from the sound equipment. We sometimes run these kits off a 3-phase outlet so as we can run more lights than off GPOs without blowing fuses (some nights we can run up to 12-14 kilowatts of lights.) Are there any laws against using a low power laser within a public bar as I want to use the Oatley 2mW laser with the deflec­tion kit as a lighting back drop when the band stops playing. (D. Y., Edgewater, WA). • It seems likely that you have had Triac failure because you have been using bigger lamp loads than we recommended. We pub­lished a 4-channel dimmer using 40A Triacs in the June & July 1991 issues but even for this we would only recommend 2400 watts maximum lamp load per channel. Using higher lamp loads would be inviting failure, even with 40A Triacs because the surge currents at switchon are so high. In any case, normal mains circuits should only be loaded with 15 amps as a maximum. The only way to handle higher lamp loads is to have more channels (and more 15A circuits) and to have some Triacs slaved via the MOC3021 opto­ couplers. We strongly caution against using the Discolight or our 4-channel dimmer in a 3-phase setup – it is just too dangerous. We considered the design of a 12-channel light dimmer across 3-phase some years ago and decided against it, partly because of the difficulty of ensuring safety. We suggest you use the same interference suppression net­ work as May 1994  91 Problem with capacitance meter I have had a problem with the performance of the Digital Capacitance Meter Kit (May 1990). The problem is that the readings are slightly unstable; eg, a 22pF capacitor varies from 19-22pF on the pF range, while a 2200pF capacitor varies from 2189-2196. It is also necessary to carry out the calibration procedure each time the instrument is used, as the setting varies. I wonder if perhaps you could offer a solution to my problem. (R. D., NZ). • The problem with drifting calibration can be caused by the master oscillator comprising IC4, trimpot VR2 and the 100pF styro capacitor. We suspect that one of these used in our 4-channel lighting desk. This used a 0.22µF/250VAC capacitor and an inductor consisting of 0.8mm enamelled copper wire on a much larger toroid. You can upgrade the 680Ω resistors to 1W but they should not burn out under normal use. We should also point out that our 4-channel lighting desk also incorporated lamp preheat to reduce surge currents and also had features such as chaser and lamp flash. Back issues are available at $7 each (includes p&p). Some states do have laws controlling the use of lasers in public places. You would be wise to consult the Department of Labour and Industry in your state. Optical pickup for high energy ignition I am writing regarding adapting a circuit published in SILICON CHIP in June 1988 for a high energy electronic ignition conversion. Could this circuit be adapted to use an optical sensor (switch) as my car is a 1978 Skyline and does not suit the Hall Effect Siemens setup and the Sparkrite parts are not now available? I have an optical switch from a Lumenition brand setup and the companion chopper for this unit. Three wires go to the optical switch. (B. K., New Lambton, NSW). • Based on the voltages you have 92  Silicon Chip components is faulty. First, check that the IC is labelled LMC555CN, TLC555CN or ICM­7555. If the IC is labelled LM555­ CN, then this is only a standard 555 timer and should be replaced with a CMOS type. The 100pF capacitor or VR2 could also be faulty and you may like to try substituting for these components. With regard to the display jitter, check that regulator REG2 is correctly earthed to the mains supply earth as shown in the wiring diagram. Similarly, check that the transformer is earthed to the metal plate at the rear of the case. Note that the transformer body is usually heavily covered in varnish so you may need to scrape this away at the mounting points to ensure a good earth to the transformer case. +12V 2.2k LUMENITION MODULE OPTO PICKUP 0.1 Q2 TO IC1 10k 10k GND given for when the optical switch is interrupted or not, it should be possible to adapt it to our High Energy Ignit­ion quite simply. Just modify the circuit published in June 1988 as follows: remove the 820Ω resis­tor at the input and change the 56kΩ resistor at the base of Q2 to 10kΩ. The accompanying circuit shows the details. Controlling a motor driven actuator I have developed a project that I have been working on part-time for three years. This is a 12-volt nicad powered elec­tric motor driven actuator. This assembly is now developed to a satisfactory stage, however I am now stumped as I have an elec­tronic problem I can’t solve. I wish to control my actuator remotely which isn’t the problem. My problem is telling the motor to start and then stop at a pre-selected and adjustable RPM, then pause momentarily for the motor to come to rest, then reverse to the same RPM. This is then a completed cycle. I have sought and received varied and widely conflicting advice that all terminate in the “too hard – can’t do” basket. Is expensive computing power necessary as I have been told or is there a low-cost circuit that will do the job? (G. B., Carra­jong Lower, Vic). • There are a number of ways of approaching your problem but they don’t need to be complicated and they certainly don’t require a computer or a microprocessor, although that is a possible solution. All you need to do is to measure the motor RPM and then when a certain figure is reached, let the motor stop, reverse it and so on. The simplest way to measure and sense the RPM would be to use a frequency to voltage converter and use it to drive a com­parator which would switch the motor off when the preselected speed was reached. After that, you need some logic circuitry to reverse the motor and go through the cycle again. We can’t pro­vide a complete design for you but can give you a good start in the “Overspeed Alarm” published in our June 1990 issue. How to get ultra bass in a small room I was wondering if you could help me with a problem to do with speakers and room posi­tioning. I have built an 88W per channel amplifier and I am using a pair of homemade speakers utilis­ing one 12-inch 68W woofer, one 4-inch 48W midrange and two 3-inch 28W tweeters. This combination gives me just the right level of power I am looking for in my small room (loud, and damn loud if I want to show off!). There is only one discrepancy; ie, I have problems getting enough bass. I don’t mean normal bass. I mean headache inducing bass! I have always put it down to my small room size but in my experimentation, I found that if I stand on my bed, right against the wall opposite the speakers, I get more than enough bass to satisfy my sub 200Hz hungry ears! Since my parents weren’t keen on my idea of attaching a hanging chair to my ceiling, I must turn to the experts for more suggestions. I hope you don’t tell me I need a bigger room be­cause I haven’t had much luck convincing my parents to swap my room for the lounge room! One other thing – what is the maximum continuous temperature rating SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. Now you can search through all the articles ever published for the one you want. Whether it is a feature article, a project, a circuit notebook item, or a major product review, it doesn’t matter; they are all there for you to browse through. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you can use a word processor or our special file viewer to search for keywords. Now with handy file viewer: the Silicon Chip Floppy Index now comes with a file viewer which makes searching for that article or project so much easier. You can look at the index line by line or page by page for quick browsing, or you can make use of the search function. Simply enter in a keyword(s) and the index will quickly find all the relevant entries. All commands are listed on the screen, so you’ll always know what to do next. Note: requires CGA, EGA or VGA graphics card, IBM-compatible PC, MSDOS 3.3 and above. Disc size:   ❏ 3.5-inch disc   ❏ 5.25-inch disc ❏ ❏ ❏ ❏ ❏ ❏ ❏ Floppy Index (incl. file viewer): $A7 + p&p Notes & Errata (incl. file viewer): $A7 + p&p Bytefree.bas /obj / exe (Computer Bits, May 1994): $A7 + p&p Alphanumeric LCD Demo Board Software (May 1993): $A7 + p&p Stepper Motor Controller Software (January 1994): $A7 + p&p Printer Status Indicator Software (January 1994): $A7 + p&p Switchers Made Simple – Design Software (March 1994): $A12 + p&p Note: Aust, NZ & PNG please add $A3 (elsewhere $A5) for p&p with your order Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date______/______ Name _____________________________________________________ PLEASE PRINT Street _____________________________________________________ Suburb/town __________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 979 6503; or ring (02) 979 5644 and quote your credit card number (Bankcard, Visacard or Mastercard). ✂ for a 2N3055 power transistor? I am developing some really high power 13.8V power supplies and am using 3055s because I have obtained around 30 of them secondhand at low cost. How many would you expect a 40amp supply to need? (J. P., Teralba, NSW). • The question you ask about getting more bass could easily take a whole magazine to answer in detail. You don’t necessarily need a larger room to get more bass and in fact you can get huge amounts of bass inside a car and that is much smaller than any room. However, as you have found, loudspeakers do set up standing waves in any room at particular frequencies and when you stand in the right place you get copious amounts of bass. So what to do? Try changing the position of the loudspeakers. In general, the closer into the corners you place the speakers, the more bass you will get. You will also get more muddy sound but that may not matter depending on what sort of music you are listening to. You will probably find that there is a good compromise between the amount of bass and the overall clarity of the sound. Failing that, we have to ask about the size and design of the loudspeaker cabinets. This may not be suited to the speakers you are using. Your question about 2N3055s could also take a lot of space to answer fully. Briefly though, the 2N3055 is a rated at 150 watts for a case temperature of 25°C and has a maximum junction temperature of 200°C. Just how much power a 2N3055 can actually dissipate depends on its SOAR conditions (ie, voltage and current within the “safe operating area”), its junction temperature and the ability of the heatsink to get rid of the heat. Having said that, in a typical power supply designed to deliver 13.8V DC and producing around 22V unregulated, we would not like to see more than 5 or 6A through each 2N3055 in a parallel setup. So for 40A output, you would probably need eight devices and they would need to be mounted on a vary hefty heatsink capable of dissipating around 300W total. That is a big ask indeed. By the way, you would also need a transformer capable of delivering around 900W and all the other components would need ratings SC to match. May 1994  93 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 10am4.30pm; 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 Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card ✂ Card No. RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 Radio and Electrical Books 1914 Catalog Electro Importing Co ............$18 1936 Radio Data Book ...............................$15 Hammarlund Short Wave Manual (1937)....$11 Henley’s 222 Radio Circuit Designs ......$26.50 Neon Signs (1935) ................................$28.50 How to Become a Radio Amateur (1930) .....$7 How to Build & Operate Short Wave Receivers ...................................................$18 How to Build a Solar Cell ...........................$11 High Frequency Apparatus (1916) .............$29 Radio for Beginners ................................$6.50 Radio for the Millions .................................$20 Short Wave Radio Manual (1934) ..............$30 Television (1938) .........................................$7 Tesla Coil ....................................................$11 Tesla Coil Secrets .......................................$16 Tesla Said ...................................................$79 Construction of Large Induction Coils ........$23 The Wimshurst Machine How to Make .$19.50 The Wireless Man ......................................$27 Wireless Experimenter’s Manual 1920 .......$31 Electrical Goods & Radio Apparatus ..........$14 Electroplating (1911) ............................$17.75 Experimental Television How to Make ........$34 Meissner “How to Build” Instructions ........$22 How & Why of Radio Apparatus ...........$20.50 All prices include postage. Payment can be made by cheque or money order made out to Plough Book Sales, PO Box 14, Belmont, Vic. 3216. Phone (052) 66 1262. Silicon Supply and Manufacturing 4002B 4010B 4011B 4012B 4013B 4014B 40150 4017B 4019B 4023B 4025B 4027B 4040B 4048B 4050B 4053B 4060B 4069B 4070B 4071B 4075B 4082B 4094B 74HC11 74HC27 .86 .70 .86 .77 .82 1.53 1.55 1.88 .82 .67 .67 .67 2.13 1.15 .77 1.39 1.71 .69 .69 .69 .69 .69 1.31 .55 .50 74HC30 74HC76 74HC86 74LS11 74LS12 74LS13 74LS14 74LS20 74LS21 74LS27 74LS30 74LS33 74LS49 74LS73 74LS74 74LS83 74LS85 74LS90 74LS92 74LS109 74LS126 74LS138 74LS139 74LS147 74LS148 .50 .65 .55 .60 .60 1.00 .65 .65 .50 .50 .50 .60 2.85 1.35 .55 .90 .75 1.10 1.45 1.10 .60 .75 .75 2.85 1.25 74LS151 74HC138 74HC139 74HC154 74HC174 74HC373 74F00 74F02 74F08 74F10 74F11 74F20 74F30 74F32 74F36 74F38 74F151 74F163 74F169 74F175 74F241 74F244 74F257 74F258 74F353 .60 1.05 .60 3.80 .80 1.25 .50 .50 .50 .50 .50 .50 .50 .50 1.10 .80 .65 .85 2.30 .80 1.15 1.10 .75 2.15 1.75 All prices include sales tax. Phone (02) 554 3114; Fax (02) 554 9374. After hours only bulletin board on (02) 554 3114 (Ringback). Let the modem ring twice, hangup, redial the BBS number, modem answers on second call. PO Box 92, Bexley North, NSW 2207. TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. INTELLIGENT INFRARED receiver: (ref. SILICON CHIP, March 1994). Use your TV or VCR infrared remote control transmitter to control your TV or hifi appliances with an intelligent infrared receiver kit ($55). Also available infrared transmitters, preprogrammed and learning models. For details call Benetron Pty Ltd (018) 20 0108 or (02) 963 3868. ELECTRONICS REPAIR BUSINESS: Established 3 years, Finley, NSW. Authorised for major brands, contract with local retail outlet, low rent premises on highway, ideal first business for qualified technician. Well equipped workshop and office, extensive manual collection, good parts stock. Price $45,000 neg. WIWO. Phone owners (058) 83 1977 BH or (058) 85 9254 AH. Reply Paid No.7, PO Box 1058, St Marys, NSW 2760. Ph: (02) 833 1146. Fax: (02) 623 5559. SECONTRONICS COMPONENTS, COMPUTERS, ELECTRON TUBES S/H TEST EQUIPMENT, COMPUTER REPAIRS PC COMPATIBLE KEYBOARDS 101 AT:$39 I/O + IDE/FDD $35 RECYCLED EPROMS AT I/O CARDS $22 2716 $1.50 2SD1169 $2.00 2732 $1.50 2N3440 $0.80 2764 $2.00 2N3439 $0.80 27128 $3.00 2SC3157 $4.00 27256 $3.50 27C41 $0.80 27512 $3.50 7406 $0.20 27C101 $4.00 8250 $5     8251 $2 8259 $2    6809 $8 MC8050 $2 MCT275 $1.20 MOC3032  $2 VALVES: QQV07/50 $25 3D21   $8 12AU7   $6 6SG7   $8 6U8A   $8 1S2   $3 1T4   $6 CV553   $3 2C39A $30 2C40A $40 3A4   $8 5651   $6 5651A   $6 6AK5   $6 6J6WA  $7 6AM6  $5 6BA6  $4 SPECIAL: SURFACE MOUNT COMPONENT PACK – 180 RESISTORS, 40 ZENERS, 30 TRANSISTORS AND 2 ICs. $6.50 INC. PACK & POST PHONE OR MAIL ORDERS, CREDIT CARDS ACCEPTED FOR ORDERS $20 & OVER, DISCOUNTS FOR QUANTITY ORDERS. NOW AT SHOP 5, 79 RICKSTON ST, MANLEY WEST, QLD. 4179. OPEN TUES - FRID 9.30AM - 5PM, SAT. 9AM - 2PM. MAIL ORDERS TO PO BOX 34 CANNON HILL QLD. 4170. PHONE (07) 396 1859, FAX (07) 855 1014. MEMORY PRICES PRICES AT MARCH 21ST, 1994 SIMM 1Mb x 3 1Mb x 9 4Mb x 9 4Mb (72-pin) 8Mb (72-pin) 16Mb (72-pin) 70ns 70ns 70ns 70ns 70ns 70ns $63 $65 $256 $250 $520 $985 DRAM DIP 1 x 1Mb 256 x 4 70ns 70ns $8.50 $9.00 IBM PS.2 55/65SXVP L40/N33 90/95 PS1 4Mb 4Mb 4Mb $250 $300 $265 MAC 4Mb 4Mb x 80 80ns 6Mb P’BOOK $220 $420 CO-PROCESSORS 387S/DX to 40 $105 LASER PRINTER HP with 4Mb $260 COMPAQ LTE 25C 8Mb $635 TOSHIBA 2000SX 8Mb $475 46/1900 3.3 4Mb $350 SUN SPARC 10/20 16Mb $1140 PCMCIA 1Mb V2 BAT SRAM $230 2Mb V2 BAT SRAM $380 2Mb V2 FLSH SRAM $380 42Mb V2 HARD DRIVE $560 Sales tax 21%. Overnight delivery. Credit cards welcome. 5-Year Warranty Ring for Latest Prices 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 CONTROL RELAYS, Robots, Radios or Railways from LPT1: of your XT to 486 PC. 64 bits. Fully expandable. 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. SOUTHERN CROSS SBC, accessories & EPROM emulator. See SC 8/93 & 12/93. Ideal for TAFE, schools & individual use. Alpine Technolo­gies, tel/fax (03) 751 1989. ROMLoader EPROM EMULATOR (EA Jan/Feb 92) - upgrade to handle 27128, 27256 EPROMs. Includes memory edit facility. 8051 Proto-Boards (EA Feb 93) PELHAM also available. Send SAE for details. Tantau Australia, PO Box 1232, Lane Cove 2066. AH (02) 878 4715. VALVE AMPLIFIERS: Australian made. Mono, stereo, guitar using 2A3, 211, 6L6 or 807 valves. Williamson reproductions. Parts available for DIY constructors. Circuit diagrams and construction details for many types of valve amplifiers. Valve equipment repairs. Lancroft Pty Ltd, PO Box 439, Bexley 2207. Phone (02) 567 5390. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in May 1994  95 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. stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. BINARY CLOCK - OCTOBER 1993: complete documentation supplied, includes introduction to binary, how it works, PLD source list­ings, conversion tables. Kit with PCB and all components $75 + $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 + $5 p&p. Prototype Electronics, 1/29 Stewart St, Parra­ matta, NSW 2124. Phone (02) 683 3510; Fax (02) 630 3148. Pay by cheque, money order, credit card. SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 I/O pins, board space includes prototyping area. Program it on a PC (only CTOAN ELECTRONICS 4-channel piped music system for your home. Hundreds of dollars cheaper than commercial systems. Build it yourself and save heaps. Ring for details. PO Box 211, Jimboomba 4280. Phone (07) 297 5421. Advertising Index Altronics ................................ 76-78 Antique Radio Restorations.........94 Av-Comm.......................................9 Ctoan Electronics........................96 David Reid Electronics ..............73 33 instructions) with development kit which includes one “BASIC STAMP” ($249 plus S/T & post), extra modules ($66 plus S/T & post). Send 45c stamp for more information. Parallax distributor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­dale, NSW 2350. Facsimile (067) 72 8987. Dick Smith Electronics........... 10-13 Electronic Fault Info.....................61 Harbuch Electronics....................73 Instant PCBs................................95 Jaycar ................................... 45-52 Kalex............................................75 PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. L & M Video.................................26 MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. PC Computers........................63,96 WANTED Secontronics................................95 HANDBOOK & SCHEMATICS for Advance Instruments pulse generator model PG52. (Local agents were Jacoby Mitchell.) Phone Steve Dolding (02) 888 4883 B.H. or (02) 871 1073 A.H. McLean Automation.....................72 Oatley Electronics........................23 Pelham........................................95 Plough Book Sales......................95 RCS Radio ..................................94 Rod Irving Electronics .......... 27-31 Silicon Chip Back Issues....... 84-85 Silicon Chip Projects Book......OBC Silicon Chip Software.............93,96 Silicon Supply & Manufact...........95 Telecom Australia........................71 Transformer Rewinds...................95 SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. Now you can search through all the articles ever published for the one you want. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you can use any word processor or our special file viewer to search for keywords. Now with handy file viewer: the Silicon Chip Floppy Index now comes with a file viewer. You can look at the index line by line or page by page for quick browsing, or you can make use of the search function. Simply enter in a keyword(s) and the index will quickly find all the relevant entries. All commands are listed on the screen, so you’ll always know what to do next. Note: requires CGA, EGA or VGA graphics card, IBM-compatible PC, MSDOS 3.3 and above. Price $7.00 + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. 96  Silicon Chip Tektronix....................................IFC West Tech Industries.................IBC Yuga Enterprise...........................17 _________________________________ 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. WEST TECHTRONICS WEST TECHTRONICS UP TO 14-DAY MONEY BACK GUARANTEE OTHER PRODUCTS AVAIL: DEALERS REQUIRED IN ALL STATES. PLEASE APPLY IN WRITING ONLY. PLACE YOUR ORDER BY PHONE, FAX OR POST. DEALER & TRADE PRICES AVAIL. UP TO 1kg $4.50; UP TO 5kg $6.50. O/NITE & OTHER FREIGHT PLEASE CALL. SYSTEMS WITH 2YR WARRANTY 4M RAM, 210M HD, 1.44 OR 1.2 FDD, 1M SVGA CARD, 14" SVGA MONITOR 0.28DP, 101 KEYBOARD, 2S/1P/1G, 200W P.S. & EPSON PRINTER LX-400. 386DX-40 128K CACHE .............................$1750 486DX-33 258K CACHE & 3 VL/B S ...........$2260 488DX2-66 256K CACHE & 3 VL/B S .........$2570 PLEASE CALL FOR ANY CONFIGURATION AT THE BEST PRICES NOTEBOOK 386SX-33, 4M RAM, 120M HD, VGA LCD-32 GREY SCALES, 1S/1P/1VGA/1KBD/1PS/1 SCANNER PORT, CARRY CASE, BATTERY & CHARGER ..............................$2195 DOS 6.2 & WINDOWS 3.11 ..........................$169 MULTIMEDIA PERFORMANCE PACK .........$769 S/BLASTER 16 BIT WITH ASP .....................$439 COMPUTER ACCESSORIES VGA CARD CABLES - MADE TO STANDARD; WE CAN MANUFACTURE CABLES TO YOUR SPECS IBM PARALLEL PRINTER CABLES: 2M $4.00 5M $9.00, 10M ...........................$18.00 2M RIGHT ANGLED PLL P CABLE ...........$10.00 25 CORE STRAIGHT THRU CABLES D25M-D25M; 2M $5.50, 5M .........................$9.00 D25M-D25F; 2M $5.50, 5M ..........................$9.00 D9F-D25M MODEM 2M ...............................$5.50 D15 HIGH DENSITY M-M OR M-F ............$14.00 SCSI CBLE 1M; 50 CENT. M-M .................$28.00 MAINS TO MONITOR IEC 2M .....................$8.00 MONITOR TO PC IEC 2M ............................$8.00 FDD POWER SPLITTER CBLS; 3.5"-3.5", 3.5"5.25", 5.25"-5.25", 5.25" Ext. ........................$5.00 ETHERNET CABLES - 50 OHM COAX: 2M . . $8, 5M . . $15, 10M . . $25, 20M . . $37 TELEPHONE ACC. ARE TELECOM APPRVD FAX/PHONE SWITCH ...................................$155 ANSWERING MACHINE AV130 ...................$130 MUSIC ON HOLD ...........................................$49 AUST. INLINE PLUG. $2, SCKT. ..................$2.00 AUST. WALL SCKT. $2, ...........DBLE ADPT $3.50 AUST. PLUG - UD MOD. SCKT. ...................$3.00 AUST. SCKT - US MOD. SCKT. ....................$3.00 TEL. CRIMP TERMINALS 20 pack ..............$1.00 AUST. TELEPHONE EXT. LEADS: 3M . . $6, 5M . . $8 10M . . $9 15M . . $10 AUST. TO US PLUG EXT. LEADS: 5M . . $6, 10M . . $7, 15m . .$8 US MODULAR EXTENSION LEADS: 5M . . $4, 10M . . $5, 15M . . $6 HANDSET CURLED CORD 4M ........................$5 TEL. CABLE: 4 CORE FLAT 100M ..................$35 MAINS POWER ACCESSORIES: WITH ENERGY AUTHORITY APPROVAL SURGE PROTECTION POWER BOARDS: 4 WAY OUTLET $28, 6 WAY OUTLET ............$33 10M MAINS EXTENSION LEAD .....................$11 MAINS FLASHING STROBE ..........................$35 DC POWER ADAPTORS/SUPPLIES: PANTHER POWER SUPPLIES-REG.: 240VAC: <at> 2A CONT. $59, <at> 4A CONT. .......$79 240VAC/300MA <at> 3,4,5,6,7,5,9 12VDC .........$15 240VAC/500MA <at> 3,4,5,6,7,5,9 12VDC .........$19 12VDC/800MA <at> 3,4,5,6,7,5,9, 12VDC .........$15 WEST TECHTRONICS PLUGS, SOCKETS & PLUG ADAPTORS BNC PLUG/RCA SCKT. ...............................$2.50 PL259 PLUG/RCA SCKT. .............................$2.50 BNC SCKT./BNC SCKT. ...............................$3.00 BNC 3 SCKTS.-T PIECE ..............................$4.50 3.5MM PLUG/TV COAX SCKT. ....................$1.30 RCA PLUGS RD, BLCK, WHITE, YLW. ........$0.40 TV METAL COAX PLUG $1.30, SCKT. ........$1.30 TV COAX PLASTIC INLINE JOINER ...........$1.30 TV COAX MALE/MALE JOINER ..................$1.30 TV RIBBON 2 PIN PLUG - 3MM ..................$1.30 BNC CRIMP PLUG FOR RG58 ...................$2.50 TNC CRIMP PLUG FOR RG58 ....................$3.00 CB MIC 4 PIN PLUG, FEMALE ....................$3.00 CAR RADIO ANT. PLUG INLINE .................$1.30 AUDIO 6.5MM MONO PLUG, RED, BK. ......$0.90 AUDIO 3.5MM STEREO PLUG BLCK. ........$0.90 AUDIO 3.5MM STEREO SKT. & STRN. .......$1.10 HARDWARE, TRANSFORMERS & TOOLS ALLIGATOR CLIPS 32MM RED, BLCK. .......$0.40 AUTO RELAY SPST 12VDC/30 A ................$5.50 GROMMETS: 9.7 x 6.0mm CBLE HOLE .....$0.17 ..........................12.7 x 9.5mm CBLE HOLE $0.22 5A FUSES 3AG, M205 TYPES ....................$0.17 3AG FUSE HOLDER CHAS MNT. SRW ......$1.20 AC POWER TRANSFORMER 2155 ............$9.00 HOBBY KNIFE SET WITH 5 BLADES .........$3.00 COAXIAL STRIPPING TOOL-RG58,59 ..........$15 4-PCE JWLERS S/DRVR SET PHILPS ............$5 TELEVISION ACCESSORIES INDOOR BALUN 300/75 TV SCKT. ..............$1.30 INDOOR BALUN 300/75 TV PLUG ..............$1.10 75-OHM BAND SEPARATOR UHF/VHF ......$4.00 2-WAY 75 OHM COAX SPLITTER BOX ......$3.50 4-WAY 75 OHM COAX SPLITTER BOX ......$4.50 KINGRAY MASTHEAD AMPLIFIERS: MHU34T MSTHD. AMP. - UHF 34DB ..............$55 MHW34T MSTHD. A.-UHF/VHF 34DB ............$55 MH21 POWER SUPPLY ..................................$55 BATTERIES AND ACCESSORIES NICAD CHRGR & T AAA.AA,C,D,9V ..............$23 BATTERY HLDRS: 2XAA, 4XAA ..................$0.50 SHARP V/CAM BATRY PK BT-75 ...................$79 MOTOROLA T/TALKER BAT. 12V/4A ..............$99 MOTOROLA FLIP PH FAST CHGR/CND .....$180 WEST TECHTRONICS WEST TECHTRONICS GENDER CHANGES & ADAPTORS: D9: MALE-MALE, FEM.-FEM. ......................$4.00 D25: MALE-MALE, FEM.-FEM. ....................$6.50 D15 HIGH DENSITY M-M, F-F ....................$7.50 6 MINI DIN MALE - 5 DIN M OR F ...............$7.50 D9M-D15HD F, D9F-D15HD M ....................$6.50 D9M-D25M, D9M-D25F ...............................$5.00 D95-D25M, D9F-D25F .................................$5.00 HIGRADE DISKS; BX/10 3.5" DSHD ...........$9.50 MOUSE; 3 BUTTON MS COMP .................$19.50 IBM M/S MOUSE & PS2 CONVTR ...............$115 MATS: RED, BLUE OR GREY ......................$5.00 101 KEYBOARD .............................................$35 FAX MODEM; NETCOM ...............................$349 MONT; 14" SVGA 0.28DP 1024X768 ...........$490 PANASONIC FLOPPY DISK DRIVES: 1.44MB $70, MNT. KIT $9, 1.2MB ...................$86 HARD DRIVE IDE V/C 340M 13MS ..............$520 SIMM; 1M 9-70 $70 4M 9-70 .........................$290 M/BOARDS: 3 VL/B SLOTS & 256K CACHE; 488DX-33 $689; 486DX2-88 .........................$945 CARDS: GAMES CARD .............................$19.50 ETHERNET 16 BIT (NE2000 COMPAT.) .......$285 VL/B CIRRUS LOGIC SVGA 1M W/A ...........$160 IDE I/O CARD IDE HD/FDD/2S/1P/1G ...........$35 GAME CARD ..............................................$19.50 VGA CARDS; VLBUS VGA ACCEL. ..............$175 TRIDENT 3900 1MB SVGA CARD (ISA) ......$125 PRINTER CANON 10EX B/JET SQUIRT .....$495 ETHERNET ADAPTER SCSI DRIVES, CASES, NETWORKING, FIBRE OPTICS, LAB POWER SUPPLIES, TEST GEAR, EDUCATIONAL PANELS, RADIO CONTROL DEVICES, LASER ACCESS. ETC. WEST TECHTRONICS WEST TECHTRONICS TEL: (02) 872 2847, FAX: (02) 872 5329. PO BOX 336, NORTH RYDE 2113. WEST TECHTRONICS WEST TECHTRONICS