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BUMPER PREMIERE EDITION NOW AT YOUR NEWSAGENT Vol.9, No.6; June 1996 Contents FEATURES 4 Review: BassBox 5.1 Design Software For Loudspeaker Enclosures It lets you select a speaker and vary the box parameters or select a box and check the performance of various speakers – by Rick Walters 26 ‘MV Oriana’ – Luxury And Technology Afloat REVIEW: BASSBOX 5.1 LOUDSPEAKER DESIGN SOFTWARE – PAGE 4 The “Oriana” is P&O’s newest passenger liner. Here’s a brief rundown on its impressive electrical and propulsion technology. PROJECTS TO BUILD 14 A High-Performance Stereo Simulator New design uses a digital delay chip. Build it and enhance the sound from mono VCRs, AM tuners or electronic instruments – by John Clarke 22 A Rope Light For Party Fun And Frolic Build this simple chaser circuit and drive low-voltage coloured lights arranged in a plastic tube – by Robert Riede 31 Build A Laser Pointer From A Kit Five minutes is all it takes to assemble this nifty laser pointer – by D. Light 40 A Low Ohms Tester For Your DMM This handy test instrument plugs into your DMM and lets you accurately measure resistances down to 0.01Ω – by John Clarke 70 Automatic 10-Amp Battery Charger Need a charger with some oomph? This unit features automatic selection of 6V, 12V and 24V batteries & is short circuit & reverse polarity protected – by Rick Walters HIGH-PERFORMANCE STEREO SIMULATOR – PAGE 14 LOW OHMS TESTER FOR DMMs – PAGE 40 SPECIAL COLUMNS 10 Computer Bits Overcoming the 528Mb hard disc barrier in older PCs – by Geoff Cohen 53 Satellite Watch Another Long March launcher failure – by Garry Cratt 54 Serviceman’s Log Chuck it away and buy a new one – by the TV Serviceman 60 Radio Control Multi-channel radio control transmitter; Pt.5 – by Bob Young 86 Vintage Radio Testing capacitors at high voltages – by John Hill DEPARTMENTS 2 Publisher’s Letter 32 Circuit Notebook 59 Order Form 82 Product Showcase 92 Ask Silicon Chip 93 Notes & Errata 95 Market Centre 96 Advertising Index 10A AUTOMATIC BATTERY CHARGER – PAGE 70 June 1996  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Christopher Wilson Phone (02) 9979 5644 Mobile 0419 23 9375 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW 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: $54 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) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Cable TV could be a financial black hole As I write this editorial, I am contemplating a 60cm offcut of coax used in the now-contentious Optus cable rollout. It is unlike any coax that you might normally come across. For a start it is surprisingly rigid, due to its outer sheath of solid aluminium which is itself sheathed in black plastic. It is also thicker than I thought, at 17.3mm in dia­meter. Such cable would be very costly to make and even more costly to string from poles – the supposedly cheaper option. So as I look at this 60cm piece of plumbing, I am having serious misgivings about the whole process of delivering Pay TV. Sure, I’ve already stated my opposition on the grounds that these thick cables on poles are ugly but the cost of wiring up Australia with this stuff is going to be enormous. And if the cost of cabling in the street is high, it is modest compared with the cost of running the cable into each home, supposing that even 20% of homes are going to want it. It seems as though every installation involves a couple of men and their equipment for at least a day, for just a nominal rental. At this rate, the two Pay-TV contenders are going to be losing hundreds of millions of dollars a year or maybe a whole lot more. Various articles in the financial press have attempted to analyse the possible revenue and costs associated with Pay-TV delivery and they all seem to come up with the same bottom line – it is always in the red! As far as I can tell, the reason why Optus is so furiously running out cable is so that it can compete with Telstra as soon as possible in providing a telephone service. All the much vaunted other services such as on-line banking, video phones, home shopping and so on, are much further in the future so there won’t be much revenue from those in the near term. In any case, home shopping and banking could be available quite soon via the Internet and therefore via normal telephone lines. And if Optus sees its financial salvation in a future telephone service to Australian cities, it is not reckoning on Telstra being a very savage competitor and one which will be even tougher if it is privatised. No, the more I look at Pay-TV, the more I foresee a huge financial black hole. I think Optus and Telstra are galloping pell-mell into this technology when a more rational approach would say “Hang on. Where is all this leading?”. In the 1980s we had all those high flying entrepreneurs backed by starry-eyed banks. We paid for that. Are the 1990s going to be the era of the Pay-TV debacle? We’ll pay for that too! 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 electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semicustom electronics & data communications. 63 chapters, in hard cover at $120.00. Silicon Chip Bookshop Radio Frequency Transistors Newnes Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Guide to TV & Video Technology By Eugene Trundle. First pub­lish-­ ed 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. 336 pages, in paperback at $49.95. Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Digital Audio & Compact Disc Technology Electronics Engineer’s Reference Book Hard cove Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM Power Electronics Handbook Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order r Edited by F. F. Mazda. version now available First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $85.00. Surface Mount Technology By Rudolph Strauss. First pub­ lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $52.95.   Title  Newnes Guide to Satellite TV  Guide to TV & Video Technology  Servicing Personal Computers  The Art Of Linear Electronics  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Electronic Engineer's Reference Book  Radio Frequency Transistors  Surface Mount Technology  Audio Electronics Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A Price $55.95 $39.95 $59.95 $49.95 $55.95 $59.95 $120.00 $85.00 $99.00 $52.95 Review BassBox 5.1 Design Software For Loudspeaker Enclosures This comprehensive speaker enclosure design package requires Windows 3.1 & DOS 5.0 or later & allows two design approaches. You can select a speaker & vary the box parameters to suit it or you can ‘pick a box’ & check the performance of various speakers in it. By RICK WALTERS The minimum system requirements to run this package, apart from Windows and DOS, are a 486 processor, 4Mb of RAM and 7.5Mb of hard disc space to accommodate the files. Following the usual procedure of “when all else fails – read the manual”, we in­stalled the software and proceeded to explore its capabilities, without reading the manual. We were able to enter speaker parameters and plot impedance curves 4  Silicon Chip but the subtlety of a picture of a motor car with a check box beside it, which when ticked changed the response curves, had us reading through the manual very carefully. The 112-page manual is quite detailed. The major headings are Getting Started, Running BassBox, Editing the Loudspeaker Database, Testing Loudspeakers, Testing Passive Radiators and Constructing The Box. The first paragraph in “Getting Started” informs us that the product is pronounced as “base barks” (presumably with an American drawl), then goes on to list the main features of the program. These include both small and large signal analyses, plots of amplitude, phase and group delay, multiple onscreen response plots for easy comparisons, acceptance of Thiele-Small or elec­ t romechanical parameters, variable box damping, built-in test procedures for analysing speaker parameters, the ability to select imperial or metric units, with the capability to switch in the middle of a design, and the ability to save and recall designs. When you start BassBox under Windows, you get the familiar bar across the top of the screen together with drop-down menus. As mentioned previously, there are two approaches to using the program, either by selecting a speaker and operating with the box as the variable or starting with an enclosure and testing its performance with various speakers. If you run Windows in 1024 x 768 resolution, the main Bass­Box window normally displays columns for six sets of speaker data, one set of box parameters and one graph, as shown in Fig.1, or it can be switched to the display shown in Fig.2. This only applies to the main screen; no others can be changed. Speaker parameters When you begin a new enclosure design the first step is to enter the speaker parameters. The program accepts Thiele-Small (T-S) or Electro-Mechanical (E-M) parameters. T-S par­ameters are named after Neville Thiele who pioneered the development of small speaker enclosures in 1961 and Richard Small who expanded on vented box loudspeaker systems in 1973. Most speakers nowadays are supplied with Thiele-Small parameters. The electromechanical parameters are much harder to measure and are not often quoted. Only three T-S parameters are necessary for the program to be able to calculate the box size and plot a response curve. These are the speaker free-air resonance Fs, the total Q (both mechanical and electrical) Qts, and the volume of air having a compliance equivalent to the loudspeaker suspension, Vas. A database of loudspeakers listed by manufacturer is acces­sible from within the program. This includes most well known makes from the USA and Europe. Unfortunately though, when Fig.2: this alternative screen can be selected when your video resolution is set to 1024 x 768. The four plots – Amplitude Response, Power Response, Phase Response and Group Delay – are all displayed on the screen. I searched for two Peerless models which are available in this country, they weren’t included in the Peerless database of 33 units. However, you can readily add new speakers, edit existing speaker data or delete existing models. If the response curve is plotted and you wish to vary the box size, the quickest way is to duplicate the data from the optimum column into the custom column and then vary the volume, plotting this response. Both responses then appear on the same graph, giving an immediate indication of the change in performance. The standard vented enclosure only controls the low fre­quency end of the speaker response. By using a double enclosure with two ports, a bandpass vented box is created – see Fig.3. The program allows the design of 4th and 6th order bandpass boxes. BassBox also provides for the design of boxes with passive radiators. These are essentially speakers without voice coils and magnets and are often called drone cones. They effect the response in a manner similar to the port in a vented enclosure. Fig.3: by using a double enclosure with two ports, a bandpass box is created. You can design either 4th or 6th order responses. Fig.1: the opening screen for any video resolution. The other responses shown in Fig.2 are individually selectable using the GRAPH menu. June 1996  5 Fig.4: when you select a vent type the vent picture changes to reflect this. If one of the vent dimensions is entered the other is calculated immediately. There are six different response curves available for each speaker/box combination. These are the normalised response in dB, power response in dBSPL, acoustic power, impedance, phase and group delay. As the box parameters are varied these graphs can be erased and redrawn for the new conditions or superimposed on the previous ones, allowing you to see the effects of the changes. In addition, if the actual response curve of the speaker is available, this information can be entered and will be reflected in the amplitude response plot. It is also possible to enter the room or vehicle response as well, if this is available, to get a more realistic idea of the final system performance. Once the box volume has been optimised, the duct size is calculated. Normally the duct is flush with the front panel and protrudes into the interior of the box but with a bandpass Fig.5: a preview of the printout of a design. If an enclos­ ure has been designed for a client, the graphs could be supplied with the system. system both ends of the duct are flush. BassBox can take these facts into account when calculating the duct length. The calculator (see Fig.4) allows round, square or triangular vents, although round vents, using PVC pipe from your local hardware store, are the easiest to produce. OK, we have the volume and the vent size. We now need to establish the dimensions of the enclosure. The dimension calcula­tors make this easy. A large number of cabinet shapes, such as barrel, cylinders and the usual style of optimum prism, as well as many others including a wedge shape, are avail­able. The calculator lets you compensate for the space taken up by the speaker and internal bracing, by adding these to the required internal volume. Once they are entered, the three box dimensions can be calculated or for example, if the internal height was to be 860mm, Fig.6: the responses for both the 44-litre and 14-litre enclosures are shown here. As you can see the smaller box lifts the bass response slightly but at 67Hz starts dropping off more rapidly. You trade volume for extended bass response. 6  Silicon Chip this dimension can be entered and the other two will be calculated using the ratio of 1.62:1.00:0.62 for height to width to depth. Having completed the design, it can be printed out as shown in Fig.5 and filed or used to compare the performance of various combinations. As mentioned previously, the program comes with a loudspeak­ er database. If the speaker parameters you need are not available or should you wish to verify them for a suspect loudspeaker, a testing procedure is included in this program. It draws a circuit of the setup needed to make the particular measurement and gives you instructions on how to carry it out. As you enter each meas­ured value the program proceeds to the next step, changing the circuit and instructions as necessary. A procedure is also included for measuring the parameters of a passive radiator. The sequence is similar to that detailed above. The final chapter of the manual gives some details on the construction of speaker boxes. Headings are Shape, Materials, Construction and Duct Placement. Proven results All this is very impressive but how well does the program work? In the January 1993 issue of SILICON CHIP we described a 2-way speaker system using a 165mm Peerless woofer type 174WF. This design, which used the T-S parameters to calculate the box de­tails, featured a vented enclosure with an internal volume of 14 litres. YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT Fig.7: this response graph for the woofer in a 2-way system was taken from our January 1993 issue and shows excellent correlation with Fig.6. The response curve for the woofer was published in the article. By substituting those parameters in this program we did a comparison to see how closely the results agreed with one another or if they agreed at all. The data was entered into BassBox and it was asked to cal­culate the optimum enclosure. This it did, giving a figure of 44 litres. Upon checking this box response with the previous one we saw that the hump at 100Hz was missing from our new design. The hump in the older design indicates that a smaller enclosure volume was used. After entering a volume of 14 litres into the program, the two graphs were virtually identical. The previous graph shows a peak of +2.26dB at 100Hz while ours shows +2.3dB at 100Hz, an excellent correlation. Our two plots of the optimum and custom values are shown in Fig.6. The previous data is shown in Fig.7. Of course if both programs use T-S parameters and are based on the same calculations, the results should be the same. It becomes a question of whether there has been any “enhancement” of the procedures. In summary, I found this a fascinating and rewarding program to use. Its operation is reasonably intuitive and the handbook is quite detailed. Being able to select a woofer from one of the retailer’s catalogs, enter the T-S parameters and plot the bass response in a matter of seconds is a real boon. Still wondering about the motor car and check box? There is a natural bass rise of about 12dB/octave in most motor vehicles, beginning around 50Hz. Ticking the box adds this boost into the response curve to give a better idea of the speaker’s overall performance in a car. Crossover design too As an added bonus a copy of X.over 2.0, a passive crossover network design program, is included. This lets you design 2-way and 3-way cross­ overs. It can calculate values for many common 1st, 2nd, 3rd and 4th order networks including Butterworth, Bessel, Chebychev and Linkwitz-Riley. And as you would expect, woofer details can be loaded from BassBox files. It also allows you to design LCR networks to compensate for the rise in im­pedance of voice coils at higher frequencies. At its price of $299, I believe Bass­ Box 5.1 with X.over 2.0 is good value for money. The package is available from Earthquake Audio, PO Box 226, Balgowlah, NSW 2093. Phone (02) SC 9948 3771; Fax (02) 9948 8040. YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 June 1996  7 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. Macservice 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. Macservice Pty Ltd COMPUTER BITS BYhttp://www.pcug.org.au/~gcohen GEOFF COHEN Fitting a big hard disc drive to older machines Have you installed a big hard disc in your PC but then found you couldn’t format it to its full capacity? Here’s how to regain those missing megabytes. With the way hard disc prices are dropping, most people can afford to upgrade their old hard disc drive. A 1Gb hard disc drive cost over $1000 at the start of last year. Today, with a bit of haggling, one can be had for under $400 and the price is still dropping. If you have a new 486 or Pentium PC with an LBA (logical block addressing) BIOS, there’s no problem when it comes to accessing the full capacity of the larger drives. However, if you have an older machine without LBA, it will not support drives over 528Mb in size. This will apply to all 286 and 386 machines and to most other machines if the copyright date of the BIOS is earlier than 1994. I even have an old Toshiba T5100 (386SX-16MHz) which does not support hard discs over 100Mb. In this situation, the disc will still operate but the available disc space will be set at the limit set by the BIOS. As an example, let’s say that you fit a 1.6Gb drive to your machine but the BIOS only supports drives up to 528Mb capacity. In that case, you would be unable to access over 1Gb of available disc space – unless you take special steps, that is. Basically, you have three options: (1) Upgrade the BIOS to one that does support drive sizes greater than 528Mb (often difficult); (2) Use dual-drive emulation (either LBA BIOS: What’s It All About? The LBA (Logical Block Addressing) mode is a hard disc accessing scheme that overcomes the old DOS 528Mb hard disc limit. The old system only allowed a maximum of 1024 cylinders, 16 heads and 63 sectors per disc, which worked out at 528Mb. LBA allows up to 255 heads, which gives a maximum size of 8.4Gb. Although most new large capacity disc drives have more than 1024 cylinders, the LBA software automatically translates the number of cylinders, heads and sectors to numbers 10  Silicon Chip under the limits. As an example, the IBM DPEA-31080 1.08Gb hard disc) has 2100 cylinders, 16 heads and 63 sectors. Without LBA, the number of cylinders would be truncated to 1024 and over half the hard disc’s capacity would be wasted. With LBA selected (most new PCs have this as an option in the CMOS setup), then as far as DOS or Windows 95 is concerned, the hard disc has 525 cylinders, 64 heads and 63 cylinders This allows the full 1.08Gb capacity to be used. hardware or software, as available) to split the drive into two logical drives. You may then have to enter the relevant values for each in system setup, then partition and format them. (3) Install a special software driver that automatically over­ c omes the 528Mb limit. Of these, the last option is the one that will generally be preferred. What if you are unsure as to whether or not your BIOS sup­ports disc drives with greater than 528Mb capacity? The answer to this is to first check the manual for the motherboard or, failing that, enter the CMOS setup and check for any indication there. If you are still unsure, install the new hard disc in the normal manner, fdisk and format it as necessary, and type dir. If the number of bytes free is close to the formatted capacity, then all is well. If it’s less than 528Mb, then you need to choose from one of the above three options to bypass the barrier. The software option There are several utilities available to correct the disc limit problem with older PCs. For example, Ontrack has a utility called “Disk Manager” which is often supplied with the hard disc drive, although sometimes you have to ask the retailer to include this so check carefully when buying. The Seagate range of hard disc drives come with the EZ-Drive utility package. This used to come on a separate floppy disc but is now pre-installed on a section of the hard disc. After the disc has been installed in the computer, you simply follow the instructions in the manual to transfer the files to a floppy disc. In my case, I have been using EZDrive with a 540Mb hard disc on my old Toshiba 5100 for over a year. All the software I use has performed flawlessly, except for (blush) my own Diskinfo software (see August 1995). Diskinfo does actually run OK and gives me the disc parameters but then hangs the PC so that I have to reboot (I will try to fix it in my spare time). I have also tested EZ-Drive on several other 486 & Pentium PCs and it ran without any problems. Transferring the data There are several options available when you put a new hard disc in your PC. The most obvious one at first glance is to leave the old hard disc as drive C and install the new one as drive D. However, it’s generally better to install the new drive as drive C since it will invariably be much faster than the old drive. So if your old drive is a slowpoke, relegate it to the drive D posi­tion. By the way, make sure that the master and slave jumpers are correctly set on the two drives, otherwise the BIOS will not recognise them. Check also that the power and I/O cables have been plugged in correctly. And, of course, always make sure that the power cord has been removed from the back of the machine before removing the cover. If you are comfortable with setting up hardware and you have a second PC, a really nifty way to transfer the data from your old to the new hard disc drive is to use a special program such as LapLink or similar, which normally needs to be installed on both computers. After you have installed DOS on the new hard disc, temporarily put the old hard disc in your spare PC, connect the special cable between the two PCs and use Laplink to start transferring the data (a parallel cable transfers data at around 4Mb per minute). Another method is to do a full backup of the old hard disc and then transfer this to the new drive. If you have a tape or ZIP drive backup this will be straightforward but it’s a bit tedious with floppy discs. Delete the permanent swapfile on the old hard disc (assuming you have one set up) before running backup. After all, there’s not much point in backing up the swapfile. A word of warning here on backups EZ-Drive Installation Moving EZ-Drive off a Seagate hard disc is quite straight­ forward. Here’s a brief rundown of the procedure used for the Seagate ST31270A which has a formatted capacity of 1.28Gb. First, you need a bootable floppy disc and this must ob­ viously be created before you remove your old hard drive.You just put a blank floppy disc in drive A and type format A: /S. After installing the Seagate drive, you then go to the PC’s CMOS setup menu (usually accessed by pressing the Del key during boot-up), then move to the hard disc setup submenu and select type 2. If this not available, you have to manually enter the following data: 615 cylinders, 4 heads and 17 sectors. You then save and exit the CMOS setup. Note that some computers use an automatic setup system that will automatically detect the above hard disc values for you. Note also that these values are only interim numbers that allow you to access that section of the hard disc that contains the installation files. In reality, the Seagate ST31270a hard disc drive has 2485 cylinders, 16 heads and 63 sectors. The next step is to boot from the floppy disc, go to the prompt for the new drive and type seamove. This command will automatically copy the EZ-Drive software from the hard disc to the floppy disc. When it’s finished, the Seamove program then erases all the files and the drive partition on the hard disc, so that it can later be formatted to full capacity. At this stage, you again reboot the PC from the floppy, type ez and press enter.You then select the “Fully Automatic In­stallation” option which automatically creates a single partition and formats the disc. – make sure that you select the verify after backup option. It’s too late when you discover that you have a faulty floppy disc after your hard disc is dead and you can no longer recover data from it. If neither of the two above options appeal, then you can always make copies of your data files and reinstall all your applications. In fact, this is not a bad idea since it gives you a fresh installation to start with and gets rid of extraneous files that have been left over from old applications that have been deleted. then it is also necessary to install MH32BIT.386 if you want 32-bit disc access. This optional 32-bit disc access driver replaces the original Windows driver and is necessary to prevent error messages in older machines. Again, the exact proce­dure is set out in the installation guide that comes with the hard disc. If you are running Win95, then you can ignore such things as setting up permanent swapfiles and installing 32-bit disc access drivers. Win95 takes care of memory and disc access management for you. Windows speed-up Final comments After the new hard disc has been installed, it is worth­while setting up a permanent swapfile for Windows 3.1. To do this, launch Control Panel, double click the 386 Enhanced icon, then click Virtual Memory & click Change. You then select “perma­nent” from the resulting dialog box (under New Swapfile Settings). In most cases, you can use the swapfile size recommended by Windows. You should also check the 32-bit file access box. It’s then just a matter of clicking OK and rebooting Windows so that the changes can take effect. Note that if you are using EZ-Drive, The only major difference I have found when running EZ-Drive is that when I want to boot off a floppy drive, I need to wait until the message “Hold the Ctrl key down to boot from a floppy” flashes on the screen. In other respects, it seems to be extremely compatible. Finally, if you ever want to disable EZ-Drive, first make a backup, then boot up from a floppy disc (with FDISK. EXE). When DOS is up and running type FDISK/MBR. This will rewrite the master boot record and allow the drive to be used with a newer LBA SC motherboard, for example. June 1996  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au • Realistic stereo performance • Low noise and distortion • Adjustable stereo effects • Runs from a 12V plugpack A high-performance stereo simulator This high performance stereo simulator uses a digital delay chip to convert any mono signal source into stereo. You can use it to enhance the sound from mono VCRs, AM tuners or electronic musical instruments. By JOHN CLARKE If you compare the sound from a mono source to that of stereo the difference is easily perceived. Instead of appearing to come from a single point, the sound is dispersed over a wide field between the stereo speakers. Very few recordings these days are made 14  Silicon Chip with ping pong ball effects whereby the sounds bounce from one channel to another and back again. Because of this, attempting to simulate stereo sound is a reasonably straightfor­ward design exercise. In the past, the usual approach to producing a simulated stereo effect was to divide the mono signal into separate fre­ quency bands and distribute these into the left and right chan­nels. This frequency division was done by an array of filters which rejected certain bands in the audio spectrum for one chan­ nel but allowed them through for the other channel. The real drawback to this approach is that you need a fair few filters for a good result. Another method was to use bucket brigade delay chips but these are quite expensive, have high noise and distortion and the overall result is mediocre. So how have we gone about it? Our task has been made easier by Dolby surround decoders which require high-performance digital delay chips. We have used one of these devices and the results are very good. How it works In essence, we use the delay chip to provide a “comb filt­er” effect. This chops the incoming audio signal into lots of very narrow frequency bands. The narrow frequency bands are subtracted from the mono signal and the result becomes the left simulated channel. The difference between the simulated left channel and the incoming mono signal then becomes the right simulated channel. Fig.1 shows the general arrangement of our stereo simula­tor. It has an input buffer IC1a and this feeds the delay chip IC2. It also drives one input of mixer IC1d while the delay chip drives the other input. The output of mixer IC1d becomes the right channel. For the left channel, the delay chip drives inverter IC1c and its output is mixed with the input mono signal before mixing with the buffered output mono signal in IC1b. This process of mixing a signal with an identical delayed version results in some frequencies being “in phase” and these pass through without attenuation. Other frequencies are cancelled out because they are “out of phase”. If the delay chip is set at 1.5 milliseconds, for example, the input signal will be in phase with the delayed output at 666Hz (1/1.5ms), 1.333kHz, 1.999kHz and so on. Thus, these fre­ quencies will pass through to the right channel. For the left channel, the inverted signals are out of phase at 666Hz, 1.333kHz and so on and these frequencies will coincide with a dip in the response. Conversely, signals at 333Hz, 999Hz, 1.666kHz, etc will pass through to the left channel but will have dips in the right channel. Fig.2 shows the frequency response for the left and right chan­nels. The solid curve is the right channel while the dotted curve is the left channel. Note that the notches at the lower frequencies (333Hz, 666Hz, 999Hz, etc) are very deep while at higher frequencies the notch depth becomes progressively less. Looking at the responses of Fig.2, it is easy to see where the term “comb Fig.1: the stereo simulator has an input buffer (IC1a) and this feeds the delay chip (IC2). The delayed signal is then mixed with the buffered input signal to produce the right channel. The left channel is produced by mixing an inverted delay signal with the buffered input signal. filter” came from – all those notches look like the teeth of a comb. Mind you, Fig.2 shows just one possible set of frequency responses. It corresponds to a delay setting of 1.5ms. You can also select delays anywhere between 0.5ms and 4ms, in steps of 0.5ms, and each of these settings will have its own characteristic “comb filter” effect. Circuit description We have used the M65830P digital delay IC from Mitsubishi as the heart of the circuit. This is the same delay chip as used in the Dolby Pro Logic Surround Sound Decoder, as published in the November & December 1995 issue of SILICON CHIP. The delay chip works by first converting the incoming analog signal to a digital format which is then clocked into memory. This digital signal is then clocked out at the end of the delay period and converted back to an analog form. The chip is timed by a 2MHz crystal oscillator to provide a 500kHz sampling rate. In the Dolby Surround Sound Decoder, we used a microproces­sor to control the delay AUDIO PRECISION STEREO AMPL(dBr) & AMPL(dBr) vs FREQ(Hz) 0.0 21 MAR 96 12:18:53 0.0 -5.000 -5.00 -10.00 -10.0 -15.00 -15.0 -20.00 -20.0 -25.00 -25.0 -30.00 -30.0 -35.00 -35.0 -40.00 -40.0 20 100 1k 10k 20k Fig.2: these “comb filter” effects are the frequency response curves for the left and right channels. The solid curve is the right channel while the dotted curve is the left channel. June 1996  15 16  Silicon Chip chip but in this circuit we use three low cost CMOS ICs. These are required because the M65830P gets its delay setting instructions each time it is powered up. The full circuit of the Stereo Simulator is shown in Fig.3. The mono input signal is AC-coupled into unity gain buffer IC1a via a 2.2µF capacitor. IC1a then drives mixers IC1b & IC1d and the delay chip, IC2. The signal to IC2 is AC-coupled to its pin 23 via a low-pass filter comprising the 39kΩ and 18kΩ resistors and the 560pF and 150pF capacitors. This filter rolls off signals above about 15kHz to prevent higher frequencies affecting the digital conversion and causing spurious effects in the output. The capacitors at pins 17, 18 and 20 control the rate of delta modulation which is the type of analog to digital conversion used in IC2. Similarly, the .068µF capacitor at pin 16 controls the digital to analog conversion output signal appearing at pin 15. This output is applied to another 15kHz filter comprising two 39kΩ resistors, an 18kΩ resistor and 560pF and 150pF capacitors. The output of IC2 is then AC-coupled to inverter IC1c and mixer IC1d via a 4.7µF capacitor. IC1b & IC1d mix the signals applied to their inverting inputs via 10kΩ resistors. Their outputs at pins 1 & 7 become the left and right simulated stereo channels. All four op amps in IC1 are biased to +6V by a voltage divider consisting of two 10kΩ resistors across the 12V supply rail. Delay selection IC2’s delay is controlled by CMOS chips IC3-IC6. Each time IC2 is powered up it automatically resets itself to provide a 20ms delay. This is much too long for this application so we need to set it by feeding a serial data stream to the Data input at pin 6. This data is Fig.4: taken from a Tektronix TDS360 200MHz digital scope, this printout shows the timing of the SCK (top), Data, (serial clock) and REQ (request) lines to IC2. This data is sent once to the delay chip each time it is powered up. clocked in at each negative transi­tion of the SCK input and accepted on the rising edge of the REQ input. The serial data stream must include various mute, sleep and address codes as well as the delay information before IC2 will respond. Fig.4 shows the timing of the Data, SCK (serial clock) and REQ (request) lines to IC2. What happens is that when the REQ line goes low (lower trace), the serial data block (centre trace) can be clocked in. In the time that the REQ line is low, there are 12 clock pulses and these clock in the respec­tive data levels. Our data line shows two positive pulses in the data line but this is not the case as the data stream actually contains 12 separate codes which can be high or low. On the first clock pulse, the sleep data is fed in and this must be a low. The following six codes are for delay selection while the next three are the low mute, ID1 and ID2 (identification codes). The last two codes are high for the ID3 and ID4 identifi­cation signals. For the ID4 code to be valid, pin 7 of IC2 must be also high. With all this data complexity, it is easy to see why a microprocessor is the most elegant solution in Dolby Prologic decoders, particularly when it can provide a lot of other functions as well. IC5, a 74HC165 serial shift register with parallel load inputs, is used to supply the first eight bits of data. This has the advantage that the data can be initially set by parallel load inputs (inputs A-H). The E, F and G inputs are con­nected to a DIP switch to allow Performance Frequency Response................. (see graphs) Fig.3 (left): the heart of this circuit is the Mitsubishi M65830P digital delay chip. Each time it is powered up it needs a stream of serial data to set its delay time. It can be set for between 0.5ms and 4.0ms using a DIP switch (see Table 1). Once data has been sent to IC2, CMOS chips IC3, IC4 and IC5 are effectively out of circuit. Signal-to-Noise Ratio................. 96dB unweighted (22Hz to 22kHz); -100dB ................................................... A-weighted, with respect to 1V RMS. Harmonic Distortion................... <0.5% at 1kHz and 1V RMS Maximum Input Signal................ 1.2V RMS Output Level............................... 0-1V RMS Delay Options............................. 0.5-4ms in 0.5ms steps June 1996  17 Above: bird’s eye view of the Stereo Simulator – there is not much wiring to be done. Note that shielded cable is used for the connections between the board and the RCA sockets. Another view of the assembled PC board, prior to installation in the case. Take care to ensure that all ICs are correctly oriented. 18  Silicon Chip the delay to be selected. IC3 and IC4 are used to control IC5. IC3 is a 4060 binary counter which has its own oscillator, set by the components connected between pins 9, 10 & 11. IC3 supplies the clock signal for IC2 at its Q4 output. Its Q5 output at pin 5 is inverted by IC6a to drive IC4, a 4022 divide-by-8 counter which has eight outputs, O0 to O7. We use the O1 output to drive the serial input of IC5. Finally, we use the QH output of IC5 to drive the data input of IC2. When the “6” output of IC4 goes high after 12 counts of SCK, IC3 is reset, the REQ line goes high and IC5 is set into the load position with a low pin 1. At power up, the 47µF capacitor at the input of Schmitt NAND gate IC6b is high and its output is low. When the capacitor charges, the pin 3 output goes high to apply a short positive pulse to the reset input of IC4 via the .001µF capacitor. This resets IC4 and the code is fed to IC2. The resultant waveforms are shown PARTS LIST 1 PC board, code 01406961, 100 x 100mm 1 plastic case, 111 x 45 x 140mm, Arista UB14 1 front panel label, 95 x 33mm 1 rear panel label, 95 x 33mm 1 12VAC 300mA plugpack 1 SPDT toggle switch (S1) 1 4-way DIP switch (DIP1-DIP3) 1 2MHz crystal (X1) 3 panel mount RCA sockets 1 insulated panel mount DC socket 1 5mm ID rubber grommet 1 400mm length of hook-up wire 1 150mm length of shielded cable 1 250mm length of tinned copper wire 7 PC stakes Semiconductors 1 TL074, LF347 quad op amp (IC1) 1 M65830P digital delay (IC2) 1 4060 binary counter (IC3) 1 4022 divide by-8 counter (IC4) 1 74HC165 8-bit shift register (IC5) 1 4093 quad 2-input Schmitt NAND gate (IC6) 1 7805 5V regulator (REG1) 1 7812 12V regulator (REG2) 1 1B04 bridge rectifier (BR1) 1 1N914, 1N4148 signal diode (D1) 1 3mm red LED (LED1) Fig.5: the parts layout and wiring diagram for the Stereo Simula­tor. Note that the input and output leads are wired in shielded cable. in Fig.4, as previously discussed. Note that once the “6” output of IC4 goes high, it also pulls the reset line of IC3 high and this stops any further data being sent. Thus, IC3, IC4 and IC5 serve no further purpose until the circuit is powered up the next time. That completes the circuit description except for the power supply. This uses an AC plugpack fed to a bridge rectifier (BR1) and a 470µF filter capacitor. A 12V regulator supplies power for the op amps in IC1 while a 5V regulator supplies the rest of the circuit. Construction Capacitors 1 470µF 16VW PC electrolytic 3 100µF 16VW PC electrolytic 2 47µF 16VW PC electrolytic 5 10µF 16VW PC electrolytic 2 4.7µF 16VW PC electrolytic 1 2.2µF 16VW PC electrolytic 3 0.1µF MKT polyester 2 .068µF MKT polyester 1 .012µF MKT polyester 1 .001µF MKT polyester 3 560pF MKT polyester or ceramic 2 150pF ceramic 2 100pF ceramic Resistors (0.25W 1%) 1 1MΩ 11 10kΩ 1 100kΩ 3 4.7kΩ 4 47kΩ 1 2.2kΩ 4 39kΩ 3 100Ω 1 22kΩ 1 33Ω 2 18kΩ 1 10Ω The Stereo Simulator is assembled June 1996  19 A view of the Stereo Simulator with the top removed and showing the inside of the rear panel. onto a PC measuring 100 x 100mm and coded 01406961. Our prototype was housed in an Arista UB14 plastic case measuring 111 x 45 x 140mm. Self-adhesive labels, were fitted to the front and rear panels. The full wiring details and component overlay for the PC board are shown in Fig.5. You can start construction by checking the PC board against the published pattern of Fig.6. Fix any broken tracks or shorts that may be evident. Now insert the ICs, diode, resistors and links in the locations shown. Take care with the orientation of the ICs, noting that IC1 is oriented differently to the others. DIP Switch Settings DIP1 DIP2 DIP3 Delay Freq. on on on 0.5ms 2kHz on on off 1ms 1kHz on off on 1.5ms 666Hz on off off 2ms 500Hz off on on 2.5ms 400Hz off on off 3ms 333Hz off off on 3.5ms 285Hz off off off 4ms 250Hz The accompanying resistor colour code chart should be used when selecting each resistor value. Alternatively, This DIP switch can be used to change the delay chip’s setting and thus the stereo effect. Use Table 1 at left to set the DIP switches. use a digital multi­meter to measure each resistor before it is fitted into the board. RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  4 ❏  4 ❏  1 ❏  2 ❏ 11 ❏  3   ❏  1 ❏  3 ❏  1 ❏  1 20  Silicon Chip Value 1MΩ 100kΩ 47kΩ 39kΩ 22kΩ 18kΩ 10kΩ 4.7kΩ 2.2kΩ 100Ω 33Ω 10Ω 4-Band Code (1%) brown black green brown brown black yellow brown yellow violet orange brown orange white orange brown red red orange brown brown grey orange brown brown black orange brown yellow violet red brown red red red brown brown black brown brown orange orange black brown brown black black brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown yellow violet black red brown orange white black red brown red red black red brown brown grey black red brown brown black black red brown yellow violet black brown brown red red black brown brown brown black black black brown orange orange black gold brown brown black black gold brown CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.1µF   100n   104 .068µF   68n   683 .012µF   12n   123 .001µF   1n   102 560pF   560p   561 150pF   150p   151 100pF   100p   101 Seven PC stakes will need to be fitted to the board. This done, insert and solder in the capacitors taking care to orient the electrolytics with correct polarity. Next, fit the 3-terminal regulators and make sure you insert the 7812 (REG2) into the location nearest LED1. Insert the DIP switch, crystal and bridge rectifier. The LED is mounted without shortening its leads and is bent over at right angles to insert into the front panel hole. The PC board is fitted into the case and secured with four self-tapping screws into integral standoffs in the base. Affix the adhesive labels to the front and rear panels and drill out the holes for the power switch and LED on the front panel and for the RCA sockets and DC socket on the rear panel. A 3mm hole is required for the LED. Note that the DC socket must be insulated from the metal rear panel to prevent shorting the AC plugpack to ground. On our prototype, we fitted the DC socket inside a 5mm ID grommet and then secured it with a nut after shaving the grommet thinner with a sharp utility knife. After fitting the front and rear panels, the final wiring can be done. Use short lengths of shielded cable for the input and output connections. The connections from the DC socket to the switch and PC board are made with hook-up wire. Apply power and use a multimeter to check that pin 4 of IC1 is at +12V. Pin 16 of IC3, IC4 & IC5, pin 14 of IC6 and pin 24 of IC2 should all be at +5V. If the LED does not light, it is probably connected the wrong way around. Testing To test the Stereo Simulator, connect the mono input to the mono output of your VCR and the stereo outputs Fig.6: actual size artwork for the PC board. + STEREO SIMULATOR POWER + + + + + 12VAC INPUT MONO INPUT LEFT OUT RIGHT OUT Fig.7: these full-size artworks can be used as drilling templates for the front and rear panels. to the left and right inputs on your amplifier. This done, set DIP1, DIP2 and DIP3 on, apply power and listen to the stereo effect. Now set DIP 1 off and switch off the power. Reapply power after about 10 seconds and check that the stereo effect has changed. If that is the case, the circuit is working correct­ly and you can experiment with the delay settings. Table 1 table shows the delay versus frequency bands for various settings of DIP1-DIP3. We found that the most satisfying stereo effect was obtained with the delay set to either 2ms or 2.5ms. SC June 1996  21 Build a rope light for party fun & frolic You’ve seen those rope lights at discos and in shop displays. Now you can build your own with some plastic tubing, a bunch of lights and a simple driving circuit. Design by ROBERT RIEDE Rope Lights are quite intriguing to look at but essentially they are just another form of light chaser. This one is based on 12V lamps which are driven by SCRs (silicon controlled rectifi­ ers). The circuit has two refinements though. As well as have a variable speed it has a built-in electret microphone to provide triggering from the beat of the music – each beat of the 22  Silicon Chip drums is seen to move the rope lights on by one step. As is usual with most light chasers, the circuit of this Rope Light is fairly simple, although it does have a few inter­esting twists (no pun intended). For example, it uses a programmable unijunction transistor, a device rarely seen these days, and as already men­ tioned, it uses SCRs instead of tran- sistors to drive the low voltage lights. Have a look at the circuit of Fig.1. The core of the cir­cuit is the 4017 decade counter. It is clocked by transistor Q3 and four of its outputs are used to control lamps. Its fifth output, DO4, is used to drive its reset line. Each of the four outputs of IC1 drives the gate of an SCR so that while ever an output is high, its respective SCR will be turned on to drive its lamps. The lamps are not supplied from pure DC because if they were, the SCRs would be unable to turn off. Instead, the lamps are fed raw DC from the bridge rectifier (diodes D1-D4) and the 12VAC plugpack transformer. The beauty of this arrangement is that the SCRs are relatively cheap and it avoids the need for expensive electrolytic filter capacitors. The SCRs are also ideally suited for turning incandescent lamps on and off. The specified C106s have a rating of 4A RMS and a whopping peak repetitive surge current rating of 75A. This makes the C106 far more rugged than any equivalent 4A transistor and it easily handles the repetitive surges of the incandescent lamps. It also means that the circuit has no need of such niceties as filament preheating. Instead of using a 555 or other pulse generator IC to pro­vide the clock source for IC1, this circuit uses a programmable unijunction transistor or PUT. Essentially, this can be regarded as an “anode gate SCR”; it turns on whenever the anode voltage is higher than the gate. The PUT is wired as a relaxation oscillator which produces very brief positive pulses at its gate at a rate determined by potentiometer VR2, resistor R11 and capacitor C8. The beauty of the PUT oscillator compared with, say, a 4093 Schmitt trigger oscillator, is that its frequency is highly predictable. This is not really an issue in this application but it means that the PUT is still a valid approach. Each time the PUT produces a pulse at its cathode it turns on transistor Q3 and this drives the clock input of IC1. So why have the two transistors and other circuitry which appears to control the PUT? The answer is that this part of the circuit provides beat synchronisation of the lights, via the electret microphone. The electret microphone is biased from the DC supply via the 3.3kΩ resistor R1 and its signal is coupled to the base of Q1. Q1 and Q2 operate as simple common-emitter amplifiers with no feedback. Q2 has a gain of about 20 (ie, 10kΩ/470Ω) while Q1’s gain is adjustable up to a maximum figure of 20. This only ap­ plies to low frequencies (bass) since the high frequency gain is severely curtailed by the .068µF capacitors, C4 & C5. The result­ant bass signal at the collector of Q2 swings high and low, pulling the gate of PUT1 with it. When the audio signal swings high, there is no effect on PUT1 but when the gate of PUT1 is pulled low, its anode is liable to be higher than the gate and so it turns on to clock IC1 on by another step. This process means that the clocking of IC1 is effectively synchronised to the bass beat of the music. Construction There are two aspects of the construction for this project: the assembly of the controller and wiring up the “rope” in its plastic tube. We’ll deal with the controller first. It uses a PC board measuring 53 x 82mm and is housed in a plastic utility box measuring 129 x 68 x 42mm. Before inserting any components, check the Fig.1: this circuit is essentially a chaser. Four out­puts from IC1 are cycled continuously and drive four SCRs. Each SCR drives a bank of incandescent lamps from rectified but unfil­tered DC. The PUT provides the clock oscillator for IC1 and is synchronised to the bass beat of the music by the electret micro­phone and amplifier stages Q1 & Q2. PUT clock generator June 1996  23 Fig.2: follow this diagram when building the PC board and take care with component polarity. No heatsinks are required for the four SCRs. board for any defects such as undrilled holes or breaks and shorts between tracks. If any are found they should be fixed before proceeding further. Then start by inserting and soldering the small compon­ ents such as resistors and diodes. Then insert the capacitors and transistors, making sure that the semiconductors and electrolytic capacitors are installed the right way around. Finally, install the IC and the four SCRs. No heatsinks are required for the latter components. You will need to drill three holes in the lid of the case, one for the electret microphone insert and one each for the sensitivity and rate controls, VR1 & VR2. You will also need to drill one hole in each end of the case, to take the power input and output cables. There is no need to run shielded cables to the electret microphone or to the poten­tiometers VR1 & VR2 – ordinary hook-up wire will suffice. Our prototype had the electret fixed to the lid of the case with a blob of epoxy adhesive – a fairly crude but perma­nent approach. Checking the board The Rope Light consists of a length of plastic tubing with a lamp wired into the loom at intervals of about every 30cm or so. Once the wiring is complete, you will want to check the circuit operation with just four lamps connected. To do this, wire up one side of a miniature 12V lamp to each of the SCR outputs. The other side of each lamp then connects to the common line from the board; this actually connects to the +V unfiltered DC line. Now connect a 12V plugpack and switch on. Check with your multimeter for the presence of +5.6V across ZD1 and at pin 16 of IC1. The lamps should be switching on and off at a rate which is variable by VR2. Try tapping the lid of the case with a pencil or your finger nail. Each time you do so, a lamp should switch off and another should switch on. If all these checks are OK then the board is functioning correctly. Rope light assembly Fig.3: actual size artwork for the front panel. 24  Silicon Chip There are several ways of approaching the assembly of the rope light but regardless of how you do it, there will be a number of common aspects. You need a length of 12mm OD clear plastic tubing, say 6-7 metres. You will need at least 5-8 times that length of hookup wire and you will need 60 or more miniature incandescent lamps, in at least four colours. Kit Availability Kits for the Rope Light described in this article are available from Oatley Electronics who own the design copyright. The pricing details are as follows: PC board with all on board components...........................................$24.00 Two pots with knobs............................................................................$5.00 Case to suit board...............................................................................$4.00 16VAC 1.5A plugpack.......................................................................$25.00 7 metre assembled Rope Light.........................................................$40.00 60 miniature coloured lamps.............................................................$12.00 Postage & packing..............................................................................$6.00 For further information on pricing and availability, contact Oatley Electronics, PO Box 89, Oatley NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. PARTS LIST 1 PC board, 53 x 82mm (from Oatley electronics) 1 plastic utility case, 129 x 68 x 42mm 1 12VAC 1.5A plugpack transformer 6 metres 12mm OD clear plastic tubing Miniature 12V coloured incandescent lamps (see text) 1 6-way Molex plug 1 6-way Molex socket 2 knobs 1 10kΩ linear potentiometer (VR1) 1 2.2MΩ linear potentiometer (VR2) Semiconductors 1 4017 decade counter (IC1) 2 BC548 NPN transistors (Q1,Q3) 1 BC558 PNP transistor (Q2) 1 2N6028 programmable unijunction transistor (PUT1) 4 C106D1 silicon controlled rectifiers (SCR1-4) 5 GIG silicon rectifier diodes (D1-D5) 1 5.6V 400mW zener diode (ZD1) 1 electret microphone Capacitors 6 100µF 25VW electrolytic 1 0.47µF monolithic 7 .068µF ceramic Resistors (0.25W, 5%) 1 220kΩ 7 3.3kΩ 1 150kΩ 5 470Ω 1 56kΩ 1 100Ω 4 10kΩ Miscellaneous Hook-up wire, cable ties, solder, plastic sleeving. Inside the box, showing details of the PC board and its wiring. The controller has only two knobs, one for the rate at which the lamps switch on and the other a sensitivity control for the inbuilt electret microphone. Since there are five outputs from the controller PC board, you might think that five wires inside rope light cable would be adequate but that depends on the cross-section of the hook-up wire and the current rating of the lamps. If you use very light duty hook-up wire, (ie, 10 or 13 strands of 0.12mm) it should be cap­able of carrying about 500mA on a continuous basis. That means you could use one hook-up wire for each output, up to a maximum lamp load of say 1A, on the basis that the duty cycle is 25%; ie, each lamp is on for 25% of the time. However, since the common cable carries current for 100% of the time, you would need to run two or three cables together, so you would have a maximum of six or seven wires in the rope. All these can be wired up to a 6-way Molex socket. This then mates to a 6-way cable and plug from the controller. If you want to double the length of the rope light, the far end of the cable can terminate in a Molex plug which can then mate up to a further length of rope light. However, if you do this, you will need to use heavier duty hook-up wire or double up on the light duty hook-up wires. On the other hand, if you don’t fancy making your own rope light cables, you can buy them ready-made from SC Oatley Electron­ics. June 1996  25 MV Oriana being fitted out at the Meyer shipyard in Papenburg, Germany. The vessel’s hybrid drive system allows five different operating modes, combining diesel engines and electric motors. The drive system can deliver a total of 48,150kW for the ship’s propulsion. ‘MV Oriana’: luxury and technology afloat Most people who see the new P&O passenger ship “Oriana” will be impressed by its luxurious appointments but its electrical equipment is just as impressive. It uses hybrid-electric propulsion and is powered by up to six diesel engines. With a gross registered tonnage of 69,153 and a length of 260 metres, the luxury liner “MV Oriana” is among the largest passenger vessels ever to have been built in a German shipyard. The prestigious order was awarded to Jos. L. Meyer GmbH & Co, Papenburg, by the Peninsular & 26  Silicon Chip Oriental Steamship Co (P&O Cruis­es) of Southampton, UK. ABB Industrietechnik’s Marine Division in Hamburg supplied the main electrical equipment for the vessel, which is also the fastest cruise liner to have been built in the last 25 years. The vessel, which was built at the Meyer shipyard in Germa­ny, in the world’s largest (370m long) covered dry dock, had its keel laid in midMarch, 1993 and was ready to leave the dock on July 30th, 1994. The Oriana left Southampton on its maiden voyage in April 1995, on a cruise that took it to the Canary Islands, Morocco, Gibraltar and Portugal. Oriana has a crew of 760 and will normally carry 1,760 passengers (maximum capacity 1,975). It has an overall length of 260 metres, a beam of 32.2 metres and a maximum draught of 7.9m. At 69,153 tonnes gross, it even surpasses Cunard’s Queen Eliza­beth 2 (69,053 tonnes). This puts the Oriana among the largest passenger vessels operating in One of the two 5.25MW shaft generators which can also run as motors for ship propulsion. Their output is rated at 6.6kV 60Hz. the world today. Despite its impressive size, it is able to pass through the Panama Canal. Oriana has a top speed of more than 26 knots (approximately 48km/h), making it the fastest cruise vessel to have been built in the last 25 years. For passenger comfort, cruise ships normal­ly travel at speeds under rather than over 20 knots, so the Oriana will rarely make use of this top speed. Four 5.25MW diesel-generator sets work with the two shaft gen­erators to produce the ship’s electricity supply. The total installed generator rating is 31.5MW. The machines are brushless, self-excited and self-regulating. The ship has 13 decks, 11 of them passenger decks. The total number of cabins is 914, more than half (594) of which offer a view (118 have a balcony). There are eight suites and 16 luxury cabins. Eight of the cabins are specially equipped for handicapped people. Fire protection Fire is one of the greatest hazards to ships at sea. Oriana has been designed for maximum safety in the event of emergencies. For example, the ship has seven fire zones and is divided into 16 watertight sections for full compliance with the latest fire protection and fire-fighting regulations. In addition, watertight fire-doors are built into the bulkhead deck. A total of 3,700 fire detectors are installed throughout the ship. Individually addressable, they allow any Shaft generator motor 1 Diesel generator 1 Diesel generator 2 Diesel generator 3 Diesel generator 4 Shaft generator motor 2 G/M G G G G G/M M M Bow thruster 2 Stern thruster M M M Bow Bow thruster 1 thruster 3 Engine room substation P-feed A C compressor 1 Deck substation P-feed Emergency switchboard P-feed Spare M Earth Earth M transf. P transf. S AC AC comcompressor 3 pressor 2 Deck substation S-feed Engine room substation S-feed Emergency switchboard S-feed This is a single-line diagram of the ship’s power supply, showing the diesel-generator sets and the drives for the bow and stern thrusters. June 1996  27 The MV Oriana is P&O Cruises’ newest luxury liner. The ship, which has fin stabilisers and is fully air-conditioned, carries 1760 passengers and a crew of 760. The top speed of the 260 metres long and 32.2 metres wide vessel is 26 knots. fire to be pinpointed from the bridge, engine control room or fire protec­tion centre. Monitors provide the crew with a good overview of the different sections of the ship and enable relevant informa­tion to be accessed quickly. If a fire alarm is not acknowledged within a preset time, a signal is given to begin preprogrammed fire-fighting measures. Two pontoons built into each side of the ship’s hull can be swung out for easy boarding of the tenders. Four automatic gang­ways are provided for disembarking on land. as claimed by the shipyard. Fitted as standard to most passenger ships, fin stabilisers are hydraulically operated and have a similar effect to the ailerons in a plane’s wing, literally flying the ship’s hull as it moves through the water. The Oriana is fitted with two four-bladed controllable pitch propellers 5.8m in diameter, three bow thrusters and one stern thruster (each rated at 1,500kW) as well as two spade rudders in the thrust stream. These can be operated by the helms­man, using a central joystick, either together or individually. Fin stabilisers Engine room Integrated fin stabilisers effectively reduce the ship’s rolling motion, by up to 90 percent at a speed of 19 knots, The Oriana’s main propulsion system consists of two 11,925kW and two 7,950kW four-stroke diesel 28  Silicon Chip engines (MAN B&W L58/64), the former with nine and the latter with six cylinders. The engines are grouped in pairs in a so-called “father and son” arrangement, to act via couplings on a gearbox which reduces the drive speed from 428 RPM to 127.6 RPM for the controllable pitch propellers. In addition, each gearbox is equipped with an ABB shaft generator which can produce up to 5.25MW of electrical energy. The two synchronous generators are each rated at 6.6kV and 60Hz, for a rotational speed of 1,200 RPM. The shaft generators can also be used as motors, being coupled via the gearing to the drive shaft. In this case, the electrical power is taken from the auxiliary generators. Thus, five different modes of propulsion are possible: 1 The Terrace, with whirlpool 2 Children’s play area and paddling pool, next to it Peter Pan’s playroom 3 Pacific Lounge, with stage and dance floor 4 The Oriental Restaurant 5 The Terrace Bar 6 The Conservatory, restaurant with outdoor seating • Main diesel engines (“fathers”): 2 x 11,925kW. • Main diesel engines (“sons”): 2 x 7,950kW. • Shaft generators as motors: 2 x 4,200kW. • All main diesel engines: 39,750kW. • Main diesels plus shaft generators: 48,150kW. The smaller main diesel engines, the “sons”, can also be used independently of the propeller system to drive just the shaft generators. Apart from the two shaft generators, there also are four MAN B&W 5.25MW auxiliary diesel-generator sets that provide the ship’s 6.6kV 60Hz electricity supply. These bring the total available generator capacity up to 31.5MW. A standby generating 7 Decibels and Outer Space, teenager’s room with video games 15 Pontoons for easy boarding of tenders 16 Anderson’s club bar 17 Monte Carlo Club, casino 18 Curzon Room, saloon with evening entertainment 19 Royal Court and Knightsbridge – shopping on two levels 20 Tiffany Court and Bar, top level of an atrium rising over four decks, with waterfall 21 The Riviera Pool, with two whirlpools 8 The Lord’s Tavern 22 The Riviera Bar 9 Chaplin Cinema 23 Oasis, fitness centre with aerobics area, gymnastics room, whirlpools, sauna, massage room, beauty salon, hairdressers and bar 10 The Crystal Pool 11 Crichton’s, for card games, next to it the Thackeray Library 12 Harlequin’s Night Club 13 The Peninsular Restaurant 14 Deck games area (tennis, shuffleboard, golf, quoits and clay-pigeon shooting) 24 The Crow’s Nest, saloon and bar with panoramic view 25 Iberia Room, VIP area next to Crow’s Nest 26 Theatre Royal set with a 937kW generator provides back-up in emergencies. The bow thrusters are driven by three 1,500kW 3-phase induction motors. An identical 1,500kW induction motor is used to drive the stern June 1996  29 trouble-free switching. Mechanical contact position indicators and inspection windows have been added to ensure maximum safety for the personnel. This type of switchgear is currently in use on many new cruise ships in operation all over the world. The entire power supply is controlled by a management system from ABB’s marine division in Hamburg. Its duties include the automatic connection of the thrusters, the air-conditioning plant’s compressor and other major power consumers. ABB developed this system especially for power plants on large ships. Control panels The main switchboard for the ship’s 6.6kV power supply. It employs SF6-gas puffer circuit-breakers. thruster. For these machines, ABB has installed two metal-enclosed switchboards with built-in starting transform­ers, vacuum contactors and programmable controllers. The compressors for the air-conditioning systems are driven by three 3-phase AC induction motors, also from ABB. Main switchboard A main switchboard consisting of 30 panels distributes the 6.6kV produced by the four diesel-generator sets and the two shaft generators. The switchgear uses SF6-gas (silicon hexa­ fluoride) puffer circuit-breakers which allows it to be installed in confined spaces. Each of the switchboard panels is divided into metal clad compartments (for the bus-bars, cable connections, circuit-breaker, voltage transformers and instruments). Interlocks ensure Each of the 6.6kV deck substations has two discon­nectors for opening the ring network on both sides of damaged equipment or for isolating parts of the network which need to be serviced. A fuse-switch, via which power is fed to the transform­ers for the low-voltage network, is also included. Each of the generator control panels has a display that shows all the important operating data, including the voltage, current, power frequency and power factor. A second display on the panel gives the following information: • Status of the diesel-generator set; • Measured generator data; eg, revs/ min, temperature, etc; • Alarms triggered; • Status of the overall plant. The emergency switchboard consists of nine panels. The emergency power supply operates at the voltage levels 660VAC, 440VAC, 220VAC and 220VDC/110VAC. A total of seven substations are installed on the decks. Comprising 24 panels in all, they distribute electrical power in a 6.6kV ring network. Each of the deck stations has two discon­ nectors; eg, for opening the ring on both sides of damaged equip­ment, or for isolating parts of the network on which service work has to be carried out. Each station also has a fuse-switch for the transformers to the low voltage network. Another seven substations are installed on the decks for the low voltage distribution. With a total of 30 panels, they supply power at voltages of 660VAC, 440VAC, 220VAC, 220VDC and 110VAC. However else you may regard the Oriana, as a luxury liner, floating hotel or whatever, it also has a very large energy distribution system to keep it all going. Acknowledgement This article has been reproduced courtesy of the ABB Re­view, from the SC April 1996 issue. 30  Silicon Chip Build this laser pointer in just five minutes Visible solid state lasers are becoming cheaper all the time. If you have hankered after a nifty laser pointer, you can now build your own with this simple to assemble kit. By D. LIGHT As technology marches on, it was inevitable that solid state laser pointers would become readily available at reasonable prices and indeed they have with the arrival of this little kit from Dick Smith Electronics. There are plenty of applications for a laser pointer, espe­cially if you are engaged in lecturing or public speaking. A laser pointer is a boon for highlighting visual aids in lectures, during slide shows and in commercial applications such as auctions. In the education field, a laser pointer makes a fine tool for demonstrating the properties of light. A laser pointer Above: this photo shows how the kit is supplied. It only takes a few minutes to put it together. All you really have to do is fit the battery contacts and connect them to the PC board. also could form the basis of various distance measurement tools, race timing and games. OK, there are plenty of uses for a laser pointer but what if you’re not happy about assembling a tiny PC board with almost invisible surface mount components on it? Don’t worry. The PC board and its lens assembly is already complete. You can put the whole thing together in under five minutes and be “lasing” away to your heart’s content. As the photo shows, this kit comes with a 2-piece case, two AAA penlite cells, the completed PC board and lens assembly, assorted metal bits for the battery contacts and not much else. Your first task is to assemble the three battery contacts into the case. These will connect the two cells in series to give a 3V supply. You then sit the PC board assembly into its cradle in the case and connect the positive (red) and negative (black) wires to the correct battery contacts. The cell positions are moulded into the case so that you can readily see which battery contact will be positive and so on. Once the soldering is done, insert the batteries and then press the miniature button on the PC board. You will be instantly gratified with a beam of red laser light. Marvellous! You can now adjust the focus of the lens by carefully rotating the front portion. Once that it done, drop the plastic pushbutton actuator into its cutout in the case and then clip the two halves together and fit the self-tapping screw. Stick the laser warning label on the case and you are finished. You can now “lase” away. Before we conclude there are two warnings: (1) Don’t shine this laser into your eyes or anybody else’s. Although this is a low power device it may still cause eye damage; (2) Do not be tempted to adjust the miniature trimpot on the board. This has been critically adjusted to set the laser current during manufacture. If you play with it, you blow the laser diode. This laser kit is available from all Dick Smith Electronics stores and is SC priced at $69.95. (Cat K-1048). June 1996  31 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. Bridge operation for LM3886 stereo module A number of readers have asked how to provide bridge operation of the twin-LM3386 stereo power module published in the February 1995 issue of SILICON CHIP. As published, the stereo module would deliver 48 watts per channel into 8-ohm loads and up to 60 watts per channel into 4-ohm loads, with the supply rails reduced to ±28V. The modifications required to run the module in bridge mode are quite simple and are depicted in the accompanying circuit and wiring diagram. As shown, the circuit for one channel, 32  Silicon Chip involving IC1, is unchanged. The second channel, involving IC2, has its non-inverting input (pin 10) grounded, while its inverting input (pin 9) gets its input signal from the output of the first channel via a 22kΩ resistor. This means that IC2 is operated in inverting mode and so its output signal is 180° out of phase with the output signal from IC1. The result is that the two output signals from IC1 & IC2 are added across the loudspeaker and the module will deliver up to 120 watts into an 8-ohm loudspeaker. Note that a 4-ohm loudspeaker must not be used because it will trigger the overload protection on both power ICs. The circuit above shows how the two power amplifier stages are configured so that they drive each side of the loudspeaker in anti-phase. Note that IC2 operates as an inverting unity gain amplifier. The parts layout diagram for the bridge arrangement is shown at right. Note also that the specified 160VA transformer has been changed from 2 x 25V to 2 x 20VAC. The LM3886TF specified for IC1 & IC2 is the new insulated tab type, indicated by the TF suffix. This is now the preferred package from the manufacturer and eliminates the need for mica washers. SILICON CHIP. Stereo preamplifier with selectable gain A common request from readers involves the need for a stereo preamplifier to step up the gain by a modest amount. This circuit is based on the Universal Stereo Preamplifier published in the April 1994 issue of SILICON CHIP. This version can be configured to provide any gain between unity and several hundred times. The accompanying table shows resistor and capacitor values for gains of 2, 5, 10, 20 & 50. The PC board will have a number of component values vacant, while R1 is replaced with a link. The resulting preamplifier is very quiet and has very low distortion. SILICON CHIP Novel modulator for signal generators This circuit can be used with an existing signal generator or to demonstrate the process of amplitude modulation (AM). One section of an LM324 (IC1a), is configured as an inverting amplifier with unity gain. Its non-inverting input is biased to 1.3V, and hence its output voltage at pin 1 is also 1.3V. IC1b is also an inverting amplifier continued next page June 1996  33 with unity gain. The voltage on its non-inverting input and hence the voltage on pin 8 the output is switchable between 1.3V and 2.7V by IC2a (part of a 4053 analog switch). When pin 9 of IC2a is high, 1.3V is applied to pin 10 of IC1b and when the pin is low 2.7V is applied. A square-wave carrier signal of 5-6V peak-peak is applied to pin 11 of IC2b, another section of a 4053. This causes IC2b to select the voltage from IC1a when the carrier is high and the output of IC1b when the carrier is low. With the switch in the FULL position, the signal at pin 14 of IC2b will be a square wave with a frequency the same as the carrier input and an amplitude from 1.3V to 2.7V. With the switch in the SUPPRESS position, the signal at pin 14 of IC2b will be a steady 1.3V as both outputs are the same. When audio is applied to the input, the op amp outputs will be equal in amplitude but 180° out of phase. That is, when the output of IC1a is at a maximum the output of IC1b is at a minimum. These outputs are selected alternatively by IC2b, thus providing standard amplitude modulation with switch S1 in the FULL position and DSB suppressed carrier in the SUPPRESS position. Q1 is included as a buffer between IC2b and the load which should not be much less than 1kΩ. The two 1kΩ resistors and 220pF capacitors were included to improve the modulation envelope and keep RF out of the op amp outputs. The LM324 was chosen because of the low single rail voltage used. A standard 4053 will allow operation to about 1.5MHz, however a 74HC4053 can be used successfully to around 10MHz. I have been able 34  Silicon Chip to achieve 25-30dB attenuation of the carrier at 10MHz. The modulation characteristics are quite good, with a flat audio frequency response. L. Williams, ($40) Bungendore, NSW. 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. Please feel free to visit the advertiser’s website: 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. Please feel free to visit the advertiser’s website: 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 This Low Ohms Tester plugs directly into a digital multimeter and can accurately measure resistances down to 0.01Ω. It’s easy to build and runs off a 9V battery. By JOHN CLARKE Build a low ohms tester for your DMM The ability to measure low resistance values is necessary when items such as meter shunts, loudspeaker crossover networks, inductors and contact resistances are to be checked. Unfortunately, a standard digital multimeter can only accu­rately measure resistances down to about 5Ω. Resistors with lower values will give misleading results due to a lack of meter resolution. A couple of examples will serve to illustrate this point. First, let’s assume that a resistance of 0.1Ω is to be checked on a standard 3-1/2 digit multimeter. In this case, you would have to switch down to the 200Ω range (the lowest you can select) and the reading would be 0.1Ω ±1 digit (ie, ±0.1Ω). In other words, 40  Silicon Chip Fig.1: block diagram of the Low Ohms Tester. It works by applying a constant current through the test resistor (Rx). The voltage across Rx is then measured using a DMM. the resolution of the DMM limits the accuracy of the reading to ±100% which is ridiculous. This situation quickly improves with increasing resistance values. For example, a value of 1Ω will result in a reading of 1.0Ω ±1 digit, assuming that the 200Ω range is used. This represents an accuracy of 10%. For values above 10Ω, the accuracy of the instrument will be 1% or better since the resolution of the reading is considerably improved. This Low Ohms Tester overcomes the limitations of conven­tional digital multimeters for low values of resistance. It does this by applying a constant current through the test resistor Rx. The resulting voltage de- Fig.2: the full circuit for the Low Ohms Tester. REF1, IC1 and Q1 form a constant current source for the test resistor Rx. The resulting voltage across Rx is then either measured directly or amplified by IC2 before being applied to the DMM. veloped across Rx is then amplified and applied to the DMM which is set to read in millivolts. Fig.1 shows the basic scheme. As shown in the photos, all the circuitry is housed in a compact plastic case. This carries a power switch, a 4-position range switch and two binding post terminals for the test resis­tor. The output leads emerge from the top of the instrument and are fitted with banana plugs. These simply plug into the COM and VΩ terminals of the DMM. The output from the Low Ohms Tester is a voltage (in mV) which is directly proportional to the resistance being measured. In practice, you simply multiply the reading on the DMM by the range setting on the tester to get the correct value. For exam­ple, a DMM reading of 5.6mV when the 0.1Ω range is selected is equivalent to 5.6 x 0.1 = 0.56Ω. From this, it follows that if the 1Ω range is selected, the reading on the DMM is directly equivalent to the value in ohms. Values from 100Ω down to 0.01Ω can be measured via the tester. Below this, errors start to be significant due to contact and lead resistance. Values above 100Ω can also be measured via the tester but this is rather pointless. That’s because the DMM alone can be used to accurately measure values above this figure. Circuit details Refer now to Fig.2 for the complete circuit of the Low Ohms Tester. It consists of a constant current source (which supplies the current through test resistor Rx) plus an amplifier stage to drive the DMM. IC1, REF1 and Q1 are the basis of the constant current source. REF1 is a precision voltage source which provides a nominal 2.490V between its “+” and “-” terminals. This device is connected between the positive supply rail and ground via a 5.6kΩ current limiting resistor. VR1 allows • • • • Main Features Measures from 0.01Ω to 100Ω Four ranges Outputs to a digital multimeter Battery operated the reference voltage to be adjusted slightly and is used for calibration. Op amp IC1 and transistor Q1 function as a buffer stage for REF1. Because this stage is simply a voltage follower, the vol­tage on Q1’s emitter will be the same as the voltage on pin 3 of IC1. This means, in turn, that the voltage across the resistance selected by S2b is equal to the REF1 voltage. As a result, a constant current flows through the selected resistance and this current also flows through Q1, test resistor Rx and diodes D1 & D2 to ground. In greater detail, when S2b selects positions 1, 2 or 3, the 2.4kΩ resistor is in circuit and so has the REF1 voltage across it. If REF1 is adjusted to 2.4V, then 1mA will flow through the resistor and thus through Q1 and Rx. Conversely, when S2b selects position 4, the constant current source delivers 10mA to Rx (assuming that VR2 is correctly set). IC2 functions as the amplifier stage. This operates with a gain of either x10 or x100, as set by switch S2a. Switch S2c selects between the collector of Q1 and the amplifier output at pin 6. Thus, when position 1 is selected, June 1996  41 Fig.4: this is the full-size etching pattern for the PC board. 4 are selected, IC2 amplifies the voltage across Rx and drives the DMM via its pin 6 output. IC2 operates with a gain of 10 when position 2 is select­ed and a gain of 100 when positions 3 or 4 are selected. These gain values are set by the 1MΩ, 10kΩ, 1kΩ & 91kΩ resistors in the feedback network. In position 2, all four resistors are connected in parallel to give a feedback resistance of 900Ω. IC2 thus operates with a gain of 1 + 900/100 = 10. In the other Fig.3: install the parts on the PC board three positions, only the 1MΩ and complete the wiring as shown here. and 10kΩ resistors are connected and these give a feedback the amplifier is by­passed and the DMM resistance of 9.9kΩ. The gain is now directly monitors the voltage across 1 + 9900/100 = 100. Rx. Because the constant current Note that the 0.1µF capacitor is source supplies 1mA through Rx in always connected across the feedback this position, the reading in millivolts path, to reduce any high frequency is directly equivalent to the value of noise. Rx in ohms. The 91Ω resistor at pin 3 matches Conversely, when positions 2, 3 or the impedance seen by this input to that seen by the pin 2 input. This ensures that equal currents flow in the two op amp inputs and this in turn minimises the output offset voltage. VR3 nulls out any remaining offset voltage and is adjusted so that the DMM reads 0mV when Rx is 0Ω (ie, when the test terminals are shorted together). One interesting point is that the lower end of Rx is two diode drops above ground, due to series diodes D1 and D2. This ensures that IC2 operates correctly when the output is only 1mV above the lower Rx connection point. Power for the circuit is derived from a 9V battery via power switch S1. Two 47µF capacitors across the supply provide decoupling and lower the impedance of the 9V rail, while LED1 provides power on/off indication. Construction Most of the parts are mounted onto a small PC board coded 04305961 and RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 1 1 1 1 1 42  Silicon Chip Value 1MΩ 91kΩ 10kΩ 5.6kΩ 2.4kΩ 2.2kΩ 1kΩ 200Ω 100Ω 91Ω 4-Band Code (1%) brown black green brown white brown orange brown brown black orange brown green blue red brown red yellow red brown red red red brown brown black red brown red black brown brown brown black brown brown white brown black brown 5-Band Code (1%) brown black black yellow brown white brown black red brown brown black black red brown green blue black brown brown red yellow black brown brown red red black brown brown brown black black brown brown red black black black brown brown black black black brown white brown black gold brown PARTS LIST 1 PC board, code 04305961, 60 x 100mm 1 front panel label, 62 x 125mm 1 plastic case, 130 x 66 x 43mm 1 9V battery holder 1 9V battery 1 SPDT toggle switch (S1) 1 3-pole 4-way PC mount rotary switch (S2) 2 10kΩ horizontal trimpots (VR1,VR3) 1 100Ω horizontal trimpot (VR2) 1 12mm knob 2 banana plugs 2 banana panel sockets 6 PC stakes 1 6mm ID rubber grommet 1 20mm length of 0.8mm tinned copper wire 1 300mm length of hook-up wire 3 2.5mm screws and nuts Semiconductors 2 CA3140E Mosfet input op amps (IC1,IC2) 1 BC328 PNP transistor (Q1) 1 LM336Z-2.5 reference (REF1) 2 1N914, 1N4148 signal diodes (D1,D2) 1 5mm red LED (LED1) Capacitors 2 47µF 16VW PC electrolytic 1 0.1µF MKT polyester or monolithic ceramic The PC board carries nearly all the parts and is mounted by clipping it into the guide notches of a standard plastic case. Note that the locking collar of the rotary switch (under the mounting nut) must be set to position 4, as described in the text. measuring 60 x 100mm. The board clips into the inte­gral side pillars of a plastic case measuring 130 x 66 x 43mm. Begin construction by checking the PC board for shorted tracks or small breaks. Check also that it clips neatly into the case. Some filing of the PC board sides may be necessary to allow a good fit without bowing the case sides. Begin the board assembly by installing the PC stakes. These are located at the three external wiring points and at the con­ nections for switch S1. This done, insert the single wire link (it sits immediately beneath VR3). Next, install the resistors (see table for colour codes), then install the diodes and ICs, taking care to ensure that they are oriented correctly. The capacitors can go in next – note the polarity of the two 47µF electrolytic types. REF1 and Q1 can now both be installed. Note that these two devices look the same so make sure that you don’t get them mixed up. LED1 is mounted on the end of its leads so that it will later protrude through a matching hole in the front panel. For the same reason, switch S1 is soldered to the top of the previously in­stalled PC stakes. Rotary switch S2 is mounted directly on the PC board. Ensure that it has been pushed fully home and sits Resistors (0.25W, 1%) 1 1MΩ 1 2.2kΩ 1 91kΩ 1 1kΩ 1 10kΩ 1 200Ω 1 5.6kΩ 1 100Ω 1 2.4kΩ 1 91Ω 1 1Ω 1% (for calibration) Miscellaneous Hook-up wire, tinned copper wire. flat on the PC board before soldering its pins. This done, loosen the switch mounting nut, lift up the star washer and rotate the locking collar to position 4. This turns what was a 12-position rotary switch into a 4-position rotary switch. Check that the switch operates correctly, then do the nut up tight again so that the locking collar is secured. The board assembly can now be June 1996  43 LOW OHMS TESTER POWER + + VALUE per mV + 0.1Ω 0.01Ω 1Ω 1mΩ Rx + + Fig.5: this full-size artwork can be used as a drilling template for the front panel. completed by mounting the trimpots and fitting the battery holder. Note that VR2 is a 100Ω trimpot, while VR1 and VR3 are both 10kΩ types so be careful with the values here. The battery holder is secured to the PC board using the 2.5mm mounting screws supplied with it. Final assembly It’s now just a matter of installing the board and the ancillary bits and pieces in the case. First, attach the front panel label, then drill holes for the LED, switches S1 & S2, and the two test terminals. A hole will also have to be drilled in the top of the case to accept a small grommet. The PC board can now be clipped into the case, the test terminals mounted in position and the wiring completed as shown in Fig.3. This done, check that the switches and the LED line up with the front panel holes. Adjust the height of the LED and switch S1 if necessary, so that they fit correctly. The leads to the meter run through the grommetted hole in the top of the case. Keep these leads reasonably short and termi­nate them with banana plugs. It will be necessary to trim the shaft of switch S2, so that the knob sits close to the front panel. Test & calibration Now for the smoke test. Apply power and check that the LED lights (if it doesn’t, check that the LED has been oriented correctly). Now check the supply voltages on IC1 and IC2 using a multimeter. In each case, there should be about 9V between pins 7 and 4. If everything is OK so far, check the voltage between pin 3 of IC1 and the positive supply rail (ie, the voltage across REF1). Assuming VR1 is centred, you should get a reading of 2.4-2.5V. Pin 2 of IC1 should be at the same voltage as pin 3. To calibrate the unit, follow this step-by-step procedure: (1) Monitor the voltage across REF1 and adjust VR1 for a reading of 2.4V (this sets the constant current. (2) Plug the Low Ohms Tester into the DMM and short the Rx test terminals using a short length of 1mm tinned copper wire. (3) Select the 0.01Ω range and adjust VR3 for a reading of 0mV on the DMM. Check for a similar reading when the 1mΩ range is selected. (4) Connect a 1Ω 1% resistor between the test terminals, select the 0.01Ω range and adjust VR1 again for a reading of 100mV. (5) Select the 1mΩ range and adjust VR2 for a reading of 1V. (6) Short the test terminals again and verify that the DMM reads close to 0mV for all ranges. That completes the calibration procedure. The lid can now be attached to the case, the knob fitted to S2 and SC the unit pressed into service. Available Direct From Silicon Chip $8.95 PLUS P & $3 P 20 Electronic Projects For Cars This book has 20 electronic projects for cars, including high energy & breakerless ignition systems, an ultrasonic alarm, a digital tachometer, a coolant level alarm, a flashing alarm light, a talking headlight reminder, a UHF remote switch & a thermostatic switch for electrically operated radiator fans. And there are eight quick circuit ideas as well. Price: $8.95 (plus $3 for postage). Order by phoning (02) 979 5644 & quoting your credit card number; or fax the details to (02) 979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 44  Silicon Chip 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 SATELLITE WATCH The explosion of Intelsat 708, some 20 seconds after takeoff on February 14, has dealt the Chinese “Long March” launcher another blow. Previous launch failures included Optus B2, Panamsat PAS-3 and Apstar 2. INDUSTRY FEELING is now that future Long March launchers may be uninsurable. Despite the destruction of the satellite, insured for US$205 million, a back up satellite, Intelsat 707 is scheduled for imminent launch on a European Ariane booster. This satellite will take the place of Intelsat 708, at 310° east longitude, serving the Atlantic Ocean Region. • APSTAR 1R – 88° E longitude: no further details are available on the launch of this satellite and the failure of Intelsat 708 may have some affect on its schedule. • ASIASAT 2 – 100.5° E longitude: the popularity of RTPI has steadi­ ly increased amongst the Portuguese community. CCTV4 China has now commenced operations at IF 1185MHz in PAL. This is a great improvement in service availability over the identical program available prior to the launch of AS 2, on the inclined satellite Gorizont 19 (96.5E). This service has now been discontinued. CCTV4 is also available in MPEG on PAS-2. Broadcaster Deutsche Welle’s 10channel TV and radio service commenced operations in mid April. At present the only available decoders which will suit this service are used for the Galaxy pay TV service, carried on Optus B3. Simple reprogramming enables this decoder to be used on the Asiasat 2 DW service, although this may not be legal as title to Galaxy decoders always remains with Galaxy, through a unique customer leasing arrangement. • PALAPA C1 – 113° E longitude: transponder change over from the old B2P satellite, scheduled for March 23, went ahead early, commenc­ ing March 16, and should be completed by the time this report goes to press. By early April Compiled by GARRY CRATT* it was apparent that all vertically polarised transponders were down in power, affecting viewers in PNG and Asia. The launch of Palapa C2M at the end of April will give the satellite operator the flexibility to move all or only those transponders affected to the new satellite. Meanwhile interest in Palapa C1 continues to increase. Many signals are available, including: Star channel “V” (975MHz), CFI France (990MHz), MTV Asia (1030MHz), TPI Malaysia (1070 MHz), GMA Philippines (1120MHz), ANTEVE (1130MHz), CNNI (1175MHz), SCTV (1190MHz), ABN (1230MHz), TV3 Malaysia (1250MHz), ATVI (Aust­ ra­ lia) (1270MHz), RTM-1 Malaysia (1330MHz), RCTI Indonesia (1350MHz) and CNBC Asia on the new extended range band at 1530MHz. Many services feature teletext and as all but GMA are carried in PAL, a standard teletext TV set can be used to receive them. • JCSAT 3 – 128° E longitude: still no programming from this satel­ lite. Its test pattern can be seen on 1165MHz. The satellite is designed to supply a 50-channel digital pay service into Japan but one of its footprints will cover Australia and New Zealand. The service should commence late April but it is not known if it will be seen in Australia. • GORIZONT 42 – 142.5° E longitude: March 14 saw Indian broadcaster ATN make an announcement that they would be moving to PAS-4 (68° E longitude) by the end of March. This would effectively eliminate viewers from the eastern states of Australia and New Zealand. However, ATN returned to Gori-zont 42 a week later and it is planned to remain on this satellite until October. Strangely, those monitoring PAS-4 on the Western coast advise that the broadcaster has never been seen on that satellite! • PANAMSAT PAS-2 – 169° E lon­ gitude: until recently operating in the clear, MTV Asia has now gone digital on this satellite. Previous­ ly reported analog signals continue to be available and NHK signals have been boosted significantly in level, allowing recep­ tion on dishes down to 1.6m. There is one K band signal seen regularly at IF 1115 MHz. This transponder is used for special events, otherwise running the standard PAS-2 SYLMAR uplink test pattern. Most “special events” broadcast on C band can be found at 1245MHz IF. • INTELSAT 701 – 174° E longitude: daily transmissions are seen on IF 975MHz from Thailand and Taiwan. As the political situation tenses between Taiwan and China, transmissions are expected to increase in frequency and duration. This satellite will be re­placed at the end of 1996 with Intelsat 801. • INTELSAT 703 – 177° E longitude: the radio service carried on the BMAC-encrypted AFRTS service (IF 985MHz) continues to be a good source of American radio. The audio subcarrier frequency is 7.40MHz. This satellite will be replaced in the first quarter of 1997 by Intelsat 803. • INTELSAT 511 – 180° E longitude: RFO Tahiti and Worldnet continue to be the main sources of entertainment from this satellite. RFO is scheduled to introduce a second service on this satellite later in the year. There is continued but unconfirmed speculation that New Guinea broadcaster EM TV could move to this satellite mid year. SC *Garry Cratt is Managing Director of Av-Comm Pty Ltd, suppliers of satellite TV reception systems. June 1996  53 SERVICEMAN'S LOG Chuck it away and buy a new one No, that’s not my advice but it is the philosophy from one of this month’s stories – a story from the USA, where the servicing scene is very different. Even so, it has a very inter­esting connection with the local scene. My first story concerns a National Panasonic model TC-1407, 34cm colour set using an M12H chassis. This model can be any­thing up to 10 years old and is a very well made and reliable set, regarded by many as one of the best that National ever made. But of course faults do occur and, in this case, the com­plaint was total lack of colour. This is not an unusual fault in itself but the actual cause was unusual, as we shall see. When tackling colour problems, I automatically reach for the CRO leads. And the first thing I checked was whether a colour signal was coming into the chroma decoder (IC601) – see Fig.1. In fact it was, on pin 7. It was only about 0.8V p-p but this tal­lied with the circuit. Next, I checked the crystal oscillator. Again there was no problem, with plenty of 4.43MHz signal on pin 16 of the same IC. Well, that ruled out the more obvious possibilities. The next thing to check was the gating pulses (horizontally derived) which control the burst gate and similar functions. Such pulses should appear at the burst gate terminal (pin 14) of IC601 and are shown on the circuit as waveform 30, with a p-p amplitude of 4.6V. But not in this set – pin 14 was dead. Well, at least I was on the right track. Unfortunately, the track wasn’t very clear, which is just another way of saying that the best circuit diagram I could find left much to be desired. It wouldn’t have been so bad if I had been able find an original circuit but the best I had was a much copied copy of a copy – if you follow me. To be fair, the original circuit was undoubtedly very good, featuring lots of information in the form of voltages and wave­forms, but it had been much reduced and, when copied, a lot of fine detail was lost. Anyway, I was faced with the task of tracing the circuit to find where these pulses originated and at what point they were lost. And I thought I had cracked it in one as soon as I started. Not far from, and to the left of, pin 14 is a diode, D602, which connects to chassis. Naturally, I check­ed it and it was a dead short. Unfortunately, my jubilation was short lived because when I replaced it and switched on there was still no colour. A literal drawing board So, back to the drawing board –almost literally. The line split into two at this point, both moving parallel down the page for a short distance. Then one turned left and one continued down. I turned left and finished up on pin 10 of the video chip (IC301). There was supposed to be a waveform here also (designat­ ed waveform 21) which was similar to the one on pin 14. But there wasn’t. Fairly obviously, pin 10 was supposed to receive this waveform, not supply it. I followed the other line down until it spilt, going left and right. I went right, but drew another blank. It finished up at the base of transistor Q601, a blanking pulse generator – which didn’t have any pulses either. OK, back to the junction and turn 54  Silicon Chip Fig.1: the chroma decoding circuitry in the National TC-1407. IC601 is at top right, IC301 at top left, and IC501 at bottom centre. Many of the IC pin numbers are quite difficult to read. left. This brought me to pin 16 of the jungle chip, IC501. And this, I felt, had to be the source of the missing waveform. This chip performs a whole host of functions, including horizontal AFC and sync separation, both requiring a reference to pulses from the horizontal output trans­former. In fact, pin 16 was connected to the sync separator block within the IC. What’s more, this IC appeared to be performing these, and its other functions, because we had a perfectly locked picture but in monochrome. So it had to be receiving pulses from the horizontal transformer. In fact, after much more laborious cir­ cuit tracing, too complex to detail here, I confirmed that the pulses at pin 2 of the horizontal transformer were applied to pin 1 of IC501. And the CRO confirmed that the pulses here were as they should be. So why wasn’t it delivering a pulse at pin 16? I could only conclude that there was a fault in the IC. And, since I didn’t have any on hand, I had to order one. But while waiting for it, I still had an urge to confirm that this was the problem. Referring again to IC301, I noticed that on pin 11 there was a waveform (No.24) of similar shape and amplitude to the waveform that should have been present on pin 10, though somewhat smoother. So what would happen if I connected pins 10 and 11 togeth­er. At best I might get some kind of colour response. At worst, I could blow up IC301. After studying the voltages on the two pins (1.2V on pin 11 and 0V on pin 10) I decided that the risk to the IC was minimal and connected the two pins together. And it worked – well, partly. It did produce colour on the screen but it was not locked, drifting through the spectrum and producing some weird coloured scenes. But it was enough to sug­gest that my diagnosis was probably correct. And in fact it was. When the new IC arrived, I fitted it and everything came back to normal. Another satisfied customer. The American in-laws And now for a change of scene; quite a big change in fact, because my next story comes from the USA. But it also has a very close relationship with some of my previous notes and one story in particular. By way of background, my regular readers may recall that, from time to time, I have featured stories from a colleague who worked down the south coast of NSW. And I was always pleased to feature these stories because they involved factors peculiar to the area; UHF almost exclusively, long distances in many cases, and much hilly terrain. And, of course, we exchanged technical experiences and picked each other’s brains from time to time. So it came as rather a shock when, some months ago, my colleague announced that he had decided to retire and move to the US where he June 1996  55 being that muggins, “who knows all about TV sets”, could probably fix it. So, it finished up on my doorstep. I’m afraid I agreed to the idea with mixed feelings. On the one hand I had brought all my test instruments and tools with me, had organised some work­shop space, set up a bench, and begun to sort things out. However, it was all very well for the rest of the family to assume that muggins “knows all about TV sets”. The truth was that all I knew about projection TV sets was secondhand and did not even involve the same model. Nor did I have a manual, have any idea of where to find one, what it would cost if I did, and whether such an outlay could be justified. I short, I would have to fly by the seat of my pants. A bright spot had various in-laws and other family connections. So, no more stories from that source. But do TV servicemen ever retire completely? Significantly, my colleague shipped all his equipment, which was considerable, to the US with him. He had no intention of setting up in business but, I imagine, he knew he would feel lost without the means to look after his own devices and ap­ pliances, along with those of his relatives and friends. So that is one part of the background. For the other part I would refer readers to one of my own stories which appeared in the May 1995 notes under the heading “All it needs is a new fuse”. In greater detail it concerned a Mitsubishi VS-360A pro­jection TV set and the difficulty of convincing the owner that it needed a lot more than a new fuse. Linking all this together is the fact that my colleague was “in” on that story from the beginning. Neither of us had tackled projection TV sets before and he was anxious to learn all he could from what I had to learn. It was, therefore, sheer coinci­dence that one of the first family jobs he encountered after settling into his new home involved a Mitsubishi projection TV set. 56  Silicon Chip Anyway, here is my colleague’s story as he tells it. The set involved was a Mitsubishi VS-405R projection type, featuring a 100cm (40in) screen. It was about 11 years old, roughly the same age as the one my colleague had dealt with in Australia. And it came to me by a somewhat round about route. It had originally belonged to a friend of one of my in-laws and had failed some time before I came on the scene. The owner had called in a local serviceman who repaired it for $170 (I’m quoting $US, of course). It was quite a reasonable charge and the set performed perfectly. Unfortunately, it did not perform for long, failing again after about six months. And this time the owner did what so many people do in this country when something fails (particularly something 11 years old which has failed for the second time) – he chuck­ ed it away and bought a new one. And, as a matter of interest, the new set – a larger 125cm (50in) model – cost about $1200, roughly half the price of a similar set in Australia. At the same time the old set was “chucked” in the direction of my inlaws – not literally I hasten to add, because the thing weighs a ton – the idea One bright spot was that the device appeared to be fairly easy to get at; much easier than was apparently the case with the one my Australian colleague worked on, due to a slightly differ­ ent layout. One important difference was that the top part of the cabinet back could be removed, as well as the lower part, giving much better access. In addition, the 3-gun assembly was mounted on a steel subframe supported on runners on the inside of the cabinet. This allowed the subframe to be withdrawn, although not without some difficulty – more on that later. The whole system was made up from a collection of PC boards, each mount­ed on a light metal frame which served as a nominal chassis. These included a power supply board, a horizontal and vertical scan board, a signal processing board, a stereo sound board, and a convergence control board. The scan and signal boards were secured to the floor of the cabinet while the remaining boards were secured to the sides. They could all be easily unplugged and withdrawn. That much established it was time to apply power and see what happened. The answer was simple – nothing. This lead me to a 3A fuse in the power supply which had failed. This was replaced and power applied again. This time there were signs of life. The set tried to fire up but then would shut itself down and try again. In other words, there was a slow hiccup, suggesting that a protection circuit somewhere was taking over. I suspect that the set had been inadvertently left on in the hiccup condition which, if it continues long enough, can blow a fuse. I went straight to the horizontal output transistor, which was readily accessible, and picked it in one; it was shot. This was easily fixed. I didn’t have a direct replacement type but settled for a 2SD380. Unfortunately, when I switched on, the set was still hic­cuping. I found a HT rail check point and monitored it. It looked as though it was about 125V but this called for some judgement as it rose and fell. I suspected that the fault was either somewhere in the horizontal scanning circuit or in the protection circuit covering this section. Normally, I would check this second possibility by momentarily disabling the protection circuit and noting what happened. The trouble was, without a suitable diagram, I had no idea where to look for this circuit, so I put that on hold. I was also curious as to the nature of the previous fault and what work had been done. I could see that the boards had been pulled because the wiring looms had been released from their clips and, although most had been restored, a few had not. I examined the boards very carefully, in search of a clue, and finally concluded that no work had been done on them. One obvious indication was a fine layer of dust, as normally found in such situations, which had not been disturbed. At the same time, I went over each board and checked for dry joints, particularly around the horizontal scan circuitry and the four pin connections to the horizontal driver transformer. Dry joints to these pins have been a common problem with many sets in the past. In this case, the soldering quality was very good. I did remake a couple of joints which were vaguely suspicious but it was more of a gesture than anything. Why the failure? At this stage, I began to wonder why the horizontal output transistor had failed. I also wondered if there had been a previ­ous failure and if the faulty transistor I had replaced had itself been the correct type number? However, without a circuit I really had no way of knowing. Finally, having checked the most likely possibilities as I far as I could, there seemed to be only one positive check left that I could make; a check for shorted turns in the deflection coils. Fortunately, I had brought my trusty shorted turns tester with me and unearthed it after some searching. The deflection coils were plugged in, so it was easy to make the checks without pulling the metal frame assembly. I checked the horizontal windings first and the first two tested OK. But not so the third one; there was a clear indication of a short. So now I had to pull the metal frame assembly. This wasn’t quite as easy as it looked. To understand why it will help if I describe the device in greater detail. Imagine a rectangular metal frame running the width of the cabinet and sitting horizontally on two runners, one on each side of the cabinet. This frame extends from the back of the cabinet to about two thirds the way to the front. A second frame is then attached at right angles to the front of the first frame and this extends downwards to the floor of the cabinet. This supports the picture tubes and some associated circuitry. OK, having envisaged all that, consider how the frame is constructed. It is made from box section mild steel –actually two lengths of angle iron welded together to make the box sec­tion. All of which adds up to a lot of steel. Add the weight of the three picture tubes – they may be small, but they’re not light – plus a few odd pieces and you have a total weight of around 25kg. It’s not at all easy to manhandle in an enclosed space. Nor was the operation made any easier by the location of the picture tubes. These are mounted at about 45 degrees, below the level of the horizontal section so that, if it were simply removed and placed on a bench, the whole assembly would be rest­ing on the tube necks. Ouch! I tackled the problem by arranging some suitable blocks on the bench. I then unclipped all the connecting leads and careful­ly manhandled the frame out and onto the blocks. It was worth the effort. With everything out in the open it was immediately obvious why the set had failed in the first place – and why it had failed in the second place. In fact, one doesn’t often get an explanation presented as clearly and positively as this one. The faulty deflection coil assembly was coated with a brown varnish, the appearance of which exactly fitted the de­scription of the coating on the failed transformer in the set handled by my Australian colleague. Even without any other warning I would have been highly suspicious of this mixture. I had encountered a similar witch’s brew before – sometimes brown, sometimes yellow – in other makes of sets. It is sometimes used as a varnish on windings, and sometimes as a glue to secure an extra component on the copper side of a PC board. More particularly, I was well aware of its corrosive properties. It will eventually eat away any copper with which it comes in contact. In this case, of course, I had been June 1996  57 Serviceman’s Log – continued warned. I recalled that the technician in the Australian Mitsubishi service department had advised my colleague to check for this varnish on the trans­ former and for any damage it might have caused. The rest is history; that transformer was a write-off. There was one other interesting development. One of the three deflection coils – presumably fitted during the previous service –was quite free of the witch’s brew. Per­haps a message had finally penetrated. But that was all rather academic from my point of view. My more immediate concern was the fate of this set. Would I be justified in pressing on with the job or should we cut our losses? There had been a tentative agreement before I started that we would put a limit of around $100 on the cost of replace­ment parts. Labour, of course, would be no more than an extra serving of turkey at next thanksgiving – if I was lucky! I had determined that a new deflection assembly would cost about $100 58  Silicon Chip which, with a new horizontal output transistor, was already stretching this limit. To that would need to be added a second scan coil assembly, because it would be pointless to simply replace the one faulty one. The third coil was another failure just waiting to happen. On top of that, how much more of this brown varnish was there elsewhere in the system? So we were looking at $200 plus to repair an 11-year old set, which could be re­placed with a similar size modern set for around $1000. I am well aware that, in Australia, many people would regard such an oppor­tunity as a gift and be prepared to take the risk. Not so in this country. Because appliances are so much cheaper, in real terms, than in countries like Australia, the concept of service is very much different. Many people will simply discard an appliance at the first sign of trouble, without any attempt to determine whether the fault is minor or major, and whether a repair might be worthwhile. Against this background, and on my advice as to what would be involved, the decision was made to cut the losses, such as they were ( mainly my time, which nobody regarded as being very important). Not that this really worried me very much; it had been an interesting exercise and an opportunity to study another version of this type of set. The cabinet of the old set was salvaged, however. It was a very useful piece of furniture and one member of the family had it earmarked as a useful storage unit. I suppose the most interesting aspect of the story, from a technical viewpoint, was the coincidence of finding two sets, of the same make, so far apart in different countries, suffering from almost identical faults. Also, it is to be hoped that, at long last, the havoc caused by these witches’ brews has been recognised and that they will be suitably disposed of – with due regard to the environment, of course. Well that’s my colleague’s story; and a very interesting insight it is into the TV scene in another country. Thanks SC mate. 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. 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Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia June 1996  59 RADIO CONTROL BY BOB YOUNG Multi-channel radio control transmitter; Pt.5 This month we discuss the construction of the Mk.22 transmitter encoder PC board. This uses surface mount components throughout apart from the trimpots. If it had relied on conven­tional components it would have been a great deal larger. As a result of the experience gained from test flying of the Mk.22 system the transmitter has undergone a radical redesign from its original simple slide and plug concept for all modules. The original encoder layout proved difficult to program, so we have rotated the PC board through 90° and screwed it to the case as well. This results in all the programming pins being easily accessible from the rear, improved bonding to the earth for RF bypassing and a larger, less crowded PC board. There have also been some additions to the encoder as a result of customer requests. The meter has been changed to an expanded scale voltmeter as the original proved too insensitive. The meter now has zero suppression and reads from 8-10V. Fig.1 shows the circuit addition, involving trimpots VR16 and VR17, zener ZD1, and resistors R70 and R71. These have been included in the encoder PC board featured this month. TB7 also had to be extended from four to six pins. TB30 has been added at the request of a government depart­ ment. They required a hard wired system (no RF link). TB30 allows the receiver decoder to be coupled directly into the encoder with a two-wire patch cord via the existing socket on the decoder. You simply remove the receiver module, connect the patch cord between TB30 and the receiver decoder and presto, you have a hard-wired Fig.1: the zero suppression circuit for the meter which now reads from 8-10V for greater sensitivity. 60  Silicon Chip remote control system. This is also very handy for testing, as we shall see. The original circuit also did not allow for the dual con­trol (buddy box) connections, an oversight fixed by the addition of TB29. Finally and most importantly from my point of view, recent developments have indicated that a welded, seamless case is now economically possible, which will greatly improve the appearance of the finished product. AM vs FM debate The only other comment I receive on a regular basis is “why AM?”. To which I can only reply, “why FM?”. Although the following is a small diversion, I feel that I should deal with this furphy immediately. I have stated it before and will repeat it now: the FM thing is false advertising and largely a sales gimmick. Socalled FM radio control transmitters are not true FM; they are Narrow Band Frequency Shift Keying (NBFSK), with the emphasis on narrow band. Older sets use frequency shifts of as little as 400Hz. This places the signal down in the noise area and it is only recently that most imported sets have gone to a 1.5kHz shift, a small improvement. FM is supposed to offer a vast improvement in signal-to-noise ratio and of course it does when a bandwidth of 40kHz or more is used. NBFSK very definitely does not offer an improvement over AM, especially with systems running on 400Hz deviation. We flew very successfully for 30 years on AM and in the two years that have elapsed since the Mk.22 AM system began flying I have yet to receive a single receiver back due to in- June 1996  61 Fig.3: component layout for the underside of the encoder board. Fig.2: component layout for the topside of the encoder board. All surface mount components should be soldered to both sides of the board before installing the conventional (through hole) compon­ents. This is the topside of the finished encoder board. Note that some of the headers have micro shunts (shorting links) across them. terference. In fact I have only had two receivers back in those two years. One because a wing came off in flight and the crystal shattered (no other damage) and the other because the owner tried to use it with an FM transmitter which he believed to be AM. Yet to listen to the pundits, you Fig.4: this patch cord connects the servo test header, TB30, to the decoder (described in the April 1995 issue) for the final test. Fig.5: to test servos with the encoder and encoder, you will need a control stick. Wire it up to a three-pin socket as shown here. The pot wiper connects to the centre pin. Fig.6: if you do not have a control stick, this circuit can be used for testing servos with the encoder and decoder (see text). 62  Silicon Chip would believe it is no longer possible to operate an AM system. I still fly AM and feel no need to change, especially now that I have the Mk.22 transmit­ter with all its modern tricks. From a home construction point of view, AM is the best system to use because it is reliable and easier to service. It also requires less test equipment, is easier to align, the com­ponents are cheaper and, most important of all, the crystals are cheaper and readily available on the now deserted 29MHz band. Having come this far, I may as well go the full distance. I believe that most R/C manufacturers have lost the plot and are forcing the average sport flyer and hobbyist into buying expen­sive equipment they have little use for. Some of the latest gems being advertised include a transmitter with over one hundred model memories and others with rocker switch electrical trims, a very dangerous concept to my mind. At this point, it is appropriate to remind the reader that the Mk.22 is designed to expand with the user’s requirements, starting with a simple two or 4-channel system and adding as you know and grow. In other words, it is an attempt to provide the modern concepts that users feel are desirable for their applica­tions, combined with a return to the simple and more user friend­ly systems of the pre-microprocessor era. Construction The component layout diagrams for both sides of the PC board are shown in Fig.2 & Fig.3. For those not familiar with surface mount assembly, I suggest reading the article “Working With Surface Mount Components”, as featured in the January 1995 issue of SILICON CHIP. You will need a pair of magnifying specta­cles, a fine-tipped soldering iron and a pair of tweezers with very fine tips. The diagrams of Fig.2 & Fig.3 depict the full component count for a complete 8-channel system with all the trimmings. If you intend to build a simpler version then photocopy the assembly drawings and white-out all of the components you do not need. In fact it is a good idea to do this anyway and then mark off each component as you mount it. Begin by tinning one pad at each of the surface mount com­ponent position, as set out in the above article. Now is a good time to establish which components are to be mounted by only tinning those pads. The surface mount assembly is very straightforward. In fact, the whole assembly is quite straightforward; there is just a lot of it. I usually empty all of the components of one type into a small tray and beginning at the top left hand corner, mount all of the components of one type down through the PC board. When all of the surface mount components are mounted on the topside of the board, turn it over and mount all of the SM com­ponents on the reverse side. Once complete we are ready for the conventional components. The header pins come first and there is no height restric­tion to limit which way they are mounted. You can mount the whole header with the black plastic base included or you can invert the pins (long side through the PC board) as we did in the transmit­ter module, and remove the black plastic base when finished. This gives a much Underneath the assembled encoder board, showing all the surface mount components. You can use this photo as a crosscheck with the component diagram of Fig.2. This view shows how the configuration module, to be discussed in future article, fits on the header pins for the mix expansion socket TB30. neater looking finished item. This is the way the commercial units are assembled. If you do not mount the header pins first then you will not be able to remove the black base. The header pins supplied in the kit are in strips of 40 pins and must be cut into the required number of pins for each terminal block. If you have no intention of expanding beyond eight chan­nels, the header pins TB11, TB12, TB13 and TB14 can be deleted altogether. There is a short on the PC board which automatically programs the PC board to eight channels. If you do intend to go beyond eight channels then this short must be cut and the header pins installed. Do not forget also that all the components not placed during the original build can be easily added later. This close-up view shows the micro shunts fitted to pin pairs 4-11 on TB30. TB29, the dual control (buddy box) header, also has a short across it on the PC board. If you intend to install this feature, install TB29 and cut the track between the pins. Adding this feature will be described in a later column so for the moment leave this track uncut. TB30, the servo test header, must be fitted since it allows you to set up the entire system without the transmitter and receiver modules installed. TB29 is a polarised 2-pin connector so be sure it is mounted exactly as shown on the overlay. This is the only connector not made out of header pin strip. TB10, the mix expand port, is a June 1996  63 of the solder connections are complete. It is very easy to miss soldering one end of a surface mount component or to short out two pins on an IC. Testing This scope photo shows the staircase waveform at pin 1 of IC3a (upper trace) and the pulse waveform from pin 7 of IC1b (lower trace). special case and must be mounted with the plastic base left in place and the long side of the pins uppermost (short side through the PC board). The black plastic base provides the clearance height to keep the configuration module above the surface mount components. This header pin set carries the configuration modules which are used during setup and provides the mix points for the on-board mix­ers. In order to provide access for the configuration inputs, the tracks are broken between each of the pin pairs 4-11 (refer back to the encoder circuit on pages 56 & 57 of the March 1996 issue). For normal operation, shorting links (micro-shunts) must be placed across these pin pairs for circuit continuity. If you do not intend using mixing, then TB10 can be left out and hard wired shorting links wired across the pin pairs 4-11. Again, if you don’t want mixing, all of the components associated with TB27 and TB28, including the headers themselves can also be omitted. The only other item of note in the header pin department is the clipping of pin two on the power and expansion terminal blocks to provide polarisation. This is essential as these con­nectors carry the DC power to the encoder board and the 24-channel expansion board. When we come to wiring the transmitter looms, then we will talk about fitting jumpers to the header sockets. Now complete the assembly by mounting the remaining conven­tional components. Zener diode (ZD1) in the meter circuit is best left standing a little proud of the PC board to keep it well clear of the SM components. Now go back and check your work, taking particular care to ensure that all Kit Availability Kits for the Mk.22 encoder module are available in several differ­ent forms, as follows: Fully assembled module........................................................................$159.00 Encoder kit.............................................................................................$110.00 Encoder PC board...................................................................................$29.50 Post and packing of the above kits is $3.00. Payment may be made by Bank­­ card, cheque or money order payable to Silvertone Electronics. Send orders to Silvertone Electronics, PO Box 580, Riverwood, NSW 2210. Phone (02) 533 3517. 64  Silicon Chip Once you are satisfied that all is well, load the micro shunts onto pins 4-11 of TB10 (mix expand) and onto the NORMAL side of TB1, TB3, etc. Set all potentiometers to the midpoint, including VR2. This pot has been changed to a 10-turn trimpot on the production PC board (same value) to improve the accuracy and stability of the neutral adjustment. Switch your multimeter to a low “ohms” range and check between pins 3 and 6 of TB7 to ensure there isn’t a dead short across the board. Hook up a 10V supply to pins 3 and 6 of TB7 and check the voltages at the following points: input to the voltage regulator REG1, +10V; output of REG1, +5V; junction of the voltage refer­ences R22/R23 and R58/R61, 2.5V; cathode of ZD1, +7.5V and finally, the centre terminal of VR2, +1.5V. With 10V applied, run along the four output pins of IC3 (pins 1, 7, 8, 14) and check with an oscilloscope to see that pulses are present. The waveform at pin 1 should be as in the scope photo accompanying this article. Now go to pin 1 on power connector TB7 and you should have a negative going pulse of about 10V peak-to-peak with a pulse width of approximately 1.5ms. There should be nine nega­tivegoing spikes. Congratulations, you now have a working basic encoder modu­le. All that remains for this month is to make up a patch cord to connect the servo test header, TB30, to the decoder (described in the April 1995 issue) for the final test. This patch cord is quite simple, consisting of a ground and signal connection – see Fig.4. Take care to get the polarity correct on the 2-pin connector for TB30. The output of TB30 is a positive-going pulse in order to match the receiver output. The 3-pin plug for the decoder is a bit of a problem as this socket is non-polarised, so paint dots on the mated connector to ensure correct alignment during later use. The ground connec­tion is the pin closest to the receiver crystal. The socket we are discussing here is the black plastic socket used to mate the receiver to SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my Bankcard   ❏ Visa Card   ❏ MasterCard ❏ Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ ✂ the decoder. Plug the patch cord onto TB30 and into the decoder socket. Plug in a receiver battery and one or more servos or better still, a pulse width meter. If you do not have a pulse width meter, then a servo set to 1.5ms neutral (most modern servos) will be quite adequate. Remove any connections you may have to the encoder except the power lead and patch cord. Switch on the power to both the encoder and decoder and the servos should all take up the same position. Adjust VR2 to bring the servos to neutral (1.5ms) and you now have an aligned encoder. If you do not have a Mk.22 receiver then you may want to hook up the encoder to the transmitter module. Simply connect ground, 10V and signal on the two boards, set the programming shunt on TB3 in the RF module to the AM position and you should have a modulated RF signal adequate in strength to drive the receiver at close range. Carry out the above adjustment and you are all set for the programming which will be described when we deal with system alignment. Finally, for those who just cannot contain themselves and must see a servo move from an input, if you have an old control stick, just wire up a 3-pin socket as shown in Fig.5. If you do not have a control stick then wire up a 5kΩ linear pot as shown in Fig.6. The two 4.7kΩ resistors simulate the mechanical stops in the control sticks. Set the programming shunts supplied to the NORMAL position on the input programming headers TB1, TB3, etc. Plug the pot into the channel 1 input and the servo into channel 1 on the receiver/decoder. Rotating the pot or moving the stick will result in servo movement. To reverse the direction of travel, simply rotate the pot connector through 180°. When satisfied that all is working and the novelty has worn off reversing the servo, check each channel input. A word of warning here. When reversing the servo, keep in mind that the pulse width must be set at precisely 1.5ms (servo in exact neutral) or else any error in position will be multi­plied by a factor of two when you reverse the servo. In other words, if a servo is at one end of its travel (for example the throttle), then it will fly to the other end as soon as you re­verse its travel. Next month, we will discuss construction of the transmitter case. SC June 1996  65 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au c i t a m o t u 10-Amp A Battery Charger Have you tried to start your car or boat recently and found the battery wouldn’t do its job? Do you need a fast charger for the battery? This new automatic 10amp charger should fit the bill. By RICK WALTERS Although it’s possible to buy a commercial battery charger for just $30, it won’t get you out of trouble in a hurry if you have a flat battery. These chargers usually have a maximum cur­rent rating of just 4A continuous, which means that it can take many hours to bring a flat battery up to scratch. Often, it’s a case of connecting the charger and letting the battery charge 70  Silicon Chip for the rest of the day or overnight. Many low-cost commercial chargers also lack any useful indication of the charging rate. What’s more, they often only have a single fixed charging voltage and come with rather flimsy clamps and cables. When it comes to battery chargers, the old adage “you get what you pay for” is quite true. By contrast, this design is capable of pumping out a hefty 10A on a continuous basis and can automatically charge 6V, 12V or 24V batteries. You don’t have to manually set the charging vol­tage either. When connected to a battery, this unit measures its voltage and then automatically selects the correct charging rate. This scheme works because a “flat” battery is generally only a few volts below its nominal voltage. For example, a flat 12V battery generally would be at about 10V while a 24V battery would drop to about 20V. The only drawback of this scheme is that the charger will not automatically recognise a 12V battery that has gone below 8V or a 24V battery that has gone below 16V. That’s because the sensing circuit assumes that anything under 8V is a 6V battery, while anything between 8-16V is a 12V battery. Most of the compon­ents, including the main PC board, the power transformer, the electro­ly­tic capacitors and two bridge rectifiers, are mounted on an aluminium baseplate. This provides an excellent heatsink and simplifies mounting the various components. Note the heatshrink tubing covering the mains switch and fuseholder terminals. We don’t think this will happen very often but if it does, the solution lies in the “override” pushbutton switch on the back panel. All you have to do is hold this pushbutton down for short periods until the correct voltage indicator LED stays on. We’ll talk about this function later. Because of its high current rating, this battery charger is just the shot for quickly topping up a battery that’s not quite up to the job. It can really get you going again on those cold winter mornings. It’s also ideal for getting your boat or recrea­ t ional vehicle battery up to speed, if it’s been lying around neglected for a while. Seven front panel LED indicators give you a good idea as to what’s going on. First, the BATTERY CONNECTED LED lights whenever a battery is connected, even if the power is off. Three more LEDs indicate whether a 6V, 12V or 24V battery is being charged, while the remaining three LEDs indicate FEATURES ✔ Automatic selection for 6V, 12V or 24V batteries ✔ Manual override button for single voltage setting ✔ 10A maximum charging current ✔ Automatic change over from high through medium to trickle charge ✔ Battery voltage and charge status indicator LEDs ✔ Output short circuit protection ✔ Reverse polarity protection the charging rate (trickle, medium or high). How it works Refer now to Fig.1 for the circuit details. This circuit can be split into four blocks: (1) a battery voltage sensing and reference voltage summer (IC1); (2) a switching regulator (IC2 and associated circuitry) which regulates the battery charging voltage. This circuit block also senses and limits the battery charging current; (3) a power supply based on transformer T2, full-wave bridge rectifier BR1 and 3-terminal regulator REG1; and (4) charging and voltage indicators based on transistors Q5-Q7 and LEDs 1-7. Let’s take a closer look at each of the various circuit functions. The battery voltage sensing circuit consists of three com­parators: IC1a, IC1b and IC1c. As shown, pins 3 & 5 of IC1a & IC1b respectively are June 1996  71 Fig.1: comparators IC1a-IC1c provide the automatic battery voltage sensing function, while IC2 is the switching regulator. The latter generates a PWM (pulse width modulated) waveform and drives Mosfet Q4 via a buffer stage (Q2 & Q3) and isolating transformer T1. IC1d monitors the voltage across the 0.01Ω current sensing resistor and drives the charge indicator LEDs. 72  Silicon Chip PARTS LIST 1 plastic instrument case with plastic front & rear pan­els, 260 x 180 x 65mm (Jaycar HB5984 or equivalent) 1 self-adhesive front panel label, 250 x 60mm 1 PC board, code 14105961, 145 x 83mm 1 PC board, code 14105962, 51 x 48mm 1 160VA toroidal power transformer with 18V secondaries (Jaycar MT2113 or equivalent) 1 mains lead with moulded 3-pin plug 1 mains switch with plastic rocker & neon indicator (S1) (Jaycar SK0985 or equivalent) 1 pushbutton momentary contact switch (S2) 2 3AG panel-mount fuseholders (Jaycar SZ2020 or equivalent) 1 2A 3AG slow-blow fuse (F1) 1 16A 3AG fuse (F2) 1 10A battery clip - red (DSE P-6420 or equivalent) 1 10A battery clip - black (DSE P-6422 or equivalent) 5 TO-3 insulating bushes 2 TO-220 insulating washers 1 E-type ferrite transformer complete with bobbin - Jaycar LF-1270 or equivalent (T1) 3 190mm cable ties 1 ETD29 transformer assembly (Philips 2 x 4312-020-37502 ferrite cores; 1 x 4322-02134381 former; 2 x 4322-02134371 clips) (L1) 1 1.5-metre 30A battery cable (red) 1 1.5-metre 30A battery cable (black) 7 5mm LED clips 1 3mm x 10mm tapped spacer 4 3mm x 6mm tapped spacers 2 3mm x 15mm bolts 5 3mm x 12mm bolts 8 3mm x 6mm bolts 16 3mm hex nuts 11 3mm flat washers 12 3mm spring washers 2 mains cable clamps (Jaycar HP0716 or equivalent) 3 6PK x 10mm screws 4 6mm female solder quick connectors (BR1) 1 260mm length 20 B&S enamelled copper wire (for .01Ω resistor) 1 6-metre length 21 B&S enamelled copper wire (for L1) 1 9-metre length 30 B&S enamelled copper wire (for T1) connected to the positive terminal of the battery via a 20kΩ resistor and to ground via two series 10kΩ resistors. This arrangement ensures that half the battery voltage appears on pins 3 & 5, while one quarter of the battery voltage appears on pin 10 of IC1c. A voltage divider string fed from the +15V output of REG1 is used to set the bias voltages on the inverting inputs of IC1a-IC1c. As shown, pin 6 of IC1b is biased to +2V, while pins 2 & 9 of IC1a & IC1c are biased at +4V. If a 6V battery is connected, the output of IC1b will switch high, turning on Q7 and lighting LED7 (the 6V indicator LED). Similarly, a 12V battery will cause the outputs of both IC1a and IC1b to switch high. Because pin 1 of IC1a is now high, LED7 turns off and LED6 turns on (via Q6), indicating that a 12V battery is being charged. Finally, a 24V battery causes all three comparator outputs to switch high. LEDs 6 & 7 will now both be off, while LED5 will be on to show that the battery is being charged to 24V. Semiconductors 1 LM324 quad op amp (IC1) 1 TL494 or TL594 switching regulator (IC2) 1 BS170, BS170P or VN10KM N-channel IGFET (Q1) 1 BD139 NPN transistor (Q2) 1 BD140 PNP transistor (Q3) 1 MTP75N05 N-channel IGFET (Q4) 3 BC548 NPN transistors (Q5-Q7) 1 7815 3-terminal regulator 5 1N914 switching diodes Switching regulator IC2 is a TL494 PWM switching regulator IC from Texas In­struments. (D1,D2,D5-D7) 1 BYV32-200 ultra-fast diode (D3) 1 1N4004 power diode (D4) 1 400V 35A bridge rectifier (BR1) 1 400V 6A bridge rectifier - P04 (BR2) 7 5mm red LEDs (LED1-LED7) 1 15V 400mW zener diode (ZD1) Capacitors 3 4000µF 63VW chassis mounting electrolytic 1 470µF 63VW PC electrolytic 1 220µF 25VW PC electrolytic 1 100µF 16VW PC electrolytic 2 22µF 16VW PC electrolytic 3 10µF 16VW PC electrolytic 1 4.7µF 16VW PC electrolytic 3 0.1µF 100VW monolithic ceramic 1 .0022µF 100VW MKT polyester Resistors (0.25W 1%) 1 10MΩ 7 4.7kΩ 1 1MΩ 1 2.2kΩ 2 220kΩ 1 1.8kΩ 1 100kΩ 2 1.5kΩ 3 56kΩ 6 1kΩ 2 27kΩ 1 910Ω 1 20kΩ 1 470Ω 1 15kΩ 1 330Ω 3 10kΩ 1W 1 100Ω 2 10kΩ 1 91Ω 2 8.2kΩ 1 0.01Ω 1 5.6kΩ Miscellaneous Red, orange & black hook-up wire; heatshrink tubing. This device contains an on-board oscillator, a refer­ence regulator, two error amplifiers, and a pair of output driver transistors. In operation, this device monitors the voltage between its pin 1 and pin 2 inputs and adjusts its output duty cycle accordingly, to give the correct charging voltage. In greater detail, pins 1 & 2 are the non-inverting and inverting inputs respectively of an internal error amplifier (designated A1). Pin 1 monitors the battery voltage via a voltage divider (5.6kΩ and 910Ω), while pin 2 monitors the output of the reference June 1996  73 Fig.2: most of the parts are installed on these two PC boards. Make sure that transformer T1 is correctly oriented, as it’s easy to install it back-to-front. In addition, the two round plastic corner lugs on the base of this transformer must be cut off so that the pins go through the PC board. voltage summer formed by IC1a-IC1c. When a 6V battery is connected, pin 7 of IC1b goes high as we’ve already described. As well as driving Q7, this output is also applied to a voltage divider consisting of 56kΩ, 4.7kΩ and 330Ω resistors. As a result, +1V DC is applied to pin 2 of IC2. When a 12V battery is connected, the output of IC1a goes high as well and so the two 56kΩ resistors at the comparator outputs are effectively in parallel. This means that a signal of +2V is now applied to pin 2 of IC2 and this jumps to +4V for a 24V battery (all three comparator outputs high). Thus, depending on the voltage of the battery connected to the charger, the comparators apply a fixed DC voltage to pin 2 of IC2 (ie, to amplifier A1’s inverting input). This voltage is then compared with the divided battery voltage on pin 1 74  Silicon Chip of IC2 (the non-inverting input of the A1 error amplifier). As a result, IC2 adjusts its pulse width output accordingly so that the battery is charged to the correct voltage. This works out to be 7.2V for a 6V battery, 14.4V for a 12V battery, and 28.8V for a 24V battery. Note that these full-charge voltages respectively equate to 1V, 2V and 4V signal voltages on pin 1 of IC2. Override function Pushbutton switch S2 provides the override function. As explained previously, this is used in situations where the bat­tery is so flat that it is no longer automatically recognised by the charger. To simplify the circuit, however, S2 provides just one override voltage (either 6V, 12V or 24V). That’s because most individual users will only want to charge one type of battery (usually 12V). The actual override voltage is determined by the value of resistor R1 and this is selected when the unit is built. When S2 is pressed, it simulates the relevant comparator output(s) going high and applies the appropriate voltage to pin 2 of IC2. This forces switching regulator IC2 to charge the battery at the correct voltage, even though the automatic detection circuitry has failed to identify the battery. Assuming that the battery is OK, this will very quickly bring its voltage up to a level where the automatic detection circuit can take over. The battery will then charge to the cor­ rect voltage. In practice, it’s simply a matter of holding down S2 for short periods until the correct charge indicator LED remains on when the switch is released. Note, however, that it should rarely be necessary to use the override switch. Only batteries that have been severely dis­charged will have an output that’s so low that they will not be automatically recognised. And any battery that’s left in this state for too long will quickly deteriorate. Current limiting The need for current limiting is obvious – without it, a discharged battery could attempt to draw 30-40A or more. This would certainly be no good for the battery or for the charger itself. In this circuit, the maximum charging current has been limited to 10A. This is done by monitoring the voltage developed across a .01Ω current sensing resistor and applying it to the non-inverting input (pin 16) of a second error amplifier (A2) inside IC2. This voltage (ie, on pin 16) is then compared with a fixed 10mV reference on the inverting input of A2 (pin 15). As long as the charging current remains below 10A, the voltage across the .01Ω resistor remains below 10mV and no cur­rent limiting takes place. However, if the current attempts to rise above 10A, the voltage on pin 16 will rise above the voltage on pin 15. The A2 amplifier then generates an error signal and this in turn reduces the duty cycle of the pulse width modulated (PWM) output at pins 9 & 10. As a result, the maximum output current is effectively limited to 10A. If the current does try to rise above this, the error amplifier immediately reduces the PWM duty cycle to reduce the current again. Mosfet Q1 and its associated components provide a delayed start-up for the switching regulator (IC2). This is necessary to give IC1a-IC1c sufficient time to apply the correct reference voltage to pin 2. When no battery is connected, Q1’s gate is at ground and so it is turned off. As a result, pin 4 (Inhibit) of IC2 is held at the pin 14 reference voltage (5V) via a 4.7kΩ resistor and diode D2 – ie, the 22µF capacitor between pins 4 & 14 will be dis­charged. This prevents the switching regulator from producing any output. If a battery is now connected, the output of IC1b (and perhaps IC1a & IC1c as well) will go high after a short delay, as set by the 22µF capacitor at pin 5. This high turns on Mosfet Q1 The LED indicator board is mounted on the front panel by pushing the six charge indicator LEDs into matching plastic bezels. Note the 10mm spacer attached to the middle of the board – this ensures correct spacing between the board and the front panel. (via D1) and so the 22µF capacitor on pin 4 of IC2 charges via the 100kΩ resistor in Q1’s drain. As a result, the voltage on the Inhibit pin slowly reduces as the capacitor charges. This allows the output pulse width at E1 and E2 to increase slowly from zero to a width which is con­ trolled by the battery voltage. Note that pressing the override switch (S2) also applies a high (+15V) to the gate of Q1 (via D7). This ensures that IC2 starts when S2 is pressed, even if the battery voltage is so low that none of the op amp outputs has gone high. Buffer stage The paralleled emitter outputs from IC2 drive a buffer stage based on complementary emitter followers Q2 & Q3. From there, the PWM signal is fed to transformer T1. The transformer secondary then drives Mosfet Q4 via a 0.1µF capacitor. ZD1 is included to protect Q4’s gate circuit from voltages in excess of 15V. T1 is necessary to isolate the switching regulator circui­try (IC2, Q2 & Q3) from the output circuitry. This is because Q4 operates as a source follower and its source is effectively at the battery voltage. In operation, Q4 is switched on and off by the waveform ap­plied to its gate. Each time it turns on, it applies a DC pulse to the positive battery terminal via inductor L1. When Q4 turns off, the field around L1 collapses and D3 conducts so that the energy stored in the inductor can continue charging the battery. Note that although Q4 switches a +55V rail, the average voltage applied to the battery is determined by the duty cycle of the PWM waveform from IC2. The pulse widths are at their narrow­est for 6V batteries and at their widest for 24V batteries. Bridge rectifier BR2 is there to protect the circuit against reverse polarity connection of the battery. Using a bridge rectifier may seem a little odd here but we are really only just connecting the top two diodes in parallel and with reverse polarity across the output. The bridge rectifier is simply a low-cost way of obtaining two diodes with adequate current ratings. If the battery is connected the wrong way around, the two top diodes inside the bridge become forward biased and conduct a heavy current. This blows 15A fuse F2, thereby disconnecting the battery from the charger before any damage can occur (other than to the fuse itself). Charge indicators Op amp IC1d, together with LEDs 2-4, provides the charge rate indication – either trickle, medium or high. It does this by monitoring the June 1996  75 Fig.4: the winding details for transformer T1. Wind the primary first, cover it with insulating tape, then wind on the secondary. Fig.3: the core halves in inductor L1 are separated using washers cut from TO3 mounting insulators. voltage developed across the .01Ω current sensing resistor. This voltage is applied to pin 12 of IC1d which oper­ates with a gain of 214, as set by the 1MΩ and 4.7kΩ feedback resistors on pin 13. The output from IC1d appears at pin 14 and is applied to the charge LED indicators. If the charging rate is greater than about 3.5A, then IC1d’s output will be above 7.5V and both the HIGH and MEDIUM LEDs will be lit. At the same time, the TRICKLE LED (LED4) will be reverse biased and so it will be out. As the battery charges, the output of IC1d gradually reduc­es. Because the cathode of the HIGH current LED is biased to about 5.5V, it will gradually dim and then extinguish as IC1d’s output falls. The MEDIUM LED now remains lit until the charging current drops to about 0.75A. It then dims and goes out, by which time LED4 has come on to indicate the trickle charge mode. Note that the output from IC1d must 76  Silicon Chip Fig.5: install the power switch on the front panel with the ring on the rocker oriented as shown here. drop to about 2.4V before LED4 begins to turn on. That’s because LED4’s anode is biased to about 4.8V using a voltage divider and diode D6. In summary, LEDs 2 & 3 both light when the charging current is above 3.5A; LED3 lights when the charging current is in the range 0.75-3.5A; and LED2 lights when the charging current is below about 1A. Note that there is a transition period when both LED3 and LED4 are on (ie, LED4 gradually turns on as LED3 dims). Power supply Power for the circuit is derived from the mains via T2, a 160VA toroidal transformer with 18V secondaries. This drives full-wave bridge rectifier BR1 which, together with three 4000µF filter capacitors, produces a +55V rail for the drain of Q4. The three 4000µF filter capacitors are required in order to provide an adequate ripple rating so that the charger can deliver 10A. A neon indicator wired across the primary of the trans­former provides power on/off indication, while fuse F1 provides overload protection. D4 and 3-terminal regulator REG1 provide a regulated +15V rail to power the rest of the circuitry. Construction Most of the parts for the Autocharger 10 are installed on two PC boards: (1) a main board coded 14105961 (145 x 83mm); and (2) an indicator board coded 14105962 (51 x 48mm). Fig.2 shows the parts layout on the two PC boards. Before installing any of the parts, carefully check both boards for etching defects (in most cases there will be none). If everything is OK, start the main board assembly by fitting PC stakes to the 12 external wiring points, then install the six wire links. The diodes and resistors can be installed next, followed by the ICs, capacitors and transistors. Be sure to orient transistors Q2 and Q3 with their metal tabs facing away from T1. Fig.7: the mains cord must be anchored securely and the wiring installed exactly as shown here. Be sure to cover the switch and fuseholder terminals with heatshrink tubing. The thick lines indicate heavy-duty (30A) cable. No heat­sinks are required for these two devices. As explained previously, resistor R1 is selected to set the desired override voltage. Use 56kΩ to provide a 6V override, 27kΩ for 12V override and 15kΩ for 24V override. Care is required when mounting Q4, D3 and REG1, since their metal tabs must later line up with matching holes in a metal baseplate. Note that these devices are all mounted on the June 1996  77 copper side of the board, as shown in Fig.7. The mounting procedure is as follows: (1) Bend the device leads upwards at a suitable distance from the bodies (note: the holes in the metal tabs must match the relevant baseplate holes if this has been pre-drilled); (2) Install the devices so that the bottom faces of their metal tabs are exactly 6mm below the PC board. This can be checked out by fitting 6mm spacers to the PC board and then placing the assembly on a flat surface. Make any adjustments as necessary before cutting the device leads off flush with the top of the board. Inductor L1 consists of six lengths of wire, all wound together on a Philips 4322-021-34381 former (as one winding). This is done to achieve a high current capacity using a small, manageable gauge of wire. The winding procedure is as follows: (1) cut the 21 B&S wire into six 1-metre lengths; (2) tin one end of each wire, form it into a hook and solder each hooked end to a separate pin on the 6-lug side of the former; (3) bundle the wires together and wind on 20 turns (the direction doesn’t matter); (4) check that the ferrite core halves fit the former, then terminate the six ends on separate pins on the other side of the transformer; (5) cover the windings with a couple of layers of insula­tion tape, then slip one of the ferrite core halves into the side of the former with the six lugs and secure it with one of the clips; (6) cut three TO-3 mounting insulators as shown in Fig.3 (these serve as Fig.8: the mounting details for D3 and Q4. Make sure that the area around their mounting holes is smooth and free of metal swarf, to avoid punching through the insulating washers. spacers between each leg of the two core halves); (7) fit the second ferrite core half to the former, along with one of these insulating washers as a spacer between the two centre legs; (8) push the other two spacers into the gap between the outer legs of the core halves, then secure the assembly using a 190mm plastic cable tie. Fig.4 shows the winding details for driver transformer T1. This is wound on a plastic bobbin using 30 B&S enamelled copper wire. Be sure to wind the turns in the direction shown in Fig.4, as the phasing of this transformer is critical. The primary is wound first. To do this, terminate the start of the wire on pin 2, wind on 100 turns and ter- NOTE: THE OVERRIDE SWITCH ON THE REAR PANEL IS FOR USE WITH _____ VOLT BATTERIES ONLY. PRESS THIS SWITCH IF . . . (1) No charging voltage is indicated; or (2) The indicated charging voltage is too low. Release override switch every 10 seconds until the correct charging voltage is indicated. WARNING! – MAKE SURE THAT THE BATTERY IS BEING CHARGED AT THE CORRECT VOLTAGE BEFORE LEAVING THE CHARGER UNATTENDED & ALWAYS CHARGE IN A WELL-VENTILATED AREA. Fig.9: this label should be attached to the top of the charger. Be sure to fill in the value for the override voltage in the space indicated (either 6V, 12V or 24V). 78  Silicon Chip minate the finish on pin 1. Cover this winding with a layer of insulating tape, then wind on the 110-turn secondary, starting at pin 5 and fin­ishing on pin 7. Note that the secondary must be wound in the same direction as the primary. The last item to make is the 0.01Ω resistor, as follows: (1) take a piece of 20 B&S enamel wire and cut it to 260 mm; (2) clean each end with a knife or emery paper and tin for about 5mm; (3) wind the wire into a coil (we used a pencil as a former and ended up with nine turns). T1, L1 and the .01Ω resistor can now be installed on the PC board, as shown on Fig.2. Be sure to match the start and finish windings of T1 to their designated locations. It will be necessary to cut off the two plastic lugs on the botton of T1, so that it can be pushed all the way down onto the board. LED indicator board The LED indicator board will only take a few minutes to assemble. Begin by installing PC stakes on the copper side of the board at the external wiring points, or if you wish just solder flying leads into the holes as shown in one of the photo­graphs. This done, fit the resistors, transistors Q5-Q7, diode D1 and the six indicator LEDs. Note that the LEDs must be mount­ed so that the bottom of each LED is 6mm above the board. The easiest way to do this is to cut a 6mm-wide cardboard jig. This jig is then insert­ed between the LED leads as they are being pushed down on the board. Finally, a 10mm spacer is fitted to the top of the board – see photo. Case assembly A standard plastic instrument case with plastic front and rear panels is used to house the circuitry. Most of the compon­ents, including the main PC board, power transformer, electro­ly­tic capacitors and the two bridge rectifiers, are mounted on an aluminium baseplate. This provides an excellent heatsink and simplifies mounting the various components. Begin by attaching the label to the front panel, then use this as a drilling template for the LED indicators (6.57mm), the fuseholder and the battery cable clamp. Note that larger holes are best made by first drilling a small pilot hole and then carefully enlarging Fig.10: this full-size artwork can be used as a drilling template for the front panel. them using a tapered reamer or, for the battery cable clamp hole, a small file. The cutout for the mains switch is made by drilling a series of small holes around the inside circumference, then knocking out the centre piece and carefully filing the hole to shape. Don’t make this hole too big – the mains switch must be a tight fit so that it is held securely. The LED bezels, fuseholder F2 and the mains switch (see Fig.5) can now be fitted to the front panel. The battery cables consist of 1.5-metre lengths of 30A cable (red for positive and black for negative). These are each fitted with a large battery clip at one end. Secure them using a cordgrip clamp, leaving a length of about 250mm for each cable at the back of the panel. The LED indicator board is now fitted by pushing the LEDs into the bezels, until the spacer contacts the front panel. Once the front panel assembly has been completed, the rear panel can be drilled to accept the mains cord clamp, fuseholder F2 and pushbutton switch S2. The locations of these holes can be gauged from the photographs and from the wiring diagram (Fig.6). Note that the mains cord hole should be carefully profiled to match the cordgrip grommet. The next step is to drill the baseplate. This will need to be drilled for the transformer mounting bolt, the two bridge rectifiers, three filter capacitors, the PC board mounting screws, the three TO-220 devices (Q4, D3 & REG1), and the three fixing points to secure the baseplate into the base of the case. The latter three holes take self-tapping screws into inte­gral pillars in the base of the case. One of these is adjacent to the front-panel power switch, while the other two are just in front of the three filter capacitors. When the drilling is done, all the hardware is mounted on the baseplate before it is mounted into the case. Transformer T2 is secured using a large bolt, two rubber washers and a large metal washer. One of the rubber washers sits under the transformer, while the second sits under the metal washer at the top. The main PC board, the bridge rectifiers and the electroly­tic capacitors can now be installed on the baseplate. The board is secured at the front and rear using the 6mm spacers and 12mm long bolts. Note that Q4 and D3 must be isolated from the baseplate using standard TO-220 mounting kits – see Fig.8. After mounting, check that the device tabs are indeed isolated using a multimeter switched to a high ohms range. REG1 can be bolted directly to the baseplate, since its metal tab is at earth potential. Final wiring Fig.6 shows the final wiring details. Exercise extreme care when installing the mains wiring, as your safety depends on it. In particular, make sure that the mains cord is securely anchored by the cordgrip grommet on the rear panel and that it cannot be pulled out. The Active (brown) and Neutral (blue) wires from the mains cord go directly to the mains switch, while the Earth (yellow/ green) wire is soldered to an earth lug which is bolted securely to the baseplate. Use a star washer and an additional lock nut to ensure that the earth lug cannot come loose. The terminals of the fuseholder and mains switch should be covered with heatshrink tubing to prevent accidental contact with the mains. This involves slipping a length of June 1996  79 Fig.11: the full-size etching patterns for the two PC boards are shown here. Check your boards carefully for etching defects by comparing them with these patterns, before installing any of the parts. heatshrink tubing over all the leads before they are soldered to the terminals. After soldering, the heatshrink tubing is pushed over the fuse­holder and mains switch bodies and shrunk using a hot-air gun. The two thin orange wires from the transformer are the primary leads and these go to the mains switch and the fusehold­ er, as shown. The low voltage secondary leads are much thicker. Twist the ends of the pink and yellow leads together (to form the centre tap) and solder a short length of hook-up wire to them. The resulting joint should then be sleeved using heat­shrink tubing. The red and white transformer leads go to the AC terminals of the bridge rectifier via spade terminals, while the lead connected to the transformer centre-tap goes to D4 on the PC board. All leads between BR2, the fuse­ WARNING! Lead-acid batteries generate hydrogen gas which is explo­sive. This charger should only be used in a well-ventilated area and you should always connect the battery to the charger before turning the mains switch on. This is done to prevent sparks from being generated. If the BATTERY LED does not light when the battery is con­nected, check the 15A fuse and the battery polarity. This fuse will blow if the battery is connected the wrong way around and is there to protect the internal circuitry. Finally, always turn the charger off before disconnecting the battery leads. Again, this is done to prevent sparks from causing an explosion. 80  Silicon Chip holder and the PC board must be run using 30A cable. The only exception is the lead between the fuseholder and the battery sense terminal on the PC board. The connection between the positive terminal of BR2 and the fuseholder is made using the bridge rectifier lead – it’s simply bent over to contact the fuseholder terminal. Again because of the currents involved, three separate leads are run from the +55V terminal on the PC board to the positive terminals of the 4000µF capacitors. Three more leads are run from the GND point to the negative terminals. Similarly, separate leads are run from the plus and minus terminals of the capacitors to the corresponding terminals on bridge rectifier BR1 (see Fig.6). Note the 10kΩ resistors across the capacitors – they’re there to discharge the capacitors after switch off. Warning: don’t touch the capacitor terminals as they can give you a shock. The remainder of the wiring be- tween the LED indicator board, LED1 and the main PC board can be run using light-duty hook-up wire. Complete the construction by fitting the fuses in the fuseholders. The 2A fuse goes in fuseholder F1, while the 15A fuse goes in fuseholder F2. Testing Before plugging the unit in and switching it on, it is a good idea to check the mains wiring using an ohmmeter. To do this, first check that there is an open circuit bet­ween the Active and Neutral pins of the mains plug when switch S1 is off and a resistance of about 13Ω when it is on. If this is OK, check that there is an open circuit between each of these two pins (Active & Neutral) and the earth pin. Finally, check that the meter reads zero ohms when connect­ed between the Earth pin on the plug and the metal baseplate. If everything checks out, plug the charger into the mains and turn it on. Both the mains switch neon and the TRICKLE LED (LED4) should light. If they don’t, switch off immediately, pull the mains plug and locate the problem before proceeding further. Now turn the mains switch off and connect a 6V or 12V DC battery to the charger leads (positive to positive, negative to negative). Check that the BATTERY CONNECTED LED lights. Next, disconnect the battery, switch on the mains and (carefully) measure the voltage across the 4000µF electrolytic capacitors (warning: do not touch or short any of the termi­nals). You should get a reading of about 55V. The voltage on pin 8 of IC2 should be around 15V, while pin 14 should read around 5V. If everything is OK so far, the unit is ready for its first trial. To do this, turn the charger off and connect it to a car battery (disconnect the battery from the car’s electrical system first). The BATTERY CONNECTED LED should immediately light. Now switch on the mains and check that the 12V LED lights (assuming that a 12V battery is connected). Depending on the state of the battery, one of the charge indicator LEDs should also illuminate. If the HIGH LED lights it will probably only be for a short period of time, then the charg­er will switch to MEDIUM. Eventually, depending on the condition of the The wiring connections to the LED indicator board can either be run directly to the copper pads on the back of the board, as shown here, or to PC stakes. Use cable ties to keep the wiring neat and tidy. Heatsinking is provided for REG1 (left), D3 and Q4 by attaching them to the baseplate. After mounting these devices, use a multimeter to confirm that the metal tabs of D3 and Q4 are correctly isolated from the heatsink. battery, the charger should switch to TRICKLE. Using the override button Before concluding, here are a few tips on using the over­ride pushbutton. First, remember that you have only one override voltage available. So if you selected a 27kΩ resistor for R1, the over­ride function is only available for 12V batteries. Of course, you can easily get around this if by adding a 3-way switch to select between the three possible resistor values. That way, you can provide an override function for all three battery types. The override function is easy to use. If the battery does not start charging at the correct voltage, hold the pushbutton down for 10 seconds, then release it and check to see if the correct charge indicator LED stays alight. If it doesn’t, repeat this procedure until it does. The battery should then charge to the correct voltage. Finally, note that the power transformer specified for the charger is rated at 160VA. While it is suitable for topping up 24V batteries, if prolonged high current charging of these bat­teries is envisaged, a 300VA transformer should be used. This will necessitate SC using a bigger case. June 1996  81 PRODUCT SHOWCASE New range of DMMs from Tektronix There are three major features of the new DMM800 series “true RMS” digital multimeter range just released by Tektronix. These are high accuracy (up to twice that of competing brands), high resolution (up to 10 times) and, according to Textronix, lower prices. The DMM800 series is the company’s new flagship range, designed specifically to meet the needs of electronic design engineers and technicians. The family consists of the entry level DMM830, mid-range DMM850 and the high-end DMM870. All offer a full range of industry-standard features –voltage, current, resistance, capacitance and frequency, and incorporate the new TC8129/8131 chip set, for which Tektronix has exclusive rights. This chip set is the first full featured, autoranging, autocalibrated DMM A-D converter, offering complete DMM functions and the highest resolution and accuracy available on the market today: 4¾ digits or 40,000 counts and 0.06% basic DC volts. The DMM850 and DMM870 feature BassBox® Design low frequency loudspeaker enclos­ures fast and accurately with BassBox® software. Uses both Thiele-Small and Electro-Mechanical parameters with equal ease. Includes X. Over 2.03 passive cross­over design program. $299.00 Plus $6.00 postage. Pay by cheque, Bankcard, Mastercard, Visacard. EARTHQUAKE AUDIO PH: (02) 9948 3771 FAX: (02) 9948 8040 PO BOX 226 BALGOWLAH NSW 2093 82  Silicon Chip dual numeric displays, allowing sim­ ultaneous measurement of two functions without switching (eg voltage and frequency). These models can also time stamp (labelling minimum and maximum values during measurement), as well as measure temperature directly in degrees Fahrenheit or Celsius. The DMM870 also features high/ low limit setting, with a beep to warn when measurements exceed user-set limits, along with a peak-hold function, holding and time stamping even very short mode (1ms) events. All three models are true RMS meters that feature adjustable auto power-off, memory store/recall and a durable water/dust resistant casing. Each meets IEC, UL and CSA standards and comes with a 3-year warranty. Prices are $399 for the 830, $449 for the 850 and $499 for the 870. For further information, contact Tektronix Australia, 80 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 7066, fax (02) 888 0125 Ghost killer chip for consumer products Cancellation Reference signal. Suitable for both PAL and NTSC, the MV52661SP chip provides the first cost-effective means of reducing ghost­ ing in consumer devices. The 52-pin DIP-package chip contains a 4fsc burst-lock clock generator, a sync separator, a clamping circuit for digital signal processing, an analog video switch and a 10 bit D-A con­verter, along with a timebase error detector circuit to detect channel change or VCR signal. For further information, contact Mit­ su­­bishi Electric; phone (02) 684 7777. Mitsubishi Electric has announced the release of the M52661SP, the first anti-ghost pre-processor chip for tele­ visions, set-top boxes and VCRs. According to Mitsubishi, use of their chip in conjunction with an adaptive filter chip (made by Oren Semiconductor) and a standard 8 or 9-bit video A-D converter, makes it possible to dynamically cancel multipath ghosts – if the TV station transmits a Ghost TDK’s first global PC Card 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.emona.com.au/ TDK has introduced the first legal “international” PC data/fax modem card, the DF2814, giving computer users the freedom to call up data from other computers, send and receive faxes without a fax machine, check e-mail and even surf the Internet both here in Australia and overseas. Usable in up to 17 countries, the PC Card (which used to be called PCMCIA) supports V.34 (28,800bps) data, 14,400 fax, MNP5 and V.42 bis data compression proto­cols, and MNP2-4, V.42 and MNP 10 error correction pro­to­cols. It is also compatible with the existing V.FAST class and will automatically fall back to slower speeds as required. When used overseas, country selector software allows the user to select the appropriate telephone system. Its default power-up is the country of origin, avoiding faulty setup. The card plugs directly into an PC or Apple Power Book sporting the appropriate PC Card slot. As well as the international business traveller, the card is ideal for SOHO and remote access applications. Fast charger for lithium-ion batteries The bq2054 fast charge IC from Benchmarq now optimises the charging of lithium-ion (Li-Ion) batteries. The bq2054 incorpo­ rates a pulse- width modulator (PWM), on-chip reference, charge timer, and status indicators to provide a full-features lithium ion charge controller. The PWM frequency is set by an external resistor-capacitor network. The bq2054 is suited to switch­­ mode designs and may be configured for linear or gated current regulation. In use, the device terminates charging when the current falls below a userselect­able minimum current limit. For safety, it also inhibits charging when the battery voltage and temperature are outside set limits. A user-selectable maximum charge time is also available. Also possible are multiple LED display options for charge status and fault conditions; user-selectable time-out and minimum current charge termination; battery temperature and voltage qualification before fast charge; and fast charge suspension with temperature fault. For further information, contact Reptechnic, 3/36 Bydown St, Neutral Bay, NSW 2089. Phone (02) 9953 9844. June 1996  83 Complete mixer on a chip Active matrix liquid crystal displays Philips has just appointed Amtex Electronics as sole Aus­tralian distributor for its range of FPD active matrix liquid crystal displays. This range of Active Matrix LCDs uses Thin Film Diode (TFD) technology which is simpler and more reliable than the current TFT technology. Ranging in size from 2.8 to 10.4-inches, with an 11.3-inch version soon to be released, these LCDs are designed for industrial, transportation, medical equipment and defence-related applications. For further information, contact Amtex Electronics on (02) 805 0844; fax (02) 805 0750. KITS-R-US PO Box 314 Blackwood SA 5051 Ph 018 806794 TRANSMITTER KITS $49: a simple to build 2.5 watt free running CD level input, FM band runs from 12-24VDC. •• FMTX1 FMTX2B $49: the best transmitter on the market, FM-Band XTAL locked on 100MHz. CD level input 3 stage design, very stable up to 30mW RF output. $49: a universal digital stereo encoder for use on either of our transmitters. XTAL locked. •• FMTX2A FMTX5 $99: both FMTX2A & FMTX2B on one PCB. FMTX10 $599: a complete FMTX5 built and tested, enclosed in a quality case with plugpack, DIN input •connector for audio and a 1/2mtr internal antenna, also available in 1U rack mount with balanced cannon input sockets, dual VU meter and BNC RF $1299. Ideal for cable FM or broadcast transmission over distances of up to 300 mtrs, i.e. drive-in theatres, sports arenas, football grounds up to 50mW RF out. FMTX10B $2599: same as rack mount version but also includes dual SCA coder with 67 & 92kHz subcarriers. • AUDIO Audio Power Amp: this has been the most popular kit of all time with some 24,000 PCBs being •soldDIGI-125 since 1987. Easy to build, small in size, high power, clever design, uses KISS principle. Manufacturing rights available with full technical support and PCB CAD artwork available to companies for a small royalty. 200 Watt Kit $29, PCB only $4.95. AEM 35 Watt Single Chip Audio Power Amp $19.95: this is an ideal amp for the beginner to construct; uses an LM1875 chip and a few parts on a 1 inch square PCB. Low Distortion Balanced Line Audio Oscillator Kit $69: designed to pump out line up tone around studio complexes at 400Hz or any other audio frequency you wish to us. Maximum output +21dBm. MONO Audio DA Amp Kit, 15 splits: $69. Universal BALUN Balanced Line Converter Kit $69: converts what you have to what you want, unbalanced to balanced or vice versa. Adjustable gain. Stereo. • • •• COMPUTERS I/O Card for PCs Kit $169: originally published in Silicon Chip, this is a real low cost way to interface •to Max the outside world from your PC, 7 relays, 8 TTL inputs, ADC & DAC, stepper motor drive/open collector 1 amp outputs. Sample software in basic supplied on disk. PC 8255 24 Line I/O Card Kit $69, PCB $39: described in ETI, this board is easy to construct with •onlyIBM3 chips and a double sided plated through hole PCB. Any of the 24 lines can be used as an input or output. Good value. 19" Rack Mount PC Case: $999. •• Professional All-In-One 486SLC-33 CPU Board $799: includes dual serial, games, printer floppy & IDE hard disk drive interface, up to 4Mb RAM 1/2 size card. PC104 486SLC CPU Board with 2Mb RAM included: 2 serial, printer, floppy & IDE hard disk $999; VGA •PC104 card $399. KIT WARRANTY – CHECK THIS OUT!!! If your kit does not work, provided good workmanship has been applied in assembly and all original parts have been correctly assembled, we will repair your kit FREE if returned within 14 days of purchase. Your only cost is postage both ways. Now, that’s a WARRANTY! KITS-R-US sell the entire range of designs by Graham Dicker. The designer has not extended his agreement with the previous distributor, PC Computers, in Adelaide. All products can be purchased with Visa/Bankcard by phone and shipped overnight via Australia EXPRESS POST for $6.80 per order. You can speak to the designer Mon-Fri direct from 6-7pm or place orders 24 hours a day on: PH 018 80 6794; FAX 08 270 3175. 84  Silicon Chip Analog Devices’ new SSM2163 is a complete 8-input audio mixer on a chip. It accepts eight audio channels, provides con­trol of volume in 63 1dB steps and can mix individual channels to either the right, left or both outputs. The SSM2163 employs an industry-standard three-wire serial interface and one data output terminal to daisy-chain multiple SSM2163s for high-end multi-track audio systems. A single mute pin, when driven by a micro­ processor reset signal, will silence all eight audio channels simultaneously. The SSM2163 is a companion to Analog Devices’ family of stereo codecs and provides excellent audio quality. Signal-to-noise is -82dBu (0dBu = 0.775V RMS) with an additional 10dBu of headroom, resulting in a total dynamic range of 92dBu. Total harmonic distortion plus noise is .007% at 1kHz with all levels set for unity gain. This mixer-in-a-chip can be powered by a single (+5V-14V) supply or dual (±4V to ±14V) supplies and is available in 28-pin plastic New range of filters for 3-phase variable speed motor drives Schaffner has a range of filters for 3-phase industrial frequency inverters. The new FN258 series have a voltage rating of 480V, meeting the requirements of variable speed motor drive manufacturers and users around the world. The new filter is the first Schaffner component to meet EN133200 – the new harmonised European standard for this product sector –in addition to the USA’s UL1283. The new filter is available in a family of nine variants to cover a current range from 7-180A, simplifying the task of making variable frequency drives (VFDs) comply with EMC regulations. A standard temperature rating of 50°C obviates the need to derate specifications to match actual working conditions in countries such as Australia. For further information, contact Westing­house Industrial Products, Locked Bag 66, South Melbourne, Vic 3205. Phone (03) 9676 8888; fax (03) 9676 8702. DIP and SOIC packages. The SSM2163 is suited for automating many computer audio systems, from high-end multimedia work­ stations to low-cost PC sound cards. Other applications include professional audio mixing consoles, broadcast equipment, intercom and paging systems and musical instruments. For further information, contact Hartec, 205A Middleborough Rd, Box Hill, Vic. 3128. Phone 1 800 335 623. Windows software for robots Procon Technology has released Windows software capable of controlling robotic kits. Complete source code is provided for VisualBASIC for Windows version 3 or greater. The supplied rou­tines may also be used by other Windows-based languages. The Windows Robotics software an be used to control motors, switches, lamps, electromag­ nets and buzzers. You could program automatic responses to change light, temperature or motion as detected by sensors. Extending the control of the screen to actual machines and robots enhances the computer’s learning environment in problem solving, science, maths and logic. The Fischertechnik interface unit provides eight digital inputs, two analog inputs and four bidirectional motor outputs. The unit connects to any IBM-PC parallel printer port and allows a second unit to be attached for a total of 16 digital inputs and eight motor outputs (or 16 lamp/relay outputs). The analog inputs may be used with potentiometers (for position control), light dependent resistors (for measuring light), thermistors (for measuring temperature) or other resistive devices. The Windows Robotics software costs $45. For further de­tails contact, Procon Technology, PO Box 655, Mount Waverley, Vic 3149. Phone (03) 9807 5660; fax (03) 9807 8220. Electronics Workbench software upgrade The popular “Electronics Workbench” software which allows users to simulate analog and digital circuits as well as test equipment such as an oscilloscope, function generator and spec­trum analyser on a PC, has now been updated with the release of version 4. This new version expands the selec- PCB POWER TRANSFORMERS 1VA to 25VA Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 476-5854 Fx (02) 476-3231 tion of analog and digi­tal components available to users. Real world models which make all active components selectable by part number, as found in standard data books, have been extended. For more information, contact Emona Instruments on (02) 519 3933 or SC fax (02) 550 1378. Scan Audio Pty Ltd June 1996  85 VINTAGE RADIO By JOHN HILL Testing capacitors at high voltages using a megohm meter Faulty capacitors can cause lots of problems in old valve receivers. Although this topic has been covered in previous Vintage Radio columns, other aspects keep arising which suggest that another session on capacitors is in order. When it comes to valve receivers, we are not looking at one particular type of capacitor. There are high and low-voltage paper capacitors, high and low-voltage electrolytics, and stan­dard mica and silvered mica capacitors. There were even a few “late model” valve receivers fitted with polyester capacitors. Discarding all paper capacitors when restoring a receiver has been a standard procedure for me for a long time. Although I do this, there is no reason to replace all paper capacitors as even (slightly) leaky ones will work OK in some applications; eg, when used as a cathode bypass capacitor. If one is prepared to properly test paper capacitors, many can be reused although not always in their original positions. Leaky capacitors should not be used in any high tension application or the AGC (automatic gain control) circuit, for example. Personally, I prefer to replace all This Altronics megohm meter is assembled from a kit. It tests at 500V and 1000V and is powered by a 9V “AA” battery pack. 86  Silicon Chip suspect capacitors in an old radio set. That way, I can be absolutely certain of elimi­ nating one common source of problems. However, the following information will be of use to those restorers who like to retain as many of the original components as possible in their radios. This means replacing only those capacitors which really are faulty. When this is the case, those capacitors that are not replaced should be thoroughly tested and their serviceability properly established. Leakage problems When restoring a radio receiver, I often find that the high tension voltage can rise by as much as 100V after the paper capacitors have been replaced. This gives some insight as to the amount of leakage that can be involved with faulty capacitors. Without going into details, capacitor leakage can seriously overload a variety of components such as valves, screen resis­ tors, chokes, field coils and output and power transformers, to name just a few. This means that any paper capacitors left in the high tension circuit must be carefully tested for leakage. What’s more, they should also retain their original capacitance and that may not always be the case. Sometimes a paper capacitor with no leakage also has little or no capacitance, due to internal open circuits. Quite simply, it boils down to this: all capacitors must be carefully checked for both leakage and capacitance before using them in a high tension circuit. I was recently embroiled in a debate over how capacitors should be tested for leakage. This is a difficult subject Above: this Megger is self-contained and requires no batter­ ies. “Megger” is a registered trademark used by Evershed and Vignoles Limited, England. Right: a modern electronic Megger. Gone is the old crank handle used in early design to generate the test voltage. The trademark is faintly visible at right, just below the meter scale. for some to appreciate, especially when they are accustomed to low voltage circuits. It is difficult to appreciate the stress placed on a capacitor when it has hundreds of volts across it. My opposition claimed that all that was needed was a ca­ pacitance test and, if the capacitor was leaky, then the ca­pacitance reading on the meter would slowly drop away. It is incredible the things some people say when they have not even tried out such a theory. In fact, it was immediately disproved by testing a known faulty capacitor with a multimeter set to capacitance. The reading remained static for quite some time, then it increased slightly, a characteristic of that par­ticular meter. Yet the same capacitor measured about 2MΩ when tested with the same meter set on the ohms x 1000 scale. My counter argument was that a high voltage megohm meter – such as a “Megger” – should be the ideal instrument to conven­iently test suspect capacitors. If the dielectric can withstand a 400-500V potential without showing leakage on the meter, then there would be little to worry about if that capacitor were to be put back into service. Again, unproven theories were thrown into the discussion on the basis that a Megger was never intended to test capacitors. According to my opponent, “a Megger would produce high voltage spikes that would blast holes in the dielectric, thus rendering what may have been a perfectly good capacitor totally useless”. Well, that’s what I was told! Now before going any further, let’s clear up the terminolo­ gy regarding the word “Megger”, which is often carelessly and incorrectly used. The word “Megger” is in fact a trade name for a particular brand of megohm meter. The old familiar type used a black bakel­ite cabinet fitted with a dual range meter scale and used a folding crank handle that was used to spin a small generator! Anything else – without the Megger trademark – is simply a megohm meter. Trial runs Doing a few tests on a range of capacitors with a borrowed megohm meter seemed to support all my assumptions. Testing ca­ pacitors at 400V clearly showed up any leakage problems. Good capacitors kept the meter needle hovering around the infinity mark, while the not-so-good ones showed various amounts of leak­age in megohms, or zero ohms in the case of a shorted capacitor. (Editorial comment: our oldest contributor recalls that one of the first jobs he was given when he entered the radio industry back in the mid-30s – yes, mid-30s – was to help test hundreds of paper capacitors, as they came from the makers. And his job was to crank the Megger while another operator applied the test prods to rows of the capacitors laid out on the bench. There was never any suggestion that this was detrimental). The interesting aspect of the high voltage test is that a crook capacitor that shows a leakage of around 1-2MΩ at 400V will appear quite good when checked with a normal multimeter set to the ohms x 1000 range. Leakage and straight resistance are two different things. A 10MΩ resistor will measure the same on both types of meters but leakage through a capacitor will usually increase with the vol­tage and that is why capacitors require a high voltage test. If an old paper capacitor is going to be operated at several hundred volts, then it needs to be tested at that voltage or more. Many of the old capacitors from the early 1930s have the test voltage June 1996  87 A close-up view of Altronics meter. Despite the 1000V warning, there is little sensation at the test terminals but always be sure to discharge fully-charged capacitors before touching their test leads, or you could get a nasty shock. selected by a rotary switch –see photo. These voltages can be varied to some extent by internal adjustment. Although the megohm meter tests at potentials as high as 1000V, one can hold the test leads and not feel as much as a tickle. This is because there is a 10MΩ resistor in series with the test leads and this restricts the current flow to such a degree that the instrument is quite shock proof, even though it carries a warning referring to the 1000V potential at the test leads. But a charged capacitor is another story and they can really bite! The 10MΩ resistor also overcomes another of the “anti megohm meter” comments made during the great debate. Because of this high value resistor, there is no great inrush current to internally damage any delicate capacitor. As a result of this resistor, it takes about 20 seconds to fully charge a 0.47µF capacitor. But there is no doubt about the effectiveness of the high voltage test if a capacitor is shorted. The discharge spark can be clearly seen and heard. ZAP! (Editorial note: shorting a charged capacitor is not good practice, as it can cause internal damage). If the capacitor is left connected after test­ing, it will discharge through the meter. Larger capacitors need longer discharge times, so be careful here. Mica capacitors Most 100V greencaps will withstand a 1000V test. That indicates that they should work OK in a lot of valve radio situa­tions without much trouble. clearly marked on them and a 400V capacitor was often tested at 1500V – well above its normal operating poten­tial. Using a borrowed megohm meter was a great help in estab­lishing whether or not it was a suitable test instrument for capacitors. But someone else’s Megger is not mine, so I set about finding an equivalent for my own use. A kit-based meter After a period of unsuccessful searching, I came across an advertise88  Silicon Chip ment for a megohm meter in kit form for $80 from Altron­ics. There was a minor problem with the kit, with the parts layout diagram and circuit board showing the wrong battery polar­ity. However, that problem has since been rectified if you are thinking of buying one. So, despite the minor hiccup, I eventual­ ly had myself a working megohm meter. The Altronics kit seems to be a good design and is an elec­tronic type, not an electromechanical device like the old Meg­ger. It has two test potentials (500V and 1000V) with the desired voltage One very interesting test procedure was carried out on a couple of known faulty silvered mica capacitors that were causing a distinct crackle in a receiver. When tested with the megohm meter, the needle continually fluctuated up and down the scale. In other words, the problem could be clearly seen when the capacitor was subjected to a high voltage test. However, when one of these capacitors was reversed, the needle swung over to infinity and held steady. This test seems to indicate that whatever happens inside a faulty silvered mica capacitor can create a rectifying effect whereby there is current leakage in one direction but not the other. The next time I have a crackly mica capacitor problem, I will reverse the capacitor to see if that cures the fault. Although there is some possibility that it might, whether it lasts is another K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS The test voltage should be in excess of normal operating poten­tials and 400V paper capacitors were often tested at 1500V. Both of these capacitors dismally failed the high voltage test. ● 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 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES All of these old capacitors failed the high voltage test. They have varying amounts of leakage, with some registering less than a megohm of resistance when tested on a megohm meter. A good capacitor should not show any DC current leakage. question. While I am not suggesting that this technique be adopted as a recommended practice, it will be an interesting experiment. In conclusion, it would appear that a high voltage megohm meter is an entirely suitable instrument for checking capacitors for leakage. It works on all types of capacitors, except electro­lytics, provided that the voltage rating of the capacitor to be tested is appropriate for the test voltage. Finally, high voltage testing of pow­ er transformers, chokes, field coils, etc can also be carried out using a meg­ ohm meter. Footnote: the High-Voltage Insulation Tester described in the May 1996 issue of SILICON CHIP is also ideal for testing capacitors for leakage. It has a 10-step LED bargraph display and provides five selectable test voltages ranging from 1000V down to as low SC as 100V. STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 June 1996  89 Silicon Chip Back Issues September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; 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. A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; A 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; 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. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: 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; Using The NE602 In Home-Brew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. July 1991: Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. 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Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503. ✂ Card No. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Alti­meter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach. 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. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 – Lesson 2. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ories; Valve Substitution In Vintage Radios. April 1992: IR 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; Low-Cost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; 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; Build A 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 Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; MAL-4 Micro­controller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5. March 1993: Build A Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders;A 24-Hour Sidereal Clock For Astronomers. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; Experiments For Games Cards. April 1995: Build An FM Radio Trainer, Pt.1; Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. May 1995: What To Do When the Battery On Your Mother­ board Goes Flat; Mains Music Transmitter & Receiver; Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/ Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control. 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; Electronic Engine Management, Pt.4. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; A 1W Audio Amplifier Trainer; Low-Cost Video Security System; A Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. 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 – How They Work. July 1995: Low-Power Electric Fence Controller; How To Run Two Trains On A Single Track (Plus Level Crossing Lights & Sound Effects); Setting Up A Satellite TV Ground Station; Build A Door Minder; Adding RAM To A Computer. 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. August 1995: Vifa JV-60 2-Way Bass Reflex Loudspeaker System; A Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; The Audio Lab PC Controlled Test Instrument, Pt.1; The Mighty-Mite Powered Loudspeaker; An Easy Way To Identify IDE Hard Disc Drive Parameters. 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. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver Circuits; Electronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electronic Engine Management, Pt.9 September 1995: A Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Build A Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. October 1995: Compact Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walk­around Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. November 1995: LANsmart – A LAN For Home Or A Small Office; Mixture Display For Fuel Injected Cars; CB Transverter For The 80M Amateur Band, Pt.1; Low Cost PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. December 1995: Engine Immobiliser For Cars; Five Band Equaliser For Musicians; CB Transverter For The 80M Amateur Band, Pt.2; Build A Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; RAM Doubler Reviewed; Index To Volume 8. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Electronic Engine Management, Pt.11. January 1996: Surround Sound Mixer & Decoder, Pt.1; Build a Magnetic Card Reader & Display; Rain Brain Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Aircraft Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Build A Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; The Fluke 98 Automotive ScopeMeter. October 1994: Dolby Surround Sound – How It Works; Dual Rail Variable Power Supply (±1.25V to ±15V); Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; The Micro­soft Windows Sound System. November 1994: Dry Cell Battery Rejuv­enator; A Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. June 1993: Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Remote Volume Control For Hifi Systems, Pt.2. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-Based Computer; A Look At Satellites & Their Orbits. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. 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. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 – Lesson 1; Antenna Tuners – Why They Are Useful. With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier; The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer March 1996: Programmable Electronic Ignition System For Cars; Zener Diode Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. May 1996: Upgrading The CPU In Your PC; High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, Aug­ust 1989, May 1990, February 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (includes. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. June 1996  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Parts wanted for cassette deck repair I am repairing a Philips cassette deck model F6133/10 and I am having trouble locating parts for it. Philips’ main office and spare parts advise me that the parts are no longer available and that no substitute parts exist. I am hoping that one of your readers may have a dis­used unit lying about from which either whole or part of the cassette unit may be salvaged. Ron Tree, Kent St Electrical & Electronics, 7 Kent St, Bowen, Qld 4805. Phone (077) 864 300. Dolby surround sound queries I am having problems with the Dolby Surround Sound Decoder. For all the situations listed below, the surround/3-stereo switch is in surround position. When the effects/Pro-Logic switch is in Pro-Logic mode and the noise generator is used, I get “noise” from the left, centre and right channels but nothing from the surround channels. When the effects/Pro-Logic switch is in Effects mode and the noise generator is used, I get “noise” from the centre and surround channels but nothing Remote control for Dolby decoder I would like to construct the Dolby Pro-Logic Surround Sound Decoder & Amplifier, as detailed in your November and December 1995 issues. However, it does not have a remote control. Do you have, or are there any plans to develop an add-on kit which will provide remote control of all the functions of this unit? If there isn’t, could you please provide me with some details of advice on how the 8-channel remote in your latest issue could be used to provide a remote control 92  Silicon Chip from the left and right channels (the display shows L-C-R-S). When the Effects/Pro-Logic switch is in Pro-Logic mode and a Dolby surround line input signal is used, I get perfect sound from the left, centre (although the trim for the centre channel has no effect) and right channels but nothing from the surround speakers. When the effects/Pro-Logic switch is in the Effects mode and a Dolby surround line input signal is used, I get perfect sound from the left, centre (although the trim for the centre channel has no effect) and right channels and what sounds like a low nonamplified signal from the surround speakers (ie, there is sound but it is badly distorted). I have thoroughly checked all the wiring, especially to the Effects/Pro-Logic switch but still have the same results as described above. Before I replace the Pro-Logic chip, I would like to be sure that the problem does not lie elsewhere. (D. A., Karana Downs, Qld). • The noise generator should only be used in the Dolby Pro-Logic mode, not Effects. This explains why it does not operate correctly for Effects. Check that the A, B & E lines on IC1 at pins 24, 25 and 23 do change for for the Dolby project. Is there a multi-turn logarithmic potentiometer available which could be motor driven to provide the volume and trim con­trols, in conjunction with your remote control kit? Is there a solid state device, an IC, which could be used instead? (D. H., Melbourne, Vic). • We are not planning to add remote control to the Pro-Logic Decoder. You could use the 8-channel remote control to operate the noise sequencer and up & down buttons using the momentary outputs. Effects can be changed with a 6-pole 2-way cradle relay triggered on the toggle outputs. the LCR&S&S channels during a noise test. There could be a fault with the centre trim wiring if this does not adjust gain; or an incorrect pot value. All else sug­gests the IC1 is not decoding the surround signal. Try tracing through the surround signal path through S2, IC3 and IC4. Electric fence snuffed it I recently built the Low-Power Electric Fence Controller as described in the July 1995 issue but could not get it to work. Upon application of power, either the 6.8Ω or 1.2Ω resistor emitted a small puff of smoke immediately, resulting in it being burnt out. The fuse did not blow and all other components were OK. My ignition coil is a new one, having a resistance of 1.4Ω. A careful check of my wiring and components could not reveal the fault. I hope you can help me solve the problems. (Y. L., Ontario, Canada). • The only reason why the 6.8Ω or the now-recommended 1.2Ω resistor should burn out is that the circuit is drawing too much current. The possible reasons for the excessive current drain are defective or wrongly We understand that both Altron­ ic Distributors and Dick Smith Electronics now have motorised pots. These can be driven by two relays, to momentarily apply power in either the forward or reverse directions. The accompanying diagram shows how this is done. Fig.1 Loudspeaker protection Thank you for producing the Automatic Level Control for PA systems in the latest (March 1996) issue of SILICON CHIP. If it works as well as claimed it would be ideal for bands and public address systems. I was hoping that the unit could be adapted to my particular application and that you could describe how to set it up. I am responsible for maintaining a public address system which is used by many people and some are not as caring of the equipment as they should be. Consequently, there is the risk of them blowing the loudspeakers by, for example, dropping a microphone. This can produce excessive signal levels and cause the amplifier to go into clipping. Can the Automatic Level Control be used as a limiter so that signals above a certain level will be restricted? This will prevent the main amplifier from clipping and possibly damaging the PA loudspeakers. (J. connected transistors or a 555 which is delivering current pulses which are too long. Are the time-constant components at pins 6 & 7 correct? Of course, if the 555 is defective it, too, could cause excessive current drain. Components for fluorescent light ballast Can you advise me where to pur- Fig.2 B., North Lambton, NSW). • It is certainly possible to use the ALC as a limiter since the relevant parameters of attack, decay and gain limit are adjustable. In fact, when the ALC is used normally for volume control or compression, any overload signal is quickly attenuated back to normal levels and so it acts as a limiter by default. If the ALC is to be used purely as a limiter, the gain limit would be set so that compression occurs at a low enough signal level before the power amplifier clips but high enough so that normal signals are not compressed. Typically, power amplifiers have an input sensitivity of around 1V RMS. The attack and decay rates should be at their fastest settings so that limiting will occur almost instantly and then quickly recover. The accompanying digital scope plot (Fig.1) shows ALC response when a signal above the gain limit is applied. The top trace is the input signal of 600mV RMS with bursts at 1.27V RMS (3.6V p-p). The lower trace is the output of the ALC with chase a kit for the Fluo­rescent Light Electronic Ballast published in the October 1994 issue of SILICON CHIP? (R. B., Pomona, Qld). • This design is not available as a kit. The MC34262P can be obtained from VSI, phone (07) 262 5200. Other parts can be ob­tained from Jaycar Electronics, phone (02) 743 5222 and Farnell Electronic Components, phone (02) 645 8888. The PC board can be ob- the gain limit set at a nominal 1V RMS. The output is limited above 2.72V p-p (960mV RMS). However, input headroom is not good since the input amplifier (IC1a) will clip at 1.35V RMS. This is undesirable so the input amplifier gain should be reduced from 5.5 to unity by removing the 22kΩ resistor from pin 6 to ground. This will allow the input signal to rise to about 8V RMS before it clips. You will need to set VR3 (the output preset trimmer) so that the ALC produces 1V output with a 1V input. The second scope shot (Fig.2) shows the performance with this gain modification. It shows a 1V RMS signal together with a 6V RMS (16.8V p-p) burst. Note the short 1ms overshoot in the output at 10.8V p-p (3.8V RMS). Recovery time after the 6V RMS input burst takes about one second at the fastest decay setting. The unweighted signal-to-noise ratio is -85dB with respect to 1V out (20Hz to 22kHz bandwidth). The A-weighted figure is also -85dB. tained from RCS Radio Pty Ltd, phone (02) 587 3491. Notes & Errata Insulation Tester, May 1996: the overlay and wiring diagram on page 34 is incorrect. It shows the battery connections re­versed. Also the 47kΩ resistor adjacent to the 36kΩ and 120kΩ resistors should be 43kΩ. SC June 1996  93 S IC RON T C 23 2 E 2 L 7910 y, NSW EY E OATL ox 89, OatleFax (02) 570 C a rd reflective tape with self-adhesive backing. Other motorists will see you better at night if this is stuck to chromed or unpainted car bumpers or on bicycles: 3 metres for $5. Visa PO B 579 4985 fax a rd , ) C 2 0 SOUND FOR CCD CAMERAS / UNIVERSAL ( r ne & rs: e e o t n s h o a p h AMPLIFIER P , M ith rde d o w r a d d c e Uses an LM386 audio amplifier IC and a B a n k x accepte most mix 0. Orders BC548 pre-amp. Signals picked up from e r 1 an electret microphone are amplified and & Am . P & P fo (airmail) $ drive a speaker. Intended for use for s order 4-$10; NZ world.net listening to sound in the location of a $ <at> . CCD camera installation, but this kit tley a Aust o : L could also be used as a simple utility AI M E y amplifier. Very high audio gain (adjustable) makes this b unit suitable for use with directional parabolic reflectors etc. PCB: 63 x 37mm: $10 (K64). FLUORESCENT LIGHT HIGH FREQUENCY BALLASTS European made, new, “slim line” cased high frequency (HF) electronic ballasts. They feature flicker free starting, extended tube life, improved efficiency, no visual flicker during operation (as high frequency operation), reduced chance of strobing with rotating machinery, generate no audible noise and generate much reduced radio frequency interference compared to conventional ballasts. Some models include a dimming option which requires either an external 100kΩ potentiometer or a 0-10V DC source. Some models require the use of a separate filter choke (with dimensions of 16 x 4 x 3.2cm) - this is supplied where required. We have a limited stock of these and are offering them at fraction of the cost of the parts used in them! Type B: 1 x 16W tube, dimmable, filter used, 43 x 4 x 3cm: $16. Type F: 1 x 32W or 36W tube, dimmable, no filter, 34 x 4 x 3cm: $18 (Cat G09, specify type). 27MHz RECEIVER CLEARANCE Soiled 27MHz telemetry receivers. Enclosed in waterproof die cast metal boxes, telescopic antenna supplied. 270 x 145 x 65mm. 2.8kg. Two separate PCBs. Receiver PCB has audio output. Signal filter/squelch PCB is used to detect various tones. Circuit provided: $12. 40-CHANNEL FM MICROPHONE A hand held crystal locked 40-channel FM transmitter with LCD display: 88-92MHz in 100kHz steps, 50m transmission range. Perfect for use with synthesized FM receivers: $50. SPEED CONTROLLED GEARED MOTOR Experiment with powering small vehicles, large children’s cars, garage door openers, electric wheelchairs, rotisseries, etc. etc. We supply a speed control PCB and components kit, A 25A MOSFET and a 30A diode (flyback), and a used 12V geared windscreen wiper motor for a total price of: $30. CHARACTER DISPLAYS We are offering three types of liquid crystal character displays at bargain prices. The 40 x 2 character display (SED1300F) is similar to the Hitachi 44780 type but is not directly compatible. We will also have similar displays - data available for a 16 x 4 and 32 x 4 display. Any mixture of these displays is available for a crazy price of $22 each or 4 for $70. IR TESTER USING IR CONVERTER TUBE Convert infra red into visible light with this kit. Useful for testing infra red remote controls and infra red laser diodes. We supply a badly blemished IR converter tube with either 25 or 40mm diameter fibre optically coupled input and output windows and our night vision high voltage power supply kit, which can be powered from a 9V battery. These tubes respond to IR and visible light. A very cheap IR scope could be made with the addition of a suitable casing and objective lens and eyepiece. $30. MISCELLANEOUS ITEMS 2708 EEPROMS: $1 each; 4164 MEMORY ICs: 16 for $10: AC MOTOR, 1RPM Geared 24V-5W Synchronous motor plus a 0.1 to 1RPM driver kit to vary speed, works from 12V DC: $12 K38 + M30; SPRING REVERB, 30cm long with three springs: $30 A10; MICROSONIC MICRO RECORD PLAYER, Includes amplifier: $4 A11; LARGE METER MOVEMENTS: moving iron, 150 x 150mm square face, with mounting hardware: $10. REFLECTIVE TAPE High quality Mitsubishi brand all weather 50mm wide red 94  Silicon Chip VHF MODULATOR KIT For channels 7 and 11 in the VHF TV band. This is designed for use in conjunction with monochrome CCD cameras to give adequate results with a cheap TV. The incoming video simply directly modulates the VHF oscillator. This allows operation with a TV without the necessity of connecting up wires, if not desired, by simply placing the modulator within about 50cm from the TV antenna. Suits PAL and NTSC systems. PCB: 63 x 37mm: $12 (K63). ‘MIRACLE’ ACTIVE AM ANTENNA KIT Available soon. To be published in EA. After the popularity of our Miracle UHF/VHF antenna kits we have produced this AM version for our ‘Miracle’ series. Large antennas are not the most attractive inside a house but sometimes this is needed to receive a weak radio signal. This kit will connect to a remote loop of wire, preferably outside where reception is good, via coax cable and allow it to be tuned from inside via varactor diodes. Radio reception is greatly improved and it can even pickup remote stations that a radio can’t receive with its ferrite rod antenna. No connections are required to the existing radio as the receiving end is coupled to the ferrite rod in the radio with a loop of wire around the radio. Excellent kit for remote country areas where radio reception isn’t very good, or where a large antenna is not possible. Great for caravanners, boats that venture far out to sea, etc. 2 x PCBs and all on-board components. BATTERY CHARGER WITH MECHANICAL TIMER Simple kit which is based on a commercial 12 hour mechanical timer switch which sets the battery charging period from 0 to 12 hrs. Employs a power transistor and five additional components. Can easily be “hard wired”. Information that shows how to select the charging current is included. We supply information, circuit and wiring diagram, a hobby box with aluminium cover that doubles up as a heatsink, a timer switch with knob, a power transistor and a few other small components to give you a wide selection of charge current. You will also need a DC supply with an output voltage which is greater by about 2V than the highest battery voltage you need to charge. As an example a cheap standard car battery charger could be used as the power source to charge any chargeable battery with a voltage range of 0-15V. Or you could use it in your car. No current is drawn at the end of the charging period: $15. AUTOMATIC LASER LIGHT SHOW KIT Kit as published in Silicon Chip May 96 issue. The display changes every 5 - 60 seconds, and the time is manually adjustable. For each of the new displays there are 8 different possible speeds for each of the 3 motors, one of the motors can be reversed in rotation direction, and one of the motors can be stopped. There are countless possible interesting displays which vary from single to multiple flowers, collapsing circles, rotating single and multiple ellipses, stars, etc. etc. Kit makes an excellent addition to any lightshow and all these patterns are enhanced by the use of a fog machine. Kit includes PCB, all on board components, three small DC motors, 3 high quality/low loss dichroic mirrors: $90. Suitable 12V DC plugpack: $14. LASER LIGHTSHOW PACKAGE Our 12V Universal inverter kit plus a used 5mW+ helium-neon laser tube head plus a used Wang power supply plus an automatic laser light show kit with dichroic mirrors (as above): $200. ARGON-ION HEADS Used Argon - Ion heads with 30-100mW output in the blue - green spectrum. Head only supplied. Needs 3Vac <at> 15A for the filament and approx 100Vdc <at> 10A into the driver circuitry that is built into the head. We provide a circuit for a suitable power supply the main cost of which is for the large transformer required: $170 from the mentioned supplier. Basic information on power supply provided. Dimensions: 35 x 16 x 16cm. Weight: 5.9kg. 1 year guarantee on head. Price graded according to hours on the hour meter: We have had no serious problems with any of these heads as they were used at a very low current in their original application. Argon heads only: $300. SIREN USING SPEAKER Uses the same siren driver circuit as in the “Protect anything alarm kit”. 4-inch cone / 8-ohm speaker is included. Generates a very loud and irritating sound with penetrating high and low frequency components. Output has frequency components between 500Hz and 4kHz. Current consumption is about 0.5A at 12V. PCB: 46 x 40mm. As a bonus, we include all the extra PCBs as used in the “Protect anything alarm kit”: $12. DC MOTORS We have good stocks of the following high quality DC motors. These should suit many industrial, hobby, robotics and other applications. Types: Type M9 : 12V. I no load = 0.52A <at> 15800 RPM at 12V. Weight: 150g. Main body is 36mm diameter. 67mm long: $7 (Cat M9) Type M14 : Made for slot cars. 4 to 8V. I no load = 0.84A at 6V. At max. efficiency I = 5.7A <at> 7500 RPM. Weight: 220g. Main body diameter is 30mm. 57mm long: $7 (Cat M14). ULTRASONIC COMMUNICATOR KIT Ref: EA Sep/Oct 93. Signals picked up by an electret microphone are modulated onto an oscillator which drives a 40kHz ultrasonic transducer. This is received by a 40kHz ultrasonic receiving transducer and is amplified and detected. The detected signal is amplified by a simple three transistor amplifier to drive a speaker. This makes a communications link using ultrasound which can transmit over a few metres. The quality of the sound is limited by the narrow bandwidth of the transducers but this is an interesting experiment. Both transmitter and receiver PCBs are 63 x 33mm: $16 (K45). BOG DEPTH SOUNDER KIT Detect the presence and depth of any body filler on your car. This simple circuit uses an oscillator which is oscillating weakly. When steel is placed near the small search coil the inductance shifts and the oscillator components are arranged so the oscillator will stop running. The remainder of the circuit simply detects when the oscillator stops and gives a visual or audible indication of this. The circuit is arranged so that the change in inductance needed to stop the oscillator can be varied. This allows variable depth of filler sensing, between 0 and about 3mm. Large areas of body filler over 3mm thick are generally considered undesirable as the filler may lift or crack. Kit supplied includes pre-wound search coil (33 x 22 x 10mm). A LED is supplied in the kit as the visual indication. An audible indication can be obtained by using a low power piezo buzzer, which is recommended but not supplied with the kit: $12 (K62). $2 for optional low power piezo buzzer. HIGH VOLTAGE AC DRIVER This kit produces a high frequency high voltage AC output that is suitable for ionizing most gas filled tubes up to 1.2m long. It will partially light standard fluorescent tubes up to 1.2m long with just 2 connections being made, and produce useful white light output whilst drawing less than 200mA from a 12V battery. Great for experimenting with energy efficient lighting and high voltage gas ionization. PCB plus all on board components, including high voltage transformer: $18. PC CONTROLLED PROGRAMMABLE POWER SWITCH MODULE This module is a four-channel programmable on/off timer switch for high power relays. The timer software application is included with the module. Using this software the operator can program the on/off status of four independent devices in a period of a week within a resolution of 10 minutes. The module can be controlled through the Centronics or RS232 port. The computer is opto-isolated from the unit. Although the high power relays included are designed for 240V operation, they have not been approved by the electrical authorities for attachment to the mains. Main module: 146 x 53 x 40mm. Display panel: 146 x 15mm. We supply: two fully assembled and tested PCBs (main plus control panel), four relays (each with 3 x 10A / 240V AC relay contacts), and software on 3.5-inch disk. We do not supply a casing or front panels: $92 (Cat G20). MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE KITS KITS KITS: Electronic kits for enthusiasts of all ages and abilities. Top quality. Large range. Free catalog and price list available. Call Ozitronics, 24 Ballandry Crescent, Greensborough 3088. Tel/Fax: (03) 9434 3806 email: ozitronics<at>c031.aone.net.au. VALVE BANK NOW OPEN: 700 types many new and hard to get types. Phone (058) 71 1921 or send SAE to Retrieval Radio, 25 Wirbill St, Cobram, Vic 3644. SATELLITE DISHES: international reception of Intelsat, Panamsat, Gori­ zont,Rimsat. Warehouse Sale – 4.6m dish & pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 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): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Salisbury Rd, Hornsby. Phone (02) 482 3100 8.30-5.00 M-F. A REAL BARGAIN: Riston type copper clad laminate. Develop cold, no toxic fumes, easy to use. Excellent results. Single sided 610x304 $34; 305 x 304 $17.50; 152 x 305 $9.95; 152 x 152 $6.50. Double-sided also available. 2 litre developer mix, worth $2.50, free this month. Add sales tax if applicable. Delivery $6.00. Money back guarantee. Ph (02) 743 9235. Fax (02) 644 2862. RAIN BRAIN 8 STATION SPRINKLER KIT: Ultra reliable & versatile Hi Q kit. Rain switch & LED B/L Free!!! (SC JAN ’96). Mantis Micro Products, 38 Garnet St, Niddrie, 3042 P/F/A (03) 9337 1917 man­tismp<at>c031.aone.net.au DonTronics: has the world’s first PIC Basic Compiler. This is also compatible with the Stamp-1 and makes PIC programming avail­ able to everyone with its “School Boy” instruction set. Designed for the 84’s EEPROM, it’s easily adapted to others as Assembly and Binary code is generated. $135 plus $5 p&p. VISA-MC-BC. Ask for free Promo Disk. 29 Ellesmere Crescent, Tullamarine 3043. Phone 03 9338 6286; Fax 03-9338-2935. http://www.labyrinth. net.au/~donmck SATELLITE SYSTEM: 3.0m Mesh, C/Ku band, fully automatic opera­tion, excellent condition, full package, private sale. $3200. 0414 250525. ❏ Bankcard   ❏ Visa Card   ❏ Master Card ✂ Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 June 1996  95 PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 722 777 – may time out to Mobile 014 036 775 Fax (067) 728 987    (Credit Cards OK) Specialising in easy-to-get-going hard/software kits with on-board interpreters. Also Assembler tools. Range of support hardware too. Get your project going in hours, not months Send 2 x 45c stamps for information package Microchip Programmers, Simulators and PIC chips ➡ MicroZed Computers Altronics ................................ 66-69 68HC11 F1 boards and now 80535 (up spec 8051) Extra I/O and peripheral plug-ins too Av-Comm.......................................7 Scott Edwards Electronics Car Projects Book....................OBC ingamebo Th Australian made bs NEW Prototype wiring kit NEW Micro Accessories for Stamp and second source for Stamp 1 Data Collection Proto Board now in stock BASIC Stamp I and II Macintosh patch now available Advertising Index Dick Smith Electronics........... 12-13 Earthquake Audio........................82 Emona.........................................83 MEMORY * DRIVES * MODEMS SPECIAL! (ExTax) 1Mbx9 – 70ns $25 30-pin Simms TEACHERS/DESIGNERS/ENTHUSIASTS THIS MONTH’S X-ON SPECIAL MC68HC705-C8P $20.00 EACH! FOR THIS AND THOUSANDS OF OTHER GREAT ELECTRONIC COMPONENT BARGAINS, CALL FOR FREE CATALOGUE AND PRICE LIST WHOLESALE TO THE PUBLIC 1161 ALBANY HWY, BENTLEY WA 6102. PH 09 351 9202 FAX 458 4445 C COMPILERS: Dunfield compilers are now even better value. Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/2, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140 for the set. Debug monitors: $70 for 6 CPUs. All compilers, XASMs and monitors: $400. 8051/52 or 80C320 simulator (fast): $70. Demo disk: FREE. All prices + $5 p&p. GRANTRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/ Fax (02) 631 1236 or Internet: lgrant<at> mpx.com.au. MicroZed HAVE range of PIC chips. OTP and /JW versions available. PIC 16C84 /04 one off price $9.76 incl. S/T. VALVES – AUDIO, VINTAGE, RECEIV­ ING, TRANSMITTING: Catalogue 85c stamp. Hadgraft, 17 Paxton St, Holland Park, Qld 4121. (07) 3397 3751. MICROCRAFT PRESENTS: Dunfield (DDS) products are now available exstock at a new low price; please ask for SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $71 $90 4Mb 72 PIN-70 $75 $53 8Mb 72 PIN-70 $133 $100 16Mb 72 PIN-70 $230 $192 32Mb 72 PIN-70 $456 $378 EDO SIMMS 8Mb (1Mbx32) – 60ns $118 16Mb (2Mbx32) – 60ns $210 MAC MEMORY 8Mb P’BOOK 190 $240 VIDEO MEMORY 256K x 16 70ns (SOJ) $17 256K x 16 70ns (ZIP) $48 LASER PRINTER MEMORY 2Mb UPGRADE $140 CO-PROCESSORS 80387SX/DX to 40MHz $100 COMPAQ 8Mb CONTURA AERO $240 All other models available $Call TOSHIBA PORTEGE/SATELLITE 8Mb / 16Mb EDO $294 / $550 All other models available $Call IDE DRIVES: SEAGATE/CONNER 1080Mb EIDE 10.5ms 3yr $283 1620Mb EIDE 14ms 3yr $360 2113Mb EIDE 10.5ms 3yr $384 MODEMS: BANKSIA / SPIRIT 28,800 BANKSIA V.34 $360* 28,800 SPIRIT V.34/V.FC $350* *Plus 14% sales tax on modems Ex Tax Pricing – Delivery $8. Pricing as at 26/6/96. Phone for latest. Sales Tax On Modems 14%. Everything Else 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM Memory Pty Ltd Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au Instant PCBs................................96 Jaycar ................................... 45-52 Kalex............................................89 Kits-R-US.....................................84 Macservice................................ 8-9 MicroZed Computers...................96 Oatley Electronics........................94 Pelham........................................96 our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $399 + $6 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/PALs etc from $1.50 • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent certified mail • Call Bob for more de­tails. MICROCRAFT, PO Box 514, Concord NSW 2137. Phone (02) 744 5440 or fax (02) 744 9280. MUSCLE WIRES are available from MicroZed. Microprocessors For Silicon Chip Circuits We have stocks of the 68HC705-C8P pre-programmed micro­pro­cessor ICs for the Digital Effects Unit (Feb­ruary 1995) and the Remote Controlled Stereo Preamplifier (Sept.-Oct. 1993). Also available is the pre-programmed Z86E08 microprocessor for the Railpower Mk.2. 68HC705-C8P – $45 ea; Z86E08 $18 ea. Prices include p&p. Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­tions, PO Box 139, Collaroy, NSW 2097. Phone (02) 9979 5644; Fax (02) 9979 6503. 96  Silicon Chip Harbuch Electronics....................84 RCS Radio ..................................95 Rod Irving Electronics .......... 35-39 Scan Audio..................................82 Silicon Chip Back Issues.............90 Silicon Chip Bookshop...................3 Silicon Chip Software..................65 Silicon Ship Wallchart................IBC Tortech.........................................89 X-On Electronic Services............96 Zoom.........................................IFC _________________________________ 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. Order by phone or fax from SILICON CHIP - or use the handy order form inside