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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 Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 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 Glenn A. Keep 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 Putting those old computers to work This month we have three computer-related articles which emphasise the usefulness of older computers. The first is the article on networking, starting on page 4. This was prompted by an application in our office but is typical of situations which occur in small offices or homes with more than one computer. It is a boon when printing from more than one computer is a common requirement. The second article is the computer controlled power supply which starts on page 56. This is an interesting project because it can be built as a conventional power supply or as one which is under full control of a computer. Such a supply can be turned on and off or the voltage varied automatically. As well, the current drain can be recorded, which could be useful in some applica­tions. The third article relates to the Digi-Temp which can moni­tor up to eight temperature sensors in different locations via two wires. Again, it can be built as a self-contained unit or it can be hooked up to a computer for logging applications. It starts on page 80. On the same theme, next month we will publish a computer controlled message board. None of these applications require the latest Pentium-based machine but can use older 286, 386 or 486-based machines. They emphasise that the older machines still have a multitude of uses and don’t need to gather dust in the back of a closet. We are very conscious of the market pressures to upgrade computers, particularly with the advent of Windows 95 software which is so hungry for RAM and hard disc space. These pressures are bad enough in a commercial environment where it is almost mandatory to obtain the latest upgrades of every software pack­age. Where it does seem unnecessary is with the tens of thousands of home machines which are seldom used to even a fraction of their potential. This was driven home to me just recently concerning the computer of one of my close relatives. She has a 100MHz Pentium machine with a large hard disc, quad-speed CD ROM, sound card and all the bells and whistles. It is only 12 months old and the video monitor has just failed. However, instead of getting the monitor repaired, she is seriously considering replacing the system with a 166MHz Pentium machine, partly because she has had a few hassles with the Windows 95 setup and the sound card. I was flabbergasted, as you can imagine. For probably less than $100 the monitor could be repaired and a few hours or so spent optimising the Windows 95 setup would be required to make it do all she could want. The difference in speed in upgrading to a 166MHz machine would be marginal – for much of the time it is merely used to play games. But she was being swayed by the market hype for the new machines. Such an outlook is extremely wasteful and yet all too common. 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