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Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Marketing Manager Sharon Lightner Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER It’s your magazine – tell us what you want No doubt many of you have filled in the reader survey which is included with this issue and will be in the coming March issue. It was also inserted into the January issue and the re­sponse so far easily exceeds the survey we ran late in 1990. If you have not filled in yours, please do so, either this month or next month since we want as many responses as possible. There is a good incentive to do so because prizes of Tektronix test equip­ment will be won by a few lucky readers. We need to run a survey such as this every now and again to make sure that we are meeting the needs of you, the reader. While we can’t be all things to all people, we can read what you say and take note. In the main, we expect that the result of the survey will enable us to enhance and fine-tune the editorial content of SILICON CHIP and thus make it more useful and enjoy­able to read. Some readers have been very thoughtful and have included letters with their surveys but in some cases we are not able to reply since they have not included their name and address. If you decide to write a letter as well as filling in the survey, please include your name and address so we can acknowledge it. While I am on this topic, many readers do send in letters which are ultimately featured in the “Ask Silicon Chip” pages, while others send in contributions to the “Circuit Notebook” pages and these are very welcome. However, relatively few readers are moved to send letters to the Editor which can ultimately appear in the “Mailbag” pages, although this month has been something of a purple patch and we have two pages of readers’ letters. We’re keen to receive letters for this page – it’s your chance to comment on events in the world of electronics or on topics in SILICON CHIP. Ultimately, SILICON CHIP is a distillation of the thoughts and needs of thousands of readers. You write or fax your letters in and we respond with technical articles and projects to meet your needs. In fact, in this issue alone, three of the articles – the Level Crossing Detector, the Voice Activated Audio Switch and the LED Chaser – have been presented in response to recent spe­cific suggestions from readers. And of course, some articles are directly contributed by readers, which is great. We acknowledge every letter we receive although some are inevitably delayed as monthly deadlines inexorably come around. So don’t be backward – if you want to ask a technical question, send in a Circuit Notebook contribution or express an opinion, please put pen to paper or fingers to the keyboard and make contact with us. We’d love to hear from you. 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