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SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Editorial Viewpoint Take mains safety seriously! We have been describing mains-powered projects in Silicon Chip since the first issue in November 1987. As far as we are aware, nobody has been seriously hurt by an accidental shock while building or operating such equipment. That good record extends back to the days of Electronics Australia, and I would like to keep it that way. I am writing this because we have seen evidence of constructors skipping critical safety steps in our assembly instructions, creating potentially hazardous devices. Part of the reason we have a good record is that our mains-powered projects include safety redundancy. The idea is that even if one or two things go wrong, the result should not be a shock hazard. To achieve this, we direct constructors do things like insulate all exposed mains conductors (even those that are usually inaccessible inside the case), use cable ties to bundle wires together (into separate mains and low-voltage bundles), anchor wires so they can’t float around inside the device, Earth all exposed metal, incorporate mains fuses and so on. Say a mains wire happens to break loose in one of our designs. As it’s cable tied to adjacent wires, it shouldn’t be able to move far enough to touch anything. If another wire or two breaks, maybe that bundle of wires could contact the Earthed case. In that case, the fuse should blow so the case doesn’t become live. You could lose this redundancy if you don’t follow our instructions fully. So, if you are building one of our mains-powered projects, please follow all the instructions carefully, even if you don’t understand why they are necessary. Remember that a poorly built device could be hazardous to anyone in your household who could come in contact with it. The steps we describe are not expensive, onerous or overly time-consuming. Some further advice: • Don’t take on a mains-powered project if you are inexperienced. Build a low-voltage device (or several) until you are confident in your assembly skills, including soldering, crimping, screwing, machining and so on. That way, when you build a mains-powered device, you will be confident that you will not make a bad solder joint or skip an important step. • If you are not fully confident in your abilities, get someone else who has more experience to help you. Even if they are not an expert, having a second pair of eyes and hands can be invaluable. They might spot something you missed or prevent you from making a mistake. • Respect mains voltages and keep your hands (and any uninsulated tools they hold) away from equipment that’s plugged into the mains, even if it is not switched on. Some conductors could still be live; something simple like a miswired extension cord or power point could make everything live, even with the Active conductor broken by a switch. • During testing, troubleshooting or calibration, adopt an approach of connecting equipment to the device, withdrawing physically from it, plugging it in, switching it on and observing the results. Then switch it off and unplug it before you approach it again. Be mindful that capacitors can keep a charge for minutes or even hours after power is applied. • Remember that with a metal chassis, the mains Earth must go straight to a chassis Earth point and then fan out from there, and that screw or bolt must not be used for any other purpose (eg, to hold a module to the chassis). This way, you will be able to happily and safely continue to build and work on electronics for many years. Subscription price reminder As mentioned in the August & September editorials, the cover price has now gone up by $1 (both AUD and NZD). The new subscription rates will take effect from the first of November, so there’s still time to get in at the old price if you want to. Cover Image: https://unsplash.com/photos/pAm8MHK0KqI Australia's electronics magazine by Nicholas Vinen siliconchip.com.au