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  SILICON CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Kevin Poulter Stan Swan Dave Thompson SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Noble Park, Victoria. Distribution: Network Distribution Company. Subscription rates: $105.00 per year in Australia. For overseas rates, see our website or the subscriptions page in this issue. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. Fax (02) 9939 2648. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Recommended and maximum price only. 2  Silicon Chip Publisher’s Letter Lithium batteries set to take over This month, we have two articles which reflect the present and future of battery-powered electronics. Rechargeable batteries such as sealed lead acid, nickel cadmium and nickel metal hydride are on the way out. They are rapidly being displaced by lithium batteries in their various versions: lithium-ion, lithium polymer and lithium iron phosphate (LiFePO4). This process is already well under way with mobile phones, cameras, laptops and tablets. They are also being used in more heavy-duty applications such as portable power tools, electric cars and bikes and even as boat batteries. In boating applications, their much lighter weight is a big advantage, off-setting the much greater cost compared to deep-cycle lead acid batteries. Stan Swan’s article on LiFePO4 cells gives the background on what is happening. These cells are lighter and more energy dense than nickel cadmium/hydride cells, they have more than twice the voltage and they can be more deeply and repeatedly discharged. Sure, they do have drawbacks but technology is rapidly adapting to those too. In fact, on the power tool front, it has now got to the stage where you would definitely think twice about buying a tool which was not lithium powered; power tools with nickel cadmium/hydride batteries all too often succumb prematurely with a dead battery pack which is probably not economic to replace. In recent months, readers may have noticed that we have designed a number of projects around lithium button cells instead of the more traditional 9V alkaline battery. While button cells are not rechargeable, they have the benefit of being a very compact power source which is becoming more and more usable because more chips are being released which work on 3V supply rails. A lithium button cell and its PC-mount holder also have the benefit of being cheaper than a 9V battery and its snap connector. The most recent example of lithium power is this month’s article on a compact mixer for PA systems, designed to provide a number of input permutations when extra inputs are not available on the PA itself. Ross Tester has a lot of experience in PA work and he refers to it as a “Lump In The Coax”. That’s an interesting variation on the old theme of a hifi amplifier being a “straight wire with gain”. So is the mixer equivalent to a “straight wire with gain”? You might think that an audio circuit involving a significant number of op amps running from a 3V supply would have fairly mediocre performance but using new devices designed for this type of application, it gives a very creditable account of itself. Furthermore, that lithium button cell can give over 200 hours of life. That’s incredible when you think about it. The final icing on the cake is that you can use a rechargeable lithium-polymer battery from a mobile phone. The mixer PCB has an on-board lithium polymer battery charger but with the capacity of these batteries, they could potentially give more than a thousand hours of service before needing a recharge! Note that the overall concept of this mixer is really quite simple but by employing the latest rail-to-rail low-voltage op amps, combined with lithium power, a compact little performer has been produced. What can we come up with next? Given that mobile phones and tablets are galloping ahead with features and performance, the future looks really bright. Leo Simpson Download charges: ever since SILICON CHIP has had a website, we have had a policy of making downloads for microcontroller software and PCB patterns available free. I regret that in these days of “user pays” we now have to apply a nominal charge for this service: $3 per item. The good news it that if you have a current subscription to SILICON CHIP – print or online – all downloads will remain free. siliconchip.com.au