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Practical Electronics Volume 54. No. 4 April 2025 ISSN 2632 573X Contents Projects and Circuits Calibrated MEMS Microphones by Phil Prosser 19 MEMS (micro-electromechanical system) microphones have advantages over electret mics, such as operating at ultrasonic frequencies. They also have good frequency response characteristics. ESR Test Tweezers by Tim Blythman 38 These ESR Test Tweezers can measure ESR and capacitance while being significantly more compact than our previous ESR meter. ESR meters are great for finding faulty electrolytic capacitors in failed equipment. Low-Noise Mains Fan Speed Controller, Mk2 by John Clarke On a hot night, a gentle cooling breeze from a fan can keep you cool and help you to sleep. This new Fan Speed Controller is an effective, noise-free, low-speed fan controller. It works with ceiling, pedestal and box fans. 58 Series, Features and Columns Net Work by Alan Winstanley This month I report on forthcoming ‘energy smart appliances’, problems with Economy 7 electricity meters and nearly 30 years of using the Internet. 4 Max’s Cool Beans by Max The Magnificent 8 Weird & Wonderful Arduino Projects, part four: full power to the NeoPixel LED array! The History of Electronics, part four by Dr David Maddison 22 We wouldn’t have computers, smartphones or AI without the work of thousands of people who created the foundations of modern electronics. This fourth article in the series covers inventors and discoverers born from 1882 to the 1960s. Circuit Surgery by Ian Bell 30 Topics in digital signal processing – LTspice symbols and filter impulse responses The Fox Report by Barry Fox Trying Linux Mint and, at last, a real torch! 36 Audio Out by Jake Rothman 48 Using Capacitors for HiFi, part two – special and unusual audio capacitors, plus a ranking of capacitors for audio circuits, from the best to the worst. Techno Talk by Max The Magnificent In the future, could we have conversations with holographic clones of real people? 56 Precision Electronics, part four by Andrew Levido 68 This series about precision electronics design covers a range of topics and uses real examples and real components to demonstrate the concepts. This instalment covers the principles and pitfalls of signal switching. Regulars and Services Made in Australia & the UK. Written in Britain, Australia, the USA and Ireland. Editorial Equivalent Series Resistance testers are very useful Reader services – Editorial and Advertising Departments Subscribe to Practical Electronics and save money Practical Electronics back issue downloads Practical Electronics PCB Service PCBs for Practical Electronics projects Classified ads and Advertiser index Next month! – highlights of our next issue of Practical Electronics 2 2 29 57 76 79 80 Read everywhere. © Silicon Chip Publications Pty Ltd 2025 Copyright in all drawings, photographs, articles, technical designs, software and intellectual property published in Practical Electronics is fully protected, and reproduction or imitation in whole or in part are expressly forbidden. The May 2025 issue of Practical Electronics will be published on Thursday, 3rd of April 2025 (see p80). Practical Electronics | April | 2025 Renewals paid by PayPal, Visa and Mastercard are now handled via our website: www.electronpublishing.com 1