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Practical Electronics Volume 54. No. 9 September 2025 ISSN 2632 573X Contents Projects and Circuits Compact Hi-Fi Headphone Amplifier, part one by Nicholas Vinen 4 This Headphone Amplifier is easy to build, sounds great, is inexpensive and fits into a compact case. It’s ideal for beginners or those who want to get the best out of a set of traditional wired headphones. It’s plugpack-powered, so no mains wiring is required. Two Discrete Ideal Bridge Rectifiers by Phil Prosser & Ian Ashford 18 This simple circuit uses just a handful of transistors, diodes and resistors. But it still provides a very useful function: active rectification of the output of a centre-tapped transformer or combining two DC supplies with low losses. Automatic LQ Meter by Charles Kosina 34 A Q Meter is an indispensable tool for anyone contemplating RF design. This new design features two instruments in one, measuring inductance from 0.1 to 999μH and Q from 10 to 300 with a test frequency from 100kHz to 90MHz! Dual-Rail Load Protector by Stefan Keller-Tuberg 60 It disconnects a load from its power supply if the voltage is reversed or too high. It also disconnects the load if it draws current above the adjustable trip level. Its dual-rail support means it can work with devices like audio amplifiers with a split supply. Series, Features and Columns The Fox Report by Barry Fox A reasonably priced solution for high-quality analog audio to digital conversion. 3 0.91-inch monochrome OLED display modules by Jim Rowe 12 Small monochrome OLED display modules have become widely available at a low cost in the last few years. This one measures just 37.5 × 11.5 × 4.5mm but has a useful 128 × 32 pixel display that’s either white or blue. Techno Talk by Max The Magnificent 16 We take breadboards for granted, but the modern version evolved over several decades. Max’s Cool Beans by Max The Magnificent Weird & Wonderful Arduino Projects, part 9: a crash course in digital logic. 26 Net Work by Alan Winstanley 44 The return of my occasional column brings news of trends in smart meters, the onslaught of Chinese-made electric vehicles, and tempts readers into trying Temu. Circuit Surgery by Ian Bell 48 Topics in digital signal processing – Implementing DSP on a microcontroller, part 4. It is finally time to implement an FIR low-pass filter on our microcontroller board. Altium Designer 2025 review by Tim Blythman 56 We look at the features and improvements added to this EDA software in its last update. Audio Out by Jake Rothman 70 You can now easily build my cascode amplifier using this custom-designed PCB. Regulars and Services Made in Australia & the UK. Written in Britain, Australia, the USA and Ireland. 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 October 2025 issue of Practical Electronics will be published on Tuesday, 4th of September 2025 (see p80). Practical Electronics | September | 2025 Editorial Values and units shouldn’t be separated Reader services – Editorial and Advertising Departments Subscribe to Practical Electronics and save money Practical Electronics Back Issue DOWNLOADS – 2024 now available! 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 43 69 76 79 80 Renewals paid by PayPal, Visa and Mastercard are now handled via our website: www.electronpublishing.com 1