April 2025

Calibrated MEMS Microphone

MEMS (Micro-Electro-Mechanical System) microphones have advantages over electret (ECM – electret capsule microphone) types, such as operating at ultrasonic frequencies and having superior frequency response characteristics. This project shows how to use a MEMS microphone as a calibrated reference microphone. Such devices are tiny (the one illustrated measures just 4mm x 3mm) so reflow soldering skills are needed to construct this project successfully.

ESR Test Tweezers

This significant upgrade of our earlier designs can display a capacitor’s equivalent series resistance (ESR) and capacitance on a crystal-clear OLED. Menu-driven setup. “Tweezer” form factor with mirroring display for left or right-handed use. PIC micro based, surface mount soldering skills are used throughout.

Mains Fan Speed Controller Mk. 2

This clever design will control the speed of ceiling, pedestal and box fans containing ‘shaded pole’ motors [only], and is designed to offer effective, low noise speed control. Safety features include over-current and over-temperature protection. Rated up to 80W maximum. Discrete through-hole design.

  Mains voltages are present throughout. This project is intended for experienced, competent constructors only.

The History of Electronics, Part 4
Inventors and their Inventions

The final part of an incredibly insightful series describing key discoveries in the evolution of electronics. This part covers the period (listed by their inventors’ date of birth) from 1882 to 1969, describing more than 60 inventions from the FET to Linux.

Precision Electronics, Part 4

In this fourth article, we look at how to extend the current measurement range of our demo circuit.

Audio Out
Using Capacitors for HiFi (Part 2)

A seriously in-depth analysis of the use of many different capacitor types in audio applications. A must-read for DIY audiophiles.

Also in this issue

• Net Work –  The latest industry move for ‘energy smart appliances’ that will connect to the Smart Meter Home Area Network (SMHAN) of the future, to optimise the energy consumption of domestic appliances. This month’s column also marks the last in the regular series as, after nearly 29 years of uninterrupted publication, our writer signs off for the time being. He reminisces about how the Internet evolved from those early days and describes the journey from basic 14.4k dial-up all the way to present-day high-speed fibre connectivity. Check the Net Work blog for more details.
• Max’s Cool Beans – Max presses on with his retro games console LED array, covering more Arduino programming and power supply considerations this month.
• Circuit Surgery – Topics in digital signal processing – LTspice symbols and impulse responses.
• The Fox Report – Barry Fox dodges a Windows upgrade by trying Linux Mint instead, and he tries a high-spec torch made by Sandberg.
• Techno Talk – Max muses over the latest innovations in generating full-size 3D holographic human forms, giving rise to the possibility in future of ‘digitally re-incarnating’ people from the past.

In next month’s issue

Skill Tester 9000 – wire and buzzer game; fully compliant USB-C Serial Adaptor; DC Supply Protectors. Contents may be subject to last-minute change.