Cold War-style Geiger counter runs on a single AA battery with no microcontroller

Maker has built an analog Geiger counter that deliberately avoids microcontrollers and digital displays, relying instead on classic CMOS Schmitt trigger logic and an old-school analog dial to show radiation levels.

The heart of the device is a large Chinese J306β Geiger tube, measuring 200 mm in length and 18 mm in diameter. It is rated at 88 counts per minute at typical background radiation levels and 8 counts per second when exposed to 1 µSv/h. Because the tube is sensitive enough to produce plenty of pulses even at low radiation levels, decided to use a simple analog low-pass filter to average the output rather than a digital counter.

The entire circuit runs on a single AA battery. A built-in power supply steps the voltage up to 5 V for the integrated circuits and to 400 V for the Geiger tube itself. Two measurement ranges are available: 1 µSv/h and 10 µSv/h. The author notes that a higher range is unnecessary — if the needle ever pegs the 10 µSv/h scale, it is better to run away than to measure the exact dose.

The project is designed for hobbyists who want a Geiger counter with the aesthetic of the Cold War era, without fancy displays or digital readouts. Full schematics, build instructions, and component details are published on the author's website.