An inexpensive, very basic, bare bones Geiger counter. This unit does not have a display and thus does not count, so is effectively not an actual counter. It does have an LED and sounder from which clicks can be heard.

This unit could be purchased (it seems there are few on the market at the time of writing) from many outlets selling Chinese goods, such as Ebay, Amazon, Aliexpress etc for around £45 GBP. It appears there is a newer version called the GC-1602-NANO which has an Arduino Nano and 1602 LCD display.

This unit is easily connected to a micro controller or a PC via the pulse output or audio output respectively in order to log and count. Connecting this unit to an ESP8266, such as the Wemos D1 Mini, is as simple as connecting power and one wire.

This unit usually comes with either a J305 or a M4011 Geiger–Müller tube. Adjustment of the high voltage is by way of a multi-turn potentiometer. The anode resistor is soldered in place but could be easily changed to suit other tubes.

Some of the glass tubes such as the J305 are sensitive to UV and sunlight and can cause false counts. A demonstration of this can be seen in the video below. Measures should be taken to shield the glass tube from light.