Low Cost DIY Geiger Counter with SI3BG Tube ATmega168PA and TM1638 Display

In this project, I designed and built a compact Geiger-Müller radiation detector using the SI3BG GM tube and a custom PCB. The device is powered by three AA batteries and features a 4-digit 7-segment LED display driven by a TM1638 controller.

The high voltage for the GM tube is generated using a RadiationD-V1.1 style boost and multiplier circuit based on the NE555 timer and MMBTA42 transistor. The output voltage is adjustable and calibrated to operate the SI3BG tube in its optimal plateau region (~400–450V).

The microcontroller is an ATmega168PA (TQFP-32), fully compatible with ATmega328P. Pulse counting is handled using the INT0 external interrupt to ensure accurate event detection even during sleep mode.

The device supports:

• CPM (Counts Per Minute) display
• µSv/h display with automatic decimal formatting
• 10-minute background calibration mode (via jumper)
• EEPROM storage of calibration values
• Automatic sleep after 5 minutes of inactivity
• Wake-up via push button
• Support for both Common Cathode and Common Anode 7-segment displays

All PCB files (Gerbers, KiCad project, schematics) and source code are provided.

This design aims to be:

• Compact
• Low power
• Electrically safe (proper creepage in HV area)
• Flexible for different display types