Monday, December 10, 2012

Geiger Counter Prototype with PIC16F628A MCU

I wish to share some photos of my new prototype for Geiger Counter DIY project. It can be powered from 4x AA Ni-MH batteries, USB or USB-UART adapter. High Voltage circuit section stay same like in my previously Radiation Detector DIY Kit.
PIC16F628A microcontroller part count events from tube cathode. Then it calculate CPM (counts per minute) and radiation dose.

How to convert CPM to radiation dose? (Thanks to about all conversion information)

Let's check first the SBM20 datasheet. It tell that the tube has Gamma Sensitivity for Ra226 29 cps/mR/hr and for Co60 is 22cps/mR/hr. I used arithmetic average of 25.5 cps/mR/hr because I do not have radioactive calibration sources.

1. Convert cps to cpm:
    25.5 x 60 = 1530 cpm/mR/hr
2. Divide to absorption constant to convert from mR to uSv:
    1530 / 8.77 = 174.46 cmp/uSv/hr
3. Calculate the tube Conversion Factor:
    1 cpm = 1 / 174.46 = 0.0057
4. Now you just need to multiply your CPM reading to Conversion Factor. The picture above shows 8.344 uSv/hr for 1464 cpm:
   1464 x 0.0057 = 8.344

The program code can be changed and calibrated to any other Geiger tube type, just required to change conversion factor in source file.
Microcontroller send CPM readings via UART. It can be used with COM port or FTDI USB module for communication with PC.
DIY Kit for this project is expected to be produced soon. Please follow our updates!

No comments:

Post a Comment