Sunday, April 4, 2010

Geiger Counter - Part 2 (complete)

[Edit 4/10/11] This project is now available in kit form - with PCB and parts. Please click here for more information.

This post describes how I went about integrating the circuit described in the previous post with an Arduino and a LCD display.

I put it all into an old laptop power supply case - not my best work, but as we said in Arkansas, "it ain't no piano". It does have a nice sturdy feel though.

After experimenting with an LED bar graph and a Nokia 3310 cell phone display, I settled on a simple and cheap 8x2 LCD display from Sure Electronics.

First I moved the Geiger circuit off the breadboard and on to a proto board.
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I kept things fairly tight which left a little room for future expansion. The piezo is mounted on the bottom of the board. I cut an opening in the bottom of the case under the tube.

On the other side of the case, I added the batteries, display and a small board for the Arduino MCU. It's just a simple stand-alone Arduino circuit using a resonator.
There are also 2 slide switches on the bottom - one to turn off the piezo, and the other to turn off the Arduino and display to save batteries. A salvaged push button on top turns the whole thing on and off.

The code counts the interrupts from the tube for a period of time, and displays the counts / minute as a value on the 1st line and as a bar graph on the second. I adapted the code for the bar graph from DeFex . It's nice because it uses custom characters to make partial blocks.

I used two different counting periods - a longer period when the CPM is below 100 (counting background radiation) and a shorter period when there is more activity. You can download the code here.

Here is the obligatory short movie . . .

It was a nice surprise to find our bathroom tile was hot. (Should help kill the germs!) Since the house was built in the '20s, I imagine it's uranium green glaze.