Tuesday, August 9, 2011

GM45 Geiger counter connected to iphone mic via the battery box.

I purchased
Black Cat System GM45 and battery box , which come in handy to use GM45 without PC or Mac outside.
a problem is that during connecting the battery box, only click sound and LED light are ways to communicate with human, no measuring numbers like μSv/h or CPM

Here is an iphone app Geiger bot, which can show us human readable numbers like CPM, and if you know what is conversion of your geiger tube, other readable numbers like μSv/h can be shown as well.
then another problem, if you measuring it at a place where not much noise is generated, only the clicks from the box are counted, it is ok. iphone can pick the clicks generated from the battery box, but not if you are outside, noise is counted as clicks ,causing Geigerbot show high dose rate . so then I need to connect it to iphone mic directly.

iphone's 3.5 φ mini stereo plug is 4 terminals one. the plug is available here, http://www.radiocenter.jp/shop/sh45.htm .
(at first I bought ear phone with mic for iphone and tore it down, but wires of it are too thin to re-solder.)
this page is very helpful to figure out how those things should be connected, soldered.
but mine is more simple , just got 1KΩ register connected.

Oscilloscope shows 0.85V is charged to between iphone Mic and GND, and when click generated apx 1.4 v is charged. I am not sure if this number is ok for iphone , Geiger bot shows input signal not huge tho. so ,probably ok

covering the wires with a heat shrink tube.

Done ! it is working !
yet another problem: a speaker on the battery box picks some amount of sounds , which is small tho, because it is working as a microphone , I need to figure out how stop it working as a microphone.

Here is a circuit picture but this is not accurate at all but you get an idea.


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