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 2.GQ Geiger Muller Counter
 Using Geigerbot/Safecast-App with Iphone&GMC320
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Posted - 03/11/2016 :  00:39:46  Show Profile  Reply with Quote
Finally I had some spare time to hook the GMC320 up with an Iphone 4s and find parameters for the safecast app.

The first problem I encountered was the Iphone, not accepting audio input from the headphones mic in.
I knew, this needs an extra resistor across mic in and ground for the iphone to switch the input path from built in mic to headphones mic. The internet suggested 1kohm.

Guess what, I was out of 1k resistors so I tried a first shot with 680ohm but that didn't work. Then I tried 1.2kohm but that didn't work either.

I then fiddled around with capacitors and serial resistors and what not, with no result. To make a long story short, after using a combination of 1.5kohm and 100kohm my Iphone finally decided to accept the 'headphone mic in' as audio input path.

In app settings:

Gamma sensitivity conversion factor:
CO60: 39 (M4011 geiger bot default)
Cs137: 33 (for 0.005 If you prefer 0.0065 set to 26)

Offset CPM: 0 Not sure if I should set cpm offset to 12 due to tube noise (see datasheet)?

Deadtime Correction: off

RMS window: 1
Dead Time: 27
Sample Rate: 44.1kHz (max count: cpm = 60/(RMSxDT/SR) = 98.000cpm)

Volume threshold: 10000
Input polarity: Both
Input gain control: 0.90

These are preliminary parameters which seem to work. I will do further testing with different count rates and may come up with updated values.


PS: sorry for my english. I'm not a native speaker.

Edited by - Nudnik on 03/11/2016 03:22:38
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1132 Posts

Posted - 03/15/2016 :  22:52:07  Show Profile  Reply with Quote
Thanks for sharing.
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