Modified Geiger Counter with Case

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geigerguate
Posts: 5
Joined: Sun Mar 09, 2014 11:10 am

Modified Geiger Counter with Case

Post by geigerguate »

Good day!
I just wanted to share a few pics of the recent mods I made to my Geiger counter kit. After assembly I wanted to fit everything into a case that was approximately 5" x 3" x 2" so I broke out the hack saw and chopped off as much of the surrounding PCB as possible without causing damage to any of the traces. Once the excess was removed the inside of the enclosure was also modified to smoothly fit the board. Ironically, my solder station died during the building of the kit so I took the on/off switch from it and replaced the switch that came with the kit. There is still enough room to access all PIN locations and I'll be adding a panel mount TRS jack to be able to use Geigerbot with the unit.

Perhaps the biggest modification made to the unit was the swapping of the SBM-20 with a compact and fairly sensitive SI-29BG (about $30). This tube shares the same voltage as the SBM-20 but has radial connections rather than axial. Using my Meter in concert with a 10M ohm resistor I was able to set the working voltage to approximately 410v which is perfect. Though the tube is less sensitive than the SBM-20 (seems about 60-70% as effective) it is nearly half the size which makes it perfect for small enclosures. To give you an idea it responds very well to my high R-active sources of radium, uranium, and thorium, but is sensitive enough to detect the CPM coming from Potassium Chloride (salt substitute). Background clicks per minute show approx 18 cpm vs approx 32 cpm with my SMB-20 based unit.

The unit is very light and extremely portable and has space on the front to mount my Ipod with Geigerbot using some simple double sided tape. The enclosure came from ebay and was about $4. It did require some plastic modification to fit the board, switch, hole for LED, and a 3x3 series of holes to allow the sound to be heard. I used a small drill bit and some perf-board for my template to drill the tiny holes, (i'm still trying to figure out the best way to access the mute function with the least amount of surgery), and then used an old Rad Shack solder iron to melt and modify any interior plastic parts. (Note, melting plastic is not only icky in general but will most assuredly ruin your solder iron, just fyi. )
Just wanted to share! If you've got any questions or comments please feel free to post.

[attachment=2]DSC01369 (2).jpg[/attachment]
[attachment=1]DSC01363.JPG[/attachment]
[attachment=0]front side.jpg[/attachment]
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front side.jpg
DSC01363.JPG
DSC01369 (2).jpg
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mightyohm
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Re: Modified Geiger Counter with Case

Post by mightyohm »

Wow, very nice work!

Thanks for the tip on the SI-29BG. I have a couple of these around but haven't played with them. They are a little bit harder to find than the SBM-20.
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