My DIY Geiger Counter

This is the Geiger counter I just prototyped. I wanted to make sure it would work before committing it to a layout and an enclosure.



The circuit is based on the Wenzel high voltage generator for Geiger-Muller tubes and uses a line isolation transformer from an old modem to step up the voltage.




The tube I used is a NOS Russian unit from eBay I got for a project that got put on hold years ago. I just have to acquire a 50uA meter meter and a few other parts to make the pulse averaging circuitry to finish it up.




The transistor I used to drive the inductor is a 2SC3150 I pulled from a old TV. It's a little under utilized in this application although it works fine and it only cost a few minutes of time and labor to scavenge. Its Hfe tested to be only 20, so its it ends up being a little less efficient than a higher gain device.



Because I lacked the exact transistors Wenzel used in his articles I had to spent hours with my SPICE simulator determining component values that would work. After a goodly number of hours I discovered the only thing I had to change was the timing cap connected to the emitter of the PNP transistor diving the main switching transistor and the base resistor for the main switching transistor. All the other values used in Wenzel's article worked fine.



From the SPICE simulations I determined an input voltage of 6 volts would work well. 3V turned out to be a little to little for my implementation. Also, the SPICE simulations made it evident that I could use the line isolation transformer with the secondary coil connected as a booster to generate the 450 VDC required by the detector tube without the use of voltage doubling circuitry. That was a pleasant surprise.



The other transistors I used were two BC640 and three 2n2222. I have the bread board hooked up to a variable voltage bench power supply at the moment, although as it is it will work fine from 4 D cells. I choose the Wenzel circuit because of it's efficiency. The circuit now, only draws about 8mA of quiescent current from the power supply.




This is without the throttle circuitry to reduce the quiescent current. That is simple to add and should reduce the quiescent current draw of the HV generator to only 1mA. A higher gain main switching transistor should result in a quiescent current of less than 0.5mA. That is low enough to run the counter continuously for over a month from only one set of four D cells.

Category:

Science & Technology

Tags:

• Geiger
• Muller
• counter
• radiation
• Wenzel

[syberraith]

Thanks, Now if I can just get myself to create a perf-board layout for it and put it in an enclosure... :)

[madamerotten]

Nice! I always wanted to build one of these, but I couldn't find a tube anywhere.

[sjoerdbeukers]

nice work!

[RossOverstreet]

Nice work. Thanks for posting!