# DIY "Geiger-Muller" counter - "prooof of concept" circuit

#### FlyingDutch

##### Full Member level 5
Hello,

I have bought an "SBM-20" Geiger-Muller tube counter detector. I would like to test this counter - it needs 400V powering (for tube). I found such prooof of concept circuit:

It is schematics from book titled "Raspbberi Pi - Awesome projects (Insane Genius). In general I understand this circuit - it is generator with transformer and "voltage multiplier" (Villard cascade). And there also is (tube) simple circuit shaping impulses from Geiger tube - in order to count them on microcontroller.

I have an query regarding the "Villard cascade" (voltage multipiler) on diodes and capacitors: Is in this attached schematic the multiplier factor of cascade equal eight times (8x)?

I am asking because original schematics was for "K2645" geiger tube wich needs 600V powering and I have "SBm-20" which needs only 400V.

Gates on schematics are CMOS 4000 series. I have to properly select transformer and "Villard cascade" (voltage multiplier). What should be permisible voltage for capacitors and their values? And also types of diodes in voltage multiplier? Could somebody help me with this a little?

Polish goverment is going to build "Nuclear Plant" in Poland so I would like to have a "Geiger Counter" on my own (just in case).

Thanks and Regards
--- Updated ---

BTW: here is link to SBM-20 Geiger tube:

https://www.ebay.pl/itm/NEW-SBM-20-...eiger-Muller-Tube-Counter-TESTED/191831193846

Regards

#### vfone

For $75 you can get a working Geiger-Muller detector, which have the advantage that record continuously the detected radiation, and you know that the exposure to gamma radiations is cumulative.. The link have a Q&A section interesting to read. #### FlyingDutch ##### Full Member level 5 For$75 you can get a working Geiger-Muller detector, which have the advantage that record continuously the detected radiation, and you know that the exposure to gamma radiations is cumulative.. The link have a Q&A section interesting to read.
Hello @vfone,

thanks for link - the price is very good, but I would like to gain knowledge enabling me build my own "Geiger counter". I am rather going to expriment with few "Geiger-Muller counter tubes". I also find www page with full project of such "DIY Geiger Counter" (more advanced than attached by me schematic). Here is link to this page:

You know I would like to have fun building such "Geiger Counter" on my own

Best Regards
--- Updated ---

BTW: You know, when I have circuit shaping impulses from the tube (counter) ready I will be able to count them on microcontroller and also record them for example in "FRAM" (non-volatile) memory.

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##### Super Moderator
Staff member
I have experience working on my Geiger counter with GM tube. In general you'll obtain a transformer, find out what voltage you get from it, then attach the correct amount of Villard (diode-capacitor) stages until you reach a voltage sufficient to trigger your GM tube.

That type of voltage multiplier can also be constructed with two symmetrical sections when it is known by the name Cockcroft-Walton. It's popular because no component must endure more than the incoming supply voltage. (Thus if you have 120 VAC, each diode can be rated 200V, and each capacitor can be rated 200V.)

I built a similar voltage multiplier in order to step up house voltage 120VAC to about 900 VDC. It required several diode-capacitor stages. The caps were 500 pF but this value was insufficient and I ended up joining a second cap in parallel to each. Eventually I was able to test my GM tubes. A click showed up on my oscilloscope. As a precaution I installed one or more 1 Mohm resistors.

The tube needs a minimum voltage so that it starts to detect normally. It can tolerate a higher voltage and presumably increase sensitivity however if you apply too great voltage it shortens its useful lifetime.

FlyingDutch

### FlyingDutch

points: 1
Thanks

#### FlyingDutch

##### Full Member level 5
Hello,

just in context of "DIY Geiger Counter" has somebody know a company offering small power DC-DC converters? For example 12V to 400V (15 mA max. current / 6W).

##### Super Moderator
Staff member
The transformer and driving circuit is a step-up power inverter. Variations appear in different projects. You can use a different topology than is shown in your schematic.

I suspect your GM tube requires less than a few hundred uA at 400 V. (1/2 W). It's hard to measure of course because the discharge is brief.

If you try some 'wall wart' transformers you may find one that is suitable to operate in reverse, that is to step-up battery voltage to 100 or 200 VAC. Then attach a voltage multiplier to obtain 400 VDC. It may only need a voltage doubler or tripler.

To experiment you can use house voltage and attach a voltage doubler or tripler.

Your meter section can run on low power low voltage. Its power supply can be isolated and separate from the supply to the GM tube.