My Very Own Geiger Counter

As far as Geiger counter kits go, I did a bit of trawling around before settling on one.

If memory serves, my criteria ended up going something like this:

• Affordable (for me this meant < $100 USD)
• Comprehensible
• Documented
• Open Source
• Attributed
• Quality
• Bring Your Own Tube (I have the one from my dad)

Searching on the web led to several kits of varying documentation and quality. One in particular stood out to me:

https://mightyohm.com/blog/products/geiger-counter/

(Note that this is also sold by AdaFruit.)

I very nearly bought this one, and it is a wonderfully straightforward design. One of the most amazingly human and connective things MightyOhm does is to acknowledge a source of inspiration for the design: DIYGeiger.

When I followed that lead, I found a much more sophisticated set of kits that are under active development by person with passion for the projects and a predilection for documentation.

When I was a kid, i wanted a box that clicked around radiation, allowing me to peer into the unseen world of nuclear physics. MightyOhm's kits do just that.

DIYGeiger's kits add to that the worlds of WiFi connectivity, signal analysis, colorful GUIs, useful DC input ranges, SD card logging, microcontroller programming, and GPS tracking. Source code is available and documentation doesn't stop with 'put 1/8W 1Kohm resistor in slot R5'--it goes on to talk about power supply selection, schematics, and instructions for tweaking the high voltage along with background information about making HV measurements and characterizing GM tubes. On top of that, the kits did not necessarily come with a GM tube and were adjustable to work with whatever tube is available.

I went with the GK Plus (with Display Adapter), Pololu regulator, and GK WiFi Kit. I think I'll add a GPS module eventually. Note that at this point I had not really settled on a power source beyond using a battery. I got the Pololu as a matter of flexibililty.

BroHogan's customer service was responsive and helpful when I had a problem with the shipping address, and he threw in a couple of amazing little freebies that I expect to put to good use.

After realizing that electronics weren't as simple as my 12-year-old brain expected--like transformers not working on DC--I started collecting bits and pieces of knowledge so I could design and build a Geiger counter that I actually understood.

My dad bought me a Geiger Muller tube off eBay to encourage me, and pointed me to something he saw at university for building compact SMPS circuits: pot core transformers. These ferrite toroidal cores allow for traditional transformers in the 5-25kHz range (IIRC) to be relatively compact and light, allowing them to be used in weather balloon payloads or handheld electronics. This project is, in a small way, in his memory.

My mom also liked to encourage me. When she saw the little nylon bobbins that came with the Amidon cores I ordered, she gave me her embroidery floss card-bobbin winder and helped me figure out how to trim the cards so the flat floss card bobbins would hold the nylon bobbin for winding. This project is, in a small way, in her memory as well.

Secondary school gave me some mathematics and physics. Circuit Analysis I and II at university certainly helped, and the DC+transformer problem was neatly rammed home by my intro to electromagnetism class. I had the great fortune to work for a man who designed at least one of the famed Eberline GM counters at the same time I was learning enough circuit analysis to start to appreciate his genius (it was a one-transistor regulated HV SMPS design, IIRC; he handed me the maintenance manual once). He was the one who taught me the power of a good block diagram. (He also taught me to always check the power rails first, and that has saved me many hours since then...)

In the end I did wind my own transformer with some magnet wire my dad gave me so many eons ago. In spite of a 1:10 winding ratio, I got closer to 1:5, so I fed that into a (now-comprehensible-to-me) 5x voltage multiplier. Alas, I was starting from a 9V battery and something else was wrong, so that still left me with something like 150VDC. This led me to shelve the project for another few years. (I later learned it might actually have been working fine since my measurement rig was probably too heavy of a load. Oh well :)

My Real Grown Up Job recently provided me an idea: If I buy a kit instead of designing my own, I can grok it and save myself the hassles and joys of part selection, board layout, troubleshooting, winding my own transformer, and the other joys of designing from first principles. Unfortunately, unlike some amazingly smart and gifted people chronicled on the Hackaday Blog, I don't actually have the time to plunge into all of these topics and actually find myself satisfied with simply carefully grokking another's design.

Welcome to my little project log where I'll share my experiences from kit selection to case design to characterization. I hope you find something useful!