An Introduction

A project log for My Very Own Geiger Counter

fulfilling a childhood dream

Jon KunkeeJon Kunkee 09/18/2019 at 06:100 Comments

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!