Modern physics, especially radioactivity has always fascinated me. How can something that can’t be seen, smelled or otherwise sensed by human have such a large part in our perceivable universe, and at the same time be deadly to us organic lifeforms? It can be bit frightening due its properties, but it still is everywhere and humans have harnessed it from medical and scientific triumphs to weapons of mass destruction. So how we can detect it then? Well, two smart men, Geiger and Müller invented and developed a gas-filled tube that can detect radiation and particles by ionization. This Geiger-Müller tube (shortly GM tube or informally Geiger tube) is the heart of the Geiger counter I built. I’ll skip the theoretical part which you can read from Wikipedia (or preferably its sources) and tell about the building process itself.
Couple months ago I found out that cheap new-old-stock of Soviet/Russian made GM tubes were available on ebay. I bought one from a Hungarian seller just before thing went sour in Ukraine. While waiting for the tube, I started to browse the Internet for schematics and completed projects to be used as an example. Many of them used weird high-voltage generation circuits with parts made of unobtainium. This site proved to be most resourceful and a big thanks goes to its original author. I based my project on that diy arduino based Geiger counter kit, and borrowed high voltage and detection circuitry and some open source firmware from it. It saved me a lot of work, mostly on software side which I’m not too fond of.
I had a vision to include everything needed to one circuit board the size of an LCD screen I would use, and attach them together with screws and spacers. Connection to LCD would be made with pin-headers. I used a Arduino Nano clone to save space and to get an easy USB-connection for data logging and firmware updating. Arduino has all needed circuitry to support AVR micro controller and FTDI usb-to-serial adapter. They are easy to learn and develop and ideal for hobbyist- and school projects.
After making couple of crude mock-ups on component placement, I soldered them down and started a long and painful wiring operation. I made some bad mistakes during the project, and was forced to de-solder parts. Sadly this shows, as connections on final device are ugly and some solder pads detached from board and this caused other problems along the way.
Sadly the first version of a HV-supply did not work out. I used an old 555 timer IC (that tincan on the right) that drew too much current even when just sitting there. Also, I did not have the proper parts for HV, so I added some transistors, resistors and capacitors to the shopping list and went back to drawing board.
While having a pause from inhaling soldering smoke I made some parts for the case. Housing itself came from an old industrial wall switch (those white watertight plastic boxes). Making clean holes and cuts to ABS plastic did not work out as I planned and I wanted to highlight the user panels and the display. Hence the metallic switch plate and plastic display cover. Tools I had on hand were a hacksaw, a cordless drill and some files. Some creativity was needed and my methods probably would not be approved by any school or workplace (like hand-drilling holes to plastic by using screwdrivers and knifes). Considering that the aftermath was surprisingly good; all fingers still in place (just kidding) and even case for device in one piece and decent looking.
The LCD is covered with plexiglass which protects it from hits and scrapes and also gives it a bit more professional look when label is applied under to underside. I designed a simple front label with GIMP and laser printed it to ordinary paper. Another purpose for metal and plastic panels are to maintain semi water- and dust-proof features for the box. After all you do not want any radioactive particles inside the meter, do you?
The case had several versions too, and at this moment it still waits for the 3rd LCD plexpanel as one screw hole is in the wrong place and I tried to glue paper on it u