- sztojanov
Fukushima, Japan, 11th March 2011, the day of the terrible nuclear disaster. That's when I decided I should build a Geiger-Müller counter, steampunk style. The 25th anniversary of the Chernobyl Catastrophe (26th April) was a month later, which as well had a great impression on me. I remember how the Hungarian news on public service broadcasters muddied the water about the happenings over there, when I was young. So I started thinking about what kind of a dosimeter shall I make: an analogue type with a deprez display began to outline in my head, lacking any kind of digital parts, and another model as well, but more on that later.
I found the degree work of the Hungarian group Omega Labs quite interesting, just like what I had in mind, no digital voltage involved (Geiger-Müller counters work with high voltage, usually from 300V!), it operates by setting up a Cockroft-Walton Generator instead.
A curious fact about it is that the whole PCB¬¬ – with a few modifications – could have been built 50 years ago, more than that, the original schematics of the panel appeared first in the 1980's in a German electrical engineering magazine. After some small modifications and the redesigning of the panel based on the original we can proceed to build the prototype of the PCB panel.
We have all the parts we need without exceptions. Let's inspect the PCB put together before washing the flux. If we observe it carefully we will find a text on the bottom of the panel: "dedicated to Vladimir Shevchenko". He was that incredibly brave (and ignorant) cameraman who recorded the early activities of the emergency services during the disaster in Chernobyl and practically died of the making of his film. I dedicate this Geiger counter to him.
After the testing – which by the way brought great results – I started thinking about the boxing, what kind of characteristics should it have, what sorts of specialties should it have?
In parallel with that, I thought it would be too simple to build just one instrument, make it two, and if one of them is wholly analogue then the other should be a high-tech, digital Geiger counter! I've found a starting pointfor that too, more than that, I had help from John Giametti as well, let me say thanks for that again. For both projects I used Russian SBM-20 (CБM-20) tubes, because they're reliable, fairly cheap and they detect both beta (ß) and gamma (γ) rays.
Panel designing, as always, in Sprint Layout! We can see the single page plan of the second prototype of the digital panel.
The tests after having the parts built in to the digital counter were a success as well, so I proceeded to prepare the cases. I found the case of certain types of ampmeters and ohmmeters suitable for the task, so I got two of those kinds. The case of the analogue belonged to an original ohmmeter used regularly in the American army back in the 60's. I've kept the deprez frame of it, but I had to make its obverse out of brass, of course, it couldn't stay plastic (the only plastic I use is bakelite, which is one of the oldest "plastics").
I only noticed after the arrival of the box (aside from the fact that it was quite dingy from the outside) that the original case was made out of aluminum and it gave me a fantastic idea: polished aluminum has never been made by my hand afterall! Besides drawing an analogue-digital parallel between the two dosimeters, while the analogue is supposed to be a more industrial type, the digital one will rather represent the classic steampunk style!
First I designed the templates of the panels in Illustrator then came the usual sawing-rasping procedure, and finally the burnishing. There were no CNC or laser involved; these were made 100% by hand!
The case of the digital dosimeter was originally a Bulgarian ohmmeter; it was still functioning on arrival. It was made purely out of bakelite, however it couldn't stay like that, and it received a special coating, which is an easy touch paint that looks indeed exclusive.
The two "detectors" on the front of the dosimeter were hard to find, I've spent half a year browsing and hunting until I came upon the most decent. There is a pair of 1" marble in it, and fits perfectly in the project! The layout of the PCB during size trial can be seen on the image below; it is quite amorphous, but it was the only way it could be fitted into that small space.
The digital display got a leather cover, regarding the question of the colour of the soft touch paint the bakelite handle was a big help. Fortunately, the bakelite can be polished nicely, so it's easy to work with; I only had to remove a bit of burr from around the edges and to glue a metal dowel in it, which I could support it with.
Meanwhile, the analogue radiation meter started turning on the home-stretch; a problem arose though, in connection with the black deprez bakelite, namely that it is very thin and fragile (cca. 50 years old!). That's when the idea hit and I filled its inside with gypsum that lent it strength for polishing. It worked.
Consecutively I designed the background of the device that had been printed to a semi-gloss papper. In parallel, the boxing of the electronics had been started, too.
At the same time I suited a 2x8 lined mini LCD to the digital dosimeter, as the size of the 2x16 one wasn't adequate. I had help with the redesigning of the microcontroller's software in John's person. The screen displays tube voltage, warns for discharged batteries, and during the detection in real time (counts/minute) and the extent of the radiation (µSv). The amber colour of the LCD's background lighting suits just perfectly to the style of the dosimeter.
Brass parts after polishing.
As there is a lot of less space as in the analogue's case, the regular 9V batteries didn't fit in. I had to come up with something else: I soldered four 12V MN21 batteries together parallelly. Beside in the picture, the bandaged accumulator can be seen the Thorium (232Th) too, which I can test the finished electronics and Geiger-Müller tubes with, on live.
Lot of screws, decorative rivets and switches, then comes the assembly.
More HQ images in the gallery.
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