nsuccesfully. Lesson of this project is you should do your work properly, or you will need to redo it.
This tube can detect mainly gamma radiation and some beta particles though a thick plastic case may stop all the particles except the very high energy ones. The tube didn’t rattle, and seemed to be in good condition despite one small dent. I do not know if calibration still holds in, as gas inside may have decayed or leaked. This tube may be military specked as it has that diamond marking with 5 inside. If I remember correctly it had something to do with the military. Some other military surplus parts from soviet area have had these markings too.
For the power source I chose a lithium-ion battery cell. The 18650 cell type is readily available as it is used in many laptops, flashlights and so on. I recycled some batteries from an old laptop. For charging I bought a 5V USB-charger board from DX.com. It charges the battery while the device is connected to USB. When using a lithium-ion battery there is no need to discharge it completely before a recharge. It may even damage the device if the battery voltage goes under 3.2V or so. I have an alarm that goes off if the battery level reaches 3.2v, but it does not have a cutoff circuit yet. I have a plan to buy a protected lithium-ion cell that has built-in protection for under- and overvoltage. As the lithium-ion battery only gives voltage between 4.2V to 3.2V, I need something that iccreases it to a steady 5V supply. If the voltage changes, it messes up the contrast oft the display. The voltage of the tube may vary as well, causing some accuracy issues. I bought a small switching mode power supply from DX.com that increases 1-5V to a steady 5.2V. While the USB is connected, the device works with 5V from there, and the current from battery is not drawn. Otherwise the Li-Ion charger would not know when to stop charging. First it starts to charge in a full 500mA current, but when voltage rises it starts to limit the current with a constant 4.2 voltage. When the battery is full the current flow stops, and the charger stops, which turns the red light green. Battery voltage can be constantly seen on display because I connected the battery to the Arduino’s analog-to-digital converter. This is the main difference to original diy-geigercounter kit.
After I got the charging and the power supply working a new problem came up. I could not get the Arduino detected when I connected the USB to the computer. I changed all my wiring and connectors, even bought new Arduino boards. It was infuriating. Nothing helped and whenever the Arduino was powered by an external source and USB was connected, the computer would just show the “Unrecognized device”-popup. If I removed the Arduino from the board, and connected it separately, it worked. Only after de-soldering the board twice, and trying three different Arduinos I found out that fault was in Arduino itself! All boards, clones and genuine, have same thing. FTDI FT232 USB to Serial bridges datasheet notes that the “TEST” pin must be connected to ground, or the USB will not work. Well, someone designing the original Arduino had not noticed that, and the “TEST” pin was floating freely, not connected to anything. If there was a charge that would pull the signal up, the USB would not work. After connecting that signal pin to ground everything started to work. So much work wasted when fault was already there in bought factory-made parts. Still… I’m happy that it was so simple to fix and I could get the whole device to work properly.
After there was no problems with other circuitry, I continued to the high voltage supply. Geiger-Müller tubes need high voltage to work, because ionization and avalanche would not happen with lower voltages. The tube I used needs approximately 400V to work. Good thing is that GM tubes are not that picky, because they work as long as the voltage is inside the plateau region. It can have an impact on the results received, but just marginally. Getting the voltage right is difficult as it cannot be measured with ordinary multim