This is the first breadboard mock-up Geiger counter working. Background count is about 20cpm using a BOI-33 G-M tube. Anode voltage 400V, supply 3V.
The indicator section of the circuit is a simple transistor switch. Its nowhere near good enough for a finished project - the LED flash is too dim and the sounder 'click' is far too quiet. There is also too much leakage through it meaning the LED is very dimly lit all the time. This section then needs more gain, and perhaps a pulse extender to allow a much more robust indication.
The current drawn from 2xAA cells in the absence of a pulse, is about 1.8mA. Its a bit higher than I would like, but quite acceptable. Ideally, I would get the quiescent current down to under 1mA, which might be achievable with some component value changes. Ive also tested this circuit with my huge STS-6 G-M tube, and it works great. Background count is appreciably higher of course, due to the much larger sensitive area of the tube.
Clearly though there are things with the breadboard version that will need changing for a complete, enclosed project. One thing to change is the high voltage capacitors - the ones used on the mock-up are about 4x the physical size of the ones i've recently bought, yet have identical ratings. The neon lamp as part of the regulator does take up more space than zener diodes, but I will keep that - the glow is a perfect indicator that the circuit is live!
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| BOI-33 G-M tube mock-up |
The current drawn from 2xAA cells in the absence of a pulse, is about 1.8mA. Its a bit higher than I would like, but quite acceptable. Ideally, I would get the quiescent current down to under 1mA, which might be achievable with some component value changes. Ive also tested this circuit with my huge STS-6 G-M tube, and it works great. Background count is appreciably higher of course, due to the much larger sensitive area of the tube.
Clearly though there are things with the breadboard version that will need changing for a complete, enclosed project. One thing to change is the high voltage capacitors - the ones used on the mock-up are about 4x the physical size of the ones i've recently bought, yet have identical ratings. The neon lamp as part of the regulator does take up more space than zener diodes, but I will keep that - the glow is a perfect indicator that the circuit is live!
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