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Author Topic: geiger tube schematic, help with components sourcing?  (Read 2037 times)
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Hi, I recently found a cool schematic for a cheap Geiger counter. The schematic is fairly simple, but since I am new to this, I don't understand the labels they have put for the components. I copied all of labels for the parts and searched them, and I have found all of them (or at least I think so). If anybody could read the schematic and give me the parts list (if I have read it wrong), it would be greatly appreciated. smiley 

Here is the link to the schematic:
http://madscientisthut.com/wordpress/wp-content/uploads/2011/03/Geiger_board.jpg
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What have you located so far?
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Everything in the schematic (except for the optional part). Although I could be wrong.
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You can search at digikey.com for N-Channel Logic Level MOSFET, they are plentiful.

I'd be more worried about the 500V or whatever the high voltage is that drives the geiger counter.
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The mosfet is a low power one, probably only need an amp or less Ids rating - its purpose is to provide an open-drain output signal.  I think an NPN (2n2222) transistor could be used to make an open-collector output instead (anyone see why not?).
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Yes it would work.

However I think the OP is missing something. This is not a complete circuit of a Geiger counter because it misses out the circuit that supplies the HV_input. This stands for High Voltage input and depending on the tube is normally between 400 to 800 Volts. So the normal way to get this is to have an inverter circuit. In most GM (Geiger Muller) circuits this is the major part, the bit you have posted seems over complicated as all it does is to take the high voltage pulse from the GM tube and make a speaker click.
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Most of the geiger circuits I see, have a major failing, they do not provide any regulation for the high voltage power supply, which can contribute  multiple pulses being displayed for a single event, such as the Sparkfun circuit.



Whereas, the proper waveform should look more like,

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I forgot to mention that I am acquiring the HV power supply from a disposable camera flash. I only need to know the resistors and capacitors. The left side of the schematic ( from resistor R8 down) is optional. I only need to know if the object I'm measuring is radioactive or not. (For radioactive antique hunting.)
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There are 5 - 12V DC input devices to be purchased on the internet in the $40.00 - $60.00 range and it can be done for quite a bit less money. But as voltages of that level are generally fatal, a project like that is not for the less experienced. IMO

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Disposable cameras are in the $5-$10 range. They would be cheaper.
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Don't take really good pictures though...

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 smiley
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Camera flash supplies are rarely over 350v whereas most geiger tubes need ar least 400v and most are around 500v.

Cheap is possible but not likely achievable by someone without considerable experience.
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The guy who made the schematic posted videos of it working. I am looking at a Geiger tube to buy that runs on that voltage. Can anyone tell me the parts list? smiley
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Geiger tubes that run on voltages that low only detect gamma...  something your not likely to encounter in antique objects..
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