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MarkusB of Lets Make robots designed this simple Geiger counter. If you’ve somehow come across a Geiger counter tube and want to make a detector out of it, this could be just the thing you need. His design uses only commonly available parts, and is powered by a 5v power supply. He plans to make a radiation-seeking robot out of it, perhaps as an atomic version to Natalie Jeremijenko’s feral robotic dogs?

This is all well and good, but how does the circuit work? Let’s take a look:

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Looking at the circuit, it basically breaks down into three parts: On the far left, a 555 timer is configured in an astable mode, causing it to generate a square wave at some frequency. This square wave is then fed into a charge pump, creating a (claimed) 300-1000v potential, which is used to power the Geiger counter tube. When a particle or photon of radiation moves through the tube, it allows the inert gas in the tube to conduct electricity (source: Wikipedia), allowing some charge to flow from the high-voltage lead of the tube to the other side. This causes the on the sensing lead to go up for a short amount of time, which then causes a second 555 timer to put out a short pulse.

Note that I haven’t simulated this circuit, so I don’t know if it actually works with the specific components specified, however the general topology (layout) appears to be correct. Have you designed or built a similar circuit for a geiger counter? Have any suggestions to improve this one?

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Comments

  1. MadRat says:

    A radiation seeking robot seems a good idea, but the problem is radiation tends to get weaker the further away from it you are by orders of magnitude. There is also the problem that there really isn’t that much in the world that’s radioactive. Not to mention, alpha and beta radiation dosen’t travel far in air so you’d have to use a gamma/x-ray emitter, which are pretty hard to come by. It’s also going to be harder if you’re using a Geiger tube instead of a Geiger pancake sensor because a tube isn’t as sensitive as a pancake.

  2. Carnes says:

    Goldmine electronics has a few Geiger tubes for sale. They also have a cicuit for a DIY counter: http://www.goldmine-elec.com/pdf/g17339.pdf

    This little tube could easily fit into an altoids tin.. that would make for a neat project: http://www.goldmine-elec-products.com/prodinfo.asp?number=G2903

  3. AntonyG says:

    Looks OK to me.

    If you’re wanting to maximize battery life, there are a few tweaks that could be made. A CMOS version of the 555 would draw less current, and you could use a dual version while you’re at it to save pins (e.g. 7556). Also, you could replace R7-R9 with some zeners, and switch the oscillator on and off directly via its RST input. (The CMOS version helps with this, because the much higher pin input impedance means you can use larger resistor values, and draw less current).

    Getting a decent transformer is worthwhile too. I’m guessing the one in the diagram is a small mains transformer in reverse. Should be OK at 500 Hz, but core losses may cost you a bit of power. A ferrite design pushed up to 10-50 kHz would be more efficient.

    Otherwise, with a trusty 555, it’s pretty easy to get a basic Geiger counter going.

    Here’s my design, if you’re interested:

    http://www.circuitsarchive.org/index.php/Geiger_counter

    Antony

  4. AntonyG says:

    The hardest bit is getting hold of the GM tube. Last time I used them, LND inc (http://www.lndinc.com/) were pretty good about taking credit card orders for small quantities. The all-purpose 712 is a firm industry-standard favourite.

    And as MadRat points out, don’t be disappointed if you struggle to find things that you can pick up with your counter. Your best bet may be to buy some bits of pitchblende off eBay, or perhaps look for an old luminous clock. For robot experiments, I’d be tempted to pot whatever it is in epoxy, in a small box. (Safer). With a 712-sized tube, you should get maybe a few hundred counts per minute nearby, against 15-20 per minute background. It could be quite interesting designing an efficient search algorithm. Even at a metre or more distance, you’ll get just enough above background to triangulate a position (if you don’t mind taking your time to accumulate the counts).

    Antony

  5. Chip says:

    It should work, it matches the specs I’ve seen in other actual in use schematics in ancient tech books.

  6. Make magazine needs to make this a genuine feature story in the print edition… Now that we know the ambient radioactive levels in North America are higher than EPA set limits because of rainfall from Fukushima, it’s time US citizens mobilized for survival. The cost of commercial Geiger counters is intentionally prohibitive to the general public, so the only solution, is to do it ourselves!

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