Print PDF
Favorite
Email
Publishing this one in a hurry, in case it is useful to our friends in Japan. This is a simple Geiger counter circuit. It does require some specialized parts, in particular a Geiger tube and some high voltage Zener diodes, but the rest of the components are readily available. If you're feeling like experimenting, try making your own Geiger tube... see the last step of this instructable for some comments on that.
This is the second electronic circuit I ever made, so it's pretty basic, suitable for beginners.
This is the second electronic circuit I ever made, so it's pretty basic, suitable for beginners.
Remove these ads by
Signing UpStep 1The circuit
Click on the "i" in the top left of the picture and select the full image resolution to see the schematic diagram more clearly. I am assuming you have some electronics experience so you know how to solder and which way to connect a diode etc., but if not or if you have any questions please ask.
I didn't have components to make a high voltage power supply, so I improvised using a transformer from a 10V AC adapter (the little black box you plug into the wall to convert 120VAC to 10VDC). It is not that important to use a 10V transformer, I'm sure anything in the 3V to 12V range would work. Just break open the plastic box and remove the transformer. I used a 1.5V battery (C cell) and a pushbutton switch on the 10V side of the transformer, and the high voltage is generated on the 120V side. You will have to experiment with which polarity to connect the 120V wires of the transformer so as to generate the correct polarity of high voltage, with the wrong polarity the voltage generated will be much smaller.
Tech note: How the high voltage circuit works .
The output voltage of a transformer is proportional to the rate of change of the input current. When you press the pushbutton switch, a fairly large current builds up in the low voltage side of the transformer. When you release the switch, this current instantly drops to zero, and since the rate of change of current is very high (dropping from a large current to zero in a very short time), a high voltage spike is generated on the high voltage side of the transformer. High voltage generating circuits work in much the same way, but they use transistors to switch on and off the current in the low voltage side of the transformer. Since the high voltage is generated only when the button is released, you want to press the button for only a short time so you don't waste the battery current.
The generated high voltage is stored on capacitors and is regulated to 500V using three high voltage Zener diodes in series (200V, 200V, and 100V, adding up to 500V). Such high voltage Zener diodes are not common, you will have to get them at a specialty electronics distributor. Of course whatever reasonably high voltages you can find (for example 1N5271 through 1N5279 are rated 100V through 180V), just add enough in series to equal the voltage rating of the Geiger tube. Make sure to use capacitors rated at least 1000V, and put enough in parallel to add to about 0.02 microfarads. Note that you can't put lower-voltage capacitors in series to get a higher voltage rating, this doesn't work. The Geiger tube I had required 450-500V, other tubes require different voltages, 900V is common, if so use more Zener diodes accordingly.
The diode labeled "1000V PIV" is a rectifier diode with 1000V peak inverse voltage (or peak reverse voltage), to rectify the high voltage (for example 1N4007). I actually used two of these in series because with just one the leakage current was too high, and the high voltage decayed too quickly. If you have lower voltage diodes such as 1N4004 you can put several of them in series. I opened a compact fluorescent light bulb once and it contained several 400V PIV diodes, 3 to 5 of those in series would work. The two unlabeled diodes are 1N914 type.
The signal from the Geiger tube is strong enough to trigger a 555 timer. The 555 timer then drives a small speaker directly, making a 'click' noise each time the Geiger tube detects radiation. Use an IC socket for the 555 timer chip, so you don't fry the chip when trying to solder it into the circuit, also it makes it easier to replace if you make a wrong connection and fry the chip.
Here is a similar design which you can also refer to for other ideas and information:
http://www.galacticelectronics.com/GeigerCounter.HTML
I didn't have components to make a high voltage power supply, so I improvised using a transformer from a 10V AC adapter (the little black box you plug into the wall to convert 120VAC to 10VDC). It is not that important to use a 10V transformer, I'm sure anything in the 3V to 12V range would work. Just break open the plastic box and remove the transformer. I used a 1.5V battery (C cell) and a pushbutton switch on the 10V side of the transformer, and the high voltage is generated on the 120V side. You will have to experiment with which polarity to connect the 120V wires of the transformer so as to generate the correct polarity of high voltage, with the wrong polarity the voltage generated will be much smaller.
Tech note: How the high voltage circuit works .
The output voltage of a transformer is proportional to the rate of change of the input current. When you press the pushbutton switch, a fairly large current builds up in the low voltage side of the transformer. When you release the switch, this current instantly drops to zero, and since the rate of change of current is very high (dropping from a large current to zero in a very short time), a high voltage spike is generated on the high voltage side of the transformer. High voltage generating circuits work in much the same way, but they use transistors to switch on and off the current in the low voltage side of the transformer. Since the high voltage is generated only when the button is released, you want to press the button for only a short time so you don't waste the battery current.
The generated high voltage is stored on capacitors and is regulated to 500V using three high voltage Zener diodes in series (200V, 200V, and 100V, adding up to 500V). Such high voltage Zener diodes are not common, you will have to get them at a specialty electronics distributor. Of course whatever reasonably high voltages you can find (for example 1N5271 through 1N5279 are rated 100V through 180V), just add enough in series to equal the voltage rating of the Geiger tube. Make sure to use capacitors rated at least 1000V, and put enough in parallel to add to about 0.02 microfarads. Note that you can't put lower-voltage capacitors in series to get a higher voltage rating, this doesn't work. The Geiger tube I had required 450-500V, other tubes require different voltages, 900V is common, if so use more Zener diodes accordingly.
The diode labeled "1000V PIV" is a rectifier diode with 1000V peak inverse voltage (or peak reverse voltage), to rectify the high voltage (for example 1N4007). I actually used two of these in series because with just one the leakage current was too high, and the high voltage decayed too quickly. If you have lower voltage diodes such as 1N4004 you can put several of them in series. I opened a compact fluorescent light bulb once and it contained several 400V PIV diodes, 3 to 5 of those in series would work. The two unlabeled diodes are 1N914 type.
The signal from the Geiger tube is strong enough to trigger a 555 timer. The 555 timer then drives a small speaker directly, making a 'click' noise each time the Geiger tube detects radiation. Use an IC socket for the 555 timer chip, so you don't fry the chip when trying to solder it into the circuit, also it makes it easier to replace if you make a wrong connection and fry the chip.
Here is a similar design which you can also refer to for other ideas and information:
http://www.galacticelectronics.com/GeigerCounter.HTML
| « Previous Step | Download PDFView All Steps | Next Step » |
?
It would be quite easy to connect an optocoupler to my circuit, just connect it to the speaker output through a ~1 kohm resistor.
I am on the east coast so I don't expect to pick up anything from Japan. I think even after Chernobyl it took very specialized equipment capable of detecting the gamma ray energies to pick up fallout in North America and distinguish it from normal background radiation, so I don't expect a Geiger counter would be able to do it. But definitely fun to try!
I would suggest that when/if you get more time, to flesh this I'ble out abit as it's not fantastically clear... But well done anyway I enjoyed giving it a read
Homebrew radioactivity detector... interesting idea
High Five for you
This is the only Geiger counter I have made, I did it as a project for an electronics course years ago. With 5 counts/minute for background radiation it is not as efficient as most Geiger counters which will give 15-30 counts, but that's because of the small tube I used, not the circuit.
What' I'd really like to do is figure a way to make a Geiger tube, that's the big disadvantage of this project, Geiger tubes are hard to come by. They are normally filled with special gases, but I think they can work when just filled with air..
http://www.techlib.com/science/ion.html#Experimenters%20Chamber
Reasonable price, too.
If you want your counter to be interesting, I'd spring for at least an alpha, beta radiation detector. That way you can detect the radioactivity in nature (rocks, cosmic rays, etc.)
The example circuit that they provide is a Geiger counter, not an ion chamber type detector, so I think it really is a Geiger tube and will react to rocks, cosmic rays, etc.
Russian military Geiger tubes counter Ci-3BG.
Lot of 50.
Plateau > 80 V.
Plateau inclination , % / V, no more: 0,25
Sensitivity countable characteristic Imp/sec //( R/h) > 1,3 * 10-5 (188) > 2 * 10-5 (282)
U on the anode in an impulse mode V 380-460
U on the anode in a current a mode V 382-398
The greatest working current uA > 15, < 20
I'm not sure what all of that means, but the 'plateau' seems to refer to ionization type detectors (see this link), and the apparent mention of 188 and 282 rad/hour suggests it is only sensitive to high radiation fields.
Russian Geiger TUBE Counter SI-3BG
New, old stock.
Lot of 1
Russian made (CI-3BG) glass geiger mueller tube is designed to detect betta and gamma rays.
Working range of Dose POWER 300R/h
Sensitivity to Gamma Radiation 188-235 Pulses/s/R/h
Working Current 0.015-0.02 mA
Plateau Length/ Inclination 80V/0.25%/V
Working Voltage 380-460V
Working Current 0.015-0.02 mA
Maximum registering range 300 Roentgen/hour
Length 55mm
Diameter 10mm