You might have seen this little creation on one of the Facebook groups already, but I figured I’d post it here too.
This module is based on a cheap Geiger counter which can be found all over the web. Every time an ionising particle is detected, the module generates a decaying pulse of variable length. This means you can use it as a random event generator, or you could play if with anyting radioactive, like a… banana?
Below is the circuit which I have piggy-backed on the Geiger counter. It cleans-up and inverts the pulses, and adds the decaying envelope. Also, it powers the counter through a 5v regulator.
I think I mentioned here previously that after making this module I heard that David Cockerell and Peter Zinovieff had done the same thing in 1965, using a geiger counter and wristwatch with glowing numbers, to create randomness for compositional purposes…
Either way, you deal with decay.
However this fruit, to me is a better substitute.
Its a funny display, pardon the wordplay.
For if random be the dictum, I say Potassium over Uranium!
I’ve been looking at this schematic. Is the first op amp, the comparator, correctly oriented? The Geiger counter signal connects to the inverting input and the threshold is on the non inverting. This means normally the comparator output is +5 V, dropping to 0 when a pulse comes in. The capacitor charges quickly and discharges slowly, so it only discharges a little before the pulse ends and it charges back up again. Result is an output that’s normally +5 V and just dips a little.
If the op amp inputs were reversed then the comparator output would be normally 0 V, switching to +5 V when a pulse comes in. Output would be normally 0 V, jumps to +5 V when a pulse comes in, then decays slowly back to 0 V, which makes much more sense to me.
I don’t have the module at my place, so I cannot verify. But, if I remember correctly, the output from the Geiger counter module is inverted. It’s 5v, then gives a pulse to 0v when a particle is detected. So I configured this opamp as an inverting comparator. Hope that clears it up!
Got the Geiger counter, plugged it in, turned it on, power LED came on and… nothing.
Looking it over I saw there was no jumper on J4. Per the schematic that’s how HV gets to the tube, which seems kind of necessary. So I put a jumper on it. Still nothing.
I saw the calibration instructions GeigerCounter-V1.1/En_Calibration_GMv1.1.pdf at master · 2969773606/GeigerCounter-V1.1 · GitHub but had no idea what “Connect positive Tube Clip to pins (J4) with a jumper wire” meant. So I decided what the heck, left the tube installed, and measured at J2. I got 50.8 V instead of the 57 V they mention. So I turned up R100 until I was measuring 57 V.
And now it clicks, and the indicator LED flashes. Not often, maybe about once or twice a minute average, but seems it is doing something anyway.
I haven’t hooked it to a scope yet but there is indeed normally about +5 V at the confusingly named VIN (output) pin.
Once or twice a minute seems about right. At least, I got the same rate while inside. I haven’t actually checked whether it matches with the expected level of background radiation. I saw a noticeable increase when taking it outside in direct sunlight, that’s a check you could do.
Certainly being inside a building partially shields against cosmic rays and will contribute different levels of terrestrial sources. (Less or more, the latter especially in certain basements due to radon accumulation.)
Or I could buy some uranium ore. But I’m not sure that’s in the budget.
)
