[Swlug] DIY Geiger counter

[terry at happysoft.co.uk]

As the pulses are quite short how about feeding them into a hardware 
binary counter and reading and resetting the counter every second. That 
way you will get a direct counts/second which is a good way to measure 
radiation.

How you display that then is up to you. A typical Geiger counter needle 
will have its own intrinsic delay so gives a rough average reading over 
a few seconds. You could use a real needle with a DAC and capacitor of 
some type to slug the value or a clever screen based one with the delay 
built in sooftware.

Terry
(Long time lurker)

On 2025-03-06 16:33, Rhys Sage via Swlug wrote:
> I'm in the middle of a project - to build a Geiger counter. It's a fun 
> project so far.
> 
> I have all the bits I need (I think) but as with all projects there's a 
> lot of experimentation and changes made on the fly. 
> 
> I'm using a Thalium-doped Cesium Iodide crystal in combination with a 
> BPX61 photo diode. For those that don't know- the BPX61 is slightly 
> more sensitive to green light. The crystal emits blue/green light when 
> struck by gamma radiation. Whether it emits light when struck by Alpha, 
> Beta or X-Ray, I don't know. I do know there are other crystals more 
> suited to those.
> 
> The BPX61 output will feed into an OPA134PA amplifier and then that 
> will in turn feed into a microcontroller. Given that the events 
> generated by radioactive decay are very brief, would microcontroller 
> speed make much difference? I could use an ATTiny13/ATTiny85 or 
> something small like a micro RP2040 or an ESP32 C3 Super Mini.
> 
> With a regular Geiger counter,does the system store the events somehow 
> or does it just rely upon measuring maximum pulses when a pulse happens 
> during a sampling period?
> 
> Rhys Sage