High Voltage Forum

Ionizing radiation => Detection, Counting and Measurements => Topic started by: Da_Stier on May 02, 2021, 03:00:20 PM

Title: Yet another homemade geiger counter with a sovjet tube
Post by: Da_Stier on May 02, 2021, 03:00:20 PM
Hi,

While looking through some boxes in my lab in a moment of boredom, I came across a old geiger counter kit from a german electronics store (Pollin), that I got many years ago.
In the box I found a second counter tube which I had for many years as well.
So I decided to go ahead and build a second counter.

The boost converter is based around a MC34063 buck boost controller.
(Mainly because I'm familiar with them since the same store sells them for 39cts a piece.)
I based my boost converter on their circuit.
This is what I built:

 [ Invalid Attachment ]

For the rest I used a simple BJT to detect the pulses, followed by a few 74HC14 stages to clean up the pulses and make them sqare.
I thought that would be it but the resulting pulses were only 6 us long.
I could have gone ahead and built some kind of RC time constant into the pulse detector but I felt more like adding a 555 as monostable pulse extender.
So that is what I did.
For giving feedback, I added a LED and a little beeper.
This is what the finished circuit looks like:

 [ Invalid Attachment ]

The wet looking parts are the 400V parts, which I conformaly coated with some nailpolish.

 [ Invalid Attachment ]

Next I printed a case for the unit and it was completed:

 [ Invalid Attachment ]

 [ Invalid Attachment ]

 [ Invalid Attachment ]

 [ Invalid Attachment ]

I actually managed to get a picture while it detected a particle :)

 [ Invalid Attachment ]

It seems to work fine, the sensitivity is about the same as the other kit with around 10 to 20 counts a minute.
I'm not sure if this is good or bad but I guess it is enough to be able to tell a difference if there is to much.


If someone wants a complete schematic, feel free to ask, but I guess everything should be straight forward enough without it.



Greetings,
Michael
Title: Re: Yet another homemade geiger counter with a sovjet tube
Post by: TMaxElectronics on May 02, 2021, 03:11:01 PM
That prototyping board looks pretty interesting, is that a standard part somewhere?

How fast is the recovery time with that boost converter? From my experience they are either slow or have poor output stability (from the output capacitance). No idea if that's an issue here though... I haven't done much with geiger tubes.
Otherwise it might be interesting to either use a transformer in flyback mode (maybe even one of those tiny camera flash chargers that are designed to go to 350V or so) or a large output capacitor with an rc network between that and the tube for faster recovery at high count rates.

I might built a quick test later with a custom transformer, as I just got a whole bunch of e-cores from aliexpress.
Title: Re: Yet another homemade geiger counter with a sovjet tube
Post by: Da_Stier on May 02, 2021, 03:20:58 PM
Hi,

these prototyping boards are something I drew in KICAD and got made by myself.
I think there is something similar on Digikey but if I remember correctly, they are outrageously expensive.

I didn't check the recovery time but it seems good enough. The pulse extender gives anywhere from 100 to 300ms pulses (settable by one of the trimpots).
Sometimes there are multiple beeps directly one after another, which I guess means that the supply is quick enough.
The tube is coupled to the 400V supply by a 10meg ohm resistor. This means a max. current of 40uA, which I guess shouldn't be to hard to handle, even for a simple boost converter.

You are absolutely right about the flyback, it would propably be a way better solution.
The current draw of the boost converter is around 80mA.
I built some small flyback boost converters with a transformer for similar projects that only drew around 10mA and were way more stable and clean.

I guess if I ever find it to be a problem, I could still add a capacitor.

I might built a quick test later with a custom transformer, as I just got a whole bunch of e-cores from aliexpress.

Sounds interesting, feel free to report back, how it went. :)


Greetings,
Michael
Title: Re: Yet another homemade geiger counter with a sovjet tube
Post by: TMaxElectronics on May 02, 2021, 03:39:45 PM
Quote
The tube is coupled to the 400V supply by a 10meg ohm resistor.
Ah ok I thought it was just hooked to the 100n capacitor directly somehow and it would get discharged completely every time :-[

Quote
The current draw of the boost converter is around 80mA.
yeah I've had the same issues with the booster for my nixie clocks, and that only goes to 180V. Still need to put a flyback into those too :P

Quote
these prototyping boards are something I drew in KICAD and got made by myself.
Do you still have the files around? I might order some of those too :D
Title: Re: Yet another homemade geiger counter with a sovjet tube
Post by: Da_Stier on May 02, 2021, 03:46:12 PM
Quote
The tube is coupled to the 400V supply by a 10meg ohm resistor.
Ah ok I thought it was just hooked to the 100n capacitor directly somehow and it would get discharged completely every time :-[

Maybe I should have addes this info in the first place. 

Quote
The current draw of the boost converter is around 80mA.
yeah I've had the same issues with the booster for my nixie clocks, and that only goes to 180V. Still need to put a flyback into those too :P

I might give this a try as well at some point, but winding transformers is just so much work.  ;)

Quote
these prototyping boards are something I drew in KICAD and got made by myself.
Do you still have the files around? I might order some of those too :D

Sure, here you go, feel free to get some, but please don't sell them.

 [ Invalid Attachment ]


Greetings,
Michael
SimplePortal 2.3.6 © 2008-2014, SimplePortal