radiation meter November 2011

[micro_pepe]

Hello,

Is it possible to feed the meter amplifier with 5V?

Thanks for everything.

[Elektor Editor]

Sadly that's not possible. The meter amplifier was designed to operate at about 9 volts.

Jan

[micro_pepe]

Hi all,

Will the control pcb, is necessary to have double ground plane?

Thanks for your attention.

[moonlight]

I am having problems with getting my radiation meter working. For a start the display does not look like all those I have seen in the magazine and update. It reads L 10 not Counter!(see attachment). Also cannot get any counts with the sensor in circuit. Have tried swapping sensors as well but to no avail.

[evfarm]

Same here as moonlight says.
Top left is just "L 10" rather than "Counter".

Only differnce in my case is that the number in top right is continually counting up. Could this be because I haven't wrapped the whole thing in foil yet? I have black tape over the sensor (otherwise carefully fitted as describe in January issue) but does it really all need wrapping in foil too?

Oh, and both pins of my BPW had tabs so I took the K pin to be the substrate pin (the one without the gold wire internally) as pictures in photo 4 in the January issue).

I think I will download the firmware sounrce and take a look top see if that offers any enlightenment.

[evfarm]

I downloaded the firmware source from the web site. Thanks.
It does indeed display a L there followed by a number it reads from eeprom or defaults to 10. This appears to be the trigger threshold described in the article.

The firmware will not compile successfully as provided.
I tried BASCOM 1.11.9.8
I also upgraded to BASCOM 2.0.7.3
Same results. It does not like the use of "Max" as a variable name.
I suppose I can just renname that.

I a tried tinfoil wrapper but got same result - it just counts upwards. So now I need to figure out why this is triggering all the time. Out with the scope next I think.

[evfarm]

Hmmm....

OK, at top of R4 I have 2.3V. That looks OK.
But at output of amplifier board I have a nice 50Hz square wave.
Even if wrapped in Al foil.

Maybe my bench PSU cables and/or a ground loop? Tomorrow I shall try running from a 9V battery and will double check the foil.

[thijsbeckers]

Hi Guys,

I was enjoying my days off last week, so I apologize for not being able to reply earlier. But here goes...

@ Moonlight:
L10... This is correct. As EvFarm already deducted, this is the threshold level that defaults to level 10. It was thought to be more convenient than the 'Counter' text (after pics were taken&article was sent to printer). So this is what's in the display (from left to right):
1st line: Threshold level; Counted # pulses that exceeded the threshold.
2nd line: measurement time; average pulses per minute.

The sensorboard is VERY, I repeat - VERY, sensitive. So ANY light that hits the sensor will clip the output of the board and prevent the uC from counting - or it will count like crazy... So be sure to protect the sensor from any light. Best is to use can of some sort (see attached pictures). And don't forget to connect your shielding to the GND of the sensorboard!

@EvFarm

Only difference in my case is that the number in top right is continually counting up.

It works!!!

Could this be because I haven't wrapped the whole thing in foil yet? I have black tape over the sensor (otherwise carefully fitted as describe in January issue) but does it really all need wrapping in foil too?

Yes and yes. Like I said, the sensorboard is VERY sensitive (and needs to be).
Unfortunately, the sensor eventually ending up in the kit was slightly different from the one I used in the prototype (different supplier, and again, pics were already taken and article just left for printing ). You guessed it: it has tabs on both pins... But look closely, and you will find one lead with two tabs and one lead with only one tab. The one with the ONE tab is the cathode, see also the attached close up - which shows the ANODE, by the way!
Let me investigate the matter with the compilation issues. The .hex file should be ok. Fuses should be set as in the attached screen dump, see below. I will update the download with the fuse settings.

But at output of amplifier board I have a nice 50Hz square wave.

I got that when I didnt ground my shielding. Did you connect the foil firmly to GND of the PCB?

Let us know when it works! What radiation source are you planning to use?'

[moonlight]

Hi thijsbeckers

Hope your Xmas & New Year was great. Thanks for the follow up. I have tried to shield my BPW but not properly as described in the project notes and update as I expected over sensitivity would be the problem, not no counts at all. I'll give it a go and do it properly! I plan to use some pressure lamp mantles as a source which work well with another type of radiation detector I have.

I too was confused by the orientation of the BPW and have since sourced a replacement which has only one tab on the cathode instead of the two supplied in the kit.

I'll post an update soon on my progress.

Thanks....

[thijsbeckers]

Hi Moonlight,

Are you sure those mantles are radioactive? I ask, because I have some old ones that are and some new ones that aren't! I should read better, you tested them already with another radiation detector...

Ok, you should be able to detect some radiation with those mantles, but with a BPW34 you'll probably only detect beta particles. If you are in the possession of an oscilloscope, you can display the output of the sensor amplifier on it (connect to the header marked 'out' on the main PCB) and watch each radiation particle hit the silicon. Switch your scope to persistence mode and watch the peaks rising above the noise floor. This also helps with determining the correct threshold setting.

BTW, we are planning a webinar on this project somewhere in February...