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radiation meter November 2011

Equipment, circuits, projects, procedures

Postby bee boyes » Wed Sep 12, 2012 12:00 am

We have found several issues with the Radiation Detector kit. The LCD shipped with our kit (TC1602C) is not the same as on the BOM. And they are not identical esp in backlight current ratings. The schematic of the LCD shows the pins in incorrect physical locations. Worse, the PC board has the LCD backlight power backwards. Pin 16 should be L- or gnd and pin 15 should be the L+. We did not discover this until the LCD was soldered to the board (there's no good way to test it without doing that, and now it is harder to correct this. I can post a sketch and photo but no one else seems to have reported this - did we get the wrong LCD in our kit?

Spacers should have been provided to hold the LCD off the PCB. We used .25 tall 4-40 clearance spacers. BUT the holes on the LCD and the PCB are different sizes! The LCD holes are too small to clear 4-40; the PCB are fine for 4-40 clearance. We drilled the LCD holes out to 4-40 clearance.

Given the popularity of Arduino I wonder why the processor was not programmed with that. We have ordered an ATmega 328P to swap in and plan to write the code in Arduino. Then the PC SW could be written in Processing, both free tools.

It's a great idea for a project, and the concept of using a diode as a radiation detector is great.

Using something like Teensy or the MSP430 and a small OLED display it should be possible to make something the size of two AA or AAA batteries in a holder. This would be great for taking into the desert hiking (there are a lot of old uranium mines and tailing piles in Utah!).

We plan to deploy something like this in a well bore to sense gamma radiation. Commercial systems seem to use a PMT http://site.ge-energy.com/prod_serv/products/oc/en/oilfield_technology/drilling_measurements/gamma_module.htm which are on the order of $1500 (Hamamatsu) and up. So if we can use a solid state detector that would be awesome.
bee boyes
 
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Postby thijsbeckers » Thu Sep 13, 2012 12:00 am

thijsbeckersI regret I have to admit you're wright. I checked a kit from the latest batch and it seems the anode and cathode are switched.

Hi Bee (and everybody else),

I checked the latest batch of our kits, and the first thing that pops out of the box is the description how to make sure your backlight connections are correct!

So the kit is in fact correct. You should switch the solder blobs on the backside of the LCD, as described in the note.

Best regards,
Thijs
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Postby bee boyes » Fri Sep 14, 2012 12:00 am

There was no such paper in our box. Is this update online somewhere? In any case we don't have access to the back side of the LCD so we will do another fix and post it here.
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Postby ben22 » Sun Sep 16, 2012 12:00 am

I haven't taken many pictures, here are some of the SM board.
The PCB is about5cmx5cm. It was initially for another project, and I reused (this is the prototype version) this one to make a sort of handheld radiation sensor. how i hooked it to arduino :
I used a 9-12V alimentation (like a 9V battery).
I soldered one end to the sensor and the other I plugged to the input of the arduino (arduino has a 9-12V regulator-5).
and tadah =)

I machined the cover by myself, it doesn't change much between this and 2-3 layers of aluminium foil. it's better to cover your whole circuit with foil and leave the diode and just cover it with black tape.

I made a little hole on the cover to let the diode out so it can detect beta/gamma. since beta can be stopped by metal.
Attachments
photo--13-.JPG
photo--10-.JPG
photo--11-.JPG
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Postby thijsbeckers » Wed Sep 26, 2012 12:00 am

Very nice, Ben! Looks like a very sturdy case .
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Postby thijsbeckers » Wed Sep 26, 2012 12:00 am

bee boyesThere was no such paper in our box. Is this update online somewhere? In any case we don't have access to the back side of the LCD so we will do another fix and post it here.

I apologize for my delayed answer (been to a convention; upon return work had piled up to the roof).

That must have been a mistake. Every kit with this LCD should have this note. It's not available on line, so I attached it to this post.

It is very difficult to reach if you've already mounted the LCD... I hope it works out for you.

Best regards,
Thijs
Attachments
120061-LCD-backlight-configuration.pdf
(1000.38 KiB) Downloaded 66 times
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Postby thomastheo » Sun Nov 18, 2012 12:00 am

Hello! I'm a previous lurker of the forum, but thought i'd chime in and add my two cents. I've been trying to get a reliable version of this circuit working for a while now, with cutting down on the microphonics/sensitivity to EM interference as a major requirement for my application, and I have found out that *smaller* is better. Therefore I simply glued the BPW34 on top of the JFET and fitted all the related circuitry onto it (by using 0805 parts). It's a bit fiddly, but it works a treat. The gain of the opamp stage is not that high, so it doesnt need as much shielding, so you can get away with shielding only this tiny 5mm^3 gizmo, and it works! Thanks all,

Th.
Attachments
pindetectorsmall.jpg
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Postby thijsbeckers » Mon Nov 19, 2012 12:00 am

Thank you Theo. That is a nice addition. The shorter the connection from the diode to the JFET, the better.
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Postby ab64 » Wed Feb 13, 2013 12:00 am

Hi. I've made some test and even made my own SMD version only for the detector (photodiode, jfet, resistors and capacitor) connected to the amp through a masshed cable. The problem is the microphonics nosie when i hit the amp board. I've through make amp. board in SMD to solve that problem but is it a solution or just a lost of time??? What do think??? some rcomendation??
Thanks and sorry for my english..
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Postby thijsbeckers » Thu Feb 14, 2013 12:00 am

Hi ab64,

I'm afraid microphonics will still be a problem, even if you use all SMD. I could be wrong, but I think the origin lays within the sensor. The separate layers of silicon act like a condenser mic, I think that's the most simplified explanation.

You could build some sort of enclosure like Ben22's and suspend the whole amplifier PCB on rubbers or something. If the enclosure is somewhat soundproof, I think that will be enough to stop most of the interferences.

No need to apologize. As long as we can understand what you're saying it's fine. At least you try!
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