radiation meter November 2011

Equipment, circuits, projects, procedures

Postby thijsbeckers » Mon Feb 13, 2012 12:00 am

Hi JJL,
The problem is the voltages. If your serial port uses TTL levels, it will be no problem. Otherwise (which is more likely) the voltages of the COM port are too high and will damage the microcontroller. If you want to use a 'standard' COM port, you should use a max232 (or similar) to protect the circuit from too high voltages. See also here and here. The latter also has a pinout for DB9-COM ports.'
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Postby alefbe » Sat Mar 10, 2012 12:00 am

Hi everybody,

I successfully built the radiation meter and managed to reasonably shield the sensor diode. My only problem left is the following: when I connect it to my PC through the BOB and run the PC software I am able to see on the screen the radiation spectrum slowly forming. What I was not able to do is change the L threshold level: no matter which value I choose and button I push (level or eeprom)
L always stays at 10.
Any suggestion?
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Postby micro_pepe » Mon Mar 12, 2012 12:00 am

I have the COM port set to 19200 baud, but I can not see anything on the chart, and I can not set the level. I noticed that in the lower left display, the second moving very slowly. Right? or, can it be that the error?

Thanks for your attention.
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Postby micro_pepe » Tue Mar 13, 2012 12:00 am

micro_pepeI have the COM port set to 19200 baud, but I can not see anything on the chart, and I can not set the level. I noticed that in the lower left display, the second moving very slowly. Right? or, can it be that the error?

Thanks for your attention.


Well, that was a problem with micro fuses.

Now I have the problem that is very sensitive, with a level of 100 is still very sensitive. How can you raise the level?

Thanks again.
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Postby micro_pepe » Thu Mar 22, 2012 12:00 am

Also, in steps:
- On the oscilloscope observe a noisy signal about 800mVpp.
- For the resistors, I have found that in the scheme and the list of materials, R5 and R7 are 10Khom in editing the journal in English, but Spanish version, R5 = 3K3 and R7 = 1K Could be such an error?
- On the other hand, my transistor is a BF245C, Should be a BF245B or A?
- Another issue is that when setting the level to 100 with the software, turning on the meter again, mark "L154"

Thanks for your attention. Greetings: Juanjo.
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Postby thijsbeckers » Thu Mar 22, 2012 12:00 am

micro_pepe...Now I have the problem that is very sensitive, with a level of 100 is still very sensitive. How can you raise the level?


In our software that is not possible. I would suggest you use a scope and check the output (K4). Does the signal look like noise or is it clipped? Clipping could be the result of a bad solder point or wrong resistor somewhere around the opamp.
What the threshold level does, is dampen signals below the set threshold, but if the amplification of your sensor board is too large, the noise will be rising over the threshold and trigger the counter. You really should end up with a threshold level between 10 and 50 or so. Or are you testing in a VERY radioactive environment?
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Postby thijsbeckers » Thu Mar 22, 2012 12:00 am

alefbe... What I was not able to do is change the L threshold level: no matter which value I choose and button I push (level or eeprom). L always stays at 10.

Hi Alefbe,

Did you order a kit or did you program the controller yourself? If the latter, could it be a fuse setting?
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Postby thijsbeckers » Fri Mar 23, 2012 12:00 am

800 mVpp seems too much to me. My prototype only shows about 50 mVpp noise.
R5 and R7 should both be 10k. There were some last minute corrections in the schematic, that perhaps couldn't be entered anymore/magazine was already at the printer.
You should use a BF245B. As written in the article, the operating point is shifted when you use an A or C version.
I didn't notice the strange L154 indication yet, but I also didn't set the threshold to 100. I guess this will be ok when you have your hardware running properly.

Good luck and let us know if it works out!
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Postby alefbe » Fri Mar 23, 2012 12:00 am

I ordered a full kit, I do not know how to program the ATmega88 on the board.
I do have some experience with programming the Arduino UNO board but I think that is a totally different environment.

By the way, just for fun, I connected the "probe" circuit to Arduino
and then adapted your program for Arduino and it works great and was also able to use the VB program as is to collect data on the PC.
However I still would like to use the original board with its nice display.
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Postby Elektor Editor » Sun Mar 25, 2012 12:00 am

Kit of parts # 110538-71 should include a ready-programmed controller, so there is no need for programming.

Please send me details of your Arduino alternative, this might be worth publishing. I can be reached at the editorial email address
editor [at] elektor.com

Jan
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