radiation meter November 2011

Equipment, circuits, projects, procedures

Postby evfarm » Fri Jan 13, 2012 12:00 am

Hi thijsbeckers

Now I have it running off a 9v battery rather than my bench PSU it seems to have settled down.

Anyone trying this please note... battery PSU is a good idea and as above, the grounded foil (or tin can) wrapper are essential.

I have to say it does not seem very sensitive. I have a small jar of thorianite next to the sensor and I have seen just a few counts. So that I get an average level of between 0.8 and 1.3
This same thorianite sample causes many clicks per second on my GM counter.
evfarm
 
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Postby al.harding » Wed Jan 18, 2012 12:00 am

Do you think the radiation meter is capable of detecting the presence of radon gas. My home has been tested a few years ago and found to be within safe limits but it would be good to know if the concentration of radon varies significantly from room to room?
thanks Alan
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Postby jjl » Tue Jan 24, 2012 12:00 am

Hello,

I'm trying to test the 'Improved Radiation Detector' (PCB purchased from Elektor) but I can't figure out how to make the connection to PC from the K7 Jumper.

If I look in the article at the circuit diagram (p21) pin 2 of the ATMEGA88 (RXD) is drawn connecting to the middle pin of the K7 jumper labelled TXD. If I check this on the PCB, the track from pin 2 on the chip is clearly connected to the top pin of the K7. (A simple test with a scope shows that pin3 on the chip is talking)

I'm unsure if this is a mistake in the circuit diagram, so I test all the pins, but then I'm unsure of the pin connections on the PC serial port.
I have the associated software running on a PC. I test all the pins with a scope and find that pin3 on my com port has signal when pressing either the 'level' or the 'eprom' button on the software.

However, the only way I have found to change the threshold (the Lxx on the display) is to connect pin 3 to the TXD pin which doesn't make sense. A pin-pin diagram for the program or instructions on how to connect it to the K7 terminal would be very helpful!! (no need to use the BoB FT232 board as I have a serial port already)

Thanks,
jjl
 
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Postby ronwer » Fri Jan 27, 2012 12:00 am

I want to build the meter in SMD...any advice regarding the components?

What about the capacitors, are good quality ceramic C's usable for the 100nF's?

Is there an alternative for the BF245? (I only have the MMBFJ310 in stock at this time.)
ronwer
 
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Postby moonlight » Fri Jan 27, 2012 12:00 am

Hi thijsbeckers

I am at wits end with this project. Have mounted the PCB in a can and connected an earth lead to the board but all I get are continuous counts. Tried various BPW34s in circuit. All behave the same way.

BTW I would attend your Web seminar but it's scheduled at 2AM Australian time. Any chance future seminars can be run earlier so us downunders get to participate.

Thanks
moonlight
 
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Postby jjl » Mon Jan 30, 2012 12:00 am

Have you tried setting the threshold level to different points?
The threshold works as a comparator, counting only values above the threshold value. This is helpful to get above the noise background.
You set this via the K7 jumper with the associated computer program (a manual for the computer program or a explanation of how the K7 pins connect to a serial port would be very helpful for making this connection, I'm having trouble with this point)
jjl
 
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Postby jakket » Thu Feb 02, 2012 12:00 am

Hello,

I did some testing with another Photodiode SLCD-61N1 (not PIN) from Silonex I found @ Farnell for next to nothing. It is a 5x2,5 mm. bare chip that is passivated and can be soldered, but don't try this after a heavy night in the pub )
The thing is... it works extremely well for Alfa emitters, an Americum241 from a fire detector @ 2cm from the diode gives around 2800+ tics per minute. I did change the gate resistance to ground to 10Mohm i.o. 20.
Attachments
Alfa1.jpg
jakket
 
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Postby evfarm » Tue Feb 07, 2012 12:00 am

> SLCD-61N1

Thanks for the tip-off Jakket. They look interesting (and very cheap, especially for the remaining stock of non-rohs parts).

I have ordered a few of those, plus some of the larger-area parts (SLCD-61n...) to experiment with.
evfarm
 
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Postby thijsbeckers » Tue Feb 07, 2012 12:00 am

First let me sincerely apologize for my absence in this thread. I was in the presumption I activated the e-mail monitor for this thread, but due to several spam filters on my mailbox I didn’t receive any of the mails. Since it’s rather busy in the office, I haven’t had the time to surf around in the forum.
So here goes:

@EvFarm:
Good to see it’s working. The ‘sensor’ indeed isn’t very sensitive; you need a sufficiently energetic radioactive sample for the pulses to rise above the noise level. That’s a bit of a downside of the BPW34. Perhaps other semiconductors are more sensitive? I see Jakket has some good results with an SLCD-61N1.

@al.harding:
As you can read in the Wiki-article on Radon it’s alfa decay-energy is quite high, I think it should be measurable with a 2N3055 as sensor. But please keep in mind even a couple of cm’s (or inches) of air are enough to stop alfa radiation. Also, you should completely darken your room, since any light will generate a false trigger.
As for the beta-component of the Rn-224 isotope (0.8 MeV), I don’t know if this is measurable with the BPW34-sensor; we didn’t test (we don’t have the necessary equipment for this...).
Perhaps the multiple-sensor setup on http://www.b-kainka.de/bastel131.html (a little past the first half the page) is something for you.

@JJL:
Good of you to notice. After carefully checking with the designer of the BOB we discovered an error in the schematic (not on the PCB!): in fig 1 RXD and TXD on connector K7 should be physically exchanged. So, the connections are correct, but the layout of K7 is misleading. A picture is worth a thousand words... (see attached image)


@ronwer:
No special components were used, so you’re free to substitute. Ceramics are ok for decoupling, I see no problems there. As for the FET: I’m not saying it doesn’t work with an MMBFJ310, but a BFR30, BFR31 or an MMBF4416 is the recommended SMT replacement.

@Moonlight:
What happens if you leave the sensor out? So no sensor connected at all... I’m beginning to think that perhaps you have a very good BF245 (with a high amplification factor). Have you tried raising the detection threshold level, as JJL suggested?
2AM in the morning? O dear… It’s scheduled at 4 PM here in The Netherlands. The webinar will be available afterwards on the element14 website, so you can watch it at a more convenient time. You don’t have the possibility to participate in the Q&A afterwards then, but you can send me an e-mail if you have questions after viewing the webinar.
Attachments
110538-Connection-to-BOB.jpg
thijsbeckers
 
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Postby jjl » Mon Feb 13, 2012 12:00 am

Thanks thijsbeckers, that helps alot.

Can I ask how to connect the board to a PC without using the BoB addition.
Does the K7 jumper just connect to pins 1,2,3 of a (9pin) serial port? Something like:
pin1 - gnd?
pin2 - RX?
pin3 - TX?

Thanks
jjl
 
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