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Greetings:
PICO Board question.
I need to monitor temperature at 90-100 degrees centigrade and then take
a light level every few minutes.
Can anyone tell me which thermister probe to use on connect-A?
If I need to measure light in the sub lux (0.1 lux) range for fluorescent light emission what photoresister would anyone suggest?
THANKS
Richard
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I think paddle2see has played with thermistors, so you may want to drop him a note. I suspect that almost any standard thermistor will work: it's just a matter of how accurate you want it to be and how much range and resolution you want. Remember that the resistive inputs are not linear (I think the FAQ in this section discusses the relationship), so you would want to calibrate it at at least 90 degrees and 100 degrees and see how it works.
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I just found my note re the non-linearity of the resistance inputs. Here's what I found:
From experiments on our board, the resistance sensor value (0-100) that the PicoBoard produces is related to the actual resistance, R, (in KOhms) across the alligator clips by the something like the following equation:
sensor value = a*ln(b*R+1) where, approximately:
a=19.5
b=0.9
BUT, if you are only interested in low resistance values between 0-10 KOhm, the following simple relation works real well (and yep, it's linear):
sensor value = a*x, where a is approximately 5.57
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Thanks!
I'm working on a real time PCR thermocyler for a low cost "field" molecular research platform and need to monitor the temperature so I can get a light reading from a fluorescent signal (0.1 lux range) from a photoresistor. It needs to be at the same temperature point on each ramp cycle. Oh, yeh mostly doing a not too obvious star trek ripoff control panel background. No sense not having some fun.
Cheers.
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Sounds cool. I like the Star Trek angle. Make sure you post some links to pictures/results when you get it all up and running. You may also want to consider interfacing to a small Arduino board, since they are actually cheaper than the Picoboard and can be used in many more ways (though they are much more difficult to work with, of course, since you have to use the external sensors capabilities of Scratch for data acquisition).
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Would you be able to tell me what the "x" stands for in the simplified equation?
Thanks
chalkmarrow wrote:
I just found my note re the non-linearity of the resistance inputs. Here's what I found:
From experiments on our board, the resistance sensor value (0-100) that the PicoBoard produces is related to the actual resistance, R, (in KOhms) across the alligator clips by the something like the following equation:
sensor value = a*ln(b*R+1) where, approximately:
a=19.5
b=0.9
BUT, if you are only interested in low resistance values between 0-10 KOhm, the following simple relation works real well (and yep, it's linear):
sensor value = a*x, where a is approximately 5.57
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sorry. that should have been an 'R'. I'll have to change that...
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