Public Lab Research note


Getting Ready to Start Building.

by Kaya9804 | February 20, 2013 18:58 | 1,898 views | 4 comments | #6066 | 1,898 views | 4 comments | #6066 20 Feb 18:58

Read more: publiclab.org/n/6066


About to start building my thermal flashlight! Just picked up a 10k thermistor. Construction underway...


4 Comments

I'd be curious to know what the transfer function on the thermistor is.

Are there vendor specs? Even if there are, you'll probably want to calibrate the thermistor by putting it into fluids of known temperature (using a properly calibrated thermometer) and measure the resistance of the thermistor.

I ripped apart a bluetooth hands-free unit and found the microphone wires to be pretty adaptable to any 2-wire resistive device. My particular unit's microphone had a base of 1440 Ohms with a variability of +/- 200 Ohms when I blow on the microphone (white noise should stress the microphone to its limits). If I had an idea of the thermistor's resistance ranges, I might be able to figure out an easy way to integrate it into a hands-free unit for BlueTooth transmission of the analog signal. -Bryan

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That sounds real interesting! I had never thought to use the microphone as temperature input. Keep us updated on this!

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Unfortunately I don't have any thermistors or even potentiometers available for testing right now. I do have a heaping helping of resistors that I can twist and tie in series and parallel to effect whatever resistance I want to test, one test point at a time.

However, I will follow up with a research note of its own and post it in a comment here when I do. I have some wave data I recorded on my smart phone that I created by testing 3 different levels of resistance (based on the microphone's own resistance measurements). I wanted to see if I could read a fairly flat line if resistance did not change 48000 cycles per second or whatever my BT unit samples at.

As of right now, the methodology sounds cool, but for some reason my bluetooth hands-free unit has become very picky about whom it will send microphone data to. I must have zapped something useful somewhere on the circuit board. The unit now sends a flatline to my PC. It will send audio to my smartphone every other time I turn it on; happily, that is good enough for recording and testing.

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I couldn't get statistically significant differences in the measured amplitude levels using the resistor ranges I chose, which were based on measuring the microphone.

Unfortunately it looks like either the bluetooth hands-free unit is doing DC offset correction or the resistances I was testing with weren't significant enough. If I had an oscilloscope and potentiometer I could more definitively rule this out as a communications possibility (or figure out what went wrong).

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