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Electronic thermometer project needed.

8bit

Oct 30, 2013
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I am after building a electronic thermometer but have had no luck trying to find one. Ideally I would like it to be able to read the temperate outside so perhaps some basic sealed protective housing will be needed.Has anyone any plans I can use?
 

AnalogKid

Jun 10, 2015
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The single most difficult thing about building your own electronic thermometer is calibrating it. There are many electronic outdoor thermometers on ebay for very low cost. Is there a particular reason why you want to build one, or is it just a home project for fun?

ak
 

Bluejets

Oct 5, 2014
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Calibrate at sea level with ice fresh water or boiling fresh water.
 

AnalogKid

Jun 10, 2015
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That assumes that the pivot point for gain calibration is at 0degC. Many (most?) solid state sensors asimtote to 0 V at 0degK.

ak
 

8bit

Oct 30, 2013
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I had no idea it would be quite completed. It was on;ly out of interest and not an essential tool. I think perhaps I'll just buy a cheap one and use that. :)
 

AnalogKid

Jun 10, 2015
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I've done temperature sensing using many different technologies, and all of them have - issues. Overall I like precision thermistors the best because their performance is very accurate, repeatable, and interchangeable. That is, I can plug in a new sensor and not have to recalibrate anything. The bad news is that they are weirdly non-linear, so to get a digital readout it takes a small microcontroller like a PIC with a lookup table in firmware. Not hard, but not a beginner-level project.

Solid state temp sensors can be very linear, but both the absolute accuracy and gain function vary from part to part more than a few degrees. So as long as you don't care of 70 really means 65 to 75, they're fine. Adding a gain and offset trim circuit reduces this error greatly, but to calibrate it you need two known temperature baths pretty far apart, as in post #3 above.

ak
 
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