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May 14, 2012 AT 11:09 am

From the Adafruit Forums: Fun With Thermistors

Adafruit forums user EasternStarGeek posted some great new code for our 10K Precision Epoxy Thermistor.

My approach differs slightly in that I use a lookup table instead of the logarithmic formula given in the Adafruit tutorial. I didnt make any measurements, but it could very well run faster, since it doesn’t depend on a lot of complex floating-point math. In any case, Lookup tables are useful sometimes, and my example not only shows how to do a lookup, but also how to interpolate between the two closest entries to the measured value.

You will also find a helper spreadsheet that was used to create the LUT used in the sketch, along with some interesting charts that show graphically, the relationship between temperature and thermistor resistance, as well as temperature versus ADC voltage.

Check out the rest of his post in the forums, and get the updated library here.

Need to measure something damp? This epoxy-coated precision 1% 10K thermistor is an inexpensive way to measure temperature in weather or liquids. The resistance in 25 °C is 10K (+- 1%). The resistance goes down as it gets warmer and goes up as it gets cooler. For specific temperature-to-resistance, check the lookup table.

These are often used for air conditioners, water lines, and other places where they can get damp. The PVC coating of the wires is good up to 105 °C so this isn’t good for very hot stuff.

We even toss in an additional 1% 10K resistor which you can use as calibration or for a resistor divider.

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  1. There seems to be a disconnect between the forum post and the blog post and the blog title. On the one hand there’s talk about thermistors, on the other hand there’s the DS18B20 which is not a thermistor in any way.

    I think the product the forum post is referring to is the waterproof 10k thermistor.

  2. Thanks for catching that Stephanie! Fixed.

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