Reading an NTC Thermistor via an Atmega32's adc pin

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I have looked at several tables for 10K NTC's and noticed that they don't have exactly same resistance for other temp than 25 deg. C

That isn't "inaccuracy"; that is because they are built with different characteristics. The bias resistors will "pull" the curves differently depending on the specific characteristics of that model. I.e., "10k thermistors" are not all alike, even from the same manufacturer.

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the resolution at lower temps using 10 bit ADC is lower than 1 degree

Again, a different choice of bias resistor can help to expand the area of interest. We have one app with an area of interst on the low-temperature end. When the [refrigerated] device is empty, we are concerned with overheating but the thermistor curve with our given bias cannot really "reach" above room temperature. I change the bias on-the-fly by turing on the internal pullup for that pin turning the 31k bias resistor into something much lower and giving me a good picture at the high-temperature end.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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oversampling is free....
Dig

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So is the pullup... ;)
Lee

[I typically "oversample" in my apps. Do continuous conversions on all the used channels, and grab the latest conversion result every (say) 10ms and close the loop every (say) 500ms with an accumulated total of 50 samples or so. I don't truly oversample as I then take the average. But the scheme sure seems to reduce/eliminate any "jitter" on the signals, and reduces the effects of noise.]

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Quote:
Quote:

I have looked at several tables for 10K NTC's and noticed that they don't have exactly same resistance for other temp than 25 deg. C

That isn't "inaccuracy"; that is because they are built with different characteristics. The bias resistors will "pull" the curves differently depending on the specific characteristics of that model. I.e., "10k thermistors" are not all alike, even from the same manufacturer.


I have never said or believed these differences to be because of inaccuracy. When I constructed my Flash-table I used the nominal values of a 10K NTC from different brand then mine. Since my body test then read out 37 degrees I was pretty assured that I wasn't wrong by much. Now I just would like to check if my table is as accurate at i.e. 20 and 80 degrees maybe by using something like DS18B??.

With the bias resistor chosen I have enough resolution over my 0-99 degrees range to display 0.25 or 0.5 degrees resolution but this is not interesting since my LCD couldn't display that many characters (I display four different temperatures on LCD.) So resolution is not a problem.

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Quote:
But the scheme sure seems to reduce/eliminate any "jitter" on the signals, and reduces the effects of noise.]

I use this averaging scheme too. It helps a lot to avoid avoid jitter.

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