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Topic: NTC Thermistor readings varying... (Read 2 times) previous topic - next topic


Afternoon, I'm having some issues with my NTC thermistor and would appreciate some extra input.

I have calibrated the thermistor, and it should switch on and off a heat source according to the temperature.

After some tweaking, I was able to get the environment to stabilize at around 29 degrees on both the thermistor reading and the manual mercury-like thermometer.

It was fine a few days ago. Now I have returned to it, switched the circuit on again, and after leaving to stabilize I discover the manual thermometer is reading 25 degrees, but the thermistor still reading 29!?

This has happened a few times now. I'm certain there is no differing power drain caused by other entities in the circuit.

Any ideas?




Servo is not currently connected, latching relay triggers the 12v heat circuit.


Any difference in power source from prior run to present run?



Feb 22, 2011, 04:31 pm Last Edit: Feb 22, 2011, 04:34 pm by Savers Reason: 1
Thats the trail of thought I originally had, but I'm using the USB on my laptop. Then I remembered the arduino has a 5v regulator built in so it couldn't really be the power source anyway unless using AC opposed to DC. I have also tried a 5v DC USB wall plug, to which it is still not reading correctly.

Connecting the thermistor to a spare output pin instead of the power rail on the breadboard would give the full 5v regardless would it not?

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