wvmarle:
Create a voltage divider with a resistor that's roughly the value of this sensor at the average temperature you will use it, then you can read the mid point on an analog pin, calculate the resistance of the PTC, and using the table calculate the temperature (I'd just do a linear interpolation between values, will be good enough).
Thank you wvmarle.
I will try here to explain how to proceed:
I assume Vin (+5V) is applied to one end of the PTC thermistor, while the other end of it is connected both to Analog Pin and to ground with a R2 resistence.
I have appled this formula to link the PTC Thermistor Resitance (R1) changes to Tension changes:
Vout=R2*Vin/(R2+R1).
I know I can calculate Vin more accurately using the "Secret voltmeter", but here I assume Vin=5V
I then can linear interpolate the Vout values, calculated with the relarive R1 in the range of interest (-10..+30), with temeprature T.
With R2=1kOhm, I got the following: Vout=0,00547*T+2,4991.
This gives an Standard Deviations of 0,17335 of calcualted T vs. Ni1000 datasheet, that is an error of +/-0.2°C in the range -15..25°C
My doubts are:
- is this approach correct?
- Is R2=1kOhm adequate, with R1 in the range of 1kOhm?
- Is Arduino accurate enaugh to measure Vout variations in the range of 4-5mV?
Thnaks for you great support.
Regards
Andrea