Hi,

I want to use NTC in my circuit to get the board temperature. I have selected one NTC (Part No: NTCS0603E3472FHT). But I am not confident about the conditioning circuit of NTC to interface with the 3.3V ADC pins of the microcontroller. I have made this circuit, but resistor values i have to calculate. .Can anyone help me how to calculate R1,by considering NTC resistance range.

 

calculate R1,by considering NTC resistance range.

Not enough info.
What is the temperature range you want to measure and the NTC resistance change for that range?
What voltage change for the micro input should this generate?

 

hi ashad,
With the NTC sensor in the lower end of that divider, the ADC voltage will fall with a temperature increase, is that what you want.?
Usually the NTC will be in the top of the divider to give a rising ADC voltage with arising temperature.
E

Added the NTC d/s

Is it this one:???

 

Hi ashad,
Look at this basic option.
E
The Vt X axis is the temperature

 

I would suggest connecting the top of R1 to the Microcontroller's Vcc and the junction of R1/R2 to the ADC. That way, any variations in the microcontroller's Vcc is cancelled out.
Choose the value of R1 to be the same as the resistance of the thermistor at the temperature you are most interested in.
Then use Excel to write yourself a look-up table.
(And forget the op-amp, external supplies, references, R3 and R4)
Even with an 8-bit ADC, averaging several readings will get you an output that is as good as the tolerance of the thermistor over quite a wide temperature range.

 

I would suggest connecting the top of R1 to the Microcontroller's Vcc and the junction of R1/R2 to the ADC.

Here's a simulation of that showing the output voltage and the thermistor resistance versus temperature using Erics's thermistor equation:
Note that the output voltage is fairly linear with temperature.

 

hi ashad,
For reference, showing the difference between the Steinhart-Hart equation and the model from Vishay for that thermistor.
The first image shows the simulation results for the two model source.
Second image, have overlaid the two plots on the right side plot for comparison.
I would say a reasonable match.
E