how to connect linear thermistor to the mcu

I would like to connect linear temp. probe to one of the 8 bit A/D convertor of my PIC mcu.
Below is the schematics I found on the internet.
**broken link removed**
Equation for the voltage divider Vout=Vin*R2/R1+R2.

So if I take te specifications for common 100pt linear thermistor:
1kohm at 0°C
0.385ohm/K
max voltage 9V
max current 2mA (1mA suggested)

I need 4kohm R2 to limit the current to 1mA. So if I put those data to the upper equation I get Vout at 0°C to be 1V and at 100°C also rounnd 1V.

If I change R1 and R2 (thermistor up) I get Vout at 0°C to be 4V and at 100°C also round 4V.

So how can I get that output voltage will be between 0 and 5V?

Add an OpAMP or use the AVREF pin on the microcontroller.

merk said:

I would like to connect linear temp. probe to one of the 8 bit A/D convertor of my PIC mcu.
Below is the schematics I found on the internet.
**broken link removed**
Equation for the voltage divider Vout=Vin*R2/R1+R2.

So if I take te specifications for common 100pt linear thermistor:
1kohm at 0°C
0.385ohm/K
max voltage 9V
max current 2mA (1mA suggested)

I need 4kohm R2 to limit the current to 1mA. So if I put those data to the upper equation I get Vout at 0°C to be 1V and at 100°C also rounnd 1V.

If I change R1 and R2 (thermistor up) I get Vout at 0°C to be 4V and at 100°C also round 4V.

So how can I get that output voltage will be between 0 and 5V?

Click to expand...

that circuit is not for a platinum ("linear") sensor.

That Platinum (not thermistor) sensor only changes by 38.5 ohms between 0C and 100C, thus the divider output voltage obviously changes very little. If you want 0V to 5V output over that range, then you will need to use an op amp to offset and amplify the signal.

But why are you listing a platinum sensor when the circuit diagram shows a thermistor? Platinum sensors are generally only used if you need very high accuracy and/or linearity, since they tend to be expensive and have a very small change with temperature. Otherwise there are many other types of temp sensors, including dedicated ICs, that give a much larger voltage or resistance change with temperature, and are thus easier to interface to a micro.