PT100 Based Temperature Measurement Thermometer Using Arduino Uno. PT100 Temperature Sensor on Ice and Flame. PT100 on Wheatstone Bridge.

In this Instructable I'm going to make a thermometer using Arduino Uno. I'm using PT100 temperature sensor to read the temperature. The PT 100 is wired in Wheatstone bridge. The output of the Wheatstone bridge is amplified using OPAMP LM324. The OPAMP output is further fed to Arduino Uno. Arduino Uno scales the analog data and displays on LCD display.

Bill of materials

1. IC OPAMP LM324 1pc
2. 1K 1/4 W 2 pc
3. 10K 1/4W 2 pc
4. 100 ohm 1 Watt 1 pc
5. 100 ohm 1/4 watt 3 pc
6. PT100 RTD 1 pc
7. IC 7805 1 pc
8. Arduino Uno 1 pc
9. I2C LCD 1 pc
10. Wires and cables
11. Bread board
12. Arduino Uno programming USB cable

In this Instructable I'm going to explain how to make a thermometer using Arduino Uno. I'm using PT100 temperature sensor to read the temperature. PT100 temperature sensor reads 100 ohm at 0 Deg C. As temperature increases the value of PT 100 also increases.

The PT 100 is wired in a Wheatstone bridge. As we know Wheatstone bridge has four arms. In this case we are using three arms 100 ohms. The fourth arm is the PT100. When we heat the PT100 the bridge becomes unbalanced and gives output in millivolts.

The output of the Wheatstone bridge is amplified using OPAMP LM324.The OPAMP is wired in differential amplifier mode. The voltage difference of the arms of the Wheatstone bridge is fed to the difference amplifier. The differential amplifier has a gain of 10. The feedback resistor is 10K and input resistor is 1K. So gain is 10K / 1 K = 10. The Wheatstone bridge output will be amplified 10 times. Finally this is fed to the unity gain buffer. The unity gain buffer matches impedance of Arduino and OPAMP amplifier.

The OPAMP output is further fed to Arduino Uno. Arduino Uno scales the analog data and displays on LCD display. Arduino uses map() function to display data on LCD.