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How to Wire a Thermistor

by Phil Lamass
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A thermistor is a resistor that is more sensitive to temperature changes than a standard resistor. By wiring a thermistor in series with a standard resistor you can measure changes in temperature. The two resistors form a voltage divider. As the resistance of the thermistor changes with temperature, the voltage at the point where the thermistor and resistor are connected also changes.

Step 1

Purchase a thermistor from an electronics supply store.

Step 2

Check the resistance versus temperature chart that accompanies the thermistor. It should list the resistance value of the thermistor at 25 degrees centigrade (about 77 degrees Fahrenheit). Purchase a resistor with the same value.

Step 3

Connect the positive terminal of the power supply to one end of the thermistor.

Step 4

Connect the other end of the thermistor to the resistor.

Step 5

Connect the resistor to the negative terminal of the power supply.

Step 6

Attach the negative probe of the voltmeter to the negative terminal of the power supply.

Step 7

Attach the positive probe of the voltmeter to the thermistor-resistor junction point.

Step 8

Set the hair dryer to low heat, turn it on and point it at the circuit for approximately 30 seconds. Note that voltage begins to rise as the thermistor detects the heat from the hair dryer.

Turn off the hair dryer and note that the voltage gradually decreases.

Warning

  • Ensure you use the hair dryer's lowest heat setting.

Items you will need

  • Thermistor
  • Resistor
  • Voltmeter
  • 5 volt power supply
  • Hair dryer

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