Thermistors / Temperature Sensors

1. Definition

A Thermistor is a special type of resistor whose resistance changes with temperature.

  • NTC (Negative Temperature Coefficient): Resistance decreases when temperature increases.
  • PTC (Positive Temperature Coefficient): Resistance increases when temperature increases.

They are widely used in temperature sensing for fans, air conditioners, 3D printers, digital thermometers, and battery packs.

thermistor example

Thermistor Symbol

thermistor symbol

2. Features

  • Temperature Sensitive: Resistance changes with heat or cold.
  • Non-Polarized: Can be connected in any direction.
  • High Accuracy: Especially in narrow temperature ranges.
  • Low Cost: Easy to use in DIY and commercial devices.

4. How to Use

4.1. Identify the Thermistor

  • Small bead, disc, or cylinder shape with two legs.
  • Often marked as NTC or PTC.
  • Sometimes covered in epoxy or glass for protection.

thermistor identify

4.2. Choose the Right Thermistor

  • Type: NTC for most temperature sensing; PTC for overcurrent or overheating protection.
  • Temperature Range: Match your application (e.g., –40°C to +125°C for general use).
  • Resistance Value at 25°C: Common values are 10kΩ, 100kΩ.
  • Tolerance: Accuracy of measurement (e.g., ±1%, ±5%).

4.3. Connect It Correctly

  • Thermistors are non-polarized, so either leg can go to positive or negative.
  • Usually used in a voltage divider with another resistor to create a voltage signal that changes with temperature.
  • Keep the sensor in good thermal contact with what you want to measure.

4.4. Test It

  • Use a multimeter in resistance mode:
    • Warm it gently with your fingers → resistance changes.
    • Cool it down (ice pack) → resistance changes in the opposite way.
  • If using with Arduino or similar, connect to an analog input and read the voltage change.

4.5. Mount Securely

  • On breadboard: Push the legs into the holes.
  • On PCB: Solder the legs firmly.
  • Keep away from direct sunlight or drafts unless that’s part of your measurement.

5. Video Explanation

video coming soon