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A thermistor is a type of resistor whose resistance changes significantly with temperature. There are two main types: NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient). NTC thermistors are more common in temperature sensing. Their resistance decreases as temperature increases. This characteristic is exploited in temperature measurement. In a microcontroller-based system, a thermistor is typically connected in a voltage divider circuit. The microcontroller measures the voltage across the thermistor and, using a known resistance value (typically a fixed resistor in the circuit), calculates the temperature using the Steinhart-Hart equation or a simplified approximation.

Advantages of thermistors:

• High sensitivity: Significant resistance change per degree Celsius.
• Relatively inexpensive.
• Small size.

Disadvantages of thermistors:

• Non-linear response: Requires calibration or approximation formulas.
• Limited temperature range compared to thermocouples.
• Can be affected by self-heating due to current flow.

Comparison with thermocouples: Thermocouples generate a voltage proportional to the temperature difference between two dissimilar metals. They offer a wider temperature range than thermistors and are less susceptible to self-heating. However, they require more complex signal conditioning (amplification and cold junction compensation) and are generally less sensitive.