Build Your 15k-45k Temperature Alarm Circuit

Circuit diagram

Notes:

The utilized thermistor exhibits a resistance value of 15,000 ohms at 25 degrees Celsius and 45,000 ohms at 0 degrees Celsius. A comparable bead-type thermistor can be located within the Maplin catalogue. The 100k potentiometer facilitates operation across a broad spectrum of temperatures. Hysteresis is introduced into the system via the incorporation of the 270k resistor, thereby minimizing relay oscillation when the temperature approaches the circuit’s switching point.

Thermistor Description

Thermistors, or thermal resistors, are semiconductor devices whose resistance changes significantly with temperature variations. They are commonly employed in temperature-sensing applications. The resistance of a thermistor is inversely proportional to the temperature. A bead thermistor is a specific type of thermistor formed into a small, cylindrical shape. These components are easily integrated into circuits and provide a robust and reliable means of measuring temperature changes. Precise measurements are achieved due to the thermistor's sensitivity to temperature fluctuations. Their temperature coefficient of resistance (TCR) indicates how much the resistance changes for each degree Celsius change in temperature – a key factor in their application.