Overheat Detector Alarm LM35

At the heart of this over heat detector circuit is a precision integrated temperature sensor type LM35 (IC1), which provides an accurately linear and directly proportional output in mV, over the zero to +155 degrees C temperature range.

The LM35 develops an output voltage of 10 mV/K change in measured temperature. Designed to draw a minimal current of its own, the LM35 has very low self heating in still air. Here the output of the LM35 is applied to the non-inverting input of a comparator wired around a CA3130 opamp (IC2). A voltage divider network R3-P1 sets the threshold voltage, at the inverting input of the opamp. The threshold voltage determines the adjustable temperature trip level at which the circuit is activated.

Circuit diagram:

Overheat Detector Alarm/Switch Circuit Diagram