@▷ Temperature Monitor Circuit | Diagram for Schematic

Temperature Monitor Circuit

This temperature monitor circuit is used where a continous analog display of temperature value being monitored is not necessary. A simple indication whether the temperature value exceeded a maximum level or went below the minimum level is sometimes enough. The circuit here does just that, it indicated the temperature level about +25oC (77oF) or below +20oC (68oF) by lighting one of the two LEDs.

The temperature sensor is an NTC resistor coupled to two comparators. When D1 lights, the temperature is above +25oC and when D2 lights, the temperature is below +20oC.

Temperature monitor calibration

Place the NTC resistor in cold water. Slowly heat the water until the desired maximum temperature level is reached, then adjust P1 until D2 lights up.

To set the minimum level, stop heating the water then slowly add cold water to it until the desired lower temperature level is reached as indicated by the thermomter. This time adjust P2 until D1 lights up.

Temperature level monitor circuit schematic

temperature monitor circuit schematic