Temperature sensor circuit diagrams

Hot Water Level Indicator

A simple device to indicate various levels of hot water in a tank.

Fridge door Alarm

Beeps if you leave open the door over 20 seconds 3V battery operation, simple circuitry

Heating System Thermostat

Controlled by indoor and outdoor temperature Simple, high reliability design

Digital Remote Thermometer

Remote sensor sends data via mains supply Temperature range: 00.0 to 99.9 °C

Temperature-controlled 12V dc Fan

Suitable for computer cooling fans. LED motor speed indicator

Temperature Monitor

A simple op-amp circuit that will trigger a relay when a preset temperature is reached. Please note that there is no hysteresis in this circuit, so that if the temperature changes rapidly, then the relay may switch rapidly.

Energy Leak Detector

High sensitivity, portable temperature comparator Detects draughts around doors, windows, etc.

Fan Controller

This circuit controls very accurately a fan of any size. Just adjust the associated resistors for a different type like the R6 resistor of 100 ohm, 2 watt type and you're all set. The above circuit diagram is for a small 12 volt fan, the size and type determined by the user.

Frost Alarm

A simple thermistor triggered switch with adjustable threshold. It triggers with cold temperatures so may be used as a frost alarm or cold temperature switch.

Temperature-controlled Fan

Gradually increases speed as temperature increases Widely adjustable temperature range