In some areas there is a need of temperature detectors which help them to detect temperature and indicate them whether the temperature is low or not.
Below shown circuit is the simple high temperature indicator circuit. It will not show the current temperature but if it exceeds some threshold temperature it will detect and indicate. You can use this circuit anywhere you needed.
The components needed for the circuit are:
And the circuit working is actually very simple, the Op-amp is connected as Non-inverting comparator. And a bridge circuit is made with the resistors and a Temperature Dependent Resistor. From above circuit R1, R2 and R3 are normal resistors but RT is Temperature Dependent Resistor.
The bridge resistance and RT are selected in such a way that as long as temperature is less than threshold value, the bridge is unbalanced by making Voltage at B more than voltage at A . Hence Vo = -Vsat and LED is reverse biased and remains OFF. When temperature becomes more than threshold then Voltage at B becomes less that Voltage at A hence it drives Vo = +Vsat. Due to this, LED glows and gives high temperature indication.
If you have any doubts about the above circuit, don’t hesitate to comment.