HIGH TEMPERATURE INDICATOR CIRCUIT

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:
3 Resistors
1 Temperature dependent resistor
5v battery
Two 1n4007 diodes
One Op-Amp
One LED
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.