3 Review(s)

The fire alarm circuit is based upon one of the 2 Op-( Operational Amplifiers ) of the LM358 IC, The Op-Amp here is used as a comparator, It compares the two voltages present at its inverting input ( Pin 2 ) and non-Inverting input ( Pin 3 ). The voltage at the Non-Inverting input is set using the potentiometer, such that the buzzer does not sounds in ambient room temperature. The voltage on the inverting input varies with the temperature, when the IR Receiver hot its resistance drops rapidly resulting in the drop of voltage at the inverting input, when the voltage of inverting gets less than that of the non-inverting input the buzzer gives a loud noise, alarming you of a potential fire