Fire Alarm

Fire Alarm Using NE555
This fire alarm circuit should be placed in places prone to fire. Fire will cause a fire which caused enough smoke that will reduce the intensity of light to the LDR, which can pass light to the surrounding environment.

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With decreasing light intensity will increase resistor value of the LDR and the voltage on PIN2 of IC 555 will drop to be 1-3V. This will trigger the use of bistable mode of IC 555 that cause increased voltage on pin 3 to 9V, which provides voltage to activate the Chip on Board (COB). The signal output from the COB will give sound then be amplified by an audio amplifier IC.

In this circuit, the audio amplifier-wired around IC TDA 2002. The sensitivity of the circuit depends on the distance between the lamp and LDR and the creation of preset VR1. So, by placing the lamp and LDR at appropriate distances, can be varied preset VR1 to obtain optimum sensitivity. S1 reset switch is provided in the circuit to turn off the fire alarm after the fire was noticed by the user.