Fire Alarm with LDR Sensor

Fire Alarm with LDR Sensor

This is a fire alarm circuit that uses an LDR to sense smoke from a fire, so it can be used to detect any black smoke. With the arrival of summer, the likelihood of fire incidents increases. These fire accidents can be avoided if the alarm is raised in time. The circuit given here reminds the user to be aware of these fire incidents. This circuit needs to be placed in a fire-prone area, such as a kitchen. Everyone knows that when everything catches fire, smoke is produced. As the smoke passes between the bulb and the LDR, the amount of light falling on the LDR is reduced. This causes the resistance of the LDR to rise and the voltage at pin 2 of the IC 555 to fall below 1/3 Vcc, thus triggering the IC 555, which is used in the dual-stable mode here. as a result, the voltage at pin 3 becomes high. This high voltage (about +9V) completes the power supply to the COB (chip on board).

There are various COBs on the market that can produce various sounds. Even so, one can choose a COB that produces sound, such as "aag lag gai hai". The signal generated by the COB is amplified by an audio amplifier. In this circuit, the audio power amplifier is connected close to IC2 TDA 2002.

The sensitivity of the circuit depends on the distance between the light bulb and the LDR as well as the preset VR1 setting. Therefore, by placing the lamps and LDRs at the proper distance from each other, the preset VR1 can be changed to obtain the best sensitivity.

A reset switch S1 is provided in the circuit to turn off the alarm as soon as a fire is detected by the user.

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