used as a light sensor.
A 10K variable resistor is used to adjust the sensitivity of the circuit. An 8 ohms speaker is used at the output of the circuit to produce sound. Changing the value of the 0.05uF capacitor can change the frequency of the sound. The operating voltage of the circuit is 9V to 12V DC.
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The figure below shows project of a light activated alarm circuit using 555 timer IC. The circuit will produce sound when light falls on the surface of the LDR. The heart of the circuit is a famous 555 timer IC that is wired as an astable multivibrator in the circuit. An LDR (Light Dependent Resistor) is
