The circuit described here stops the musical sound when darkness is detected like when you put your hand above the sensor. This circuit can be used as morning alarm. Install it on your window so when the light falls on it will start giving you melodious sound to wake up. In night you can use it to switch off the light of staircase. When you switch off the light of your room with little modification like you can connect relay at output (in place of speaker) to off the bulb. This circuit can be operated with pencil cell as it require less only 3V for its operation. It can easily be mounted because of number of components used in circuit are quite small. LDR is a device whose sensitivity depends upon the intensity of light falling on it.
Simple LDR Dark Sensor Circuit
The circuit described here stops the musical sound when darkness is detected like when you put your hand above the sensor. This circuit can be used as morning alarm. Install it on your window so when the light falls on it will start giving you melodious sound to wake up. In night you can use it to switch off the light of staircase. When you switch off the light of your room with little modification like you can connect relay at output (in place of speaker) to off the bulb. This circuit can be operated with pencil cell as it require less only 3V for its operation. It can easily be mounted because of number of components used in circuit are quite small. LDR is a device whose sensitivity depends upon the intensity of light falling on it.