ABSTRACT
This circuit automatically turns on a night lamp when bedroom light is switched off. The lamp remains ‘on’ until the light sensor senses daylight in the morning. A super-bright white LED is used as the night lamp. It gives bright and cool
light in the room. When the sensor detects the daylight in the morning, a melodious morning alarm sounds.
The circuit is powered from a standard 0-9V transformer. Regulator IC 7806 gives regulated 6V DC to the circuit. A battery backup is provided to power the circuit when mains fail. In the event of mains failure, the battery automatically takes up the load without any delay. The circuit utilises light-dependant resistors (LDRs) for sensing darkness and light in the room. The resistance of LDR is very high in darkness, which reduces to minimum when LDR is fully illuminated. LDR1 detects darkness, while LDR2 detects light in the morning.
The circuit consists of a regulated IC (IC 7806), a timer IC (IC NE555) which is used as a monostable multivibrator and a melody generator IC(IC UM66).