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Automatic night lamp with morning alarm

Loterature review
This circuit project automatically turns on a night light when the bedroom light is off. The lamp stays on until the light sensor detects daylight in the morning. Super bright white LED is used as the night lamp. It gives bright and fresh light in the room. When the sensor detects daylight in the morning, a melodious morning alarm sounds.

The automatic night light circuit uses light dependent resistors (LDR) to detect darkness and light in the room. The LDR resistance is very high in the dark, which is minimized when the LDR is fully illuminated. LDR1 detects darkness, while LDR2 detects light in the morning.

Operation of the night lamp circuit

When LDR1 illuminates with ambient light in the room, its resistance remains low, which keeps trigger 2 of IC2 at a positive potential. As a result, output pin 3 of IC2 goes down and the white LED remains off. As the illumination of the sensitive window of LDR1 is reduced, the resistance of the device increases.

In total darkness, the specified LDR has a resistance greater than 280 kilohms. When the LDR1 resistance increases, a short pulse is applied to trigger 2 of IC2 through resistance R2 (150 kilohms). This activates the monostable and its output goes high, causing the white LED to glow.

LDR2 and associated components generate the alarm from morning to dawn. LDR2 etects the ambient light in the room at dawn and its resistance drops gradually and the T1 transistor starts to drive. When T1 leads, the melody-generator IC (IC3) gets the source voltage of the T1 emitter and begins to produce the melody. The musical tone generated by IC3 is amplified by the amplifier T2 of a single transistor. The resistor R7 limits the current to IC3 and the zener diode ZD limits the voltage to a level of 3.3 volts.

The night lamp with alarm circuit can be easily mounted on a general purpose PCB. Enclose in a good quality plastic box with provisions for LDR and LED. Use a white LED reflective bracket to get a projector effect for reading. Place the LDRs away from the white LED, preferably on the back of the case, to avoid unnecessary lighting. The speaker should be small to make the gadget compact.

Night lamp with alarm circuit

[Image: night-lamp-alarm.gif]

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