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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. Diodes D1 through D4 rectify the AC voltage and the resulting DC voltage is smoothed by C1. Regulator IC 7806 gives regulated 6V DC to the circuit. A battery backup is provided to power the circuit when mains fails. When mains supply is available, the 9V rechargeable battery charges via diode D5 and resistor R1 with a reasonably constant current. In the event of mains failure, the battery automatically takes up the load without any delay. Diode D5 prevents the battery from discharging backwards following the mains failure and diode D6 provides current path from the battery.  Automatic Ni...

There are many approaches to the problem of activating a light when it becomes dark, and a recent Design Idea covers this topic (Reference 1). Some approaches require a dc power supply and an electromechanical relay, but a better approach involves feeding the device directly from the ac line, minimizing the number of components  ( Figure 1 ). Figure 1. The photoresistor activates the TRIAC and the load when darkness falls. The heart of the device is a light-sensitive cadmium-sulphide resistor, PR, with a resistance of approximately 200 kΩ in the dark and decreasing to a few kilohms in the light. PR and capacitor C1 form an ac-voltage divider. In daylight, the voltage across PR is too low to generate the required gate-trigger current to turn on bidirectional ac switch Q1, thus keeping the load – usually a lamp – off. When it becomes dark, PR’s resistance rises, resulting in an increase in the TRIAC’s gate current that triggers the TRIAC and lights the lamp. The circuit uses inexpens...

Ultra-low current drawing / 1.5V battery supply This circuit is usable as a Night Lamp when a wall mains socket is not available to plug-in an ever running small neon lamp device. In order to ensure minimum battery consumption, one 1.5V cell is used and simple voltage doublers drives a pulsating ultra-bright LED: current drawing is less than 500µA. An optional Photo resistor will switch-off the circuit in daylight or when room lamps illuminate, allowing further current economy. This device will run for about 3 months continuously on an ordinary AA sized cell or for around 6 months on an alkaline type cell but, adding the Photo resistor circuitry, running time will be doubled or, very likely, triplicates. IC1 generates a square wave at about 4 Hz frequencies. C2 & D2 form voltage doublers, necessary to raise the battery voltage to a peak value able to drive the LED. Circuit Diagram: Parts: R1 = 1M R2 = 1M R3 = 47K R4 = LDR C1 = 100nF - 63V C2 = 220uF - 25V D1 = Ultra Bright 10mm LE...

This source uses LEDs and an astable oscillator to control the switch, duty-cycle, and effective IR illumination output.  Circuit Diagram

Description This is a simple circuit which is build around a CMOS Ic 4060 and LDR. During the day time LDR has low resistance which keeps the pin 12 of the IC1 high. And also for the night LDR resistance become high and the pin 12 or IC1 is becomes low and the IC start oscillating, which indicate by the flashing of LED D3.The values of the timing components R1, R2, C4 are so selected that the out put pin3 of IC1 goes high after 8 hours. That means the high output drives the triac to switch on the lamp around 2’O clock.At morning time the LDR resistance drops and the pin 12 of IC1 goes high and stop the oscillating which makes the lamp off. Where Switch S1 is used to manually ON the lamp.The capacitor C2 prevents false triggering. Circuit Diagram Notes. * Assemble the circuit on a good quality PCB or common board. * The LDR can be general purpose LDR. * The light sensitivity can be adjusted using the preset R6. *  The IC1 must be mounted on an  IC holder.