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L35, Midnight Security Lamp

The circuit is fully automatic and uses a CMOS IC CD 4060 to get the desired time delay.Most thefts happen after midnight hours when people enter the second phase of sleep called ‘paradoxical’ sleep.It’s an energy-saving circuit that causes the thieves to abort the theft attempt by lighting up the possible sites of intrusion (such as kitchen or backyard of your house) at around 1:00 am. It automatically resets in the morning.

Light-dependent resistor LDR control the reset pin 12 of IC1 CD4060 for its automatic action. During day time, the low resistance of LDR makes High on pin 12 of IC1, so it will not oscillate. After sun rising, the high resistance of LDR makes low on pin 12 of IC1 and it will start oscillating, which is indicated by the facing of LED2. The values of oscillator components (resistors R1 and R2 and capacitor C4) are chosen such that output of IC1 (PIN 3) goes ‘high’ after seven hours, i.e., around 1:00 am.


  • IC1 = CD4060

  • R1 = 120K. R2 = 1M, R3 = R4 = 150 ohm, VR1 = 100K

  • C1 = 1000uf, C2 = 100uf, C3 = 01uf, C4 = 1uf, (All 25Volt)

  • TRIAC1 = BT136

  • D1 - D4 = 1N4007

  • 9-0-9 Transformer 300 mA

  • Green & Red LEDs

  • LDR & 230volt 60Watt bulb

This gate pulse pin of triac1 (BT136) is connected the pin 3 of IC1. Bulb L1 connected between the phase line and M2 terminal of triac1 turns on when the gate of triac1 gets the trigger voltage from pin 3 of IC1. It remains ‘on’ until pin 12 of IC1 becomes high again in the morning. Capacitor C2 keeps trigger pin 12 of IC1 high during day time, so slight changes in light intensity will not effect on the circuit.

Using variable resistor VR1 you can adjust the sensitivity of LDR1. Power supply to the circuit is derived by a 9v DC transformer, rectified by a full-wave rectifier comprising diodes D1 through D4 and filtered by capacitor C1. Using switch S1 you can turn on the lamp manually. Enclose the unit in a plastic case and mount at a location that allows adequate daylight.


Since the circuit uses 230V AC, many of its points are at AC mains voltage. It could give you lethal shock if you are not careful. So if you don’t know much about working with line voltages, do not attempt to make this circuit. No one will not be responsible for any kind of resulting loss or damage.

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