Learning Electronics

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Dark Activated Terrace Lamp

Compact circuit, Can be wired in parallel to existing switches

This device allows one or more lamps to illuminate at sunset and turn off at dawn.Q1 and Q2 form a trigger device for the SCR, providing short pulses at 100Hz frequency. Pulse duration is set by R2 and C1.When the light hits R1, the photo resistor assumes a very low resistance value, almost shorting C1 and preventing circuit operation. When R1 is in the dark, its resistance value becomes very high thus enabling circuit operation.

Circuit Diagram:

Dark Activated 220 volt AC Lamp Circuit Diagram


R1 = LDR
R2 = 100K
R3 = 200K
R4 = 470R
R5 = 12K
R6 = 1K
R7 = 470R
C1 = 10nF-63V
D1 = TIC106D
D2 = 1N4007
D3 = 1N4007
D4 = 1N4007
D5 = 1N4007
Q1 = BD327
Q2 = BD337
SK1 = Female Mains Socket


Source: Red Free Circuit Design