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07-28-2009

Dark-activated 230V Lamp

Compact circuitry using small-size parts only. Can be wired in parallel to existing switches

Circuit diagram:

Dark-activated 230V Lamp

Parts:

R1

Photo resistor (any type)

R2

100K     1W Resistor

R3

200K   1/2W Trimmer Cermet

R4,R7

470R   1/4W Resistors

R5

12K   1/4W Resistor

R6

1K   1/4W Resistor

   

C1

10nF   63V Polyester Capacitor

   

D1

TIC106D   400V 5A SCR

D2-D5

1N4007 1000V 1A Diodes

   

Q1

BC327    45V 800mA PNP Transistor

Q2

BC337    45V 800mA NPN Transistor

   

SK1

Female Mains socket

   

PL1

Male Mains plug & cable

Comments:

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.

Notes:

  • R3 allows fine setting of operating threshold and R2 value can be raised to 150K maximum.
  • Several lamps wired in parallel can be connected to the circuit, provided total power dissipation of the load does not exceed about 300 - 500W.
  • PL1 can be omitted and the input mains supply wires connected in parallel to any switch controlling lamps. In this case, if the switch is left open, the circuit will be able to drive the lamps; if the switch is closed, the lamps will illuminate and the circuit will be by-passed.
  • Warning! The circuit is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential!. Avoid touching the circuit when plugged and enclose it in a plastic box.

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