light sensor switch circuit schematic

Light Sensor Switch Circuit

This light sensor switch circuit allows the automatic connection of a lamp when the light is low (at nightfall) and will maintain the lamp ON for a certain period of time.
This time can be adjusted with P1 between 1 and 5 hours. The switch is a semiconductor relay S202DS2 and the oscillator is 4060.

Sensor Light Switch Schematic

light sensor switch circuit schematic

From the moment that T4 and T5 are opened, relay’s LED start to light and powers the lamp. As soon as one of the transistors is blocked the lamp will go OFF. The phototransistor T3 will be the one that blocks T5 if there is light that falls on T3.

The T2’s base-emitter junction is connected in parallel with T3 and so will be blocked as long there is light. T2 will continuously reset IC1 whose counter outputs will be in “0” state.

When the night falls R7 provides base current for T2 and the transistor starts to conduct. The counter can now starts to count the impulses from the internal oscillator and in this time the light will bulb will stay lit. After a time, when the output of Q13 goes in state “1” T4 is blocked. This causes the relay’s LED to go off and the lamp too.

There is no need for external power supply because the light sensor switch is powered directly from the 220V mains. D1 … D5 diodes rectifies the voltage and C4 filters it.
C5 is working as a resistor so will need to have the working voltage of minimum 400V but the 630V is preferable.

S202DS2 is a Triac-Full-Wave-Output Optocoupler produced by Sharp Electronics in a TO-220 package.

The maximum peak-to-peak voltage is 600V, max on-state current is 8 Ampere and the input trigger current is 8 mA.

Caution! This circuit is powered directly from 220V. Attention will be given for appropriate isolation of the switch block.


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  • Anuo

    Can 12 v light sensor sire can be use as switch for direct current? What is i connect it in neutral side as a switch?

  • Kabir

    Please show me the circuit for stairs which will turn on at human presence nearby, and turn off 30 seconds after the person leave.

  • kcarring

    i forgot to answer one thing: R2, is, indeed used to tie P3 to T5 @ 22k ohms

  • kcarring

    @Popescu Thanks for looking into it. I went over your concerns, in this video which will be live 3/8/2013. (uploading now) I think I may have the wrong sort of photo-transistor, i tmay not work properly with visible life, as demonstrated using an infrared emitter LED – in this video…


  • kcarring

    I think it’s just the wrong kind of phototransistor, unable to perform with visible light, I guess.

  • kcarring

    Excuse me.. I just tested it by using an infrared emitter, and it effectively, immediately shuts down the output LED. I guess the “room light” contained no real infrared spectrum, and thus had me fooled?

  • kcarring

    The odd thing, is, that, when I turn on the circuit, nothing happens. If, though, I take a very intense light and shine it on the photo-transistor, the LED (that represents the optocoupler) DOES come on. Is this what I want? I expected it would come on in the dark, and disappear in the light…

  • kcarring

    Just to be sure I replaced every transistor with new ones, and the IC too. Then I checked the value of every resistor again, and all connections.

    This time I got 5+ volts on the rail. And about 35 mA draw on the circuit with 200 ohms, and about double that with 100 ohms.

    No operation though. I have an LED in place of the optocoupler.

    This HD demo should be live 3/7/2013

    • Popescu Marian

      I was looking at your video and want to ask you some things:
      1 – is the ground connected as shown in the schematic on the website? at pin 8 and the line that connects the emitters of T4 and T2?
      BTW: you show at 5:25 that there is no connection to ground on a certain place. My answer is there shouldn’t be any. That network of R3, R4, P1, C1 and C2 are necessary for the internal oscillator of 4060 IC (sets the time).
      2 – is the R2 connected from pin 3 to the base of T5 (BC557 PNP transistor)? I am asking because in the video is unclear.

  • kcarring

    Even with only a 10W / 39 ohm resistor, I still get less than 2 volts on the rails, and it draws over 200 mA

  • kcarring

    I had originally tried an LM3805 and it just smoked that in like 20 seconds.

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