Wednesday, May 27, 2015

$0.1 Dusk to Dawn Switch Low cost simple dusk to dawn switch Dark Sensing Light Automatic Lights

Worlds simplest Dusk to Down Switch

Turn your security lighting or task lighting on and off automatically each night with this circuit. It's easy to install

Step 1: Components Required
1. TRIAC BT136 or BTA16
2. LDR
3. 104 (0.1uF) Capacitor
4. 1K Ohm 1/4 Watt Resistor
5. DB3 Diac
6. Connecting Wires

Step 2: Connection Diagram

Step 3: Testing
1. Warning This Circuit Operates at AC 120V or 230V
2. Connect This circuit in series with lamp as Shown in Circuit diagram.
3. Take care that Lamp Light should not fall on LDR, This can cause false turn off or looping oscillations.
4. Save energy Go green..


  1. Hi,
    I am a 12th standard student and I am fond of electronics. Can you please explain how the given circuit works.

  2. TRIAC is a device that will acts as relay, Semiconductor Switch. It can handle 400V AC 16Amps (BTA16) More than enough. No need of diode, we want to pass the AC supply. It works on basic principle, LDR when Light is more the resistance of LDR becomes low, so the charging of capacitor voltage is not enough to trigger the TRIAC. So it remains off during day time. At night LDR resistance become high and allows capacitor to charge above TRAIC triggering voltage threshold so Lights are on at night.

  3. i tried to do this circuit but the 1k resistor burns, with light.

  4. I tried this circute, but the light is not getting off during day time or when light falls on the LDR. All components are connected as mentioned. Also please guide me whether I can use a LED bulb at the lamp load.

  5. Hi, what is resistance of LDR when is totaly dark ? trying to find alternatives. Could be used LDR with total dark 300 k ?

  6. I tried this but 1k resister burn please reply me

  7. I assembled as what you shown in the picture but the light is always on

  8. I tried this but the light glowing continuously. LDR play no role