Introduction: $0.1 Dusk to Dawn Switch Low Cost Simple Dusk to Dawn Switch Dark Sensing Light Automatic Lights

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

Step 1: Components List

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

Make connections as shown in circuit, for more details Visit Link

Step 3: Test Your Circuit

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..

5. Find difficulty in building circuit comment me on my


SanjeewaB (author)2017-07-17

Not working !!!

RobertV4 made it! (author)2015-12-17


i made it, but circuit still turn on light connected. probably wrong LDR used ?
i use 5 - 10k /LDR07

which one is described in this instructable ?


braytonlarson (author)2015-06-08

What exactly does a Triac do? I've heard people use them in place of Relays but you have to be careful with them. It looks like a mosfet / transitor but it can handle AC voltage. Aren't you supposed to put a diode between the output of the Triac and the second Mains wire?


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.

seamster (author)2015-05-30

Nicely done. Thanks for sharing this!

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