Simple Mini Dusk to Dawn Switch for 220v AC





Introduction: Simple Mini Dusk to Dawn Switch for 220v AC

At or farms, we required to install a few lights that would

automatically turn on at night and turn off at dawn and since we required quite a few, it had to be cost effective and efficient. I thought about installing a timer switch at first but gave up on the idea. Finally after searching through numerous circuits the internet, I figured that an effective, small and cheap circuit could be designed with ease. The entire switch costs under 50 cents (Rupees 31/- in India). I extend my heartfelt thanks and gratitude to all the contributors of the many designs and circuits on the internet from where I have drawn the inspiration, the names of the contributors I do not individually know but my thanks to all.

Step 1: Parts List & Diagram

Parts Required Cost

1” x 1” Strip Board Rs.2/-

1 x BT136 or BTA12 Triac Rs.12/-

1 x DB3 Diac Re.1/-

1 x 1w. 100K Resistor Re.1/-

5mm LDR Rs.10/-

Assorted Wires for wiring Rs.2/-

Old Plastic Film Canister Rs.0/-

Total Parts Cost Rs.28/-


Soldering Iron

Solder Wire

Wire Strippers

Glue Gun

Assorted Small Tools


The circuit works on 220v AC and if you are not accustomed to working with mains voltage or do not have ample experience in working with 220v AC Mains Voltage please stay away from this project.

I assume no responsibility for any loss or damage arising directly out of or as a consequence of following this project.

It is always advised to take proper care and precaution while working with AC Mains.

Step 2: The Triac

Step 1.

Cut the strip board to the desired size and trim & file the edeges.

Place the BT136/BTA12 Triac through the holes in the center leaving a couple of lines on either side. Solder and trim.

Step 3: The Diac

Insert the Diac, 1 leg of the Diac should connect to the

Gate of the Triac and the other leg to an empty strip on the strip board, solder and trim.

Step 4: The LDR

Insert the LDR, one leg of the LDR should connect to T1

or M1 of the Triac and the other to the same strip to which the second leg of the Diac is connected, solder and trim.

Step 5: The Resistor

Insert the Resistor as shown in the picture, the first

leg should be connected to the same strip on which the second legs of the Diac and the LDR are connected and the second leg, place across the Triac and connect to an empty strip on the strip board, solder and trim.

Step 6: The Mains Connection

Now connect the Mains Connection Wires.

Connect 2 wires, preferably of the same colour (I have used Black & blue)to the strip on the strip board on which the second leg of the Resistor is connected.

Connect 1 wire (RED) to the strip on the strip board on which the 1st leg (M1) of the Triac is connected

Connect 1 wire (WHITE) to the strip on the strip board on which the 2nd leg (M2) of the Triac is connected. Solder and trim as required

Refer to the drawing for the connections.

Mains Connections –

The Black Wire and the Red Wire go to the Mains AC Supply, this is the input.

The remaining two wires (White & Blue) go to the BULB

Step 7: Done

You can seal the entire circuit in a small plastic

translucent film canister which will keep the water out and also let the LDR function normally in outdoor use.

Thanks for viewing, I must add here that I have been using these circuits on the lamp-posts at our farms for the past couple of months now and they have been connected ever since and I have never had reason to complain as yet. We do have regular power outages for around 4 to 6 hours a day a and that is probably the only rest the circuit gets. Otherwise, the circuit is working as it was intended to and every evening the lights go on and at day break they turn off automatically. I will post pictures of the working lamp-posts ASAP.



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    23 Discussions

    Hi this is a just small and low cost one, if PIR is used it will be good but that will cross our budget!.


    Question 4 months ago

    What is the meaning of DIAC 3
    What is the value of this part

    i have made this diagram same as you described, but it is not working for me, when i switch on the circuit, the light just blink once and turned off, please suggest me what should i do

    i have made this diagram same as you described, but it is not working for me, when i switch on the circuit, the light just blink once and turned off, please suggest me what should i do

    I asked for 1W 100K Resistor. But the shop guy gave me a resistor with color codes of 'Red,Brown,Black and Gold'. Is it ok to use this.

    1 reply

    Red,Brown,Black and Gold is just 21 ohms. 100k is Brown Black Yellow (Gold is the tolerance) and 1 watt is the power handling capacity.

    About LDR: what is the part number? Or, if you don't know that, then what's its rated resistance for daytime?

    I tried with 100k/200k LDR and instead 100k I used 2M - because with 100k the led was on all the time - but even then he was not much sensitive. Are you using 10K LDR or even smaller?

    1 reply

    I'll get back to you on the resistance measurements after physically checking the resistance in the day time.
    The ones I have used are commonly available here and all we have to ask for are 5mm ldr (more commonly known by the size) the resistor value that I have used is not common to all types of ldr that are available and a little bit of experiment is required to figure out what works best for a particular type of Ldr.
    I will take physical readings as soon as I can and post an update on this

    I have a question: where do you put the photoresistor in that canister? As far as I tested, if you put a photoresistor into something, it will not work as it should because the canister is not letting enough sunlight in. Or maybe it's different with translucent film canister?

    1 reply

    it works fine with a translucent film container like the ones shown in the pictures.

    Here you go. For you and for whoever need it.


    Hello. I like your Circuit. I have a question that if is full moon then it will turn off light?

    1 reply

    Thanks for your comment,

    I am using it for past 3 months or so, no problem with full moon, I suppose the light from the moon is not bright enough to turn off the circuit.

    I suppose, you can experiment with the value of the resistor to change the sensitivity of the LDR, I am using 100k, you could try 120k or 80k and see the difference it makes.



    1 year ago

    Do you have any issues with dark clouds turning on the lights? I ask because I didn't see any hysteresis delay or any time delay for the circuit to switch the lights on. If you were to cover over the LDR, I am pretty sure it would switch instantly. And usually to stop that, it has to stay dark for about a minute or so to keep it from oscillating. Also, the higher the wattage you are switching, the more you need to heat sink the TRIAC. It can only handle the max current ratings when using a heatsink. Just some observation. Nice circuit anyways. Thumbs Up!

    1 reply

    Thanks for your comments and observations, yes the lights do turn on when we have clouds that are dark enough, also there is no time delay circuit incorporated in this design. As for the heat sink not being used, we normally run very small loads on these circuits, max to max a 60w CFL, so far the Bt136 triac has been able to handle this.
    But yes, thanks for your suggestions, there is certainly much scope of improvement and I will try to incorporate your valued ideas in the next batch.

    Well done. thanks. I realise we could use this alongside PIR circuits to feed a relay to make the circuit turn on only at dark. Will try to use in my own farm illumination project. Would love to see your lightpost pics. Any economical way to have complete post fabricated. Also the choice of lights from amongst the numerous dubious LED modules rated frivolously at 50, 60 or 100W.

    1 reply

    thanks, it makes me happy that you wish to adapt the idea for your farm illumination.

    I simply used this circuit with the existing Lamp posts and they are working just fine since the last 2 months or so. I am using them with regular 60 watt CFL bulbs, they provide sufficient light since the posts are only about 9' high.. There are a total of 29 lamp posts placed randomly wherever required. I am thinking of upgrading to LED lights and I plan to fabricate these lights at the first opportunity.

    It should not be too difficult to get the lamp posts fabricated at a local workshop near your farms, guessing that your farms are in India, we normally have an abundance of these small fabricators and workshops near small townships.

    Regards and thanks