Light Switch reverse engineered

So basically I bought a light switch and stole the circuit design to make it better.

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This commercial light switch which is super popular here (even the government uses it for city light poles) has a weird problem in its design, if you try to turn on and off a big contactor with the output, it trips all the fuses on its way.
So I wanted to improve the design and fix this.
Now I think that this problem occurs cuz it takes the circuit power input (220vAC) and connects it to the relay NO pin to use it as the output phase, and when the contactor on the output turns off, the voltage spike messes with the circuit and "something" happens that makes the fuses to trip.

So anyway, I took the circuit from the device PCB and fixed that problem to see if that helps. (I haven't received my PCBs yet to find out).

Step 1:

I just took out the PCB and followed the traces and recreated the circuit.

Step 2:

Then I put everything together on a breadboard, fixed the drawn circuit problems, and tested everything.

Step 3:

Designed a new PCB with the changes needed so far.

Now I'm waiting for the PCB to arrive to see if the changes I made have done anything good.

Down below you can download the last version of the schematic and the PCB I designed. It's a working device which you can make for yourself and use it! 

I will update both files as soon as I made any changes to them.

p.s: [Not recommended] in the file info means I haven't tested the PCB or schematic myself or there is a problem with it.

Light switch PCB V1.3.PcbDoc

Light Switch PCB V1.3

pcbdoc - 2.01 MB - 11/27/2021 at 13:15


Light Switch V1.3 Schem c.pdf

Light Switch Schematics V1.2

Adobe Portable Document Format - 113.74 kB - 11/27/2021 at 13:14


Light switch PCB V1.2.PcbDoc

Light Switch PCB V1.2 [Not recomended]

pcbdoc - 1.85 MB - 11/15/2021 at 08:20


Light Switch Schematics.pdf

Light Switch Schematics V1.2

Adobe Portable Document Format - 191.47 kB - 11/15/2021 at 08:13


  • 2 × 330KΩ 1206 Resistor
  • 1 × 330Ω 1W Resistor
  • 1 × 4.7MΩ 1206 Resistor
  • 1 × 100Ω 1206 Resistor
  • 1 × 12KΩ 1206 Resistor

View all 16 components

  • Open Light Switch PCB V1.3

    setCREATE11/27/2021 at 13:26 0 comments

    Log no.2: Open Light Switch PCB V1.3

    What I've done?

    I edited the schematics and redesigned the PCB.

    What's New?

    • A fuse is added to the circuit
    • PCB is designed to be able to mount on the casing
    • Power, Input, and output wires are all on the bottom
    • PCB is more standard, clearance between tracks is better now (still not perfect)
    • PCB is a bit bigger
    • It just looks way better, tracks are more organized and no jumper is needed

    Where are the files?

    You can download the Scheme and the PCB documents in the project files.

    What's next?

    I will design a casing for the PCB and 3D print it.

  • Open Light Switch V1.2 Prototype

    setCREATE11/27/2021 at 13:10 0 comments

    Log no.1: Open Light Switch V1.2 Prototype

    What I've done?

    I received the V1.2 PCB, soldered everything, and tested the circuit.


    The Assembled PCB

    This might be the worst quality you've ever seen for a PCB


    Well, everything worked fine that's it.

    Next Step:

    I will update the PCB.

View all 2 project logs

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