This is the control board (including power supply) for the touch switch plates that I made for Livolo.
The project complements the previous touch switch plates that I made a long time ago providing a full solution for creating a custom in wall RF switch which works with no neutral line.
The project is based on the DER-622 design from Power Integrations which is free to download and study in order to understand how it works (schematic is available also). There's also another one called DER-832 which is more recent and a little bit improved.
And now the why
Why I did this? I wanted to see that it can be done and not impossible to make it work and have a full solution for my home when there's only the live wire present. And if Livolo or other companies did it why shouldn't I? More than that I wanted to learn more about electronics in general (especially designing custom ac/dc power supplies and such).
And now the how
All I did on my side was to customize it a little bit by changing the stand-by power supply with another one based on the LNK364 chip which is another solution provided by Power Integrations also. The PCB was made so that it has the same dimensions as the one from the original Livolo switch except the screw terminals which are not aligned/positioned the same way. The pin header is also positioned so that the custom touch plates that I made should fit and uses the same pinout.
V_SENSE functionality is there but not used on the custom touch plates as it wasn't planned at that time (the only thing that it does is to signal whenever the switch changes the internal power supply used or when the series MOSFET regulator kicks in).
And yes, it took some effort to finish the custom board as it has to be pretty compact and also to take care of keeping as much as possible the minimum distance between tracks where high voltages are implied. Also for high current paths to make sure that the traces are more wide and mirror on both sides of the PCB (using via stitching).
I cannot say that I followed all the rules when it comes to a good PCB design but I tried to comply as much as I could and based on how much my current experience told me to :).
The design was already tested on another custom board that I made for "testing purposes" and it works. Now I'm waiting for the current PCB's to come from the factory and do some testing also for the final design.
Although there is a possibility to use loads that draw several amps I don't advise you to do so because it wasn't quite designed for it. Saying this because of the heat dissipation and pcb traces. Max current that can be drawn should be limited to 1.5 - 2 amps. The 5 amps fuse from the schematic should be changed accordingly (I forgot about it).
More details coming soon.