Sonoff S20 Basic working on 5.5v/12v

Firstly a big thank you for the excellent work of erocm1231 and I used his program guide to flash the Sonoff Basic and that can be found here:

So I had various problems using the Sonoff 5V latching module mostly around simulating a push button (non-latching) event and I decided to see if I could convert the 220v AC Sonoff basic to a low voltage DC switch and it turned out to be easier than expected.

Three simple steps :
1 Flash the Sonoff Basic using erocm1231 step by step guide and set it up on Smartthings.

2 Solder some wire to the capacitor C9 and use a 5.5V power supply to power the board. I added a stripped down 12V USB charger to get 12V dc to 5.5v dc as my gate unit is 12v.

I removed the screw terminals to cut down the size (optional) and soldered a wire to the the input and output making a push to make switch.

3 Add a rule in Smartthings that if the Sonoff switch is on then turn it off. I used Smartrules for this and it switches off after about half of a second. So when I send an ‘on’ command it goes off automatically. This simulates a button press.


An alternative to this step may be to use the “Auto Off” feature of the firmware set to 1 second. This basically turns the switch off after x seconds every time it is turned on. It can simulate a momentary press.

Good to know, thanks.

So by powering the Sonoff with 3v at the header pins, shouldnt the relay switch like a dry contact? I cant seem to get this to work?

So if you look at the photos above, the pink wires only use one side (+) of the switch and the other side is bridged on the circuit board. I used the pink wire to switch the on/off (single pole) and the other wire (-) bypasses the board.

Also I have a powered the board by wiring on to the C9 using 5V.

Thanks, I now have one working, and hopefully I can get a long life running it this way. I have many uses for a dry switch.