Hacking the onboard switch on sonoff modules

Never mind… I just pulled that exact board out of my relay box and here is the datasheet for it:

Sainsmart 16 channel relay board

It is an open source board design that a million knock offs have come from. Sainsmart created a datasheet and user manual for it.

Oh ok I figured it was a 12v powered board with 12v signal switch on the headers and contacts were dry. That’s what I’m actually after. Seems like this won’t be any good for me then

Yeah…nope. Low voltage input and it does it’s own voltage switching onboard.

You need a 12v version of this…

16 channel relay board, DIN rail

And I found one at half the price on Ali Express HERE

Yeah nah bit pricey… us dollars too… I’ll just go with these then

Oh never mind just clicked on the here link… not bad at all… I’ll consider it

So I ordered one to play around with… only a 4ch however I can achieve what I set out to do with it. The vcc is 12v supplied gnd is for the relay coil. In1,2,3,4 are switched via negative or gnd from suplly, in this test case, the battery. What I plan to do is cut the track where shown so I can use the relay as dry contacts. Now for the switches on the wall I’ll have have the negative switched instead of the positive. Simple and much cheaper than the other options​:ok_hand::ok_hand:

Bit more of a update… pics showing the hacked 4ch modules… then mounted in a board and using a busbar to output to the relays that will control them


Made a switch plate tonight cause I was excited when my switches came in… 2mm white perspex and 12v momentary push buttons. You can see the cracked perspex cause I drilled them out by a hand drill… I’ll be using a drill press next time or might go the laser cutter route.


That’ll look snazzy! SLOW is the key to hand drilling that stuff. Don’t let the bit heat up from the friction.

I have a 4 relay one of these boards (5V trigger 240V relays) that I control with a NodeMCU and Alexa.