Rain curtain problem


I’m creating a rain curtain, 64 x 12V solenoids switched through 8 x 8way relays, these are controlled by an Arduino UNO through 8 x extender modules (FR12C PORT iNTERFACE pcf8574t i/o)
The relays run perfectly until I apply voltage to the 12V side, then it stops.
I’ve watched videos about grounding issues between the relay and the UNO that suggest seperating the power to the relay control from the UNO, but I can’t get it to run without ground coming back to the UNO.
Any ideas?




It’s a bit hard to see from the size of that image, are you using the one power supply for both?

When you’re using relays you should be able to use two separate power supplies, one solely for the arduino (eg. powered by USB). If you do it that way then there shouldn’t be a common ground as you seem to imply above. Perhaps splitting the power in two will solve your problem? Or point out where a wiring issue is if I’m not making sense?

It looks like it from the picture but just confirming you also only have positive going through your relays?


NOTE: I am assuming you are using the UNO as the main power source.

don’t use the UNO to supply the voltage to the motors, use a separate power source and put the positive voltage to the motors, and the negative to the relay’s N/O contact, just use the UNO to control the relays.

not sure if that will help.


Thanks everyone for your thoughts, fixed now, problem was in the wiring on the 12V side. Just a dumb old wire in the wrong hole problem.