So recently i wired mega2560 with 6 relay shield , they have separate PSU and only one relay is active at a time for different time .
What is the deal, when relay is HIGH (220v powering small indicator lights ,one at time) all of LOW relays has 40v on my multimeter and test lamp ,with multimeter im measuring N on 220v power and L on normal-closed connector of relay and boom 40v...
It's hard to understand You, BUT.... Please post schematics! Pictures are international, understood all around the world..
Pen and paper often works well.
Are you saying the relay shield power is floating on mains hum? If its an isolated power supply, and the opto-isolator inputs are used in the fully isolated mode that could happen.
I'm not a fan of floating power supplies, but its not necessarily a problem if it is like this and the inputs are opto-isolated.