When using an opto isolator, to isolate two different circuit "sections". Do you put it on the 'noise producing' section and run wires to the 'quiet' section? Or do you run wires from the 'noisy' section and then to the opto on the 'quiet' section? These circuit "sections" are on two separate boards but belong to the same overall circuit. I know I'm probably not asking correctly, but that's nothing new.