Kind hard for me to believe as I can't find any device with 2 power plugs...
How they doing that ? How do they isolate their electronics from motors (like in fridges, washing machines, or any other machine using DC motors and electronics).
I don't follow what you are asking.
Most optos are just a transistor and a LED, there is no need for power pins and they certainly don't have "plugs".
If you want isolation then yes you need each side of the barrier to have it's own power supply, otherwise it's not isolated. One side drives the LED and the other side reads the voltage on the transistor's collector or emitter (with some help from a resistor).
Rob
Capacitors, lots and lots of capacitors.
I used optoisolating triac drivers for controlling some slide projectors microprocessor based multimedia controller. While the low voltage electronics and the projector bulbs were connected by the same AC line, the electronics were isolated by a transformer, so there was no wire connection between the low voltage electronics and the mains, making it much safer to work on.
Low voltage electronics use various transistors and relays to drive high voltage/high current stuff.
Optocouplers are not needed there.
carmamir:
So to use opto-coupler I need 2 separate power supplies?
What are you trying to do?