Check out this post for photos and schematic. I am currently trying to find out how you can maintain the isolation when the
relay board does not provide a separate screw terminal for the Relay Vcc. I understand about the opto-isolation but the schematic
at the other post seems to indicate that the little blue jumper connects the two Vccs thereby eliminating the opto-isolation and the only way to maintain it is to remove the little jumper and plug a jumper wire with a female connector onto the pin labeled
"JD-VCC". Seem like a stupid design to me. Just to save the cost of the added screw terminal.
http://forum.arduino.cc/index.php?topic=234876.new;topicseen#new