HELP 2 Relay module

I bought on of these as I wanted to play with it. It is rated at 240V/10A on both circuits with a single pole change over switch on each. The replays are isolated by opt-o-couplers.



It took me over an hour to find the circuit diagram on the web, by calling up Google images for a 2 relay module, and looking at every sit4e showing one like mine! I finally found this one:



The IN1 & IN2 are active LOW inputs which drive the Opt-o-couplers. They in turn drive the transistors Q1 & Q2 and the relays. The power supply for the relays can be taken from the VCC supply to the board (i.e. from the Arduino) or from a separate supply by removing the jumper from JD-VCC and VCC. Whatever you do DO NOT connect the jumper from VCC to GND as a place to park it, this will short circuit the Arduino +5V supply. If you want to use a separate supply for the relays then just remove the jumper and discard it.