Thought this little project I've been working might be of some use..
I need a versatile IO board that I can hook up to an Arduino, Raspberry PI, Beaglebone or Carambola. All of which have an i2c bus. So armed with a MCP23017, I’ve come up with this IO board.
* 8 Relay outputs ( relays are spec’ed at 240V 5A )
* 8 Digital inputs ( switched input, closing to ground )
* Selectable i2c address ( up to 8 of these on the one i2c bus )
* All running from +5V ( relays can be powered from an alternative power supply if 5V coils are not to hand )
* Single layer, through hole construction ( old skool! )
You'll find more info at my blog: http://mark.mckillen.com/2013/01/i2c-8-channel-io-board-with-relays/, along with info for making your own PCB, KiCad and other bits-n-bobs.
PS: In the next rev, I'm hoping to add the interrupt line from the MCP23017 back into one of the GPIO pins. This will make reading the inputs a little easier.
i2c 8 channel IO board with relays