This is a design for a board to buffer the outputs of a Raspberr Pi so that it can drive 5V devices which use up to 500ma. The buffer chips are ULN2003's which are Darlington pair arrays with open collector outputs. This means that they form low side switches. There are many articles on Google for using ULN2003's so I won't detail wiring here. The silkscreen is marked for the connections for the Camerabotics Lensmaster ActionServer to make it easier to wire up.
PLEASE NOTE: This is a first version of this design. I'm working on a second revision with more/easier connections and push/pull outputs. However, you are welcome to use this if you find it useful.
I've included pictures of the assembled board and my initial installation. The installation has three relay outputs and three 240V solid state relays. (The relay board has 8 relays of which one three are used)