Relays

Omron 3.3v relay (from www.ciseco.co.uk)

The input to the relay board is high-drive (NPN transistors), and the base resistor is 1K (small in comparison to the Bifferboard output pull-up resistor), so you would need to drive it with a PNP transistor rather than directly from a Bifferboard output.

You can do this with something like this:

Where Ic is connected to the relay board input (in this case the relay board transistor base becomes the load).

The relay board could easily be redesigned to use PNP logic, and then this wouldn't be required.