Here is another I2C I/O plug:
It combines the MCP23008 8-bit port expander with a ULN2803 darlington array which can drive up to 500 mA @ 50V. The ULN2803 includes clamping diodes, so that relays and other small inductive loads may be tied directly to this plug.
Here is an example with a little unipolar stepper motor:
The red-black wire is from a 12V lab supply.
This demo sketch pulses the lower 4 bits of the output plug to rotate this motor back and forth by 200 steps:
The above was inspired by some sample code by Chad Phillips. It has been added the the Ports library as “output_stepper” example sketch.