I’ve chosen to use my Baby Orangutan board because it can plug straight into the breadboard. This board uses an AVR ATMega168. If you want to use your $50 Robot Board then that is fine as well:- just make sure that your $50 Robot ground and +5v are also connected to the breadboard to drive pin 16 of the L293D. You can do this by connecting a lead from one of your unused analogue-to-digital ports and connecting the ground wire to the ground of your breadboard, and the +5v to pin 16 of your L293D. Obviously the 3rd pin of the connector (which would normally be used for the sensor input voltage) will be left un-connected.
Now we need to choose 4 output pins from the micro-controller that we will use to run the L293D. I selected:-
Port C5 = 1a
Port C4 = 1b
Port C3 = 2a
Port C2 = 2b