Step 2: The arduino
I grabbed an old stripboard version I had lying around.
There are various instructions available online for making these, I remember referring to the Standalone Arduino / ATMega chip on breadboard instructable and the ITP Setting up an Arduino on a breadboard tutorial.
It was a lot of learning ago, so don't copy my wiring! If I were to start from scratch I'd do it like the schematic included in the images...
Connect the pulse output wire to pin 12 and ground to GND