Hi,
I like how you used a single header pin as the keys, I wanted to make something like a stylophone interface but this looks a lot easier.
I assume that you are sending midi messages from the Arduino to the keyboard ?
Have you tried going the other way midi into Ardiuno ?
I have bought a five dollar keyboard that I plan to drive some of my recent synth experiments with -
I am considering getting a simple midi keyboard to drive them with instead - the five dollar keyboard is pretty nasty.
Duane B