Hi @chris101 and Hi all !
The project is fully working and running, so I've composed a song around this project.
If possible, use a good set of speakers or headphones 
All sounds ( exept the noise wave ) come from the String Synthesizer Littlebits arduino, processed through littlebits modules ( filters, envelopes, delay, ... ).
Even for the noise, a rather complex circuit around only littlebits modules, create a slowly moving and evolving noise sound wave. And guess what, no arduino involved here !
The rhytm track comes from the Littlebits Mini Pops project.
Everything was recorded with audacity and only some reverb was added to the mini pops rhytm.
All other tracks were just panned a bit to add stereo.
A standard MIDI keyboard with DIN ouput is connected to the serial input of the Littlebits arduino through a self made MIDI bit. Rather easy and it works. You can even adapt the sketch to use other parameters like modulation wheel etc.
The fun part is, finally polyphonic playing is possible, yes, chords, please !
It took me a week or so to rewrite the whole sketch to adapt the Littlebits arduino. I have totally no programming skills and I had to learn everything by studying the Leonardo environment. This was a good way to learn how C++ programming work and how to use registers and timers. I've written down everything in a notebook for future use.
By now, I'm gathering all info to put on the invention channel.
Greetings
