The Charlie firmware is based on the Illutron 4 voice wavetable synth. It’s worth noting that DuaneB of RCArduino has done a lot of work with this synth, explaining it carefully, turning it into a library and creating the Illutron B. Nonetheless, this version of the Charlie is based on the original Illutron code.
This firmware is currently proof-of-concept only, and is provided here in case you want to experiment with it yourself.
Download the current version: Groovesizer_Charlie_007
Here’s a video introduction to the Charlie firmware.