This wasn't supposed to work....

[karbomusic]

I did a little more POC work this evening...

PWM to simulate a sine wave.
High/Low to simulate a square wave.
Switch to choose either one or the other.

Still pretty archaic but not too much work. I'll probably add a momentary switch to create a tap tempo control, refine it some and throw into a pedal just for fun. Once I get a suitable physical framework, I can build it out, expose the USB connector and update the code after the fact which is part of the attraction. Will update as I go.