A preliminary schematic of the main (inside) portion of the project has been posted. This consists of the CPU, power supply, SD card and audio systems. It's almost the same as the GPS Voice Clock I did earlier this year, but instead of the "tick" output, the second DAC output has been hooked up. The idea is that this is effectively an audio synthesizer (done on the cheap) that has a two-note chording capability. The hope is that the two DAC channels can be run with DMA (so with minimal supervision) and can play back audio samples from the SD card independently, so that the overlapping quality of the audio will make it sound more natural.
We'll see how this works out in practice, of course.