How about multiplexing it with an ADC as well? I'm not really sure if you want to do that, but it would be nice to have a standardized analog I/O circuit to play with: microphones, light sensors, etc.That's possible, but more complex than a separate DAC and ADC. I don't think the TI84+ is capable of recording sound and playing it back. The playback is possible, but the recording and processing is pretty much impossible without proper I/O. You could also just hook your calc up to an arduino since it features pwm and ADC.