DVDdoug:
NEVER connect two outputs directly together, but if you put a 10K resistor in series with each signal, then connect the "outputs" of those resistors together, where they are connected together the left & right signals will be mixed. (That works with a line-level or headphone-level signal into a high-impedance input, like the Arduino's ADC.)
Okay, I will definitely rethink my audio output method. Why is it that adding those resistors prevents a problem? I had previously thought that the outputs would simply "stack", but my area of expertise is unrelated to most circuitry and I could be totally misled.
DVDdoug:
I don't know anything about the Rainbowduino, but if it has the same Atmel ATmega chip as the Arduino, it has an ADC with multiple inputs (and hopefully there are brought-out on the PCB for user access).
As for the chip, Seeedstudio does say (here on their store) that the Rainbowduino has the ATmega 328 installed, but I cannot find the correct pin that would be used as the ADC. Would you mind looking at this image, or the image in the original post and checking? I have been trying to understand the hardware and software for the past couple of days and it's a whole new world to me. I'm getting a bit lost.
