Not really pertinent to this project, given the model of opener I have, but a tangential point of interest non-the-less...

At first read through the manual, I mistakenly thought that my garage door opener could utilize either the 1-button (M350 model, which I have) or the 3-button (M3100 model) controllers. I was excited by the prospect of adding the ability to turn on/off the opener's light, b/c not only do I worry about whether or not I forgot to shut the garage door, but I know for certain that I somewhat regularly forget to turn off the separately wired garage lights until I'm already backing out in the car. If I could control the opener's light, then I would not use the other light source when leaving in the wee hours of the morning. So this started me on a research path of "how do you control 3 functions w/ 2-wire analog channel?"

According to what I found, two scenarios are likely:

1. "AC hackery" using diodes. In this method, the 2-wires running to door button is 12 or 24 VAC. By utilizing a properly rated diode, one could create 3 different shorts across the terminal pair:
   A. Open/Close signal = full short/dead short
   B. Light On/Off = pos single-phase short via diode in one direction
   C. RF Lock = neg single-phase short via diode in opposite direction
2. Voltage/Resistance difference. In this method, each trigger option is implemented via higher/lower resistor values for each button to create different voltage drops at the terminals.

I suspect scenario 1 is more likely, but unfortunately (and upon closer reading) my garage door opener does not support this feature set. So I won't be testing this out since it's not worth me buying a new garage door opener--otherwise, I could save myself the trouble of this project altogether and by a turn-key solution w/ Internet control already built-in. :)

Still, just thought I'd put this out there for others to consider in their future projects...