I'm going to start working on my next project - creating a garage door alert/alarm. It will let me know when I leave my door open for too long and when I arm my alarm system in stay mode at night I want it to disable wireless remotes and alarm if the door is opened.
The one part of this that is a little tougher is monitoring what the alarm system calls "keybus". It is 4 wires (+12v, gnd, data, clock). It has a limit of 1000' and I put my scope on it last night and found it is communicating at 1khz.
It supports multiple devices and the main panel knows if a device is missing or malfunctioning. My question is, with only one data, how might it communicate? Does it make sense that the panel always polls each device (keypad) in order and asks the keypad if a key has been pressed? I am presuming the clock is generated by the main panel. It seems to me that with only one data channel, that something has to be the "master" and constantly ask the slaves if they have anything to report...