I’ve been pondering retrofitting ST to my parents’ house. They (a) don’t want to see a bunch of new sensors everywhere, and (b) already have a hardwired alarm system with contact sensors and PIR sensors everywhere. It seems that this could serve as the basis for a nice ST system.
So, I’m considering using a Raspberry Pi with a large number of IO channels to passively monitor each zone/sensor at the tie-in to the alarm panel. The alarm system is active and monitored, and my parents use it regularly – so of paramount importance is not disrupting the operation of the alarm system!
- Has anybody tried a passive monitoring integration into an alarm system? What signal levels could I expect? Total off-the-wall guess: The sensors in each zone are wired in a series loop any individual sensor can open the loop if tripped. Then, you’d expect a pull-up on one side of the alarm panel and ground on the other side – meaning that the first side would read high when normal and low when tripped. Is there a standard for what voltages these systems run at? It seems that getting a multi-channel A/D board for the Raspberry Pi would be the safest/easiest bet, if possibly also overkill.
- Should I just write the software on the Raspberry Pi to make HTTPS calls to the ST hub on each observed state change? Is there a better way to do this? I could also use an Arduino with ThingShield to avoid the RPi->ST messiness, but not sure if that’s better.