I'd like to hook up a small raspberry pi project to my apartment's doorbell. I've taken the case off to take a look at the wiring and it looks pretty simple, but I have some questions about it; apart from some breadboard experiments I'm an complete newbie to electronics.
The doorbell is shared with everyone else in the building; it's got a button to listen to the person speaking down below, a button to speak to them, and a button to buzz them into the building. What I want to do is attach the pi to the circuit such that it will detect when the doorbell rings and notify me over IM, and then optionally buzz the person in (the practical reason for this is that I have a long narrow apartment and can't hear the buzzer from the bedroom). I'm fine with the software part of this project, getting the network stuff working, etc. What I need help with is the hardware part.
Here is a picture of the inside of the doorbell case
- I've labeled the leads corresponding to the door, listen, and talk buttons respectively.
What I'm curious about is this:
* It looks like each of the leads has a twisted pair of wires coming to it. What's with that? I would expect one wire per lead, and it certainly looks like each pair is electrically connected anyways.
* Are the wire colors in some sort of standardized scheme that I can look up or something? (It's not clear from the picture, but all four pairs are bundled up in a larger cable.)
* It looks from the circuit like the wire marked "X" is most likely the ground, right?
* The number on the upper right-side of the circuit board is "2/96", does that mean anything sgnificant?
* Is there a standard or common voltage for these types of doorbell systems? (I do plan on measuring it with a multimeter to before I attach anything else to it, and I'm cognizant that it could have dangerous levels of current.) Am I likely to be able to attach one of these leads to a GPIO pin directly (assuming a resistor of the right type) or would I need some more complex electronics in between?
* Any other advice about this project?
One thing that is vexing me right now if the power setup - I can probably fit some kind of batteries or something in the case along with the pi, but ideally I'd like it to just be powered through the lines in the doorbell itself, or maybe be asleep most of the time and then when the doorbell rings, awaken, connect to the wifi and send me a message.