I am currently looking for a way to connect an intercom to the raspberry pi, at the moment, the intercom wires are connected to a regular telefphone ( only two wires needed ), when someone dials the phone rings, when I pick up I can talk to them and in order to open the door I keep the 0 button pressed. The phone has a switch for Pulse / Tone and only the Pulse mode actually does something.
Is there a way in which I can capture the call into the raspberry PI and eventually send back a Pulse in order to open the door?
I saw this question How can I generate frequency / pulse signals? but I don't think it's the same thing.
Another approach I am considering is to open the phone and somehow connect only the controls to it in order to prevent any power surges or a much higher voltage. Is that possible?
In the end I wish to connect this to a web server and send a push notification to my phone whenever someone calls and be able to open the door remotely.
Thanks a lot!
EDIT: I am also aware there might be a way to do this with a modem, only I'm not sure a modem could capture those signals
SECOND EDIT: after digging even more on ways to do this I have discovered a possible way to do this, first I would need two relays, one for answering and one for sending the signal to open the door ( the 2 would be wired to control the actual buttons from the phone ) and in order to wire the incoming signal use a optocoupler ( http://en.wikipedia.org/wiki/Opto-isolator ) which I would then connect to a GPIO pin and monitor activity there. Would this work? Has anybody tried something similar?