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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?

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You might want to look at Asterisk, which is basically a telephone central (PBX) application for Raspberry Pi. I don't have first hand experience with this tools, but it should be able to do what you want, sort of.

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  • Wow, that seems really interesting, I haven't stumbled upon that before. From what I see there it doesn't work with "analog" lines so I'm not sure I can use it but it's definitely a starting point. Thanks!
    – Mircea Sandu
    Commented Feb 20, 2014 at 12:19
  • Yea asterisk is really great. There is even a distro called RasPBX. You don't need phone lines for this as you can use SIP to transmit data over Ethernet or Wireless. You have a central raspberry PBX, like at the door and a client PBX that you call, by pressing button, or maybe flat number. You even have SIP clients on your mobile phone, computer, etc. So you might be outside in the garden, or in town on 3G and your phone can ring if your doorbell button is pressed!! Its awesome!
    – Piotr Kula
    Commented Feb 20, 2014 at 15:22
  • To use Analog lines with Asterisk you need analog interface card: digium.com/products/telephony-cards/analog
    – Angsuman Chakraborty
    Commented Jul 8, 2017 at 6:52

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