Home intercom/paging system

After deploying a multi-room audio system at home (see here), I figured it would be interesting to leverage the installed raspberry pis as a way to stream voice from room to room (“diner’s ready”, without having to shout).

Requirements

For this project I wanted to have:

  • multiple push-to-talk stations available at several locations
  • streaming of voice to all other audio stations
  • reasonable latency
  • the ability to add more stations if needed

HW overview

The setup is as follows:

Overview

  • One raspberry pi running a PBX (Asterisk)
  • One raspberry pi for each station
    • with a USB audio device to sound input and output
    • running an SIP client (PJSIP) and streaming audio to/from other stations
    • using one GPIO to handle the push-to-talk button triggering calls to other stations

SW setup

The credits go to this guy for installing Asterisk & PJSIP.

Raspberry pi install

I used a Raspbian light image, but any distro will do.

Asterix PBX install

sudo apt-get install alsaplayer-alsa python2.7-dev python-daemon python-lockfile libv4l-dev libx264-dev libssl-dev libasound2-dev asterisk

PJSIP install

wget http://www.pjsip.org/release/2.3/pjproject-2.3.tar.bz2
tar xvfj pjproject-2.3.tar.bz2
cd pjproject-2.3/
./configure --disable-video --disable-l16-codec --disable-gsm-codec  --disable-g722-codec --disable-g7221-codec --disable-ilbc-codec

Then create a custom config header:

nano pjlib/include/pj/config_site.h

And fill it with:

#define PJMEDIA_AUDIO_DEV_HAS_ALSA       1
#define PJMEDIA_AUDIO_DEV_HAS_PORTAUDIO  0
#define PJMEDIA_CONF_USE_SWITCH_BOARD    1

And finally build it:

make
sudo make install

PJSUA/Python wrapper install

cd pjsip-apps/src/python
make
sudo make install

Asterisk configuration

I used a very basic Asterisk configuration to allow the stations to register to the PBX and call each other:

And in sip.conf:

[2000]
type=friend
context=home-phones
secret=1234
host=dynamic

[2001]
type=friend
context=home-phones
secret=1234
host=dynamic

[2002]
type=friend
context=home-phones
secret=1234
host=dynamic

A dialplan must be configured in extensions.conf. Here is the one I used:

  • a “home-phones” Context to hold our extension rules
  • a set of extensions:
    • Format is exten => name,priority/step(stepname),application(...)

    [home-phones] exten => 2000,1,Dial(SIP/2000) exten => 2001,1,Dial(SIP/2001) exten => 2002,1,Dial(SIP/2002)

Python intercom management script

TODO


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