This doorphone was built using several components I had lying around. A Raspberry pi, RBSNTTL relay module, 12 volt wall wart, 5 volt wall wart, computer speaker amplifier, usb soundcard, microphone, loudspeaker, lit push button, locking cash box and white dual gang surface mount box. The doorphone was wired into an existing door strike and registered to the existing FreePBX phone system. Asterisk is installed on the Pi and two simple scripts were written. One script monitors for a button press, when detected it executes an asterisk console dial to a ring group including all phones in the building. Once the call is activated the pi's asterisk server waits for DTMF 5 from the called party (not the intercom). When DTMF 5 is heard asterisk triggers the second script which triggers the RBSNTTL which unlocks the door.
Well the intercom has been installed and operational for over 8 months now and I am fairly confident in its design. My employer would like me to build a second intercom identical to this one but with two-way video. I've done a lot of reasearch and one way video seems to be fairly common but two way is not to be found, even in commercial products. I did find two products that supposedly did this but there wasn't a hint of tech specs on them or any way to purchase them; Worse yet I can't seem to find them again to share here.
So, over the next couple of weeks I will be working on a new intercom utilizing the video capabilities in asterisk console using chan_oss instead of alsa. I don't have any experience with oss but here we go.
Also, now that I actually have people following this project, I'm going to work to improve my documentation.
Having some issues with echo on the intercom side. Somehow I need to make the asterisk console ignore audio picked up from intercoms microphone IF it came out of the intercoms speaker....... Hopefully that makes sense. The echo isn't a huge deal and its not heard by people using the intercom to gain entry, just the people trying to allow entry. Its maddening to hear everything you say echoed back a second after you said it, very hard to carry on a conversation.