at the moment I have a cheap “video intercom system” that serves as doorbell and opens the entrance gate.
This intercom has two cables that go to the eletric lock of the gate. When I press a button on the intercom, I can read a 12vAC voltage on these cables for a second (or less) and the eletric gate opens.
The intercom is powered by an external power source. No 12vac is in input to the intercom.
In the picture attached:
- on the left, the power source
- on the right:
- on the top, a 4 wires connector. These wires go to the external unit (where the doorbell and the camera are)
- on the bottom, a 2 wires connector. Red and black, these are the wires where I read the 12vac only when the “open door” button is pressed, and just for a few seconds.
The project I would like to realize is: while leaving the existing as is (i.e.: the intercom should keep working as it is now), I would like to be able to add the possibility to open the gate with an Arduino.
Actually, I think I will use a nodemcu, that is a board based on esp8266 12e and compatible with arduino.
The key point to start is: how can I “output” 12vac from an arduino? Should I use a relay? I am not able to find a 12vac power source… can you help me?
What if I use a 12vdc do power up my arduino and then find some converter to get some 12vac?
The second important point is to be able to “switch” from the intercom and the arduino in safe mode. I mean, I would like to avoid that the eletric gate receive the input from the both of them at the same time. But I think I could, again, use two relays to block/allow the input from the intercom. E.g.: the circuit always opens the “channel” between the intercom and the electric gate but when the arduino get the command, switch to its channel to the intercom.
Do you think it is feasable? Do you have any suggestions/idea?