I could carry my keys to unlock my building door, but I’d rather not. I could buzz up to my apartment and my girlfriend could buzz me in if she’s around, but that’s obnoxious. It would be best if I could buzz up a short-code to my apartment (a Morse message of sorts) and have it automatically buzz me in. Fortunately, that can be done with Arduino.
The Buzzer Situation
My apartment building is equipped with a Aiphone VC-K intercom and door release system. The entire system runs on 12V DC power with low current, so it’s much safer to interact with than any devices attached to a wall outlet. A quick web search for the model yielded a wiring diagram, a screwdriver provided quick access to the terminals in the handset unit, and a multimeter allowed me to understand how it works:
I have access to the VC-K unit in my apartment; the VC-M is at the front door. Terminals 1 and 2 provide communication with the front door. Terminal 3 is ground. Terminal 4 carries 12V