Selecting proper relay for Door Buzzer

Continuing the discussion from My first Spark Project – Door buzzer:

I’m looking to accomplish something similar to @avidan, opening my apartment front door via text message with Twilio. I’m a bit stuck on putting together the correct circuit for this to work correctly. I was hoping the community could help!

From my research so far, it seems as if this type of circuit would be best:

In other words, I would connect my Core to a transistor (T1) that would amplify the current to a relay with a coil equal to the voltage of the door buzzer system. In my building, I believe I have a Pacific AF-1000 intercom system as the Intercom Station in my apartment is the Pacific 3404 4-Wire. According to this spec page, the AF-1000 uses 16V of AC current. In that case, would I need a 16V relay and a DC->AC converter? I know the Core is powered using DC. Would a 12V relay work in this case? Any advice would be greatly appreciated!

If this helps, I also found a high-level wiring diagram for the AF-1000 and the 3404 Station:

Many thanks

Use a 5V relay with the above circuit so you can power it easily. Just observe the current draw and make sure you keep that flyback diode in or get a relay with one built in. You may be able to get away with a reed relay if you don’t need a lot of current running through it. The contacts of the relay will be the only thing connected to the 16VAC and will act as the doorbell button.