Arduino to control intercom

[mordaigue]

I have the fermax 101ci15b. I have found little information about it online. Looking inside, There are 5 wires used:

Actual picture of the board (slightly difference from the source I found):

The max tension I can measure is 9V.

To open the door, I just have to short the two pins of the button that is normally used. I imagine that can be done using a transistor like the PN2222.
To catch when some one buzz, I can sense the "Call" wire, probably using a voltage divider? The call tone normally goes to the speaker. I think that the call pin is NC and the speaker is NO. When you pick up the intercom phone, the call pin is then opened to prevent the loud ringing from obliterating your ear if someone ring you? I am not really sure about this part.
I guess I could just tap into the microphone/speaker directly too.

Now, I wonder, how would I manage the microphone and speaker? Ideally, I'd like to just hook it up and figure out how I want to handle that later code wise. I had in mind to make a VOIP server so I can call my mobile line if I get ringed and remotely control the intercom using something like an ESP32.

[gilshultz]

@mordaigue

fermax 101ci15b

I used this script in google: "fermax 101ci15b schematic" and got over 800 hits. I did not drill down to find out what was there but that is a lot of manuals.
Without a circuit schematic I would use a relay and be safe, using a transistor can get you into trouble. If needed you could use an optocoupler to maintain isolation.

[mordaigue]

@gilshultz

fermax 101ci15b schematic

True, lot of hit but nothing that could truly help with the actual board schematics unfortunately. I did not think about octocoupler, tx for suggestion. The handheld speaker/phone is 4 wire and is probably pretty standard, any component to tap the signal?

[gilshultz]

I hate to fry things and do not couple into something unless I am comfortable doing that with that particular circuit. Relays for buttons are almost always safe. Otherwise I need to check polarity and voltages.