I need to interface door phone system to a pc soundcard to listen and talk to the external unit.
The door phone to interface is an as yc/200 of BPT and its a classic analog 4+n wires Door phone system and I have access only to the internal unit.
In the internal unit I have a cable with 4 wires: a Ground wire, a call wire, an audio in, an audio out; going through the power supply to the external unit.
This is a picture of the phone.
Unfortunately the datasheet doesn't say nothing regarding the audio lines and their signals. What I know is that they are probably standard for every 4+n wires door phone.
Now what I would like to understand is how to connect the audio signals to the sound card without damaging it.
Are those signals usually high voltage or high impedance?
The power supply output 11 volts DC and 15 volts AC. Also the pushbutton that open the door is connected to the audio out towards the external unit. What kind of signal is sent to open the door?