I'm working on connecting my old flat intercom to the raspberry so that I could receive a call on my smartphone when someone rings at the entrance door.
The intercom handset has 3 wires:
- blue & red connected to the speaker
- blue & white connected to the microphone
Same thing for the handset microphone with blue and white (blue for ground, white for left channel).
Then I connected the 2 jacks to a USB audio sound card plugged into the Pi.
The call to my smartphone is made using SIP software running on the Pi.
When I pickup the call on my smartphone, there is a very loud noise on the communication which you can hear in both ends.
If I disconnect the audio output jack, the receiver can hear me well.
If I disconnect the audio input jack, I can hear the receiver well.
I have no idea where this noisy sound comes from and why does it happen only when both jacks are plugged to the Pi.
Is there something wrong with the way I wired everything ?
Thank you for your help