Preventing Audio Feedback on Common line

[StudentSA]

Good Day,

Im trying to implement an "intercom" system using microcontrollers for a PoC application. We have 1 common wire line biased at 9V and two or more intercoms each with a microcontroller based on Arduino. Each TX/RX intercom device can listen and talk on the common line. Im using a non electrolytic capacitor to "AC couple" RX and TX to the microcontroller. Im trying to prevent transmitted audio by a device from being received by the same device. i.e. if I talk I do not want to hear myself. Im hoping that there exist a simple solution or a IC that is made for this application?

A high level diagram is as follows:

Thanks,
StudentSA

 

[kubeek]

I think the solution is to use an opamp that will subtract your Tx signal from what you are reading at the Rx line.

 

[JimB]

Try researching "telephone hybrid".

Here is something which may give you a good start:

AN010 - 2-4 wire converters/ hybrids

ESP Application Notes - AN010 - Telephone hybrids, 2-4 wire converters

sound-au.com

JimB

 

[audioguru]

This circuit electronically cancels (adjust R7) your voice from playing in your speaker:

 

[unclejed613]

are you sending analog audio or digital audio?

 

[audioguru]

In the good old days, a Press To Talk switch was used. All mics were disconnected by its switch at rest then when you press your switch to talk it connected your mic and disconnected your speaker.
Later, Voice Switching was used but it was messed up by noises like a person coughing, a motorcycle driving within a few miles away or a dog barking.

I worked with newer intercoms that used a digital echo canceller circuit that made a model of the room and its acoustics that cancelled feedback. It got messed up if something changed the room's acoustics like an open door or an added or missing person.