I'm working on a project that is connecting an indoor mounted touch panel PC to a front-door mounted device (VDS) that has a speaker, mike, push button switch, and video camera. The VDS appears to have a built-in circuit to mute the speaker if someone talks, but not the other way around. And to make things difficult in the VDS, mic-out, speaker-in, and a push button switch are connected to the same wire. My first attempt connected this common line to both the PC's line-in and line-out jacks. I then used a comparator to determine when the button was pressed. The customer agreed with this approach, but when he tested it, he got feedback at his touch panel PC. This PC has both a speaker and a mike, and it does have a built-in echo cancellation circuit. The approach the customer wants to take now, is to replace the PCB in the VDS with a custom one that breaks out the mic, speaker and push button switch. This would sure make things easier. VDS mic-out would be connected only to PC line-in, VDS speaker-in would be connected only to PC line-out, and the switch would be connected, via a debouncer, to a digital-in line on the PC. I am concerned about audio feedback at the VDS - that the mic could pick up sounds from the speaker. I was thinking of solving this problem using a VOX like circuit, so that when audio was detected from the mike that the speaker would be disconnected, and when when audio is detected at speaker-in (PC line-out) that the mike would be disconnected. BTW, I did have a VDS for a while for testing, but never had the touch panel PC. I was using a standard PC for testing. Does this seem like a reasonable approach, or does anyone have better ideas? TIA
-Dave Pollum