Hi,
I have a microphone line on an old intercom (which when disconnected is at around 10V, once the microphone is attached the signal drops to 6.9V). I can pull it to 6.9V with 650Ohm manually.
I have managed to get the receiving audio to a level which I can sample via ADC, but could anyone give me a hint how I could put audio onto a 6.9V line?
A simple DC bias doesn't work in that case..
I'd think about eg. pwm via resistor and mosfet attached to the dc-line? Any better idea?