Hi
I want to interface my telephone line (POTS) to 8051. I just know that the phone line carries DC signalling voltage and the voice communication is also modulated using this DC voltage. I would like to insert my processing circuitry between the phone line and the phone set.
x--------Phone Line---------x|My Circuit|x---------x|Phone Set|
I would just like to digitize the voice, do some processing and then convert it back to the voice signal.
I have been unable to figure out how to interface my circuit to the phone line and to the phone set as the signal levels are not compatible with TTL/CMOS that my circuit would use.
Any help will be appreciated. In particular, I wonder if there is any ADC and DAC that just interfaces directly with the phone set? And how do I do this without interfering with the initial signalling when a number is dialled or a call is coming in?
Thanks in advance!
-- devj