Dear all,
i'm doing a project similar to answering machine. For which i need to interface 8051 with the telephone circuit. I'm in need of ring identification circuit in the telephone line.
I'll attach my PCB in parallel connection of the telephone line. After 3 ring tones, the line should automatically switch to my PCB instead of the telephone instrument.
For that my PCB should identify the three ring tones which is required now

I would be greatful if i get the needful help

thanks & regards
veeramanikandan