Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
There have to be thousands of these circuits availble. A bit of searching should get you partway where you want to go.
A few questions to ponder though: Is it a stand-allone system or an addition to the public telephone network? How do you recognize end-off-call (hang-up)? Station-to-station call capability? System-in-use indication? Single or multiple speech path? I could go on, but....E