Here’s an entry in the Open 7400 Logic competition: Telephone Intercom from TTL
This is the only craziest project I ever made, beginning in June 2007 and completed in November 2007. Very complex circuits, and uses a lot of IC (about 38 IC). If you think this is a waste, yes! Indeed. However, why do I keep making this project? The reason is, I want to know how the phone working principle and how the analog and digital circuits work.
My stupid apartment complex has been trying to wire one of those telephone-entry systems kind of like this one for like 2 WEEKS! they need to hire you. enough said