single line telephone intercomSingle line telephone intercom

Design a micro-controlled circuit that will provide a means for telephone service over a single line extended between maple farms pomping stations which already have a cable link for a computer control between them. These are generally located around maple forest but within a few miles a each other. The existing cable is a standard telephone drop cable with 4 wires and only 2 of the wires are presently used. The other pair will be used for the proposed intercom. It will use standard touch-tone telephones except for the ringing which will be a piezo driven by the circuit. ( no ac ring voltage). Some of these farms have less then 8 stations and some with more then ten so the circuit will provide single digit calling and two digit calling. Programming each station address and single or two digit calling will be done by keying from each touch-tone phone with special code. At the main station which normally has Bell telephone service the circuit will also provide a means to connect to the Bell network by keying a code (like 9 or ?) from any station. Also at the main station the circuit will provide the 48 volt talk battery for the whole intercom network. The contractor will design the circuit, provide a draft of schematic for our review, upon acceptance layout the pcb, do the required programming, order parts and pcb for prototype test, assemble and test ten circuits. Deliverable: Final schematics, documents for PCB manufacturing, boms, testing procedure, firmware/software. The later will be described and commented for any other programmer to make any necessary future modifications to improve the circuit. We will pay for all parts and pcb manufacturing. Please read the attached for more info and specs. Any questions will be promptly answered.