Electronic gating control for manual telephone switchboard

摘要

A gating circuit for operation in conjunction with a manual cord telephone switchboard to service multiple operational modes of a subscriber telephone connected for telephone communication to a central office. In one mode, an internal intercom connection is established between the subscriber telephone and the switchboard. In a second mode a secretarial service connection is established allowing direct communication between the switchboard and the central office. A ring detection circuit detects when the subscriber telephone has been rung from the central office.