Circuit and apparatus for bridging and monitoring

Claim 1

A telephonic bridging circuit in combination with a single cord switchboard comprising: a module adapted for connection to said single cord switchboard with respect to one of the central office trunks thereof, having a connecting cord and means for retracting said connecting cord within said module with a plug on said cord at a terminal end thereof for removal and insertion extrinsic to said module; a detection circuit having an SCR with the gate thereof biased for current flow by a line spike generated when a hook switch of a telephone connected through said module is closed or opened; means for momentarily breaking the electrical circuit in said detection circuit to cause said SCR to return to a non-current flowing condition; warning means for providing a warning to an operator when said detection circuit detects the closing of a telephone hook switch of one of the telephones connected through means of said cord; intercept means for connecting the cord of said module to the trunk of an incoming call; a terminal block for interfacing said module switchboard, and said detection circuit; a bipolar bridge connected to said circuit for purposes of supplying power to said module; and, a voltage regulator connected to supply a substantially constant voltage to said detection circuit;