Monitor control unit

Claim 1

A MONITOR CONTROL UNIT FOR USE WITH A TELEPHONE SWITCHBOARD HAVING INCOMING AND OUTGOING CIRCUITS IN WHICH VOLTAGE IS AVAILABLE ON AT LEAST ONE OF SAID CIRCUITS WHEN ANSWERING AN INCOMING CALL AND EFFECTING AN OUTGOING CALL, SAID CONTROL UNIT INCLUDING: A TRANSMISSION LINE INCLUDING TIP AND RING CONDUCTORS HAVING INPUT AND OUTPUT CONNECTORS FOR CONNECTION TO SAID INCOMING AND OUTGOING CIRCUITS RESPECTIVELY; A SOURCE OF ELECTRICAL ENERGY; FIRST INDICATING MEANS; FIRST AND SECOND SWITCHES CONNECTED IN SERIES BETWEEN SAID SOURCE AND SAID FIRST INDICATING MEANS; A FIRST COIL FOR OPERATING SAID FIRST SWITCH CONNECTED IN SERIES WITH ONE OF SAID CONDUCTORS IN SAID TRANSMISSION LINE AND RESPONSIVE TO SAID VOLTAGE TO CLOSE SAID FIRST SWITCH; A SECOND COIL FOR OPERATING SAID SECOND SWITCH, SAID SECOND COIL BEING CONNECTED BETWEEN SAID SOURCE AND SAID TERMINAL TO MOVE SAID SECOND SWITCH FROM A POSITION CONNECTING SAID SOURCE TO SAID FIRST INDICATING MEANS THROUGH SAID FIRST SWITCH TO A POSITION ENGAGING SAID TERMINAL; AND A PUSH BUTTON SWITCH CONNECTED BETWEEN THE JUNCTION OF SAID FIRST AND SECOND SWITCHES AND SAID TERMINAL WHEREBY OPERATION OF SAID PUSH BUTTON WILL ENERGIZE SAID SECOND RELAY COIL WHEN SAID FIRST SWITCH IS CLOSED TO MOVE SAID SECOND SWITCH TO SAID TERMINAL AND MAINTAIN SAID SECOND RELAY COIL ENERGIZED, A CHANGE OF VOLTAGE ON SAID TRANSMISSION LINE IN RESPONSE TO TERMINATION OF A CALL MOMENTARILY DE-ENERGIZING SAID FIRST RELAY COIL TO OPEN SAID FIRST SWITCH THEREBY DE-ENERGIZING SAID SECOND RELAY COIL TO RETURN SAID SECOND SWITCH TO ITS POSITION IN ENGAGEMENT WITH SAID FIRST INDICATING MEANS TO ENERGIZE THE SAME AND INDICATE COMPLETION OF SAID CALL.