Combined intercom and door opener system

Claim 1

A COMBINED INTERCOM AND DOOR OPENER SYSTEM WITH A DOOR STATION AND AT LEAST ONE REMOTE COOPERATING STATION, COMPRISING, IN COMBINATION, A DOOR STATION HAVING TWO FIRST TERMINALS AND INCLUDING FIRST ELECTRO-ACOUSTICAL TRANSDUCER MEANS AND ELECTRICAL DOOR OPENER MEANS CONNECTED IN PARALLEL WITH EACH OTHER TO SAID TERMINALS; A CENTRAL STATION HAVING TWO SECOND TERMINALS RESPECTIVELY CONNECTED WITH SAID FIRST TERMINALS, AND INCLUDING TWO THIRD TERMINALS, AMPLIFIER MEANS CONNECTED BETWEEN SAID SECOND AND THIRD TERMINALS FOR COOPERATING WITH SAID TRANSDUCER MEANS, A PLURALITY OF RELAY MEANS FOR CONTROLLING THE OPERATION OF SAID AMPLIFIER MEANS AND THE OPERATION OF SAID DOOR OPENER MEANS, RESPECTIVELY; AND SUPPLY MEANS FOR APPLYING ELECTRICAL ENERGY TO SAID RELAY MEANS, AMPLIFIER MEANS AND DOOR OPENER MEANS, RESPECTIVELY; AT LEAST ONE COOPERATING STATION HAVING TWO FOURTH TERMINALS AND INCLUDING SECOND ELECTRO-ACOUSTICAL TRANSDUCER MEANS AND CONTROL MEANS INCLUDING SWITCH MEANS FOR CONTROLLING THE OPERATION OF SAID SECOND TRANSDUCER MEANS AND THE OPERATION OF SAID RELAY MEANS, RESPECTIVELY, SAID SECOND TRANSDUCER MEANS AND SAID CONTROL MEANS BEING CONNECTED WITH SAID FOURTH TERMINALS; AND TWO-LINE CONNECTION MEANS ARRANGED BETWEEN SAID TWO THIRD TERMINALS AND SAID TWO FOURTH TERMINALS, RESPECTIVELY, FOR TRANSMITTING CONTROL CRITERIA FROM SAID SWITCH MEANS IN SAID COOPERATING STATION TO SAID RELAY MEANS IN SAID CENTRAL STATION AND FOR TRANSMITTING SIGNALS BETWEEN SAID FIRST AND SECOND ELECTROACOUSTICAL TRANSDUCER MEANS.