Teleprinter control device

Claim 1

IN A TELEGRAPH SYSTEM WHICH COMPRISES A CENTRAL EXCHANGE, A TELEGRAPH LINE PAIR AND A TELEGRAPH INSTRUMENT ADAPTED FOR LINE SWITCHING DESTINATION SELECTION CONTROL MEANS FOR THE INSTRUMENTS COMPRISING: (1) RESISTOR MEANS AND FIRST DIODE MEANS IN CIRCUIT WITH SAID LINE FOR LIMITING CURRENT FLOW IN ONE DIRECTION TO A PREDETERMINED IDLE VALUE; (2) MOMENTARY START SWITCH MEANS AND A FIRST RELAY HAVING A PAIR OF CONTACTS, SAID START SWITCH MEANS AND SAID CONTACT BEING CONNECTED ACROSS SAID RESISTOR FOR CALLING INITIATION AND RETENTION RESPECTIVELY; (3) VARISTOR MEANS COMPRISING A PAIR OF OPPOSITELY CONDUCTING SEMICONDUCTOR DIODES CONNECTED IN PARALLEL, AND IN CIRCUIT WITH SAID LINE FOR ESTABLISHING A STABILIZED VOLTAGE DROP THEREACROSS UPON LINE CURRENT FLOW THERETHROUGH; (4) FIRST BISTABLE TRANSISTOR MEANS HAVING AND "ON" STATE AND AN "OFF" STATE, SATURABLE TRANSISTOR MEANS CONNECTED THERETO AND TO SAID VARISTOR MEANS FOR THE SWITCHING OF SAID FIRST BISTABLE TRANSISTOR MEANS CONSAID "ON" STATE ONLY UPON TRANSISTOR DESATURATION INDUCED BY VARISTOR MEANS VOLTAGE DROP EXTINCTION, BACK CONTACTS ON SAID MOMENTARY START SWITCH MEANS CONNECTED ACROSS THE SAID SATURABLE TRANSISTOR MEANS OUTPUT TO OBVIATE SATURABLE TRANSISTOR MEANS DESATURATION EFFECT DURING START SWITCH MEANS INACTION, SAID FIRST RELAY BEING CONNECTED TO SAID FIRST BISTABLE TANSISTOR MEANS AND RESPONSIVE TO THE "ON" STATE THEREOF TO CLOSE ITS SAID CONTACTS ACROSS SAID RESISTOR MEANS, FOR MAINTAINING LINE CALLING CURRENT AFTER TRANSISTOR DESATURATION; (5) DIAL MEANS IN THE LINE FOR DESTINATION CODE SIGNALLING; AND (6) SECOND DIODE MEANS CONNECTED TO SAID LINE AND TO THE TELEGRAPH INSTRUMENT AND OPPOSITELY DIRECTED TO SAID FIRST DIODE MEANS FOR FLOWING LINE CURRENT INTO THE TELEGRAPH INSTRUMENT UPON THE LINE POLARITY REVERSAL.