GB1155068A - Direct key calling telephone station having binary converting means - Google Patents

Abstract

1,155,068. Automatic exchange systems. COLUMBIA CONTROLS RESEARCH CORP. 25 May, 1967, No. 24273/67. Heading H4K. In a private inter-communication system employing a large number of push button telephone substations, relay trees located at a central point but individual to each substation receive a coded designation of a wanted party as determined by operation of the pushbuttons at that substation and effect the required connection. In the figure the equipment enclosed by the broken lines 34 is located at a substation while the remaining equipment is located at a central point. To connect to another station the receiver 11 is lifted moving a cradle switch 20 to its dotted line position thus connecting a current supply to the receiver and one of seven keys 22 to 28 is then depressed thus specifying the first digit of the wanted substation number. Isolating diodes 33 connect the keys to three lines 30 to 32 so that they are selectively energized in accordance with a binary coded representation of this digit. At the central point corresponding self-holding relays 30b to 32b are selectively energized. A relay 42 is simultaneously energized through diodes 39 to 41 moving its contacts 42a to 42c to their dotted line position charging a pair of capacitors 46 and 50. When the key is released the relay 42 is de-energized discharging capacitor 46 through a relay 36. Relay 36 which is maintained energized by its holding contacts 36b moves three contacts 30a to 32a of a twoposition switch to their dotted line position. This disconnects the relays 30b to 32b from the lines 30 to 32 and connects three further selfholding relays 30c to 32c to the lines 30 to 32. A second digit key can now be depressed setting these relays in accordance with the binary code representation of the second digit. The six relays 30b to 32b and 30c to 32c have banks of contacts which form a tree and in accordance with the digits received connect a corresponding output terminal (indicated by digits 1 to 77) to its input terminal. A push button 49 is then pressed sending a D.C. ringing signal to the called station, i.e. to its bell 21. Corresponding output terminals of all relay trees are connected together. An additional connection which connects permanently between a different one of the output terminals (1 as shown) and the input terminal for each substation determines which station responds. As each digit key is released capacitor 50 discharges, enabling a relay 51. If the called station is busy a positive potential is received over a contact 51a to maintain this relay energized. A busy signal oscillator 52 is connected to the calling party over a contact 51b. A contact 42c of the relay 42 is opened while any key is depressed preventing listening in.