Patent GB-691108-A (GB)
Title: Telephone exchange systems employing key-senders
IPC: H04M1/515
Filed: 1950-02-03
Abstract: 691,108. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Feb. 3, 1950 [Feb. 9, 1949], No. 2830/50. Class 40 ((iv). A subscriber's key-sender comprises means for defining in response to the operation of each key a predetermined cycle of time positions, said means being interconnected with key contacts to control the transmission of the elements of a direct-current signal code to the exchange, the elements of the code appearing in positions of the time cycle in accordance with the said inter-connections; and means are provided at the exchange for stepping a receiving device to successive vacant receiving positions, the stepping being controlled by the code elements. Construction of key-sender, Figs. 2, 4. Depression of a push-button 4 operates the spring-set 9 and also depresses the member 13 which is integral with levers 17, 18 which are rotatable about the shaft 19. The member 13 also comprises an extension 15 which causes the operation of the off-normal spring set 10 when the member 13 is fully depressed. A member 22 is contained in a hollow bore in the lever 18, from which it is urged by the spring 23. An extension 26 of the member 22 has two hooks 26A, 26B and when the lever 18 is moved to the left (from its normal position on the extreme right, Fig. 4), the hook 26A engages the spindle 29 attached to the lower end of the lever 27B to cause the latter also to move to the left. The spindle 29 in moving to the left operates on the lower cammed surface of the lever 31 to raise its cammed end member 31A into the path of the hook 26A of the member 26. As the lever 18 approaches the extreme left position interaction of the members 31A, 26A forces the member 22 into the bore of the lever 18. The hook 26B thereupon releases the spindle 29 to permit the lever 27 to be returned to its home position by the spring 30 under control of the speed regulating piston 42. The disc 28, mounted on a spring-loaded lever 36 pivoted at the end of the right-angled extension of the lever 27, provides electrical connection between successive pairs of contacts 34. One set of these contacts is connected to a continuous metal arc and the other set is connected, e.g. as shown in Fig. 1 (not shown), to the contacts 9 controlled by the various keys. The lever 18 is locked in its right-hand position where the hook 26A rides over the cam 31A and holds the off-normal springs 10 operated until the lever 27 reaches its home position wherein spindle 29 permits the spring 33 to press the lever 31 down to allow the hook 26A to disengage and the lever 18 to return to its home position. In one method (Figs. 8, 9, 10) of signalling a four-unit two-condition code is used, each unit being separated by a spacing signal, the spacing signal consisting of the insertion of a certain resistance R2 in the line, one code condition being the increasing of this resistance to R 1 +R 2  and the other being the short-circuiting of the line. When the subscriber's loop is completed to the register, V and Lb are operated therein and the positive pulse in the transformer TR ignites tube KT1 to bring up T. On depression of a button, when the wipers W1, W2 (representing the disc 28, Figs. 2, 4) reach the contacts CI the off-normal springs ONS open and R1 is inserted in the line loop. The resulting negative pulse in transformer TR ignites KT2 and brings up relay U which releases T and U. As each code contact (CII, CIV, CVI, CVIII) and its succeeding spacing contact (CIII, CV, CVII, CIX) are passed, relays T and U are operated separately and released together, T coming up before or after U according as the resistance R2 is short-circuited or increased by R1. At the end of transmission the off-normal springs cut out the resistance R2 from the circuit to bring up T to prepare the receiving circuit for the next digit. The impulse counting chain G, H ... Q counts the code elements as they are received and connects contact u4 in turn to relays Aa, Ab ... Ad. According as t4 is operated before or after u4, earth is or is not applied to relays Aa, Ab ... Ad on which chain the first digit is thus registered. A second chain Fa ... Fb operated from the first counts the digits and arranges that they shall be successively registered on the chains Aa ... Ad, Ba ... Bd, Ca ... Cd. In a modification, Figs. 1, 6, 7 (not shown), in which earth returns are used no spacing signals are inserted between the code signals. The code signals consist of earth or disconnection on one leg and the first and third code elements are accompanied by earth on the other leg, this latter earth operating a relay in the register whose alternate operation and release control the operation of a relay chain distributing the code impulses to the registering chains. Other combinations of earth on one, both or neither of the line wires may be used for the various code elements.