GB837137A - Improvements in or relating to dial switches for use in telephone systems - Google Patents

Abstract

837,137. Impulse transmitters. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Aug. 6, 1958 [Sept. 18, 1957], No. 29332/57. Class 40 (4). Attempts to make fraudulent calls from a coin box by taking advantage of free calls available with digits such as "0 " or " 9 " are frustrated by the provision of a cam-controlled, articulated lever which unmasks the impulsing contacts for a predetermined digit and, unless restored by full return motion of the mechanism, is deflected to disable the impulsing contacts during further dialling. As shown, the articulated lever 16 is pivoted at 17 and carries studs 56 and 60 co-operating with portion 50 of a nylon cam 28. When the finger plate sets up a " free " digit, cam 28 reaches stud 60 and deflects the lever 16 to drive a bevelled nylon stud 18 underneath a contact spring 52 to break its contact with 53 and unmask impulse springs 43, 44. When lever 16 is in this position an arm 23 articulated to the lever at 19 and biased by a spring 24 against a post 21 is drawn to the right and inclines inwardly so that an associated detent 20 is placed in the path of teeth 58 on the cam 28. Return motion of the dial mechanism, which may be the kind disclosed in Specification 784,351, idly deflects the detent 20 but does not interfere with the position of lever 16 until in the last moments cam edge 50 engages stud 56 and returns the lever to normal. Should the mechanism be halted before the finger plate is fully returned, in an attempt to hold the masking contacts open, further setting movement of the finger plate turns one of the teeth 58 of cam 28 into the detent 20 and forces the lever 16 further to the right. As the lever 16 slides arm 23 against post 21 the cranked end of the arm slides on to the post and rotates the detent out of the path of the teeth 58 leaving the lever 16 in its overthrown position in which it deflects the upper end of a bell-crank lever 30 pivoted at 31, Fig. 2, and causes its lower end to force the impulsing contacts 43, 44 open and hold them to release the connection. The mechanism now performs idly until such time as the finger plate is allowed to restore fully and cam 28 resets the lever 16 to normal.