Patent GB-524262-A (GB)
Title: Improvements in impulse senders of the type used in telephone systems
IPC: H04M17/02
Filed: 1939-01-25
Abstract: 524,262. Impulse transmitters. GENERAL ELECTRIC CO., Ltd., and PUCKETTE, C. C. Jan. 25, 1939, No. 2548. [Class 40 (iv)] In an impulse sender of the kind in which a short circuit of the sending springs is normally removed by inserting a coin but can also be removed by dialling the digit or digits of a " free call, being replaced when the dial returns to normal after sending such digits, are provided to prevent fraud by dialling a "free" digit without removing the receiver and then setting up a call without allowing to complete return of the dial after each digit or by dialling a "free" digit for each digit of the wanted number and only allowing the dial to return each time the distance necessary for sending the required number of impulses. Three arrangements are described with reference to the type of impulse transmitter described in Specification 518,721 in which the impulse springs are controlled by a rocker arm 25, (56) pivoted to a pivoted lever 31 (60) and arranged to be swung clear of the springs during the setting operation. First arrangements, Fig. 1. When the finger plate is rotated a projection 23 on the spring barrel moves clear of a spring 24 and subsequently in the case of " free " digits, which have high values, raises a pivoted lever 14 which is then latched by spring 24. In the case of " free " digits also a stud 22 engages a pin 19 on a cam disc 13 and moves the latter so that a spring 12 drops and allows short-circuiting springs 11 to open. In its return movement the stud 22 engages a stud 21 on the cam disc ana after the last impulse has been sent restores it to the position shown. At the same time the spring 24 is moved clear of lever 14 which drops. If a new digit is attempted without allowing complete restoration of the dial the lever remains latched and the arm 25 engages a projection 26 and moves a slide carried by the lever to the left in which position it is latched by a spring 27, holds up lever 31 and by .means of a stud 32 holds the impulse springs open. When the dial is allowed to return the lever 14 drops and the slide is restored by a spring. Means may be provided to hold the impulse springs closed instead of open. Second arrangement, Fig. 3. During the setting operation a frictionally coupled disc carrying projections 43, 44 is carried for a limited distance. If a new digit is attempted without allowing full restoration, the insulating bush 58 on the rocker arm 56 comes against the short-circuit-controlling spring 41 and lifts it off the cam disc 42 which corresponds to disc 13 in the first arrangement. In this case however the disc has a restoring spring 50 which becomes effective when the spring 41 is raised and brings the cam into position in which the V-shaped part of spring 41 is on the short portion of the cam between the highest and lowest parts of its profile. The short-circuit springs therefore remain closed when the finger hold plate is released. In this arrangement the first notch of the impulse wheel has a deep part 55 and it is only when his part is engaged by the rocker-arm that the latter can be swung clear during the setting operation. Consequently if the motion of the finger-plate is reversed prematurely projection 43 comes under the bush 58 to hold the impulse springs open during the setting movement and so release any switches operated. Third arrangement (not illustrated). Noise is minimized by preventing. the rocker-arm from dropping completely into the notches in the impulse wheel by spring means and replacing the deep part 55 in the first notch by an additional projection carried by the dial spindle and co-operating with a spur on the rocker-arm.