Switching arrangement for telephone subsets using impulse-type pushbutton calling

Claim 1

In a switching arrangement for a telecommunications set having a keyboard-actuated, replaceably connected selection unit, said selection unit having a pulse generator for producing pulse trains of differing characteristics in dependence on which of the keys is actuated, two relays in said selection unit, one of which controlled by said pulse generator serves for pulsing and the other, a bistable relay, is connected to disable the speech circuit of the subset during the duration of the pulse train from the pulse generator and the selection unit further including transmitting and feeding circuit means connected to the connection line to the subset upon actuation of one of the keys in the keyboard, the improvement comprising: said one of said relays being a monostable pulsing relay in said selection unit operable responsive to actuation of said pulse generator, first common key-actuated contact means including said other relay operable responsive to actuation of a key for disconnecting said speech circuit from the subset connection line, coupling means for connecting said selection unit to the subset connection line including at least a contact operated by said pulsing relay, said coupling means being short circuited by non-operation of said first common contact means, said transmitting and feeding circuit being connected to said coupling means for receiving current from the connection line and feeding said selection unit when said coupling means is connected to the connection line, said transmitting and feeding circuit including a current supply means comprising first capacitance means, charged from current received through said coupling means for functioning as a voltage doubler and supplying actuating pulses to said pulsing relay and second capacitance to said selection unit and a holding current to said pulsing relay.