Patent GB-1523370-A (GB)
Title: Dialling devices
IPC: H04M1/31
Filed: 1976-05-12
Abstract: 1523370 Impulse transmitters; powering substations SIEMENS AG 12 May 1976 [23 May 1975] 19528/76 Heading H4K In a dialling device for connection to a subscriber substation, including a keyboard, a pulse generator and a pulse emission relay, a first capacitor is used to store power when the relay is not operating and to supply current to the device and holding current to the relay when the relay is operating and a voltage multiplier comprising a second capacitor, is used to respond to pulses from the pulse generator to operate the relay. In the embodiment, a dialling device WE is connected to a substation through three connections, sl, s2 and s3. The substation includes a speech circuit SS, cradle switch contacts GU1, GU2 and a ringing circuit comprising capacitor C, bell W and resistor RW and is connected to a line L through wires a, b. The device WE comprises a digit keyboard ZT which includes common contact units Ta, Tr operated by any push button of the keyboard, a pulse generator JES for generating series of pulses corresponding to the operated pushbuttons, a monostable pulse emission relay NSI, a bi-stable relay NSA of which only contact unit nsa is shown, a resistor R for obtaining power for the device, a surge voltage protection device BS, a capacitor C 1 which is charged through a constant current source comprising Zener diode Z, resistors R1 and R2 and transistor TR1 and a capacitor C2 charged through the winding of a relay NSI. Operation.-Normally, when the cradle switch contacts GUI, GU2 are closed the speech circuit SS is connected to the line L and the device WE is effectively short-circuited by the closed contacts nsi, Tr and nsa. If a push button of the keyboard ZT is actuated, SS is short circuited by contact Ta and contact Tr is opened so that the device is supplied with power through contact nsi and resistor R. As a result capacitor C1 is charged through the constant current source and the capacitor C2 is charged through the winding of relay NSI and diodes Dl and D2. At the same time the pulse generator JES is enabled through input n and it produces an output nsa<SP>1</SP> which persists as long as digits are to be transmitted, or until the operation is interrupted by opening of contact GU1. The output nsa<SP>1</SP> sets relay NSA to its "dialling" mode. The pulses from the pulse generator JES operate an electronic switch comprising transistors T2, T3, T4 and resistors R3, R7 through input nsi', which operates relay NSI by discharging capacitor C2 through its winding. Thus each pulse opens contacts nsi to simulate a line break which is detected as a dialling pulse at an exchange to which the subscriber is connected. During such a line break the device is powered by capacitor Cl, which also provides a holding current to relay NSI so that it still operates when C2 has discharged. At the end of the pulse, relay NSI is released through the electronic switch by the input nsi'. When all the digits have been transmitted, relay NSA is reset through nsa<SP>1</SP> so that contact nsa breaks the connection of device WE and reestablishes the connection of speech circuit SS to the line L.