ES417537A1 - Push-button calling circuits for telephone sets - Google Patents

Abstract

Improvements in push-button call circuits for subscriber telephone sets of the type that use a keyboard unit (keypad) to make calls, consisting of sending impulse trains to the telephone line, by purely electronic means, and with the adequate characteristics so that they are acceptable by the Control unit to which the apparatus is connected, the apparatus being equipped with more or less conventional means of generation, storage and production of impulses (keyboard unit, integrated circuit, etc. and power supply). of the call circuit by means of the line current, said improvements being characterized in that, referring to Fig. 1, the circuit includes: transistors T1 and T7 and resistance R10, to produce the openings and closings of the line loop according to with the orders given by the impulse generating system (CON); the resistors R1 and R2, to avoid undue actions of the transistor T1 due to NO leakage currents; transistors T5 and T6, to cancel the high impedance that R10 represents and achieve the fast charge of the power capacitor of the call circuit; the thyristor TR, for connecting or disconnecting the line loop speech circuit; transistors T3 and T4 and resistor R5, to trip the thyristor TR; transistor T2 to block transistor T3 and, consequently, thyristor TR; resistors R3 and R4, to avoid undue actions of transistor T2 due to leakage current in the CON circuit; transistor T8 and resistor R11, to block transistors T5 and T6 during conversation periods; capacitor C3 and resistance R11 so that the thyristor TR turns on before the transistor T8; and resistance R12, to prime the thyristor TR. (Machine-translation by Google Translate, not legally binding)