Keyboard dialling telephone circuit - generates defined output potentials and uses bistable relay whose contact closes capacitor charging circuit on diode blocking

摘要

When the star selection switch is operated and the relay selection contact moves into dialling position, a capacitor is charged when a first four-layer diode blocks a low-ohmic parallel circuit. The capacitor energy then feeds the relay coil via a second four-layer diode and another diode. The second four-layer diode is ignited by the transmitted capacitor energy. The relay coil feed brings the relay contact into its call connecting position. Alternately, on connection to exchange, the relay contact moves into dialling position causes a voltage drop at a zener diode, conditioned by a transistor delay. The voltage drop generates a pulse actuating the relay energisation via a further diode.