Pushbutton dialling for telephone - has direct selector control and stores fast pulses and converts them to normal speed when dialling is complete

摘要

Push button dialling pulses, 4ms OFF, 4ms ON, are sent from a subscriber by an interrupter contact (li) with a current limiting resistor (Wi). At the exchange, the pulses are detected by a voltage monitor (SU) across one winding (AI) of the transmission bridge relay. The monitor short circuits the other winding (AII) during spaces to ensure that the relay does not fall out. The monitor output is fed into a store (Sp). When dialling is complete, the store is read out as 60/40ms pulses with 700ms pauses between digits. This drives a relay (AH) which has a contact (4ah) on the exchange side of the transformer (OLU). The store can be arranged to recognise free-of-charge emergency calls.