Push-button dialling drive circuit - uses buffer capacitor connected in series with switching transistor and charged by loop current (NL 13.5.80)

摘要

A circuit arrangement for executing push-button dialling for a subscriber's appts. uses the pulse selection method and simplifies the push-button dialling unit to reduce overall expenditure on circuit items. A buffer capacitor is connected in series with a switching transistor and is charged by the loop current, with the switch in the open condition. The loop current is interrupted by means of push-button elements to give the pulsed function for generating the dialling pulses for the keyed digits, with dial-repeat action controlled by a flip-flop in a circuit block where the dial keying is initiated by pressure on additional keys.