Abstract: Increased power to operate a paystation coin relay is derived from the tip/ring pair by means of a power boost circuit, which is controllably coupled to the tip/ring pair when the coin relay is to be fired. To fire the coin relay, a line coupling relay circuit is energized, so as to apply the tip/ring line voltage to a D.C.-to-D.C. converter, the output of which is coupled to current storage (capacitor) circuit. The output of the current storage circuit is coupled to a first switch circuit and monitored by a comparator. The first switch circuit has an output coupled in circuit with the coin relay.

Abstract: A call progress circuit for both a customer owned, coin operated telephone and a regulated telephone is provided that does not mute the paystation's transmitter, so that voice signals from the calling party may be heard by the called party, thereby preventing an answering party from hanging up prematurely. The call progress circuit employs a transmitter-sourced audio signal discriminator which monitors audio signals placed on the line from the called station, the calling paystation and a central office, and controllably removes or subtracts out those audio signals that originate at the paystation transmitter. The discriminator includes a pair of tunable bandpass filters respectively associated with a telephone line receiver and the paystation transmitter circuit. Coupled to these filters is an audio spectrum scanner which sequentially adjusts the sensitivity characteristics of the filters.