Abstract: A digitally activated coin control circuit for use in combination with a digitally activated ringing circuit for common manipulation of a prepaid coin station by a central processing unit of a telephone switching center to collect and alternatively to refund deposited coins.

Abstract: A ring sensing circuit for use in conjunction with a line connected between a subscriber and a switching center. The subscriber line is monitored by a service evaluation system. The ring sensing circuit in response to a microprocessor controller, detects the application of low frequency AC ringing signals applied by the switching center to the subscriber line. As a result of this ringing signal detection, the microprocessor determines that a terminating call is pending, and instructs the associated switching equipment not to switch this particular call to a service evaluation operator.

Abstract: A trunk circuit for interconnecting an electronic and a step-by-step electromechanical switching exchange including a sensing circuit that is transparent to the transmission and supervisory signals. The sensing circuit consists of a pair of voltage dividers composed of at least four resistors each with the midpoint of each voltage divider connected to a voltage differential detecting means. The midpoints of the voltage dividers have substantially equal voltage levels in one state of the transmission path and have a measurable voltage differential in another state of the transmission path. Under conditions where a subscriber flash signal is not to be propagated through, the voltage dividers are arranged to have their resistance decreased, simulating an off-hook condition.