Importance

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Abstract

An interface (10) is disclosed for coupling a conventional pay station telephone (12) to a telephone switching system (16). The interface (10) provides supervision signal detection functions normally provided by a switching system, and thus can be connected thereto by a less costly business line (28). The interface includes processor controlled tone generators (72, 76) and detectors (73, 74, 81, 106, 108) for detecting duration of tones and other audio signals, and voltages transmitted by either the telephone (12) or the switching system (16). The interface (10) further includes a detector (106) and a procedure (FIG. 8) for providing an answer call indication. Coin collection or return is controlled by the interface (10) depending on the status of the call (as indicated by audio signal duration) which is also determined by the interface (10).

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First Claim