Importance

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Abstract

A telephone call screener discriminates between desired and undesired incoming telephone calls. Desired calls are signaled by use of a two-digit code known only to persons selected by the user. The first digit of the code refers to the number of silence gaps between calling tones or rings that the calling party has to wait before entering a second digit of the code from one of the ten numbers on the touch tone or rotary dial on the telephone used to place the call. An incoming call is first detected and electronically answered, after which the output of a sine wave generator is periodically transmitted over the open telephone line to generate false calling tones simulating the periodic audible ringing sequence of a conventional telephone. An enabling circuit detects the correct code being signaled only during the proper silence gap in the false calling tone sequence. Either a touch tone decoder circuit or a rotary dial detector circuit is enabled to generate an output for activating a transducer, such as a bell or a light, to indicate that the desired call has been received. If the transducer is activated, the false calling tone sequence is extended to provide additional time for answering the phone, and when the extended sequence ends, the call is terminated. Even if the proper code is not detected during the correct silence gap, the false calling tone generator continues to produce false calling tones either until the calling party hangs up or until a maximum number of false calling tones is generated, after which the screener automatically terminates the cycle and resets for receiving the next incoming call.

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First Claim