System for selectively receiving telephone calls

Details System for selectively receiving telephone calls System for selectively receiving telephone calls

1986-09-12

1988-12-13

Dwyer, James L.

Telephonic communications

Call or terminal access alarm or control

At substation

379188, 379387, H04M 100

Patent

active

047916648

ABSTRACT:
A system for selectively receiving incoming telephone calls to a phoneset includes an automatic answering device which answers all incoming calls by placing a simulated phone load across the phone lines. The answering device also enables a dual tone multifrequency (DTMF) receiver to receive tone frequencies input by a caller. The DTMF receiver decodes the tone pulses into binary coded decimal values which are stored in successive storage registers. A comparator compares the values stored in the registers with a respective code input by the subscriber and outputs a signal when the code dialed in by the caller matches the code input by the subscriber. The signal activates an electronic ringer circuit which serves to alert the subscriber of the presence of an authorized call. An off-hook detector detects the pick-up of a phoneset by the subscriber and acts to disable the electronic ringer circuit. Upon the placing of the phoneset back into its cradle, the off-hook detector activates an automatic reset circuit which resets the automatic answering device as well as the code storage registers.

REFERENCES:
patent: 3784721 (1974-01-01), Kilby
patent: 3829616 (1974-08-01), Blouch
patent: 3902016 (1975-08-01), Blouch
patent: 4006316 (1977-02-01), Bolgiano
patent: 4074078 (1978-02-01), Jansen
patent: 4446334 (1984-05-01), Groff

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