Telephonic communications – Multi-line or key substation system with selective switching... – Line status indication or call alerting
Patent
1993-03-26
1995-02-07
Dwyer, James L.
Telephonic communications
Multi-line or key substation system with selective switching...
Line status indication or call alerting
379156, 379165, 379166, H04M 100
Patent
active
053881532
ABSTRACT:
Telephone line status indication is improved by making measurements of the differential voltage across the Tip-Ring terminals of a telephone set. The telephone set is connected to a telephone line which is shared with other parallel-connected sets. The measurement of differential line voltage is made time the set changes state (i.e., between on-hook and off-hook). The maximum magnitude of one of the last three measurements is stored to represent the state, and is arithmetically averaged with the maximum magnitude of one or the last three stored for the oil-hook state to create a reference voltage. The reference voltage is updated each time the telephone set changes state and is continually compared with the present differential line voltage to determine which one is larger A light-emitting-diode on the telephone set indicates that the telephone line is in use whenever the reference voltage exceeds the measured differential line voltage.
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Burger Theodore O.
Karpicke John A.
Keen Donald M.
Means Donald R.
Stahl Thomas A.
AT&T Corp.
Dwyer James L.
Morra Michael A.
Shankar Vijay
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