Method and apparatus for off-hook detection

Telephonic communications – Supervisory or control line signaling – Using line or loop condition detection

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Details

379194, 379373, 379377, 379387, H04M 322, H04M 168

Patent

active

057063427

ABSTRACT:
An apparatus for detecting an off-hook condition on a telephone, the apparatus being connected to the tip line and the ring line of a telephone line, a first potential difference existing between the tip line and the ring line, the telephone line connected to the telephone having a handset. A circuit generates a difference signal representative of the absolute value of the first potential difference. A first comparator, responsive to the difference signal, generates a first indicator signal when the difference signal is above a first value corresponding to a maximum value of potential difference between the tip line and the ring line when the handset is off-hook. A second comparator, responsive to the difference signal, generates a second indicator signal when the difference signal is below a second value corresponding to a minimum value of potential difference between the tip line and the ring line when the handset is off-hook. A circuit, responsive to the first indicator signal and the second indicator signal, indicates when the handset is off-hook.

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Graf, Rudolf F., Encyclopedia of Electronic Circuits, TAB Books, 1st Ed., vol. 1, p. 633 (1985).

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