Method of monitoring the on/off-hook status of a telephone...

Details Method of monitoring the on/off-hook status of a telephone... Method of monitoring the on/off-hook status of a telephone...

H - Electricity

04

M

379/57

H04M 1/72 (2006.01) H04M 3/22 (2006.01) H04M 19/02 (2006.01)

Patent

CA 1073569

A METHOD AND APPARATUS FOR MONITORING THE ON/OFF-HOOK STATUS OF A TELEPHONE SET ABSTRACT In an extension line circuit, an off-hook condition is detected during ringing by superimposing in each ringing cycle the values of the line current existing at two sampling instants exactly one-half cycle apart, and testing whether the sum (or mean value) exceeds a given threshold. When DC current starts flowing due to the set going off- hook, the mean value of the two values will pass a threshold. Sample pulses can be derived in common for all line circuits from positive-going zero crossings of the ringing supply signal. The circuit acts as a notch filter centered exactly at the actual frequency of the ringing signal.

281417

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