John E Mcclure

US Patent:

51115026, May 5, 1992

Filed:

Apr 25, 1990

Appl. No.:

7/514131

Inventors:

William C. McClure - Denver CO
Bob D. Kunce - Joplin MO
John Q. McClure - Aurora CO

Assignee:

Command Communications, Inc. - Aurora CO

International Classification:

H04M 322

US Classification:

379380

Abstract:

A telephone line bridging sensor circuit is provided which provides a variable output frequency signal to a microprocessor for measuring and storing the frequency count on a periodic basis. The circuit includes an isolation transformer to isolate the audio component of the telephone line from the sensing circuit. The loop current present in the telephone line is rectified through a full wave diode rectifier and the output of the rectifier is filtered and regulated to provide an input voltage to an astable, voltage controlled oscillator. As the current on the telephone line varies, the input voltage to the oscillator also varies a proportionate amount causing the output frequency of the oscillator to change accordingly. The output frequency is fed through an optical coupler to a suitable microprocessor circuit for measuring, storing and comparing the frequency readings on a periodic basis to detect differential change in the output frequency indicative of one or more telephone devices bridging the telephone line at the same time.