Telephone line monitoring circuitry and apparatus

摘要

A telephone line monitoring circuitry apparatus which is used to continuously monitor the telephone line and causes a light emitting diode to flash on and off and further causes an auditory sounder to sound loud and soft to provide both a visual signal and an auitory signal if the telephone line becomes inoperative. The light emitting diode is a self-flashing type which serves to modulate the auditory sounder. The monitoring circuitry and apparatus is energized by a DC battery, or by an AC power source with DC battery back-up. The monitoring circuitry and apparatus is designed to have acceptable input impedance and ringer-equivalence and complete isolation to prevent interference with the telephone network.