Telephone ringing tone injector and generator - uses expandable modular electronic automatic switching circuit, producing square wave from constant voltage

摘要

The basic module (51) comprises a connecting capacitor (30), between the output (11) and supply (9), via a diode (31) in series with a resistor (32) to ensure a continuous current through the microphone. The capacitor is also connected to switches (33,34) to the supply (9) and to the input (10) to the supply. The diode prevents an overvoltage being conducted to the dc supply (4). A second basic module, inverted w.r.t. the supply and the input provides a second output. The difference in outputs is applied as a ringing signal to the telephone and is controlled by the switches. The electronic switching circuit allows for expansion for an increasing number of telephone systems by viture of its modular construction.