Electronic ringing circuit for telephone systems

Details Electronic ringing circuit for telephone systems Electronic ringing circuit for telephone systems

1976-10-29

1978-03-28

Claffy, Kathleen H.

Oscillators

Relaxation oscillators

331 47, H04M 100

Patent

active

040816176

ABSTRACT:
This invention relates to an electronic ringing circuit for telephone systems. The inventive circuit provides a dual tone output with the tones changing at a predetermined rate. The circuit consists of a rectifying circuit connected across the telephone lines which receive the normal 90VAC/20 Hz telephone ringing signals. The rectified signal is then connected to one input terminal of a voltage comparator, the other terminal of which is connected to a reference voltage source. When a ringing signal is present, the rectified signal will be greater than the voltage of the reference source so that the voltage comparator will provide an output. This output is fed to the control terminals of electronically controlled switches, and when the switches are closed, the oscillators will be grounded through frequency determining capacitors associated with the respective oscillators. In addition, associated with one of the oscillators is a second electronically controlled switch and a second frequency determining capacitor. The control terminal of the second switch is connected to the output of the other one of the oscillators. Thus, when a ringing signal comes over the telephone lines, both of the oscillators will be turned on. The second oscillator will switch in the second frequency determining capacitor at a predetermined rate, so that the output of the one oscillator will change at this predetermined rate to thereby provide a multi-tone signal. The output of the one oscillator is fed to a speaker.

REFERENCES:
patent: 3867585 (1975-02-01), Morstadt
patent: 3965307 (1976-06-01), Dimmer

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