Frequency-selective ringing current sensor for telephone line

Claim 2

Apparatus for sensing the presence of AC ringing current in a telephone line, where such current has a frequency no less than a certain frequency, said apparatus comprising an electric light source, a circuit for connecting said source to such a line to energize the former with AC current flowing in the latter whereby the intensity of light emitted by the source varies at the same frequency as that of such current, a light-responsive circuit optically coupled to said source, operable to produce an electrical-intensity-varying signal having the same frequency as that of light-intensity variations in the source, and a digital frequency filter operatively connected to said lightresponsive circuit, operable to produce a responsive output signal for said apparatus only in the event that the frequency of a signal produced by said light-responsive circuit is no less than said certain frequency.

Claim 3

Apparatus for sensing the presence of AC ringing current in a telephone line, where such current has a frequency lying within a certain range of frequencies, said apparatus comprising an electric light source, a circuit for connecting said source to such a line to energize the former with AC current flowing in the latter whereby the intensity of light emitted by the source varies at the same frequency as that of such current, a light-responsive circuit optically coupled to said source, operable to produce an electrical-intensity-varying signal having the same frequency as that of light-intensity variations in the source, and a digital frequency filter operatively connected to said light-responsive circuit, operable to produce a responsive output signal for said apparatus only in the event that the frequency of a signal produced by said light-responsive circuit falls within said certain range of frequencies.

Claim 4

Apparatus for sensing the presence of AC ringing current in a telephone line, where such current has a frequency lying within a certain range of frequencies, said apparatus comprising an electric light source, a circuit for connecting said source to such a line to energize the former with AC current flowing in the latter whereby the intensity of light emitted by the source varies at the same frequency as that of such current, a light-responsive circuit optically coupled to said source, operable to produce an electrical-intensity-varying signal having the same frequency as that of light-intensity variations in the source, and a digital frequency filter operatively connected to said light-responsive circuit, operable to produce a responsive output signal for said apparatus only in the event that the frequency of a signal produced by said light-responsive circuit falls within said certain range of frequencies.

Claim 5

Apparatus for detecting the presence of AC ringing current in a telephone line and generating an output signal in response thereto, where such current has a frequency no less than a certain frequency, said apparatus comprising an input circuit adapted for connection to a telephone line and including means for emitting optical radiation when, with said circuit connected to such a line, AC current flows in the line, with the emitted radiation having an intensity which varies at the same frequency as that of said current, a radiation responsive circuit optically coupled to said input circuit for producing an intensity varying electrical signal upon exposure to radiation emitted by said means, with said signal being of the same frequency as the emitted radiation, and a frequency discriminating circuit comprising a digital frequency filter coupled to said radiation responsive circuit for determining if an intensity varying electrical signal produced by the radiation responsive circuit is no less than said certain frequency and for generating a responsive output signal if and only if said signal is no less than that certain frequency.

Claim 6

Apparatus for detecting the presence of AC ringing current in a telephone line and generating an output signal in response thereto, where such current has a frequency no less than a certain frequency, said apparatus comprising an input circuit adapted for connection to a telephone line and including means for emitting optical radiation when, with said circuit connected to such a line, AC current flows in the line, with the emitted radiation having an intensity which varies at the same frequency as that of said current, a radiation responsive circuit optically coupled to said input circuit for producing an intensity varying electrical signal upon exposure to radiation emitted by said means, with said signal being of the same frequency as the emitted radiation, and a frequency discriminating circuit comprising a digital frequency filter coupled to said radiation responsive circuit for determining if an intensity varying electrical signal produced by the radiation responsive circuit is no less than said certain frequency and for generating a responsive output signal if and only if said signal is no less than that certain frequency.

Claim 7

The apparatus of claim 3, wherein said means for emitting optical radiation comprises a neon lamp, and said radiation responsive circuit comprises a phototransistor.

Claim 8

Apparatus for detecting the presence of AC ringing current in a telephone line and generating an output signal in response thereto, where such current has a frequency lying within a given range of frequencies, said apparatus comprising an input circuit adapted for connection to a telephone line and including means for emitting optical radiation when, with said circuit connected to such a line, AC current flows in the line, with the emitted radiation having an intensity which varies at the same frequency as that of said current, a radiation responsive circuit optically coupled to said input circuit for producing an intensity varying electrical signal upon exposure to radiation emitted by said means, with said signal being of the same frequency as the emitted radiation, and a frequency discriminating circuit comprising a digital frequency filter coupled to said radiation responsive circuit for determining if an intensity varying electrical signal produced by the radiation responsive circuit is within said range of frequencies, and for generating a responsive output signal if and only if said signal is within said range.

Claim 9

Apparatus for detecting the presence of AC ringing current in a telephone line and generating an output signal in response thereto, where such current has a frequency lying within a given range of frequencies, said apparatus comprising an input circuit adapted for connection to a telephone line and including means for emitting optical radiation when, with said circuit connected to such a line, AC current flows in the line, with the emitted radiation having an intensity which varies at the same frequency as that of said current, a radiation responsive circuit optically coupled to said input circuit for producing an intensity varying electrical signal upon exposure to radiation emitted by said means, with said signal being of the same frequency as the emitted radiation, and a frequency discriminating circuit comprising a digital frequency filter coupled to said radiation responsive circuit for determining if an intensity varying electrical signal produced by the radiation responsive circuit is within said range of frequencies, and for generating a responsive output signal if and only if said signal is within said range.

Claim 10

The apparatus of claim 5, wherein said means for emitting optical radiation comprises a neon lamp, and said radiation responsive circuit comprises a phototransistor.