Automatic disconnect circuit
First Claim
1. In a telephone communications systems in which a telephone line couples a remote telephone to a local telephone, and wherein a substantial D.C. level shift appears on the telephone line when the local telephone goes on-hook, an automatic disconnect circuit for disconnecting the remote telephone in response to the remote telephone going on-hook, comprising:
- signal discrimination means having an input coupled to the telephone line receiving the signals thereon, including voice signals and hang-up clicks generated by the remote and local telephones going on-hook, and adapted to substantially attenuate the voice signals and to pass the hang-up clicks to an output;
comparator means coupled to the output of said signal discriminator means for generating a control signal in response to each signal which is received from said signal discrimination means and which has an amplitude in excess of a predetermined level;
a disconnect signal generator responsive to control signals which have a duration greater than a first predetermined interval but less than a second predetermined interval for generating a disconnect signal, said first predetermined interval corresponding to the minimum duration of a control signal generated in response to the remote telephone going on-hook, and said second predetermined interval being shorter than the duration of a control signal generated in response to the D.C. level shift which occurs when the local telephone goes on-hook; and
means receiving the disconnect signal for disconnecting the telephone line,whereby the attenuation of the voice signals inhibits the latter from generating a control or disconnect signal, signals having an amplitude less than the amplitude of a hang-up click fail to generate a disconnect signal, and said disconnect signal generator is insensitive to any signal on the telephone line generating a control signal whose duration is a typical of that generated by a remote hang-up click, thus preventing a control signal generated either by voice or a local hang-up from disconnecting the telephone line.
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Accused Products
Abstract
An automatic disconnect circuit is described for disconnecting a remote telephone in resonse to a hang-up click generated when the remote telephone goes on-hook. To distinguish a remote hang-up click from a local hang-up click, voice signals, and the like, all signals on the line are passed through a discriminator for attenuating high frequencies. Signals passing through the discriminator are sensed both as to their amplitude and their duration. Any such signal whose amplitude is too small results in no disconnect. Similarly, any such signal whose duration is atypical of a remote hang-up click results in no disconnect. Only a signal whose amplitude and duration are within predetermined limits, typical of a remote hang-up, causes the remote telephone to be disconnected.
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Citations
9 Claims
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1. In a telephone communications systems in which a telephone line couples a remote telephone to a local telephone, and wherein a substantial D.C. level shift appears on the telephone line when the local telephone goes on-hook, an automatic disconnect circuit for disconnecting the remote telephone in response to the remote telephone going on-hook, comprising:
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signal discrimination means having an input coupled to the telephone line receiving the signals thereon, including voice signals and hang-up clicks generated by the remote and local telephones going on-hook, and adapted to substantially attenuate the voice signals and to pass the hang-up clicks to an output; comparator means coupled to the output of said signal discriminator means for generating a control signal in response to each signal which is received from said signal discrimination means and which has an amplitude in excess of a predetermined level; a disconnect signal generator responsive to control signals which have a duration greater than a first predetermined interval but less than a second predetermined interval for generating a disconnect signal, said first predetermined interval corresponding to the minimum duration of a control signal generated in response to the remote telephone going on-hook, and said second predetermined interval being shorter than the duration of a control signal generated in response to the D.C. level shift which occurs when the local telephone goes on-hook; and means receiving the disconnect signal for disconnecting the telephone line, whereby the attenuation of the voice signals inhibits the latter from generating a control or disconnect signal, signals having an amplitude less than the amplitude of a hang-up click fail to generate a disconnect signal, and said disconnect signal generator is insensitive to any signal on the telephone line generating a control signal whose duration is a typical of that generated by a remote hang-up click, thus preventing a control signal generated either by voice or a local hang-up from disconnecting the telephone line. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. In a telephone communication system in which a local operator estabishes communication between a local telephone and a remote telephone via a telephone line, and further establishes communication between the remote telephone and local automatic message transmitting/receiving apparatus, an automatic disconnect circuit which prevents disconnect of the telephone line when the local telephone by going on-hook creates a D.C. level shift on the telephone line, but disconnects the telephone line when the remote goes on-hook, comprising:
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signal discrimination means having an input coupled to the telephone line for attenuating voice signals received therefrom and for passing to an output both the hang-up clicks generated by the remote telephone going on-hook, as well as the low frequency components of the D.C. level shift generated by the local telephone going on-hook; comparator means coupled to the output of said signal discrimination means for generating a control signal in response to any signal which is received from said signal discrimination means and which has an amplitude exceeding a predetermined level; a disconnect signal generator responsive to control signals which have a duration greater than a first predetermined interval but less than a second predetermined interval for generating a disconnect signal, said first predetermined interval corresponding to the minimum duration of a control signal generated in response to the remote telephone going on-hook, and said second predetermined interval being shorter than the duration of a control signal generated in response to the D.C. level shift which occurs when the local telephone goes on-hook; and means receiving the disconnect signal for disconnecting the telephone line, whereby the attenuation of the voice signals inhibits the latter from generating a control and disconnect signal, signals having an amplitude less than the said predetermined level fail to generate a disconnect signal, and said disconnect signal generator is insensitive to any signal on the telephone line generating a control signal whose duration is a typical of that generated by a remote hang-up click, thus preventing noise and local hang-up clicks from disconnecting the remote telephone from the automatic message transmitting/receiving apparatus, each disconnection being made only in response to a hang-up click generated by the remote telephone. - View Dependent Claims (9)
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Specification