Apparatus for detecting the level of direct current or voltage on a telephone line
First Claim
1. An apparatus for detecting the level of a direct current or voltage on a telephone line having two conductors, comprising optical isolator means wherein a first semiconductor device is adapted to emit electromagnetic radiation whose intensity represents the level of current flowing through the device and a second semiconductor device is arranged to receive radiation emitted from the first device and to generate a current whose level represents the intensity of the radiation, means for connecting the first device in the isolator means between the two conductors of the telephone line, and means for sensing only the direct current flowing through the second device in the isolator means and generating an output signal representative of the level of that direct current, and hence representative of the level of the direct current or voltage on the line.
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Abstract
An apparatus for coupling a machine, such as a telephone answering machine, to a telephone line. Included in the apparatus is an optical isolator having a first semiconductor device which, in use, is connected across the line and emits radiation whose intensity represents the level of direct current flowing through the device. A second semiconductor device receives radiation from the first device and generates a current representing the intensity of the radiation. Initially, the apparatus operates in a voltage monitoring mode, wherein the current through the first device represents the level of direct voltage on the line. The apparatus distinguishes therefore between an incoming ringing signal and an outgoing dialling signal. If an incoming ringing signal is detected and the call is not answered by the subscriber lifting his handset, the apparatus operates to connect an associated telephone answering machine to the line and is then switched to a current monitoring mode. In this mode the current through the first device represents the level of direct current on the line. The level of this current is changed if the subscriber lifts his handset, and the apparatus operates to disconnect the telephone answering machine from the line.
31 Citations
16 Claims
- 1. An apparatus for detecting the level of a direct current or voltage on a telephone line having two conductors, comprising optical isolator means wherein a first semiconductor device is adapted to emit electromagnetic radiation whose intensity represents the level of current flowing through the device and a second semiconductor device is arranged to receive radiation emitted from the first device and to generate a current whose level represents the intensity of the radiation, means for connecting the first device in the isolator means between the two conductors of the telephone line, and means for sensing only the direct current flowing through the second device in the isolator means and generating an output signal representative of the level of that direct current, and hence representative of the level of the direct current or voltage on the line.
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14. An apparatus for detecting the level of a direct current on a telephone line, comprising optical isolator means wherein a first semiconductor device is adapted to emit electromagnetic radiation whose intensity represents the level of current flowing through the device and a second semiconductor device is arranged to receive radiation emitted from the first device and to generate a current whose level represents the intensity of the radiation, means for connecting the first device in the isolator means between the conductors of the line, the connecting means comprising resistive means adapted to cause the level of direct current through the first semiconductor device to be representative of the level of direct current on the line and having a resistance which varies in accordance with the direct current applied thereto, and hence in accordance with the d.c. resistance of the line, the magnitude of the resistive means assuming a value such that the direct current on the line is not sufficient to drive the first or second semiconductor device into saturation even with a short telephone line, means for sensing only the direct current flowing through the second semiconductor device and generating a first output signal when the direct current through the first semiconductor device is that given when a telephone answering machine associated with the apparatus is connected between the conductors of the line and a second output signal when the direct current through the first semiconductor device falls upon a subscriber lifting a handset associated with the apparatus and establishing a direct current path across the line, and means which are adapted upon generation of the second output signal to decouple the telephone answering machine from the line.
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15. Apparatus for detecting the level of a direct current or voltage on a telephone line, comprising optical isolator means wherein a first semiconductor device is adapted to emit electromagnetic radiation whose intensity represents the level of current flowing through the device and a second semiconductor device is arranged to receive radiation emitted from the first device and to generate a current whose level represents the intensity of the radiation, means for connecting the first device in the isolator means between the conductors of the line, the connecting means being adapted to cause the level of direct current through the first device to represent the level of direct voltage on the line, means for sensing the direct current flowing through the second device and generating a first output signal if the direct current is above a predetermined value which represents a direct voltage on the line equal to or above that given when a subscriber has not established a direct current path across the line by lifting a handset associated with the apparatus to dial a dialing signal or to receive an incoming ringing signal, further connecting means which are adapted to cause the level of direct current through the first semiconductor device to represent the level of direct current on the line, and control means adapted, when the sensing means generate the first output signal, to couple a telephone answering machine associated with the apparatus to the line and to actuate the further connecting means so that the first device is connected between the conductors of the line by the further connecting means, the sensing means being adapted to generate a second output signal if the subscriber lifts the handset to establish a direct current path across the line and causes the level of direct current through the first device to fall below a second predetermined value whilst the telephone answering machine is in use, and the control means being adapted when the second output signal is generated to decouple the telephone answering machine from the line.
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16. An apparatus for detecting the level of a direct voltage on a telephone line, comprising optical isolator means wherein a first semiconductor device is adapted to emit electromagnetic radiation whose intensity represents the level of current flowing through the device and a second semiconductor device is arranged to receive radiation emitted from the first device and to generate a current whose level represents the intensity of the radiation, means for connecting the first device in the isolator means between the conductors of the line, the connecting means comprising switch means and means adapted to cause the level of direct current through the first semiconductor device to be representative of the level of the direct voltage on the line, means for detecting an incoming alternating ringing signal or an outgoing alternating dialling signal on the line, control means adapted, when a ringing or dialling signal is detected by the detecting means, to operate the switch means, whereby the first semiconductor device is connected between the conductors of the line, means for sensing the direct current flowing through the second device and generating an output signal if the direct current is above a predetermined value which represents a direct voltage on the line equal to or above that given when a subscriber has not established a direct current path across the line by lifting a handset associated with the apparatus to dial a dialling signal or to receive an incoming ringing signal, and means adapted upon generation of the output signal to couple a telephone answering machine associated with the apparatus to the line.
Specification