Telephone subscriber line voltage change detection

Claim 1

Apparatus for detecting changes in a subscriber line voltage between two wires of a telephone subscriber line, comprising: a potential divider having first, second, and third tapping points, the second tapping point being between the first and third tapping points; means for supplying to the potential divider a voltage dependent upon the subscriber line voltage; a low pass filter circuit having an input connected to the second tapping point; a first voltage comparator, having inputs connected to the first tapping point and an output of the low pass filter circuit, for producing an output pulse in response to a fall in the subscriber line voltage; and a second voltage comparator, having inputs connected to the third tapping point and the output of the low pass filter circuit, for producing an output pulse in response to a rise in the subscriber line voltage.

Claim 14

A method of detecting, at a first telephone set connected to a two-wire telephone subscriber line, a change from an on-hook state to an off-hook state of a second telephone set connected to the same subscriber line, comprising the steps of: (i) monitoring a subscriber line voltage between the two wires of the subscriber line; (ii) producing a pulse at a first circuit terminal in response to a fall in the subscriber line voltage; (iii) producing a pulse at a second circuit terminal in response to a rise in the subscriber line voltage; (iv) in response to a pulse at the first terminal having at least a predetermined duration, starting a window timer period; (v) detecting any pulse at the second terminal during the window timer period and, in the absence of a pulse and in the absence of an action at the first telephone set causing the subscriber line voltage to fall, determining that the second telephone set is in an off-hook state.

Claim 15

A method of detecting, at a first telephone set connected to a two-wire telephone subscriber line, a change from an on-hook state to an off-hook state of a second telephone set connected to the same subscriber line, comprising the steps of: (i) monitoring a subscriber line voltage between the two wires of the subscriber line; (ii) producing a pulse at a first circuit terminal in response to a fall in the subscriber line voltage; (iii) producing a pulse at a second circuit terminal in response to a rise in the subscriber line voltage; (iv) in response to a pulse at the first terminal having at least a predetermined duration, starting a window timer period; (v) detecting any pulse at the second terminal during the window timer period and, in the absence of a pulse and in the absence of an action at the first telephone set causing the subscriber line voltage to fall, determining that the second telephone set is in an off-hook state.

Claim 21

A method of detecting, at a first telephone set connected to a two-wire telephone subscriber line, hook state changes of a second telephone set connected to the same subscriber line, comprising the steps of: (i) monitoring a subscriber line voltage between the two wires of the subscriber line; (ii) producing a pulse at a first terminal in response to a fall in the subscriber line voltage; (iii) producing a pulse at a second terminal in response to a rise in the subscriber line voltage; (iv) detecting a first pulse at either of the first and the second terminals and noting at which terminal such a first pulse is produced; (v) determining whether the pulse has at least a predetermined duration, if so proceeding to step (ix) and if not proceeding to step (vi); (vi) detecting any pulse at either terminal starting within a predetermined cancellation period, in the absence of a pulse returning to step (iv) and in response to a pulse proceeding to step (vii); (vii) determining whether the most recent pulse has at least a predetermined duration, if so proceeding to step (viii) and if not returning to step (vi); (viii) determining whether the most recent pulse is at the terminal noted in step (iv) at which the first pulse was produced, if so proceeding to step (ix) and if not returning to step (iv); (ix) detecting any pulse, at the other terminal than that noted in step (iv) at which the first pulse was produced, starting within a predetermined window period, in the absence of a pulse proceeding to step (x) and in the presence of a pulse returning to step (iv); (x) in the absence of any action at the first telephone set to cause the first pulse detected in step (iv), determining that the second telephone set is off-hook if the first pulse was produced at the first terminal, and determining that the second telephone set is on-hook if the first pulse was at the second terminal; and (xi) returning to step (iv).

Claim 22

A method of detecting, at a first telephone set connected to a two-wire telephone subscriber line, hook state changes of a second telephone set connected to the same subscriber line, comprising the steps of: (i) monitoring a subscriber line voltage between the two wires of the subscriber line; (ii) producing a pulse at a first terminal in response to a fall in the subscriber line voltage; (iii) producing a pulse at a second terminal in response to a rise in the subscriber line voltage; (iv) detecting a first pulse at either of the first and the second terminals and noting at which terminal such a first pulse is produced; (v) determining whether the pulse has at least a predetermined duration, if so proceeding to step (ix) and if not proceeding to step (vi); (vi) detecting any pulse at either terminal starting within a predetermined cancellation period, in the absence of a pulse returning to step (iv) and in response to a pulse proceeding to step (vii); (vii) determining whether the most recent pulse has at least a predetermined duration, if so proceeding to step (viii) and if not returning to step (vi); (viii) determining whether the most recent pulse is at the terminal noted in step (iv) at which the first pulse was produced, if so proceeding to step (ix) and if not returning to step (iv); (ix) detecting any pulse, at the other terminal than that noted in step (iv) at which the first pulse was produced, starting within a predetermined window period, in the absence of a pulse proceeding to step (x) and in the presence of a pulse returning to step (iv); (x) in the absence of any action at the first telephone set to cause the first pulse detected in step (iv), determining that the second telephone set is off-hook if the first pulse was produced at the first terminal, and determining that the second telephone set is on-hook if the first pulse was at the second terminal; and (xi) returning to step (iv).