Voltage-sensitive telephone line monitor
First Claim
1. Telephone line monitor apparatus which detects an off-hook condition on a telephone line by monitoring the line voltage, said monitor apparatus comprising,means responsive to said line voltage for generating an off-hook threshold voltage based on at least one value of said line voltage, andmeans responsive to said off hook threshold voltage and to said line voltage for indicating an off hook condition when said line voltage is less than said off-hook threshold voltage.
2 Assignments
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Accused Products
Abstract
Detector circuitry monitors the line voltage on a telephone line to detect an off-hook condition. In order to accomodate varying line voltages and noise conditions, the circuitry automatically selects a threshold off-hook voltage by an iterative initialization procedure which is initiated on circuit power-up. The intialization procedure repeatedly compares the threshold voltage to the actual line voltage over a period of time to eliminate false off-hook detection due to noise.
34 Citations
12 Claims
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1. Telephone line monitor apparatus which detects an off-hook condition on a telephone line by monitoring the line voltage, said monitor apparatus comprising,
means responsive to said line voltage for generating an off-hook threshold voltage based on at least one value of said line voltage, and means responsive to said off hook threshold voltage and to said line voltage for indicating an off hook condition when said line voltage is less than said off-hook threshold voltage.
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8. Telephone line monitor apparatus which detects an off-hook condition on a telephone line by monitoring the line voltage, said monitor apparatus comprising,
means comprises means responsive to said line voltage at a given instant of time for calculating an in initial on hook line voltage value means responsive to said line voltage for calculating a trial off-hook threshold voltage by means of a predetermined relation to said initial on-hook line voltage line voltage means for verifying said trial off hook threshold voltage by comparing said trial off-hook threshold voltage to a plurality of samples of said line voltage taken at different instants of time and verifying said trial off-hook threshold voltage only if said trial off-hook threshold voltage is less than said line voltage in each comparison, and means responsive to said verified trial off-hook threshold voltage and to said line voltage for indicating an off-hook condition when said line voltage is less than said verified off hook threshold voltage.
Specification