Method and apparatus for off-hook detection
First Claim
1. An apparatus, connected to the tip line and the ring line of a telephone line, a first potential difference existing between the tip line and the ring line, the telephone line connected to a telephone having a handset, for detecting an off-hook condition on the telephone, comprising:
- a. means for generating a difference signal representative of the absolute value of the first potential difference;
b. a first comparator means, responsive to the difference signal, for generating a first indicator signal when the difference signal is above a first value corresponding to a maximum value of potential difference between the tip line and the ring line when the handset is off-hook;
c. a second comparator means, responsive to the difference signal, for generating a second indicator signal when the difference signal is below a second value corresponding to a minimum value of potential difference between the tip line and the ring line when the handset is off-hook; and
d. means, responsive to the first indicator signal and the second indicator signal, for indicating when the handset is off-hook.
1 Assignment
0 Petitions
Accused Products
Abstract
An apparatus for detecting an off-hook condition on a telephone, the apparatus being connected to the tip line and the ring line of a telephone line, a first potential difference existing between the tip line and the ring line, the telephone line connected to the telephone having a handset. A circuit generates a difference signal representative of the absolute value of the first potential difference. A first comparator, responsive to the difference signal, generates a first indicator signal when the difference signal is above a first value corresponding to a maximum value of potential difference between the tip line and the ring line when the handset is off-hook. A second comparator, responsive to the difference signal, generates a second indicator signal when the difference signal is below a second value corresponding to a minimum value of potential difference between the tip line and the ring line when the handset is off-hook. A circuit, responsive to the first indicator signal and the second indicator signal, indicates when the handset is off-hook.
69 Citations
20 Claims
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1. An apparatus, connected to the tip line and the ring line of a telephone line, a first potential difference existing between the tip line and the ring line, the telephone line connected to a telephone having a handset, for detecting an off-hook condition on the telephone, comprising:
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a. means for generating a difference signal representative of the absolute value of the first potential difference; b. a first comparator means, responsive to the difference signal, for generating a first indicator signal when the difference signal is above a first value corresponding to a maximum value of potential difference between the tip line and the ring line when the handset is off-hook; c. a second comparator means, responsive to the difference signal, for generating a second indicator signal when the difference signal is below a second value corresponding to a minimum value of potential difference between the tip line and the ring line when the handset is off-hook; and d. means, responsive to the first indicator signal and the second indicator signal, for indicating when the handset is off-hook. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus, connected to the tip line and the ring line of a telephone, a first potential difference existing between the tip line and the ring line, the telephone having a handset, for detecting an off-hook condition on a telephone, comprising:
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a. a bridge circuit having a first input connected to the tip line and a second input connected to the ring line and having a first output and a second output, a second potential difference existing between the first output and the second output, the second potential difference equal to the absolute value of the first potential difference; b. a differential amplifier, operationally coupled to the first output and the second output, that generates a difference signal representative of the second potential difference; c. a first comparator, responsive to the difference signal, that generates a first indicator signal when the difference signal is above a first value corresponding to a maximum value of potential difference between the tip line and the ring line when the handset is off-hook; d. a second comparator, responsive to the difference signal, that generates a second indicator signal when the difference signal is below a second value corresponding to a minimum value of potential difference between the tip line and the ring line when the handset is off-hook; and e. a microprocessor, responsive to the first indicator signal and the second indicator signal, directed by a computer program to; i. generate an off-hook signal indicating that the handset is off-hook when the difference signal is between the first value and the second value; ii. continue to generate the off-hook signal if the difference signal drops below the second value and remains below the second value for less than a predetermined period; and iii. cease to indicate that the handset is off-hook if the difference signal drops below the second value and remains below the second value for at least the predetermined period. - View Dependent Claims (9, 10)
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11. A series of operational steps to be performed on a computer used to detect an off-hook condition of a telephone and to perform control functions of an auxiliary telecommunications device, the telephone and the auxiliary device being operationally coupled to a telephone line on which DTMF digits are dialed, the telephone having a handset, the computer responsive to a voltage difference signal indicative of a voltage value between the tip line and the ring line of the telephone, comprising the steps of:
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a. recording DTMF digits being dialed into a memory when the difference signal indicates that the voltage value is below the maximum value corresponding to the off-hook condition; b. starting a timer when the voltage signal indicates that the voltage value has fallen below a predetermined value; and c. interrupting the recording of DTMF digits and resetting the memory when the timer indicates that a preselected period has passed while the voltage value is below the predetermined value. - View Dependent Claims (12, 13)
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14. An apparatus connected to the tip line and the ring line of a telephone line, comprising:
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a. a telephone connected to the tip line and the ring line; b. an auxiliary device connected to the tip line and the ring line; c. means for detecting an off-hook condition in the telephone, comprising i. a bridge circuit having a first input connected to the tip line and a second input connected to the ring line and having a first output and a second output, a second potential difference existing between the first output and the second output, the second potential difference equal to the absolute value of a first potential difference existing between the first output and the second output; ii. a differential amplifier, operationally coupled to the first output and the second output, that generates a difference signal representative of the second potential difference; iii. a first comparator, responsive to the difference signal, that generates a first indicator signal when the difference signal is above a first value corresponding to a maximum value of potential difference between the tip line and the ring line when the handset is off-hook; iv. a second comparator, responsive to the difference signal, that generates a second indicator signal when the difference signal is below a second value corresponding to a minimum value of potential difference between the tip line and the ring line when the handset is off-hook; and v. a microprocessor, responsive to the first indicator signal and the second indicator signal, programmed to determine when the handset is off-hook and to generate an operative control signal to a facsimile machine when the handset is off-hook, the microprocessor being directed by a computer program to; A. record DTMF digits being dialed into a memory when the values of the first indicator signal and the second indicator signal indicate that the value of the difference signal is within a range corresponding to an off-hook condition; B. start a timer when the second indicator signal indicates that the difference signal has fallen below the second value; and C. interrupt the recording of DTMF digits and reset the memory when the timer indicates a preselected period has passed while the value of the difference signal is below the second value; and d. means, responsive to the detecting means, for inhibiting the operation of the auxiliary device when the detecting means detects an off-hook condition. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification