Method and apparatus for off-hook detection

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.

Claim 2

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.

Claim 9

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: 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.

Claim 10

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: 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.

Claim 17

An apparatus connected to the tip line and the ring line of a telephone line, comprising: 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.

Claim 18

An apparatus connected to the tip line and the ring line of a telephone line, comprising: 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.