Remote hang-up detector

Claim 1

A detection system for determining whether a remote telephone system has been disconnected from a central office line, wherein during connection the central office provides a DC voltage and loop current to a local telephone system, further wherein when the central office determines that the remote telephone system has hung up, or has been disconnected, the central office causes the loop current to the local telephone system to have a reversed polarity or to be interrupted, the detection system comprising: an optically-isolated sensor coupled in parallel with the central office across the central office line at a point where the local telephone system is connected to the central office line for detecting when the polarity of the loop current to the local telephone system has been reversed or when the loop current has been interrupted by detecting a drop in voltage, wherein the detection of the drop in voltage represents an output and wherein the optically-isolated sensor includes: a resistor; a capacitor coupled in series with the resistor, wherein the capacitor charges up toward the central office DC voltage while the local telephone system is connected to the central office, and discharges when the loop current is reversed in polarity or interrupted; and an isolation assembly coupled to the capacitor, the isolation assembly including first and second opto-diodes coupled in parallel, and a transistor optically coupled to the opto-diodes, wherein when the capacitor discharges, one of the opto-diodes turns on and causes the transistor to turn on and provide the output of the optically-isolated sensor; and a computer for receiving and processing the output of the sensor, and for signaling the local telephone system to hang up and disconnect from the local office.

Claim 13

A system for indicating to a modem operable in a telephone answering machine (TAM) mode that a remote caller has hung up or has been disconnected from a central office line, thereby enabling the modem to likewise hang up or be disconnected from the central office line, the central office providing a DC line voltage and loop current to the remote caller and the TAM in an off-hook condition, i.e., during connection, wherein upon disconnection of the remote caller by the central office in response to a remote on-hook condition, i.e., when the remote caller has hung up, the central office reverses the direction of the loop current to the TAM or interrupts the loop current to the TAM, the system comprising: a controller for controlling the operation of the modem; detecting means coupled to the controller for detecting interruptions in the TAM loop current, the detecting means including: a resistor coupled to the central office line, a capacitor coupled in series with the resistor, a first diode coupled to the capacitor, a second diode coupled in parallel with the first diode, the first and second diodes together constituting an assembly being coupled in series with the capacitor, wherein the capacitor charges up to the off-hook DC line voltage, such that in an on-hook condition the capacitor discharges to produce a current, and an isolation assembly coupled in series with the first and second parallel diode assembly and the central office line, and having an output coupled to the controller, wherein an output signal is provided to the controller, the isolation assembly including first and second opto-diodes coupled in parallel, and a transistor optically coupled to the opto-diodes, the transistor having a collector and an emitter, wherein the transistor provides the isolation assembly output, wherein when the current produced as a result of the capacitor discharge is supplied to the first and second opto-diodes, the transistor is caused to turn on, thereby causing the output signal to be transmitted to the controller; and disconnect means coupled to the controller for receiving and processing the transistor output signal to cause the modem TAM to disconnect from the central office line.

Claim 14

A system for indicating to a modem operable in a telephone answering machine (TAM) mode that a remote caller has hung up or has been disconnected from a central office line, thereby enabling the modem to likewise hang up or be disconnected from the central office line, the central office providing a DC line voltage and loop current to the remote caller and the TAM in an off-hook condition, i.e., during connection, wherein upon disconnection of the remote caller by the central office in response to a remote on-hook condition, i.e., when the remote caller has hung up, the central office reverses the direction of the loop current to the TAM or interrupts the loop current to the TAM, the system comprising: a controller for controlling the operation of the modem; detecting means coupled to the controller for detecting interruptions in the TAM loop current, the detecting means including: a resistor coupled to the central office line, a capacitor coupled in series with the resistor, a first diode coupled to the capacitor, a second diode coupled in parallel with the first diode, the first and second diodes together constituting an assembly being coupled in series with the capacitor, wherein the capacitor charges up to the off-hook DC line voltage, such that in an on-hook condition the capacitor discharges to produce a current, and an isolation assembly coupled in series with the first and second parallel diode assembly and the central office line, and having an output coupled to the controller, wherein an output signal is provided to the controller, the isolation assembly including first and second opto-diodes coupled in parallel, and a transistor optically coupled to the opto-diodes, the transistor having a collector and an emitter, wherein the transistor provides the isolation assembly output, wherein when the current produced as a result of the capacitor discharge is supplied to the first and second opto-diodes, the transistor is caused to turn on, thereby causing the output signal to be transmitted to the controller; and disconnect means coupled to the controller for receiving and processing the transistor output signal to cause the modem TAM to disconnect from the central office line.