Line in-use indicator for a telephone set and facsimile machine connected to a single telephone line

Claim 1

A communications apparatus comprising: a telephone set connected to a single telephone line; a facsimile machine connected to the single telephone line including: a control circuit; a modem, connected to the control circuit, for processing facsimile messages from the facsimile machine onto the single telephone line and facsimile messages to the facsimile machine from the single telephone line; a hook detector, connected to said control circuit, for detecting voltage variations across the single telephone line and generating a hook status signal indicating when the telephone set has seized control of the single telephone line and including a capacitor for detecting voltage changes across the single telephone line; a rectifier circuit for rectifying an output of the capacitor; a comparator for comparing a voltage level of a rectifier circuit output signal with a noise threshold voltage; and a flip-flop for latching an output from the comparator, and said flip-flop providing the latched output to the control circuit; and an indicator, connected to the control circuit, for generating an availability message indicating when the single telephone line is being used by the telephone set and when the single telephone line is available to receive or transmit facsimile messages based on the hook status signal.