Apparatus and method for an inbound telemetry device to sense telephone line status

A telemetry device for collecting information at a remote location and transmitting the information over a telephone line to a host location, wherein the telephone line has an associated voltage signal that varies in accordance with an off-hook status of one or more user devices connected to the telephone line, the telemetry device comprising:

• a monitoring circuit coupled to the telephone line which periodically generates a voltage signal having an amplitude that is representative of the telephone line voltage level;
• and
• a processing circuit which collects information at a remote location, and which receives the voltage signal as an input and utilizes the voltage signal to determine the off-hook status of the user devices and thereby control the transmission of the collected information over the telephone line so as to not interfere with usage of the telephone line by the user devices, said processing circuit including a pulse-generating circuit which converts voltage signals from the monitoring circuit into a stream of binary signals, wherein each binary signal has either a first logic level or a second logic level, and wherein the binary signals having said first logic level are of variable duration, and a microcontroller which receives and analyzes the stream of binary signals at least by progressively comparing the respective durations of two nonconsecutive binary signals having said first logic level, one of which is the most recently occurring binary signal having said first logic level, wherein the microcontroller causes the telemetry device to stop transmitting collected information over the telephone line upon determining that the compared durations differ by more than a predetermined amount.

A method for monitoring the off-hook status of a user device connected to a telephone line, wherein the telephone line has an associated voltage level that varies in accordance with the off-hook status of the user device, the method comprising the steps of:

• coupling the telephone line to a monitoring circuit so that the current from the telephone line is provided to components in the monitoring circuit;
• generating periodic voltage signals using the current from the telephone line, wherein the amplitude of the voltage signals is representative of the telephone line voltage level;
• converting the voltage signals into a stream of binary signals, wherein each binary signal has either a first logic level or a second logic level;
• determining whether the stream of binary signals comprises alternating first logic level signals and second logic level signals;
• and
• concluding that a user device is off-hook if the stream consists only of binary signals having said first logic level.