Telemetry device including a dynamic off-hook detector

A telemetry device for collecting data and transmitting said data over a phone line to a central station during an active state of said telemetry device during which said device seizes the phone line, said telemetry device otherwise remaining in a static state, said phone line conducting a loop current, said telemetry device exhibiting a current load on said phone line, said telemetry device comprising:

• voltage deriving means, coupled to said phone line, for deriving a voltage dependent on the loop current of said phone line, said voltage being designated the derived voltage;
• a microprocessor for controlling said telemetry device and for collecting data from devices external to said telemetry device;
• a peripheral bus coupled to said microprocessor, said bus including a plurality of data lines;
• a plurality of pull up/load resistors respectively coupled to said plurality of data lines;
• control means, within said microprocessor, for activating during said active state an increasing number of said pull up/load resistors to increase the current load exhibited by said telemetry device on the phone line until said derived voltage reaches a first predetermined voltage level, and
• voltage drop detecting means, coupled to said voltage deriving means, for detecting when said derived voltage decreases to a second predetermined voltage level less than said first predetermined voltage level, thus indicating that a contending telephone device coupled to said phone line has come off-hook during said active state.

A telemetry device for collecting data and transmitting said data over a phone line to a central station during an active state of said telemetry device during which said telemetry device seizes the phone line, said telemetry device otherwise remaining in a static state, said telemetry device including a phone line side and a meter side coupled together by an electrically isolative barrier therebetween, said line side of said telemetry device being coupled to said phone line, said phone line conducting a loop current, said telemetry device exhibiting a current load on said phone line, said telemetry device comprising:

• a power supply situated on said meter side of said telemetry device for drawing power from said line side to provide a power supply voltage to said meter side;
• a microprocessor for controlling said telemetry device and for collecting data from devices external to said meter side;
• a peripheral bus coupled to said microprocessor, said bus including a plurality of data lines;
• a plurality of pull up/load resistors respectively coupled to said plurality of data lines;
• control means, within said microprocessor, for activating during said active state an increasing number of said pull up/load resistors to increase the current load exhibited by said telemetry device on the phone line until said power supply voltage reaches a first predetermined voltage level, and
• voltage drop detecting means, coupled to said power supply, for detecting when said power supply voltage decreases to a second predetermined voltage level less than said first predetermined voltage level, thus indicating that a contending telephone device coupled to said phone line has come off-hook during said active state.

A telemetry device for collecting data at a remote location and transmitting said data over a phone line to a central station, at least one other contending telephone device being coupled to said phone line at said remote location, said phone line conducting a loop current, said telemetry device comprising:

• data collecting means for collecting data at said remote location during a static state of said telemetry device;
• transmitting means, coupled to said collecting means, for transmitting said data over said phone line to said central station during an active state of said telemetry device during which said telemetry device seizes said phone line;
• a power supply, coupled to said phone line, for supplying power supply voltage to said telemetry device;
• static off-hook detector means for monitoring said phone line during the static state of said telemetry device to determine when said contending telephone device goes off-hook and preventing said telemetry device from entering said active state when said contending telephone device goes off-hook during said static state;
• dynamic off-hook detector means for detecting, during said active state, when said contending telephone device goes off-hook, said dynamic off-hook detector means including:
• variable load preloading means for variably loading said telemetry device to draw progressively higher amounts of loop current from said phone line until said power supply voltage decreases to a first predetermined level, and
• voltage drop detecting means, coupled to said power supply for detecting when said power supply voltage decreases to a second predetermined voltage level less than said first predetermined voltage level, thus indicating that a contending telephone device coupled to said phone line has come off-hook during said active state.