SIGNAL PROCESSING CIRCUIT FOR USE IN TELEMETRY DEVICES

A signal processing circuit is provided, one embodiment of which is employed in an inbound telemetry device such as an inbound MIU, another embodiment of which is employed in an outbound telemetry device such as an outbound MIU, for example. The inbound signal processing circuit monitors and senses conditions on a phone line coupled thereto to determine when the line is available or not available for use by the inbound telemetry device. More specifically, the processing circuit includes a sensing circuit which senses when other communications devices coupled to the phone line are off-hook and hence the line is not available. The processing circuit advantageously employs the same sensing circuit to determine when ringing signals are present on the line such that the line is not available. The processing circuit thus provides line status information to the inbound telemetry device so that the telemetry device is informed as to those times at which the telemetry device should and should not transmit collected information. The outbound signal processing circuit employs circuitry similar to the inbound processing circuit above plus analog to digital conversion circuitry to convert analog phone line information signals such as alert signals to digital signals. This embodiment includes circuitry to either pass the converted digital signals to an outbound telemetry device when the line is available or prevent the passage of converted digital signals to the outbound telemetry device if the line is not available.