Two-wire, multiple-transducer communications system

Claim 1

A system responsive to data request signals for retrieving data from a selected one of a plurality of data gathering devices remotely located and connected in parallel to a single cable, comprising: an interrogator responsive to data request signals including: means for transmitting an address signal along the cable indicative of the particular data gathering device from which data is to be retrieved; and means for applying a constant signal to the cable after the address signal has been transmitted; one or more decoders each associated with a corresponding data gathering device and each including: means for comparing the address signal transmitted along the cable with an identification signal uniquely identifying the decoder to produce an enabling signal upon correspondence thereof for activating the corresponding data gathering device; and corresponding means responsive to the enabling signal for selectively connecting a low impedance across the cable conductors in response to digital data from the data gathering device; the digital data from the selected data gathering device being reproduced at the interrogator by detecting the variations in the signal level across the cable produced by the responding means.

Claim 2

A system responsive to data request signals for retrieving data from a selected one of a plurality of data gathering devices remotely located and connected in parallel to a single cable, comprising: an interrogator responsive to data request signals including: means for transmitting an address signal along the cable indicative of the particular data gathering device from which data is to be retrieved; and means for applying a constant signal to the cable after the address signal has been transmitted; one or more decoders each associated with a corresponding data gathering device and each including: means for comparing the address signal transmitted along the cable with an identification signal uniquely identifying the decoder to produce an enabling signal upon correspondence thereof for activating the corresponding data gathering device; and corresponding means responsive to the enabling signal for selectively connecting a low impedance across the cable conductors in response to digital data from the data gathering device; the digital data from the selected data gathering device being reproduced at the interrogator by detecting the variations in the signal level across the cable produced by the responding means.

Claim 8

A method for selectively activating and receiving data from a selected one of one or more remotely located data gathering devices connected in parallel to a single two-conductor cable, comprising the steps of: at a first location along the cable: generating a first digital signal representative of a selected data gathering device to be activated; transmitting along the cable a series of pulses, the number of pulses being determined by the first digital signal; and after the number of pulses determined by the first digital signal have been transmitted, continuously connecting a constant signal to the cable; at one or more second locations along the cable having data gathering devices located thereat: receiving and counting the pulses transmitted along the cable from the first location; comparing the number of pulses received with a predetermined address number uniquely identifying each of the decoders and corresponding data gathering devices, an enabling signal being generated when the number of received pulses equal the predetermined address number; and upon the occurrence of an enabling signal, transmitting digital data from the data gathering device by selectively connecting a low impedance across the cable in response to digital signals from the data gathering device, thereby selectively reducing the voltage across the cable; and detecting the voltage across the cable at the first location to determine the transmitted digital data.

Claim 9

A method for selectively activating and receiving data from a selected one of one or more remotely located data gathering devices connected in parallel to a single two-conductor cable, comprising the steps of: at a first location along the cable: generating a first digital signal representative of a selected data gathering device to be activated; transmitting along the cable a series of pulses, the number of pulses being determined by the first digital signal; and after the number of pulses determined by the first digital signal have been transmitted, continuously connecting a constant signal to the cable; at one or more second locations along the cable having data gathering devices located thereat: receiving and counting the pulses transmitted along the cable from the first location; comparing the number of pulses received with a predetermined address number uniquely identifying each of the decoders and corresponding data gathering devices, an enabling signal being generated when the number of received pulses equal the predetermined address number; and upon the occurrence of an enabling signal, transmitting digital data from the data gathering device by selectively connecting a low impedance across the cable in response to digital signals from the data gathering device, thereby selectively reducing the voltage across the cable; and detecting the voltage across the cable at the first location to determine the transmitted digital data.

Claim 12

A system responsive to data request signals for retrieving data from a selected one among one or more digital compasses remotely located and connected in parallel to a single cable, comprising: an interrogator, including: means responsive to the data request signals for transmitting an address signal along the cable indicative of the particular digital compass from which data is to be retrieved; and means for applying a constant signal to the cable after the address signal has been transmitted; one or more decoders, each associated with a corresponding compass and each including: means for comparing the address signal transmitted along the cable with an identification signal uniquely identifying the decoder and for producing an enabling signal when the transmitted signal corresponds to the identification signal; and means responsive to the enabling signal for activating the corresponding digital compass and for selectively connecting a low impedance across the cable conductors in response to digital data therefrom; the digital data from the selected compass being reproduced at the interrogator by detecting the variations in the signal level across the cable.

Claim 13

A system responsive to data request signals for retrieving data from a selected one among one or more digital compasses remotely located and connected in parallel to a single cable, comprising: an interrogator, including: means responsive to the data request signals for transmitting an address signal along the cable indicative of the particular digital compass from which data is to be retrieved; and means for applying a constant signal to the cable after the address signal has been transmitted; one or more decoders, each associated with a corresponding compass and each including: means for comparing the address signal transmitted along the cable with an identification signal uniquely identifying the decoder and for producing an enabling signal when the transmitted signal corresponds to the identification signal; and means responsive to the enabling signal for activating the corresponding digital compass and for selectively connecting a low impedance across the cable conductors in response to digital data therefrom; the digital data from the selected compass being reproduced at the interrogator by detecting the variations in the signal level across the cable.