Remote switch position determination using duty cycle modulation

[54] REMOTE SWITCH POSITION

DETERMINATION USING DUTY CYCLE
MODULATION

[75] Inventor: Glenn T. Darilek, San Antonio, Tex.

[73] Assignee: Mobil Oil Corporation, New York, N.Y.

[21] Appl. No.: 771,966
[22] Filed: Sep. 3,1985

[51] Int. CI." H04Q 9/00; G08C 19/00

[52] U.S. CI 340/825.054; 340/825.63;

340/825.77; 340/310 A; 340/870.38

[58] Field of Search 340/825.36, 825.37,

340/870.24, 870.25, 870.38, 870.37, 825.54, 825.78, 510, 825.16, 510 A, 825.63, 825.77

[56] References Cited

U.S. PATENT DOCUMENTS

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4,580,138 4/1986 Morrison 340/870.38

Primary Examiner—Donald J. Yusko

Attorney, Agent, or Firm—Alexander J. McKillop;

Michael G. Gilman; Charles J. Speciale

[57] ABSTRACT

A system for determining the position of a plurality of remotely located switches having a binary weighted current controlling means connected to each switch for providing a waveform having a unique duty cycle corresponding to the position of each of the switches. The duty cycle is decoded at a local test station to provide digital output data indicative of the position of each of the switches. The duty cycle encoder includes a switching means connected across a two conductor line that terminates the cycle of an input waveform generated by a source generator at said local test station. The current controlling means controls the output of a constant current source which depends upon the number of switches that are open and closed. A timing means is responsive to the output of said constant current source for triggering the switching means. The resultant waveform at the local test station has a duty cycle that is decoded to indicate the position of the remote switches.

34 Claims, 6 Drawing Figures