Vehicle compass system with automatic calibration

  • US 5,737,226 A
  • Filed: 06/05/1995
  • Issued: 04/07/1998
  • Est. Priority Date: 06/05/1995
  • Status: Expired due to Fees
First Claim
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1. An electrical quick calibration compass system for use in a vehicle such as an automobile comprising:

  • a magnetic field sensor for detecting the earth'"'"'s magnetic field and for providing electrical signals representing the direction of the vehicle in relation to the earth'"'"'s magnetic field;

    a processing circuit coupled to said sensor for processing signals from said sensor and for providing display output signals in response thereto;

    a display circuit coupled to said processing circuit and responsive to said display output signals for displaying the vehicle heading; and

    said processing circuit responsive to signals from said sensor, during which time the change of direction of the vehicle is less than a closed loop, for determining that the detected signal levels from said sensor, corresponding to the effect of the earth'"'"'s magnetic field and the effect of vehicle magnetism on said sensor, have shifted such that said signal levels are outside a predetermined threshold, said processing circuit responsive to said determination that said signal levels are outside said threshold for recalibrating said compass system using the detected signal levels output from said sensor during the time in which the vehicle direction changed less than a closed loop;

    wherein said processing circuit adjusts the detected signal levels after determining that the vehicle'"'"'s direction of travel has changed a predetermined amount corresponding to a plot of said detected signal levels from said sensor creating an arc spanning a predetermined angle, said arc has a starting point and an ending point that are used to determine the center of said arc, the center of the arc being determined by assuming a radius and identifying at least one center candidate point that is spaced apart from the starting point and the ending point by the assumed radius.

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