Method for performing automatic calibrations in an electronic compass

Claim 1

An automatic calibration method for use in an electronic compass control circuit that includes a microcomputer, a flux-gate, a flux-gate driver, a bandpass filter, a synchronous detector, an integrator and a summing amplifier; the control circuit equipped with a ranging circuit that includes an operational amplifier with resistive negative feedback connected to the output of the integrator; an RC charging network connected to the non-inverting input to the operational amplifier; a gate switch connected between the RC charging network and the microcomputer such that the microcomputer charges the RC charging network when the gate switch is closed; and comparator means to respond to the output of the integrator to control the operation of the gate switch; the calibration method for use with a vehicle equipped with a display for indicating information to the operator of the vehicle; the calibration method performed completely automatically while the operator the vehicle is driving the vehicle and comprising: measuring and storing at least three compass headings, where each heading is measured and stored when the direction in which the vehicle is being driven changes; deriving the coordinates for the center of the earth's magnetic field circle by using the compass headings; computing directional offset values by using the coordinates for the center of the earth's magnetic field circle for use in magnetic compass heading computations thereby eliminating the effects of the vehicle's magnetic field on the reading of the direction that the vehicle is pointed, in the earth's magnetic field.