Patent ID: 7490944

Claim:
An interior rearview mirror system for a vehicle, said interior rearview mirror system comprising: an interior rearview mirror assembly; a casing and a reflective element supported at said casing; said casing being adjustable relative to a mounting structure that mounts said interior rearview mirror assembly to an interior portion of the vehicle, said casing being adjustable to orient said reflective element in a rearward viewing position, where said reflective element provides a rearward field of view through a rear window of the vehicle to a driver of the vehicle; a compass chip disposed behind said reflective element and within said mirror casing, said compass chip comprising a semiconductor substrate and a sensor and control circuitry disposed on said semiconductor substrate, said sensor comprising at least a first magnetoresponsive sensing element and a second magnetoresponsive sensing element; wherein said compass chip comprises substantially all of the circuitry for operation of said compass chip when a power source is connected to said compass chip; wherein said compass chip is disposed behind said reflective element and within said mirror casing so that said first magnetoresponsive sensing element is oriented generally horizontally and generally along a longitudinal axis of the vehicle when said reflective element is adjusted to said rearward viewing position; wherein said control circuitry receives a first signal indicative of a magnetic field sensed by said first magnetoresponsive sensing element, and wherein said control circuitry receives a second signal indicative of a magnetic field sensed by said second magnetoresponsive sensing element; and wherein said control circuitry determines a directional heading of the vehicle based on said first and second signals, said control circuitry automatically compensating for a deviating magnetic field of the vehicle and generating a signal indicative of the directional heading of the vehicle.