Processes for more accurately calibrating and operating e-compass for tilt error, circuits, and systems

Abstract

An electronic circuit includes an electronic compass having e-compass sensors mounted on different axes and operable to supply e-compass sensor data, memory circuitry, and an electronic processor coupled to said e-compass sensors and to said memory circuitry, said electronic processor operable to execute an electronic ellipse-fitting procedure responsive to the e-compass sensor data to generate at least one signal related to an ellipse tilt angle (ξ), and store the at least one signal in said memory circuitry as a tilt calibration parameter for the e-compass. Processes for calibrating an e-compass, as well as electronic circuits and processes for correcting measured heading, and processes of manufacture are also disclosed.

What is claimed is: 
     
         1 . A process of operating a device that includes an e-compass, the device and e-compass having three axis of motion, the process comprising:
 verifying that an accelerometer sensor output has become stable at rest;   estimating a tilt angle based on the accelerometer sensor output;   performing a first de-tilting of data from the e-compass based on the accelerometer sensor output;   perform a second de-tilting of data from the e-compass based on calibrated residual tilt angle data read from memory circuitry; and   generating a measured heading angle psi with calibration data read from the memory circuitry.   
     
     
         2 . The process of  claim 1  including displaying an instruction to a user to hold the device at rest before the verifying. 
     
     
         3 . The process of  claim 1  in which the verifying includes checking that plural samples of accelerometer output over time are within a certain amount of variability. 
     
     
         4 . The process of  claim 1  including displaying heading angle psi. 
     
     
         5 . The process of  claim 1  in which the generating a heading angle psi includes calculating a heading angle psi from an arctangent equation using calibration values obtained from the memory circuitry. 
     
     
         6 . The process of  claim 1  in which the generating includes generating with hard iron effect offset values stored in the memory circuitry.