Calibrar Mag
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Freescale Semiconductor Application Note Document Number: AN4246 Rev. 3, 04/2013 © 2013 Freescale Semiconductor, Inc. All rights reserved. Contents 1 Introduction This application note provides the theory for the in-situ calibration of a smartphone electronic compass (eCompass) for hard and soft-iron effects. The mathematical framework is that developed in AN4248 “Implementing a Tilt-Compensated eCompass using Accelerometer and Magnetometer Sensors” and AN4247 “Layout Recommendations for PCBs Using a Magnetometer Sensor.” It is therefore highly recommended to read these application notes first before reading this document. 1.1 Key Words eCompass, Geomagnetic, Magnetometer, Hard Iron, Soft Iron, Calibration. Calibrating an eCompass in the Presence of Hard and Soft-Iron Interference by : T alat Ozy agc ilar Applications Engineer 11 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Key Wor ds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Summar y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 The Hard and Soft- Iron Model . . . . . . . . . . . . . . . . . . . . . 2 3 App lyi ng Har d and Sof t-Ir on Cor rec tion s t o th e Tilt-Compensated eCompass . . . . . . . . . . . . . . . . . . . . . 3 4 Rel atin g th e Locus of Magnetomete r Me asurement s to Calibration Coefficients . . . . . . . . . . . . . . . . . . . . . . . . 5 5 Imposing a Symmetri c Co nstraint onto the Inv ers e Soft-Iron Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6 Ful l So lut ion for Fou r Pa rameter Cali bra tion. . . . . . . . . 11 7 Cal ibr ation Algorithms and Source Cod e . . . . . . . . . . . 16
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