This application note explains the integration of a Kionix MEMS tri-axis accelerometer into a handheld electronic compass application. Required theory, plots, equations and circuit block diagrams are provided with this note as guidelines.
The earth’s magnetic field is approximately 0.6 gauss or 600 milli-gauss in terms of magnetic flux density. In free air, this also correlates to 0.6 Oersted in magnetic field intensity. Other equivalents for earth field values are about 48 Amperes/meter of magnetic field intensity and about 60 micro-Tesla for magnetic flux density.
The earth’s magnetic field reference polarity is from the earth’s south pole to the north pole. So a handheld electronic compass on the equator pointed at the north pole should read about +0.6 gauss, and –0.6 gauss when pointed at the south pole. Typically two or three anisotropic magnetic sensors are used for a compass in orthogonal angles (perpendicular to each other) to measure the incident earth’s magnetic field into Cartesian coordinates X, Y and Z. For a mechanical reference, usually the X magnetic sensing element will point towards the top of a handheld device. The Y sensor will point across the assembly and to the right, and the Z sensor will point down through the device.