Application

# Principle of digital compass

A digital compass is an important navigation tool that provides the heading and attitude of moving objects in real time. With the advancement of semiconductor technology and the development of mobile phone operating systems, smart phones that integrate more and more sensors have become powerful, and many mobile phones have implemented the function of a digital compass.
And applications based on the digital compass are also popular on various software platforms. To implement the digital compass function, a three-axis magnetic sensor for detecting magnetic fields and a three-axis acceleration sensor are required. As the micromachining process matures, ERICCO's ER-EC-365A is a high-precision full attitude 3D electronic compass that uses hard and soft iron calibration algorithms to provide high-precision course information in 360° roll and +/-90° full dip range. It has the characteristics of low power consumption, which is more suitable for power consumption and volume-sensitive measurement systems.

Background knowledge of the earth's magnetic field and heading angle As shown in the figure, the earth's magnetic field is like a bar magnet from the magnetic south pole to the magnetic north pole. At the magnetic poles the magnetic field is perpendicular to the local horizontal plane, and at the equator the magnetic field is parallel to the local horizontal plane, so in the northern hemisphere the magnetic field is tilted toward the ground. The unit used to measure the magnitude of the magnetic induction is Tesla or Gauss (1Tesla=10000Gauss). Depending on the geographical location, the strength of the geomagnetic field is usually 0.4-0.6Gauss. It should be noted that the magnetic north pole and the geographic north pole do not coincide, usually there is an included angle of about 11 degrees between them.

The geomagnetic field is a vector that, for a fixed location, can be decomposed into two components parallel to the local horizontal plane and a component perpendicular to the local horizontal plane. If the digital compass is kept parallel to the local horizontal plane, then the three axes of the magnetometer in the compass correspond to these three components. In fact, for the two horizontal components, their vector sum always points to magnetic north. The heading angle (Azimuth) in the compass is the angle between the current direction and magnetic north. Since the compass is kept horizontal, the heading angle can be calculated by Equation 1 only by using the detection data of the two axes (usually the X-axis and the Y-axis) in the horizontal direction of the magnetometer. When the compass is rotated horizontally, the heading angle varies between 0º-360º.