How does a compass distinguish between southeast and northwest?

The software on the mobile phone can distinguish the southeast from the northwest because the mobile phone has an electronic compass, also called an electronic compass. Generally speaking, there are two materials to realize electronic compass, one is Hall material, and the other is magnetoresistive material.

Hall principle, simply put, is that when a constant current passes through a conductor, the voltage on one side will change linearly with the magnetic induction intensity. By measuring the voltage, the mobile phone can measure the magnetic induction intensity.

We can assume that the earth's magnetic field is parallel to the ground plane. If two such Hall elements are vertically placed on the plane of the mobile phone, the components of the magnetic induction intensity of the earth's magnetic field can be induced on the two Hall elements, and the direction of the earth's magnetic field can be obtained, which is somewhat similar to the decomposition of force.

Magnetoresistive materials, divided into AMR materials and GMR materials, have their own advantages and strong professionalism, which will not be discussed in detail here. The characteristic of magnetoresistance material is that the resistance will change with the change of magnetic induction intensity. A bridge can be formed by using magnetoresistive materials, and the magnetic induction intensity in a single direction can be measured by measuring the voltages of two nodes of the bridge. Similarly, the direction of the magnetic field can be measured by placing two mutually perpendicular bridges in the mobile phone.

Extended data:

Electronic compass, also called digital compass, is a method for modern people to determine the North Pole by using geomagnetic field and electronic technology. The magnetoresistive sensor produced by modern advanced processing technology provides a powerful help for the digitalization of compass.

At the beginning of 2 1 century, electronic compasses made of magnetoresistive sensors and fluxgates were mainly used. Although GPS is widely used in navigation, positioning, speed measurement and orientation, its accuracy is greatly reduced or even unusable because its signals are often blocked by terrain and objects. Especially in urban areas with high-rise buildings and forest areas with dense vegetation, the effectiveness of GPS signals is only 60%.

At rest, GPS can't give course information. In order to make up for this deficiency, the method of integrated navigation and positioning can be adopted. Electronic compass products are designed to meet the needs of users. It can effectively compensate the GPS signal, ensure that the navigation and positioning information 100% is effective, and it can work normally even if the GPS signal is out of lock, so as to achieve "missing the star without losing direction".

References:

Baidu encyclopedia-mobile phone electronic compass