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          How many sensors are used in mobile phones? What are their characteristics?

Do you know how many sensor combinations are used in the compass system of mobile phones? Since Android 5.0, compass system has been adding other sensors to the direction sensor. So far, the compass is not disturbed. More and more sensors are used in the compass, including these sensors. Do you know? What are the characteristics of these sensors?

sensor

1. Acceleration sensor

Acceleration sensor, also known as G-sensor, obtains the acceleration value of X, y, Z three axes.

This value includes the influence of gravity in M / S ^ 2.

Place the phone flat on the desktop. The default value of X axis is 0, Y axis is 0, and Z axis is 9.81.

Place the phone face down on the desktop, and the z-axis is -9.81.

The acceleration sensor may be the most mature MEMS product, and there are many kinds of acceleration sensors in the market. The commonly used acceleration sensors in mobile phones include Bosch BMA series, AMK 897x series, St lis3x series, etc. These sensors generally provide an acceleration measurement range of ± 2G to ± 16g, which are connected with MCU by I2C or SPI interface, and the data accuracy is less than 16bit.

2. Magnetic sensor

The magnetic sensor is called m-sensor for short, which returns the environmental magnetic field data of X, y and Z axes.

The unit of this value is micro Tesla, expressed in UT. It can also be Gauss, 1tesla = 10000 Gauss.

Generally, there is no independent magnetic sensor in hardware, and magnetic data is provided by electronic compass sensor (e-compass). The electronic compass sensor not only provides magnetic sensor data, but also provides direction sensor data.

3. Direction sensor

The direction sensor is called o-sensor for short. It returns the angle data of three axes. The unit of direction data is angle.

As mentioned above, after obtaining the data of G-sensor, e-compass calculates and produces o-sensor data and m-sensor data.

The o-sensor provides three data: azimuth, pitch and roll.

Azimuth: azimuth, the angle between magnetic north pole and Y axis when returning to horizontal, ranging from 0 ° to 360 °. 0 ° = north, 90 ° = east, 180 ° = south, 270 ° = west.

Pitch: the angle between the x-axis and the horizontal plane, ranging from - 180 ° to 180 °. When the Z-axis and y-axis rotate, the angle is positive.

Roll: the angle between the Y-axis and the horizontal plane, ranging from - 90 ° to 90 ° for historical reasons. When the x-axis and z-axis move, the angle is positive.

The electronic compass needs to be calibrated before obtaining the correct data, usually using the 8-word calibration method. In principle, the normal direction of the device should be pointed to all eight quadrants of the space.

4. Gyroscope sensor

The gyroscope sensor, called gyro sensor, returns angular acceleration data of X, y and Z axes.

The unit of angular acceleration is radians / second.

According to the actual measurement of nexus s mobile phone:

Rotate horizontally counter clockwise, and the Z axis is positive.

Rotate counterclockwise horizontally, and the z-axis is negative.

Rotate to the left, and the y-axis is negative.

Rotate to the right, and the y-axis is positive.

If you rotate up, the x-axis is negative.

Rotate downward and the x-axis is positive.

5. Gravity sensor

The gravity sensor is called GV sensor for short, which outputs gravity data.

On earth, gravity is 9.8 in M / S ^ 2.

The coordinate system is the same as the acceleration sensor.

When the equipment is reset, the output of gravity sensor is the same as that of acceleration sensor.

6. Linear acceleration sensor

Linear acceleration sensor is referred to as La sensor.

Linear acceleration sensor is the data obtained by the acceleration sensor minus the influence of gravity.

The unit is m / S ^ 2. The coordinate system is the same as the acceleration sensor.

The calculation formulas of acceleration sensor, gravity sensor and linear acceleration sensor are as follows:

Acceleration = gravity + linear acceleration.

7. Rotating vector sensor

The rotation vector sensor is called RV sensor for short.

The rotation vector represents the direction of the device and is a data obtained by mixing coordinate axes and angles.

RV sensor outputs three data:

x*sin(theta/2)

y*sin(theta/2)

z*sin(theta/2)

Sin (theta / 2) is the order of magnitude of RV.

The RV is oriented in the same direction as the axis rotation.

The three values of RV and COS (theta / 2) form a quad.

RV data has no units and uses the same coordinate system as the acceleration.

give an example:

sensors_ event_ t.data[0] = x*sin(theta/2)

sensors_ event_ t.data[1] = y*sin(theta/2)

sensors_ event_ t.data[2] = z*sin(theta/2)

sensors_ event_ t.data[3] = cos(theta/2)

The values of GV, La and RV can not be directly given by physical sensors, which need to be calculated by the algorithm of G-sensor, o-sensor and gyro sensor.