Sensors in Android smartphones allow detection, analysis, and recording of physical phenomenon into a more convenient signal.
Sensors convert physical measurements such as displacement, velocity, acceleration, force, pressure, or flow into electrical signals.
Electrical outputs are very convenient because there are well known methods for filtering and acquiring electrical signals for real-time or subsequent analysis. Sensor size is important, and small sensors are required for many reasons including easier use, a higher sensor density, and lower material cost.
Accelerometer sensors also have applications measuring hand motion by directly converting hand movement to the input of a control system. Common examples of computer control using conventional hand movement sensors are a keyboard, keypad, joystick, and the screen movement. In smartphones, it is used in touch screen applications and 3D android games.
Keyboards passes a signal based on the location of a finger pressing a button and touchscreen use potentiometers to sense two-dimensional or three-dimensional tilt of a lever controlled by the hand.
When combining the accelerometers in the earth’s gravitational field, there is always the acceleration due to gravity of earth magnetic field. Thus the signal from an accelerometer sensor can be separated into two signals, the acceleration from gravity, and external acceleration. The acceleration from gravity allows measurement of the tilt of the sensor by identifying the direction.
By excluding out the external acceleration, the orientation of a three-axis sensor can be calculated from the accelerations on the three accelerometer axes.