Accelerometers in phones – What is it?

There are different kinds of accelerometers in phones. They seem to vary in characteristics in different phones. The accelerometer can be thought up as a device that measures gravity. The way to imagine an accelerometer is that of a ball hung on a spring that is attached to a solid surface (like the phone). As you move the solid surface, the spring that is attached to the ball makes the ball move up and down. If you can measure the extension of the spring then it will be easy to measure how fast you are moving the solid surface (the phone). This can be seen in a great video at http://www.engineerguy.com/. In the case of the accelerometer that IS all on a silicon chip, the ball is a silicon surface that is free to move/oscillate with gravity in a single dimension. The motion of that silicon between two electrodes changes the capacitance and also causes a current to flow. When these tiny silicon pieces are aligned in the x, y, and z dimension then you have a 3D accelerometer.