Accelerometers

An accelerometer is an electromechanical device that will measure acceleration forces. These forces may be static, like the constant force of gravity pulling at your feet, or they could be dynamic which is caused by moving or vibrating the accelerometer.

Some accelerometers use the piezoelectric effect in which they contain microscopic crystal structures that get stressed by accelerative forces, which causes a voltage to be generated. Another way to do is by sensing changes in capacitance. If you have two microstructures next to each other, they have a certain capacitance between them. If an accelerative force moves one of the structures, then the capacitance will change. Add some circuitry to convert from capacitance to voltage and you will get accelerometer.

Accelerometer can produce either analog or digital outputs. Analog style accelerometers output a continuous voltage that is proportional to acceleration. e.g 2.5V for 0g, 2.6V for 0.5g, 2.7V for 1g. Digital accelerometers usually use pulse width modulation (PWM) for their output. This means there will be a square wave of a certain frequency, and the amount of time the voltage is high will be proportional to the amount of acceleration.

There are two common types of accelerometer, the seismic mass type and the piezoelectric accelerometer. The seismic mass type accelerometer is based on the relative motion between a mass and the supporting structure. The natural frequency of the seismic mass limits its use to low to medium frequency applications. The piezoelectric accelerometer, however, is compact and more suitable for high frequency applications.