Freescale Semiconductor Application Note Implementing Positioning Algorithms Using Accelerometers by :

This document describes and implements a positioning algorithm using the MMA7260QT 3-Axis accelerometer and a 9S08QG8 low cost 8-bit microcontroller unit (MCU). In today’s advanced electronic market, there are many multifunctional products continuously adding features and intelligence. Tracking and gaming are just a few of the markets that can benefit from obtaining positioning information. One option for obtaining this information is through the use of inertial sensors. The signal obtained from these sensors does require processing as there is no direct conversion between acceleration and position. In order to obtain position a double integral must be applied to the signal. This document describes an easy algorithm to implement a double integration of the signal obtained from the sensor using a low end 8-bit microcontroller. In order to obtain a double integration a simple integration must be made twice. This allows velocity information to be obtained as well. The algorithm shown in the following pages applies to any sensing axis; therefore, one, two or three dimensional positioning can be determined. When implementing positioning in 3 axes, extra processing is required to null the earth’s gravity effect. The implementation below includes an example for a 2-axis system (i.e. mouse).