A compact algorithm using the ADXL213 duty cycle output

In many applications, high accuracy measurement of acceleration is less important than having a simple and compact software algorithm. This application note outlines a decode algorithm that measures only the pulse width (t1) output of the ADXL213 and translates it to degrees of tilt. In this algorithm, the period (t2) is not measured, and no binary division is used.

In PIC assembly code, a total of 199bytes of program memory and 18bytes of data memory are used. Even more efficient memory usage (particularly of data memory) can be obtained with further optimization. A flowchart of the algorithm is included so that the user can modify it or port it to any 4bit or 8bit MCU with little effort. A discussion of error sources inherent in this method of measurement is also included.

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