fftArduinoAccelerator

Fast fourier transform of acceleration data with Arduino

Implementation

Arduino has a package arduinoFFT which I use to calculate the fft and FaBo9Axis_MPU9250 which I use to read the accelaration data from MPU-9250 chip.

For every loop I read acceleration data, set it to the rolling list, set IMG_ARR to zeros, compute array from RollingList and calculates the short time energy.

calculateNormalizedShortTimeEnergy

It first sets new float* for the FFT object, computest the fft, sums the absolute values of all data points and divides it with length of the return array.

Rolling List

RollingList is a object that can be store n last data points and insert new data point in O(1) time. Unfortunately the arduinoFFT need a array so I need to convert RollingList to array which is O(n) operation so I didn't save any time after all.

Due bad naming habits RollingList is named Rolling"List" even tho it uses Arrays everywhere (list -> Linked list, Array -> Memory block)

Unfortunate mistakes in my implementation

Currently, there are only 75 samples (not 100). If I try to add it to 100, the arduino crashes. I assume it is due to running out of memory. Arduino Uno R3 has 2KiB /(Kiki Bytes) of SRAM and size of float is 4B (Bytes). This program has two 128 float arrays and one 75 float array. Let's assume we had an array of 100 floats instead of 75 floats.

$2\text{KiB} - (2 \cdot 128 \cdot 4\text{B} + 100 \cdot 4 \text{B}) = 624 \text{B}$

624 Bytes of memory for everything else we need to store which I assume is not enougth for FaBo9Axis_MPU9250, arduinoFFT and all my variables.

• Size of float
• Size of memory

Picture of my Arduino setup