InfiniTime.git

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/*

	Example of use of the FFT libray to compute FFT for a signal sampled through the ADC
    with speedup through different arduinoFFT options. Based on examples/FFT_03/FFT_03.ino
  
    Copyright (C) 2020 Bim Overbohm (header-only, template, speed improvements)

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.

*/

// There are two speedup options for some of the FFT code:

// Define this to use reciprocal multiplication for division and some more speedups that might decrease precision
//#define FFT_SPEED_OVER_PRECISION

// Define this to use a low-precision square root approximation instead of the regular sqrt() call
// This might only work for specific use cases, but is significantly faster. Only works for ArduinoFFT<float>.
//#define FFT_SQRT_APPROXIMATION

#include "arduinoFFT.h"

/*
These values can be changed in order to evaluate the functions
*/
#define CHANNEL A0
const uint16_t samples = 64; //This value MUST ALWAYS be a power of 2
const float samplingFrequency = 100; //Hz, must be less than 10000 due to ADC
unsigned int sampling_period_us;
unsigned long microseconds;

/*
These are the input and output vectors
Input vectors receive computed results from FFT
*/
float vReal[samples];
float vImag[samples];

/*
Allocate space for FFT window weighing factors, so they are calculated only the first time windowing() is called.
If you don't do this, a lot of calculations are necessary, depending on the window function.
*/
float weighingFactors[samples];

/* Create FFT object with weighing factor storage */
ArduinoFFT<float> FFT = ArduinoFFT<float>(vReal, vImag, samples, samplingFrequency, weighingFactors);

#define SCL_INDEX 0x00
#define SCL_TIME 0x01
#define SCL_FREQUENCY 0x02
#define SCL_PLOT 0x03

void setup()
{
  sampling_period_us = round(1000000*(1.0/samplingFrequency));
  Serial.begin(115200);
  Serial.println("Ready");
}

void loop()
{
  /*SAMPLING*/
  microseconds = micros();
  for(int i=0; i<samples; i++)
  {
      vReal[i] = analogRead(CHANNEL);
      vImag[i] = 0;
      while(micros() - microseconds < sampling_period_us){
        //empty loop
      }
      microseconds += sampling_period_us;
  }
  /* Print the results of the sampling according to time */
  Serial.println("Data:");
  PrintVector(vReal, samples, SCL_TIME);
  FFT.windowing(FFTWindow::Hamming, FFTDirection::Forward);	/* Weigh data */
  Serial.println("Weighed data:");
  PrintVector(vReal, samples, SCL_TIME);
  FFT.compute(FFTDirection::Forward); /* Compute FFT */
  Serial.println("Computed Real values:");
  PrintVector(vReal, samples, SCL_INDEX);
  Serial.println("Computed Imaginary values:");
  PrintVector(vImag, samples, SCL_INDEX);
  FFT.complexToMagnitude(); /* Compute magnitudes */
  Serial.println("Computed magnitudes:");
  PrintVector(vReal, (samples >> 1), SCL_FREQUENCY);
  float x = FFT.majorPeak();
  Serial.println(x, 6); //Print out what frequency is the most dominant.
  while(1); /* Run Once */
  // delay(2000); /* Repeat after delay */
}

void PrintVector(float *vData, uint16_t bufferSize, uint8_t scaleType)
{
  for (uint16_t i = 0; i < bufferSize; i++)
  {
    float abscissa;
    /* Print abscissa value */
    switch (scaleType)
    {
      case SCL_INDEX:
        abscissa = (i * 1.0);
	break;
      case SCL_TIME:
        abscissa = ((i * 1.0) / samplingFrequency);
	break;
      case SCL_FREQUENCY:
        abscissa = ((i * 1.0 * samplingFrequency) / samples);
	break;
    }
    Serial.print(abscissa, 6);
    if(scaleType==SCL_FREQUENCY)
      Serial.print("Hz");
    Serial.print(" ");
    Serial.println(vData[i], 4);
  }
  Serial.println();
}