FFT.ino

/*
 This example shows the most basic usage of the Adafruit ZeroFFT library.
 * it calculates the FFT and prints out the results along with their corresponding frequency
 * 
 * The signal.h file constains a 200hz sine wave mixed with a weaker 800hz sine wave.
 * The signal was generated at a sample rate of 8000hz.
 * 
 * Note that you can print only the value (coment out the other two print statements) and use
 * the serial plotter tool to see a graph.
 */

#include <Adafruit_ZeroFFT.h>
#include "signal.h"

//the signal in signal.h has 2048 samples. Set this to a value between 16 and 2048 inclusive.
//this must be a power of 2
#define SAMPLE_SIZE 256
//the sample rate
#define SAMPLING_RATE 80
//use the existing data
#define USE_HARD_CODED_DATA 0
//analog read pin
#define CHANNEL A0

q15_t analog_signal_data[SAMPLE_SIZE];

// the setup routine runs once when you press reset:
void setup() {
  Serial.begin(9600);
  while(!Serial); //wait for serial to be ready
}

void loop() {
  if(!USE_HARD_CODED_DATA)
    read_signal_data(SAMPLE_SIZE);

  run_fft(SAMPLE_SIZE);
  if(USE_HARD_CODED_DATA)
    while(1);

  delay(5000);
}

void read_signal_data(unsigned sample_count)
{
  for(int i=0; i<sample_count; i++)
  {
    // read data from pin A0
    analog_signal_data[i] = analogRead(CHANNEL);
    float voltage = (analog_signal_data[i] + 0.5) * (5.0 / 1023.0);
    
    Serial.println(voltage);
  }
}

void run_fft(unsigned sample_count)
{
  //run the FFT
  if(USE_HARD_CODED_DATA)
    ZeroFFT(hard_coded_signal_data, sample_count); 
  else
    ZeroFFT(analog_signal_data, sample_count);

  //data is only meaningful up to sample rate/2, discard the other half
  for(int i=0; i<SAMPLE_SIZE/2; i++){
    
    //print the frequency
    Serial.print(FFT_BIN(i, SAMPLING_RATE, sample_count));
    Serial.print(" Hz: ");

    //print the corresponding FFT output
    if(USE_HARD_CODED_DATA)
      Serial.println(hard_coded_signal_data[i]);
    else
      Serial.println(analog_signal_data[i]);
    
  }

  float max_amplitude = 0;
  float dominant_frequency = 0;


  if(USE_HARD_CODED_DATA){
    // iterate through the FFT bins to find the dominant frequency
    for(int i=0; i<SAMPLE_SIZE/2; i++) {
        if(hard_coded_signal_data[i] > max_amplitude) {
            max_amplitude = hard_coded_signal_data[i];
            dominant_frequency = FFT_BIN(i, SAMPLING_RATE, sample_count);
        }
    }

    
  } else{

    // iterate through the FFT bins to find the dominant frequency
    for(int i=0; i<SAMPLE_SIZE/2; i++) {
        if(analog_signal_data[i] > max_amplitude) {
            max_amplitude = analog_signal_data[i];
            dominant_frequency = FFT_BIN(i, SAMPLING_RATE, sample_count);
        }
      }
    }

    Serial.print("Dominant frequency: ");
    Serial.print(dominant_frequency);
    Serial.println(" Hz");
}