# Calculate amplitude of a signal after application FFT

I'm using Arduino Due and sensor for noise and I applied FFT library to extract frequency and it's working perfectly. But I don't know how to calculate the amplitudes and print them on console?

Here is the code:

``````#include "arduinoFFT.h"

#define SAMPLES 32
#define SAMPLING_FREQUENCY 1000

arduinoFFT FFT = arduinoFFT();

unsigned int sampling_period_us;
unsigned long microseconds;

double vReal[SAMPLES];
double vImag[SAMPLES];

void setup() {
Serial.begin(9600);

sampling_period_us = round(1000000*(1.0/SAMPLING_FREQUENCY));
}

void loop() {

/*SAMPLING*/
for(int i=0; i<SAMPLES; i++)
{
microseconds = micros();

vImag[i] = 0;

while(micros() < (microseconds + sampling_period_us)){
}
}

/*FFT*/
FFT.Windowing(vReal, SAMPLES, FFT_WIN_TYP_HAMMING, FFT_FORWARD);
FFT.Compute(vReal, vImag, SAMPLES, FFT_FORWARD);
FFT.ComplexToMagnitude(vReal, vImag, SAMPLES);
double peak = FFT.MajorPeak(vReal, SAMPLES, SAMPLING_FREQUENCY);

Serial.println(peak);

for(int i=0; i<(SAMPLES/2); i++)
{

Serial.print((i * 1.0 * SAMPLING_FREQUENCY) / SAMPLES, 1);
Serial.print(" ");
//Serial.println(vReal[i], 1);    //View only this line in serial plotter to visualize the bins
}

delay(1000);
while(1);
}
``````
arduinofftarduino-due

answered 4 months ago Nitro #1

The serial plotter does not have a number of sample to plot functionality.

If you want to view the amplitudes for each window correctly, you will need to use the following code

``````for(int i=0; i<(SAMPLES/2); i++)
{
//  Serial.print((i * 1.0 * SAMPLING_FREQUENCY) / SAMPLES, 1);
for(int i=0; i<20; i++)//Adjust the 20 to make space between each samples.
Serial.print(0);
Serial.print(vReal[i]);
}
``````

And then adjust the size of the serial plotter to fit your window.

I hope this helps.