#include "fix_fft.h"
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

Adafruit_SSD1306 display(128, 64, &Wire, 4);

char im[128], data[128];
char x = 0, ylim = 60;
int i = 0, val;
float alpha = 0.2; // Low-pass filter coefficient

void setup()
{
  Serial.begin(9600);
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.clearDisplay();
  analogReference(DEFAULT);
}

void loop()
{
  int min = 1024, max = 0;
  float filteredValue = 0;

  for (i = 0; i < 128; i++) // take 128 samples
  {
    val = 30 * analogRead(A0); // Read LDR sensor on A0

    Serial.print("Raw Value: ");
    Serial.print(val);
    Serial.print("\t");

    // Low-pass filter
    filteredValue = alpha * val + (1 - alpha) * filteredValue;

    Serial.print("Filtered Value: ");
    Serial.println(filteredValue);

    data[i] = filteredValue / 4 - 128;
    im[i] = 0;
    if (filteredValue > max)
      max = filteredValue; // store max & min sample
    if (filteredValue < min)
      min = filteredValue;
  }
  //------------------------------------------
  fix_fft(data, im, 7, 0); // FFT on data
  //------------------------------------------
  display.clearDisplay();
  for (i = 1; i < 64; i++) // bar graph sketch on OLED display
  {
    int dat = sqrt(data[i] * data[i] + im[i] * im[i]);
    display.drawLine(i * 2 + x, ylim, i * 2 + x, ylim - dat, WHITE);
  }
  display.setCursor(0, 0);
  display.print("  Spectrum Analyzer");
  display.display();
}