OLED Spektr analyzer U8G2_SH1106

/* Arduino Spectrum Analyzer
 *
 * learnelectronics
 * 27 April 2017
 * black magic stolen from CBM80Amiga
 *
 * www.youtube.com/c/learnelectronics
 * arduino1069@gmail.com
 *
 * Fix_FFT library available @ https://github.com/kosme/arduinoFFT
 */


#include "fix_fft.h"                                  //library to perfom the Fast Fourier Transform
#include <SPI.h>                                      //SPI library
#include <U8g2lib.h>
U8G2_SH1106_128X64_NONAME_F_4W_HW_SPI  dispL(U8G2_R0,/*cs=*/ 7, /*dc=*/  6, /* reset=*/ 8); // propojeni je: clock=13, data=11, cs=7, dc=6, reset=8);

//#define SCREEN_WIDTH 128 // OLED display width, in pixels
//#define SCREEN_HEIGHT 64 // OLED display height, in pixels

char im[128], data[128];                              //variables for the FFT
char x = 0, ylim = 60;                                //variables for drawing the graphics
int i = 0, val;                                       //counters

void setup()
{
  Serial.begin(9600);                                 //serial comms for debuging
  dispL.begin();
/*  display.begin(SH1106_SWITCHCAPVCC);
  display.setTextSize(1);                             //set OLED text size to 1 (1-6)
  display.setTextColor(WHITE);                        //set text color to white
  display.clearDisplay();                             //clear display
*/
  analogReference(DEFAULT);                           // Use default (5v) aref voltage.
};

void loop()
{
  int min=1024, max=0;                                //set minumum & maximum ADC values
  for (i = 0; i < 128; i++) {                         //take 128 samples
    val = analogRead(A0);                             //get audio from Analog 0
    data[i] = val / 4 - 128;                          //each element of array is val/4-128
    im[i] = 0;                                        //
    if(val>max) max=val;                              //capture maximum level
    if(val<min) min=val;                              //capture minimum level
  };

  fix_fft(data, im, 7, 0);                            //perform the FFT on data
  dispL.clearBuffer();

//   dispL.setFont(u8g2_font_ncenB08_tr);
   dispL.setFont(u8g2_font_sandyforest_tr);
   dispL.drawStr(20,8,"Spectrum analyzer");

  for (i = 1; i < 64; i++) {                          // In the current design, 60Hz and noise
    int dat = sqrt(data[i] * data[i] + im[i] * im[i]);//filter out noise and hum
    dispL.drawLine(i*2 + x, ylim, i*2 + x, ylim - dat); // draw bar graphics for freqs above 500Hz to buffer
//    Serial.print("i*2 + x: "); Serial.print(i*2 + x); Serial.print("    ");
//    Serial.print("ylim: "); Serial.print(ylim); Serial.print("    ");
//    Serial.print("ylim - dat: "); Serial.print(ylim - dat); Serial.println("    ");
  };


   dispL.sendBuffer();
};