DIY Arduino Morse code Decoder and Trainer

/* 
 *  Morse code receiver
 */

#include <U8g2lib.h>
#include <TimerOne.h>

U8G2_ST7565_ERC12864_1_4W_SW_SPI u8g2 ( U8G2_R0, /* scl=*/  13 , /* si=*/  11 , /* cs=*/  10 , /* rs=*/  9 , /* rse=*/  8 ) ;

byte inPin1 = 0;                  //analog input to telegraph key or radio output
byte P1, P2;                      //button states
int readPin1;                     //telegraph key or radio output variableradia
int k, i;                         //iloop index
int kropka;                       //dot length
int z, s;                         //character pulses
int p, r;                         //break pulses
int wpm;                          //word per minute
String znak_M;
String litera_M;                  
char S_str[6];
char P_str[6];
char wpm_str[2];
char* znak;
char* wiersz[12];                                 //char workline*
char* wiersz1[12];                                //top line char*


const byte index_key = 48;                        //number of characters in the array 48
const char* Z_char[index_key] = {
"a","b","c","d","e","f","g","h","i","j","k","l","m",
"n","o","p","q","r","s","t","u","v","w","x","y","z",
"0","1","2","3","4","5","6","7","8","9",
"!","(",")","+",",","-",".","/","=","?","_"};

const String Morse[index_key] = {                 //Morse code
".-","-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--",
"-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--..",
"-----",".----","..---","...--","....-",".....","-....","--...","---..","----.", 
"-.-.--","-.--.","-.--.-",".-.-.","--..--","-....-",".-.-.-","-..-.","-...-","..--..","..--.-"};
/*
' (single apostrophe) • — — — — •
" (quote) • — • • — •
: (colon) — — — • • •
; (semicolon) — • — • — •
@ (monkey or at)  • — — • — •
*/

void setup() {
  
  Serial.begin(9600);
  u8g2.begin();
  u8g2.setContrast(210);
  Timer1.initialize(1000);
  Timer1.attachInterrupt(Zliczaj);
}

void loop() {
  //Serial.println(s);
  //delay(100); 
  Display(); 
}

void Display() {
  //sprintf(S_str,"%d", s);
  //sprintf(P_str,"%d", r);
  u8g2.setFontMode(1);
  u8g2.setFont(u8g2_font_10x20_tr);
  u8g2.firstPage();
  do {
     u8g2.drawStr(0, 15, "Morse"); 
     u8g2.drawStr(75, 15, wpm_str); 
     u8g2.drawStr(98, 15, "w/m");
     //u8g2.drawStr(75, 30, S_str);
     //u8g2.drawStr(105, 30, P_str);
     for (k = 0; k < 12; k++){  
       u8g2.drawStr(k*10, 40, wiersz1[k] );   //top line
       u8g2.drawStr(k*10, 60, wiersz[k] );    //workline
     }
  } while ( u8g2.nextPage() );
  delay(10);
}
  
void Zliczaj(){
  readPin1 = analogRead(inPin1);
  if (readPin1 > 10 ) {             //key is pressed
    z++;
    if (z == 1){
      r = p;
      //Display();                    //Displays the length of the last pause
      //delay(5);
      p = 0;
    }
  }
  if (readPin1 <= 10) {             //key released
    p++;
    if (p == 1) {
      s = z;
      if ( kropka == 0){
         kropka = s ;
         //wpm = 1200/s;
         //sprintf(wpm_str,"%d", wpm);
      }
      if ( z > 5 && z < 1.5 * kropka){ znak_M = "."; kropka = z ;}
      if ( z > 2 * kropka ){ znak_M = "-";}
      if ( r < 2 * kropka){ litera_M += znak_M;}
      if ( litera_M.length() == 0 ) {litera_M = znak_M;}
      z = 0;
    }
    if (p == 2 * kropka) {
      wpm = 1200/kropka;
      if (wpm > 90) {wpm = 0 ; z = 0;}
      sprintf(wpm_str,"%d", wpm);
      if ( litera_M.length() > 0 ) {
        ZnajdzZnak();
        i++;
        wiersz[i-1] = znak;
        if (i > 11) {
          for (int k = 0; k < 12; k++) {
            wiersz1[k] = " ";                        //delete the top line
            wiersz1[k] = wiersz[k];                  //rewriting characters from the working line to the top line
            wiersz[k] = " ";                         //delete work line    
          }
          i = 0;
        } 
      }   
      Display();                                   //displays the read characters
   }
    if (p == 100 * kropka && i > 0) {
       for (int k = 0; k < 12; k++) {
          wiersz1[k] = " ";                        //rewriting characters from the working line to the top line
          wiersz1[k] = wiersz[k];                  //rewriting characters from the working line to the top line
          wiersz[k] = " ";                         //delete work line    
        }
        i = 0;
        Display();                                //Displays the characters read
    }
  }
}

void ZnajdzZnak(){
  znak = "";
  for (k = 0; k <= index_key; k++){
     if (Morse[k] == litera_M) {
        znak = Z_char[k];            //converting the key code to a letter
        break;
     }
  }
  k = 0;
  litera_M = "";
}