int latch = 3;  // 74HC595 pin 9 STCP
int clock = 4;  // 74HC595 pin 10 SHCP
int data = 2;   // 74HC595 pin 8 DS

unsigned char table[] = 
{0x3f, 0x06, 0x5b, 0x4f, 0x66, 0x6d, 0x7d, 0x07, 0x7f, 0x6f, 
 0x77, 0x7c, 0x39, 0x5e, 0x79, 0x71, 0x00}; // Display digital data

const int nbrDigits = 4; // Number of digits in the LED display
const int digitPins[nbrDigits] = {5, 6, 7, 8};

int counter = 0; // Initialize counter

void setup() {
  // Configuring output pins for the 74HC595
  pinMode(latch, OUTPUT);
  pinMode(clock, OUTPUT);
  pinMode(data, OUTPUT);

  // Configuring output pins for common cathode of each 7-segment digit
  for (int i = 0; i < nbrDigits; i++) {
    pinMode(digitPins[i], OUTPUT);
    digitalWrite(digitPins[i], HIGH);
  }
}

void loop() {
  for (int i = 0; i < 100; i++) { // Increase refresh rate
    DisplayNumber(counter);
  }
  
  counter++;
  if (counter > 9999) {
    counter = 0; // Reset counter after reaching 9999
  }
  delay(10); // Small delay to slow down counter incrementing
}

// Function to display a number on a 4-digit 7-segment display
void DisplayNumber(int number) {
  if (number == 0) {
    DisplayDigit(0, nbrDigits - 1); // Display 0 in the rightmost digit
  } else {
    for (int digit = nbrDigits - 1; digit >= 0; digit--) {
      if (number > 0) {
        DisplayDigit(number % 10, digit);
        number = number / 10;
      }
    }
  }
}

// Function to display one digit on a 7-segment display
void DisplayDigit(unsigned char num, int digit) {
  digitalWrite(latch, LOW);
  shiftOut(data, clock, MSBFIRST, table[num]);
  digitalWrite(latch, HIGH);
  
  digitalWrite(digitPins[digit], LOW);
  delay(10); // Reduce delay to increase refresh rate
  digitalWrite(digitPins[digit], HIGH);
}