// 4 Digit 7-Segment Display (Common Cathode)
// Multiplexing Example - Counter from 0000 to 9999

int segPins[7] = {2, 3, 4, 5, 6, 7, 8};   // a,b,c,d,e,f,g
int digitPins[4] = {9, 10, 11, 12};       // Digit1, Digit2, Digit3, Digit4

// Segment map for numbers 0–9
byte numbers[10][7] = {
  {1,1,1,1,1,1,0}, // 0
  {0,1,1,0,0,0,0}, // 1
  {1,1,0,1,1,0,1}, // 2
  {1,1,1,1,0,0,1}, // 3
  {0,1,1,0,0,1,1}, // 4
  {1,0,1,1,0,1,1}, // 5
  {1,0,1,1,1,1,1}, // 6
  {1,1,1,0,0,0,0}, // 7
  {1,1,1,1,1,1,1}, // 8
  {1,1,1,1,0,1,1}  // 9
};

void setup() {
  for (int i=0; i<7; i++) pinMode(segPins[i], OUTPUT);
  for (int i=0; i<4; i++) pinMode(digitPins[i], OUTPUT);
}

void showDigit(int num, int digit) {
  // Set segment pins
  for (int i=0; i<7; i++) {
    digitalWrite(segPins[i], numbers[num][i]);
  }

  // Enable one digit at a time (active LOW for common cathode with transistor)
  digitalWrite(digitPins[digit], LOW);
  delay(3);  // digit ON time
  digitalWrite(digitPins[digit], HIGH); // turn OFF digit
}

void loop() {
  static int counter = 0;

  // Repeat multiplexing enough times for stability
  for (int t=0; t<100; t++) {
    showDigit((counter/1000)%10, 0); // Thousands
    showDigit((counter/100)%10, 1);  // Hundreds
    showDigit((counter/10)%10, 2);   // Tens
    showDigit(counter%10, 3);        // Ones
  }

  counter++;
  if (counter > 9999) counter = 0; // reset after 9999
}