const int segmentPins[] = {2, 3, 4, 5, 6, 7, 8};  // A-G segment pins
const int digitPins[] = {9,10,11,12};         // D1-D4 (digit control pins)

// Common Cathode: 1 = ON, 0 = OFF
const byte numbers[4][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
};

const byte letters[4][7] = {
  {1, 1, 1, 0, 1, 1, 1}, // A
  {0, 0, 1, 1, 1, 1, 1}, // b
  {1, 0, 0, 1, 1, 1, 0}, // c
  {0, 1, 1, 1, 1, 0, 1}  // d
};

void setup() {
  for (int i = 0; i < 7; i++) pinMode(segmentPins[i], OUTPUT); // Set A-G as outputs
  for (int i = 0; i < 4; i++) pinMode(digitPins[i], OUTPUT);   // Set digit control pins as outputs
}

void displayCharacter(int digit, const byte character[7]) {
  for (int i = 0; i < 4; i++) digitalWrite(digitPins[i], HIGH); // Turn OFF all digits
  
  for (int i = 0; i < 7; i++) 
    digitalWrite(segmentPins[i], character[i]); // Set segment states

  digitalWrite(digitPins[digit], LOW); // Turn ON selected digit (Common Cathode: LOW = ON)
  delayMicroseconds(3000); // Short delay for stable multiplexing (reduce flickering)
  digitalWrite(digitPins[digit], HIGH); // Turn OFF digit again
}

void loop() {
  // Display "0123"
  for (int i = 0; i < 300; i++) { // Loop to stabilize the display for 1 second
    displayCharacter(0, numbers[0]); // 0
    displayCharacter(1, numbers[1]); // 1
    displayCharacter(2, numbers[2]); // 2
    displayCharacter(3, numbers[3]); // 3
  }
  delay(1000); //delay 1 second before switching to next set

  // Display "Abcd"
  for (int i = 0; i < 300; i++) { // Loop to stabilize the display for ~1 second
    displayCharacter(0, letters[0]); // A
    displayCharacter(1, letters[1]); // b
    displayCharacter(2, letters[2]); // c
    displayCharacter(3, letters[3]); // d
  }
  delay(1000); //delay 1 second before switching to next set
}