// Define the pins for each segment (a to g) and the common cathode pin
const int segmentPins[7] = {2, 3, 4, 5, 6, 7, 8}; // Pins for a, b, c, d, e, f, g
const int commonCathodePin = 9; // Common cathode pin

// Define the numbers to display on the seven-segment display
const byte numbers[10] = {
  B00111111, // 0
  B00000110, // 1
  B01011011, // 2
  B01001111, // 3
  B01100110, // 4
  B01101101, // 5
  B01111101, // 6
  B00000111, // 7
  B01111111, // 8
  B01101111  // 9
};

void setup() {
  // Set segment pins as outputs
  for (int i = 0; i < 7; i++) {
    pinMode(segmentPins[i], OUTPUT);
  }

  // Set common cathode pin as output
  pinMode(commonCathodePin, OUTPUT);
}

void loop() {
  // Count down from 9 to 0
  for (int i = 9; i >= 0; i--) {
    displayNumber(i);
    delay(1000); // Display each number for 1 second
  }
}

// Function to display a digit on the seven-segment display
void displayNumber(int num) {
  // Turn off all segments
  for (int i = 0; i < 7; i++) {
    digitalWrite(segmentPins[i], LOW); // Start with all segments off
  }

  // Activate segments based on the number to be displayed
  for (int i = 0; i < 7; i++) {
    if (bitRead(numbers[num], i) == 1) {
      digitalWrite(segmentPins[i], HIGH); // Turn on the segment if the bit is 1
    } else {
      digitalWrite(segmentPins[i], LOW); // Turn off the segment if the bit is 0
    }
  }

  // Turn on the common cathode to display the digit
  digitalWrite(commonCathodePin, LOW); // Common cathode pin is active low
  delay(5); // Short delay to stabilize the display
  digitalWrite(commonCathodePin, HIGH); // Turn off common cathode to refresh display
}