const int ledPins[] = {23,22,17,16};  // LED GPIO pins
const int buttonPin = 15;                // Button GPIO pin
volatile int counter = 0;                // Counter value

void setup() {
  for (int i = 0; i < 4; i++) {
    pinMode(ledPins[i], OUTPUT);         // Set LED pins as OUTPUT
  }
  pinMode(buttonPin, INPUT_PULLUP);      // Set button pin as INPUT_PULLUP
  
  attachInterrupt(buttonPin, buttonPressed, FALLING);  // Interrupt on button press
}

void loop() {
  displayCounter();                      // Display counter value on LEDs
  delay(200);                            // Debounce delay
}

void buttonPressed() {
  counter = (counter + 1) % 16;          // Increment counter and reset after 15
}

void displayCounter() {
  for (int i = 0; i < 4; i++) {
    digitalWrite(ledPins[i], (counter >> i) & 0x01);   // Display binary value of counter
  }
}