// Define pins for the rotary encoder
const int encoderPinA = 2;  // CLK pin
const int encoderPinB = 3;  // DT pin

// Variable to store the counter value
volatile int counter = 0;

// Variable to store the last state of CLK pin
volatile int lastStateCLK = LOW;

void setup() {
  // Initialize Serial communication
  Serial.begin(9600);
  
  // Set encoder pins as inputs
  pinMode(encoderPinA, INPUT);
  pinMode(encoderPinB, INPUT);
  
  // Enable internal pullup resistors
  digitalWrite(encoderPinA, HIGH);
  digitalWrite(encoderPinB, HIGH);
  
  // Attach interrupt to CLK pin (pin 2)
  attachInterrupt(digitalPinToInterrupt(encoderPinA), updateEncoder, CHANGE);
  
  // Read the initial state of CLK
  lastStateCLK = digitalRead(encoderPinA);
  
  // Print the initial counter value
  Serial.print("Initial counter value: ");
  Serial.println(counter);
}

void loop() {
  // The main loop can be empty as we're using interrupts
  // You can add other code here if needed
}

void updateEncoder() {
  // Read the current state of CLK
  int currentStateCLK = digitalRead(encoderPinA);

  // If last and current state of CLK are different, then pulse occurred
  // React to only 1 state change to avoid double count
  if (currentStateCLK != lastStateCLK  && currentStateCLK == 1){

    // If the DT state is the same as the CLK state then
    // the encoder is rotating CCW so decrement
    if (digitalRead(encoderPinB) == currentStateCLK) {
      counter --;
    } else {
      // Encoder is rotating CW so increment
      counter ++;
    }

    Serial.print("Counter: ");
    Serial.println(counter);
  }

  // Remember last CLK state
  lastStateCLK = currentStateCLK;
}