// http://electronoobs.com/eng_arduino_tut125.php

// Rotary Encoder Inputs
#define Clock 9   //Clock pin connected to D9
#define Data 8    //Data pin connected to D8
#define Push 10   //Push button pin connected to D10

int counter = 0;                    //Use this variable to store "steps"
int previous_counter = 0;           //Use this variable to store previous "steps" value
int currentStateClock;              //Store the status of the clock pin (HIGH or LOW)
int StateData;                      //Store the status of the data pin (HIGH or LOW)
int lastStateClock;                 //Store the PREVIOUS status of the clock pin (HIGH or LOW)
String currentDir ="";              //Use this to print text 
unsigned long lastButtonPress = 0;  //Use this to store if the push button was pressed or not

void setup() {
  
  /*  Set encoder pins as inputs with pullups. If you use the Encoder Module, you don't need 
   *  pullups for Clock and Data, only for the push button.*/
  pinMode(Clock,INPUT_PULLUP);
  pinMode(Data,INPUT_PULLUP);
  pinMode(Push, INPUT_PULLUP);

  //Here we activate pin change interruptions on pin D8 and D9 with PCINT0 and PCINT1
  PCICR |= (1 << PCIE0);      //enable PCMSK0 scan                                                 
  PCMSK0 |= (1 << PCINT0);    //Pin 8 (Data) interrupt. Set pin D8 to trigger an interrupt on state change.  
  PCMSK0 |= (1 << PCINT1);    //Pin 9 (Clock) interrupt. Set pin D9 to trigger an interrupt on state change.  
   
  // Setup Serial Monitor
  Serial.begin(9600);

  // Read the initial state of Clock pin (it could be HIGH or LOW)
  lastStateClock = digitalRead(Clock);
}

void loop() {  
  if(counter != previous_counter)
  {
    Serial.print("Counter: ");
    Serial.println(counter);
  }
  
  delay(1);
}

/*In this case, the counter will automatically change its value in the interruption. 
  So all we need to do is to print its value in the void loop*/
ISR(PCINT0_vect){  
  cli(); //We pause interrupts happening before we read pin values
  currentStateClock =   (PINB & B00000010);       //Check pin D9 state? Clock
  StateData  =   (PINB & B00000001);              //Check pin D8 state? Data
  if (currentStateClock != lastStateClock){
    // If "clock" state is different "data" state, the encoder is rotating clockwise
    if (StateData != currentStateClock){ 
      counter  ++;                                // We increment   
      lastStateClock = currentStateClock;         // Updates the previous state of the clock with the current state
      sei(); //restart interrupts
    }
    //Else, the encoder is rotating counter-clockwise 
    else {
      counter --;                                 // We decrement
      lastStateClock = currentStateClock;         // Updates  previous state of the clock with the current state    
      sei(); //restart interrupts
    } 
  }  
}