/* Based on Oleg Mazurov's code for Reading rotary encoder on Arduino, here   
   https://chome.nerpa.tech/mcu/reading-rotary-encoder-on-arduino/ and here
   https://chome.nerpa.tech/mcu/rotary-encoder-interrupt-service-routine-for-avr-micros/

   This example does not use the port read method. Tested with Nano and ESP32

   Connections
   ===========
   Encoder | ESP32 |  Nano
   --------------------------
     A     |  D5   |  Nano D2
     B     |  D21  |  Nano D3
     GND   |  GND  |  GND
*/

// Define rotary encoder pins
#define ENC_A 23
#define ENC_B 18

volatile int counter = 0;

void setup() {

  // Set encoder pins
  pinMode(ENC_A, INPUT_PULLUP);
  pinMode(ENC_B, INPUT_PULLUP);

  // Start the serial monitor to show output
  Serial.begin(115200); // Change to 9600 for Nano, 115200 for ESP32
  delay(500);           // Wait for serial to start  
  Serial.println("Start");
}

void loop() {
  static int lastCounter = 0;
  
  read_encoder();

  // If count has changed print the new value to serial
  if(counter != lastCounter){
    Serial.println(counter);
    lastCounter = counter;
  }
}

void read_encoder() {
  // Encoder routine. Updates counter if they are valid
  // and if rotated a full indent
 
  static uint8_t old_AB = 3;  // Lookup table index
  static int8_t encval = 0;   // Encoder value  
  static const int8_t enc_states[]  = {0,-1,1,0,1,0,0,-1,-1,0,0,1,0,1,-1,0}; // Lookup table

  old_AB <<=2;  // Remember previous state  

  if (digitalRead(ENC_A)) old_AB |= 0x02; // Add current state of pin A
  if (digitalRead(ENC_B)) old_AB |= 0x01; // Add current state of pin B
  
  encval += enc_states[( old_AB & 0x0f )];

  // Update counter if encoder has rotated a full indent, that is at least 4 steps
  if( encval > 3 ) {        // Four steps forward
    counter++;              // Increase counter
    encval = 0;
  }
  else if( encval < -3 ) {  // Four steps backwards
   counter--;               // Decrease counter
   encval = 0;
  }
}