HID_volume_rotor.ino

    #include "TrinketHidCombo.h"
     
    #define PIN_ENCODER_A 4
    #define PIN_ENCODER_B 5
    #define TRINKET_PINx  PINB
     
    static uint8_t enc_prev_pos = 0;
    static uint8_t enc_flags    = 0;
     
    void setup()
    {
      // set pins as input with internal pull-up resistors enabled
      pinMode(PIN_ENCODER_A, INPUT);
      pinMode(PIN_ENCODER_B, INPUT);
      digitalWrite(PIN_ENCODER_A, HIGH);
      digitalWrite(PIN_ENCODER_B, HIGH);
     
      TrinketHidCombo.begin(); // start the USB device engine and enumerate
     
      // get an initial reading on the encoder pins
      if (digitalRead(PIN_ENCODER_A) == LOW) {
        enc_prev_pos |= (1 << 0);
      }
      if (digitalRead(PIN_ENCODER_B) == LOW) {
        enc_prev_pos |= (1 << 1);
      }
    }
     
    void loop()
    {
      int8_t enc_action = 0; // 1 or -1 if moved, sign is direction
     
      // note: for better performance, the code will now use
      // direct port access techniques
      // http://www.arduino.cc/en/Reference/PortManipulation
      uint8_t enc_cur_pos = 0;
      // read in the encoder state first
      if (bit_is_clear(TRINKET_PINx, PIN_ENCODER_A)) {
        enc_cur_pos |= (1 << 0);
      }
      if (bit_is_clear(TRINKET_PINx, PIN_ENCODER_B)) {
        enc_cur_pos |= (1 << 1);
      }
     
      // if any rotation at all
      if (enc_cur_pos != enc_prev_pos)
      {
        if (enc_prev_pos == 0x00)
        {
          // this is the first edge
          if (enc_cur_pos == 0x01) {
            enc_flags |= (1 << 0);
          }
          else if (enc_cur_pos == 0x02) {
            enc_flags |= (1 << 1);
          }
        }
     
        if (enc_cur_pos == 0x03)
        {
          // this is when the encoder is in the middle of a "step"
          enc_flags |= (1 << 4);
        }
        else if (enc_cur_pos == 0x00)
        {
          // this is the final edge
          if (enc_prev_pos == 0x02) {
            enc_flags |= (1 << 2);
          }
          else if (enc_prev_pos == 0x01) {
            enc_flags |= (1 << 3);
          }
     
          // check the first and last edge
          // or maybe one edge is missing, if missing then require the middle state
          // this will reject bounces and false movements
          if (bit_is_set(enc_flags, 0) && (bit_is_set(enc_flags, 2) || bit_is_set(enc_flags, 4))) {
            enc_action = 1;
          }
          else if (bit_is_set(enc_flags, 2) && (bit_is_set(enc_flags, 0) || bit_is_set(enc_flags, 4))) {
            enc_action = 1;
          }
          else if (bit_is_set(enc_flags, 1) && (bit_is_set(enc_flags, 3) || bit_is_set(enc_flags, 4))) {
            enc_action = -1;
          }
          else if (bit_is_set(enc_flags, 3) && (bit_is_set(enc_flags, 1) || bit_is_set(enc_flags, 4))) {
            enc_action = -1;
          }
     
          enc_flags = 0; // reset for next time
        }
      }
     
      enc_prev_pos = enc_cur_pos;
     
      if (enc_action > 0) {
        TrinketHidCombo.pressMultimediaKey(MMKEY_VOL_UP);
      }
      else if (enc_action < 0) {
        TrinketHidCombo.pressMultimediaKey(MMKEY_VOL_DOWN);
      }
      else {
        TrinketHidCombo.poll(); // do nothing, check if USB needs anything done
      }
    }