Arduino Duo Monitor-Auto-Rotate.ino

/*
 * Monitor-Auto-Rotate v1
 * 
 * Sketch that will change display orientation by using usb keyboard emultaion to  
 * press Ctrl+Alt+Up-Arrow or Ctrl+Alt+Right-Arrow (which are the default hotkeys
 * to rotate the display on windows systems with Intel graphics drivers) when it
 * senses (using a reed switch and a magnet) that the monitor has been physically
 * rotated.
 * 
 * Requires updating the Arduino's atmega8u2 USB firmware so that it can emulate
 * a USB keyboard (this stops you from being able to upload sketches, so you must
 * upoad the sketch before changing the firmware)
 * 
 * USB HID firmware can be downloaded from:
 * http://hunt.net.nz/users/darran/weblog/b3029/Arduino_UNO_Keyboard_HID_version_03.html
 * 
 * The circuit:
 * Reed switch attached from pin 12 to GND
 * Magnet should pull reed switch closed when monitor is in portrait position
 */

#define KEY_LEFT_CTRL 0b00000001
#define KEY_LEFT_ALT 0b00000100
#define KEY_UP_ARROW 82
#define KEY_LEFT_ARROW 80

const int switchPin = 12;    // the number of the pushbutton pin

int switchState;     // the current reading from the switch pin
int lastSwitchState; // the previous reading from the switch pin
long lastDebounceTime = 0;  // the last time the switch pin was toggled
long debounceDelay = 50;    // the debounce time

uint8_t buf[8] = {0};   /* Keyboard report buffer */

void setup() {
  pinMode(switchPin, INPUT_PULLUP);
  Serial.begin(9600);
}

void sendKeyPress(byte modifier, byte key) {
  buf[0] = modifier;
  buf[2] = key;
  Serial.write(buf, 8); // Send keypress
  delay(100); //Give host time to read keypress
  buf[0] = 0;
  buf[2] = 0;
  Serial.write(buf, 8);  // Release key  
}

void loop() {
  // read the state of the switch into a local variable:
  int reading = digitalRead(switchPin);

  // check to see if you just pressed the button
  // (i.e. the input went from LOW to HIGH),  and you've waited
  // long enough since the last press to ignore any noise:

  // If the switch changed, due to noise or pressing:
  if (reading != lastSwitchState) {
    // reset the debouncing timer
    lastDebounceTime = millis();
  }

  if ((millis() - lastDebounceTime) > debounceDelay) {
    // whatever the reading is at, it's been there for longer
    // than the debounce delay, so take it as the actual current state:

    // if the button state has changed:
    if (reading != switchState) {
      switchState = reading;

      if (switchState == HIGH) {
        //Send hotkey for normal (landscape) orientation
        sendKeyPress(KEY_LEFT_CTRL + KEY_LEFT_ALT, KEY_UP_ARROW);
        //Serial.println("SEND UP");
      } else {
        //Send hotkey for portrait orientation
        sendKeyPress(KEY_LEFT_CTRL + KEY_LEFT_ALT, KEY_LEFT_ARROW);
        //Serial.println("SEND LEFT");
      }
    }
  }

  // save the reading.  Next time through the loop,
  // it'll be the lastSwitchState:
  lastSwitchState = reading;
}