DigiSpark_Monitor_Rotate.ino

/*
 * Sketch for DigiSpark that will change display orientation by using usb
 * keyboard emulation to press Ctrl+Alt+Up-Arrow or Ctrl+Alt+Left-Arrow
 * (which are the default hotkeys to rotate the display on windows systems
 * with Intel graphics drivers) when it senses (using a tilt switch) that
 * the monitor has been physically rotated.
 *
 * It also illuminates the onboard LED when it thinks the monitor should
 * be in portrait mode
 * 
 * The circuit:
 * Tilt switch attached from pin 2 to pin 0 (acting as ground)
 */

#include "DigiKeyboard.h"

// For some reason these aren't defined in the library
#define KEY_ARROW_UP 0x52
#define KEY_ARROW_RIGHT 0x4F

const int ledPin = 1; // the number of the led pin
const int switchPin = 2; // the number of the tilt switch pin
const int groundPin = 0; // the number of the pin that will be used for ground (it's closer to the switchPin than the actual ground)

const int protraitSwitchMode = HIGH; //The state that the tilt switch should be in when monitor is in portrait mode
const int portraitDirection = KEY_ARROW_LEFT; //On my dell monitor, I need LEFT, but others may rotate the other way so may need RIGHT

int lastSwitchState = HIGH; // the previous reading from the input pin
int switchState = HIGH; // the current reading from the input pin

long lastDebounceTime = 0;  // the last time the output pin was toggled
long debounceDelay = 50; // the debounce time



void setLandscape() {
  DigiKeyboard.sendKeyStroke(KEY_ARROW_UP, MOD_CONTROL_LEFT | MOD_ALT_LEFT);
  digitalWrite(ledPin, LOW);
}

void setPortrait() {
  DigiKeyboard.sendKeyStroke(portraitDirection, MOD_CONTROL_LEFT | MOD_ALT_LEFT);
  digitalWrite(ledPin, HIGH);
}



void setup() {
  pinMode(switchPin, INPUT);
  digitalWrite(switchPin, HIGH); //Set internal pullup resistor

  pinMode(groundPin, OUTPUT);
  digitalWrite(groundPin, LOW); //Set to low so that it acts like ground

  pinMode(ledPin, OUTPUT);

  //Flash the LED Pin so that we know that it is now ready and not in progrmm mode
  digitalWrite(ledPin, HIGH);
  delay(20);
  digitalWrite(ledPin, LOW);
}

void loop() {
  // Prevent some older systems from missing the first char after delay
  DigiKeyboard.sendKeyStroke(0);
  
  int reading = digitalRead(switchPin);
  // if input changed, reset the debounce timer
  if (reading != lastSwitchState) {
    lastDebounceTime = millis();
  // otherwise, check if input has not changed for a while (i.e. been steady)
  // and that the switch state has changed
  } else if (((millis() - lastDebounceTime) > debounceDelay) && (reading != switchState)) {
    switchState = reading;
    //If the tilt switch is closed
    if (switchState == protraitSwitchMode) {
      setPortrait();
    } else {
      setLandscape();
    }
  }
  lastSwitchState = reading;
  
  // Allow keyboard library to interface with PC if necesarry
  DigiKeyboard.delay(0);
}