helloYouSketch.ino, annotated

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int led = 10; // led that we will toggle
char inChar;  // character we will use for messages from the RPi

int button = 15;
int buttonState;

Variable declarations

void setup() {
  Serial.begin(9600);
  pinMode(led, OUTPUT);
  pinMode(button, INPUT);
}

Setup function. The invocation of serial is always necessary for the IxE Arduino because otherwise the Arduino is not communicating with the IxE RPi.

void loop() {
  // read the character we recieve on the serial port from the RPi
  if(Serial.available()) {
    inChar = (char)Serial.read();
  }

  // if we get a 'H', turn the LED on, else turn it off
  if(inChar == 'H'){
    digitalWrite(led, HIGH);
  }
  else{
    digitalWrite(led, LOW);
  }

Serial input listener. This code listens for Serial messages from the RPi. 'H' characters turn the light on. Other characters turn the light off.

  // Button event checker - if pressed, send message to RPi
  int newState = digitalRead(button);
  if (buttonState != newState) {
    buttonState = newState;
    if(buttonState == HIGH){
      Serial.println("light");
    }
    else{
      Serial.println("dark");
    }
  }
}

Button check. This code attends to changes on the voltage on the 'button' pin. If the voltage on that pin goes high, it sends a serial message 'light' to the RPi. If the voltage goes low, it sends the message 'dark'. Note that this buttoncode does not feature debouncing.

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