illuminate left or right led with accelerometer tilt

accel_y_axis_led_swap.pde

/**
  Two LEDs triggered by tilting of accelerometer
  along Y axis.
  
  Arduino Diecimila and Memsic 2125
  */

int ledPins[] = {6,7};
int yPin = 10;
int yRaw;
double ymG, yTheta;

void setup() {
  Serial.begin(9600);
  // initialize LED driving pins to OUTPUT and LOW
  for(int i = 0; i <= size(ledPins); i++) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i], LOW);
  }
  pinMode(yPin, INPUT);
}

void loop() {
  yRaw = pulseIn(yPin, HIGH);    // Raw data from the sensor
  ymG = ((yRaw / 10) - 500) * 8; // milli-Gs
  yTheta = asin(ymG / 1000.0);   // radians of Y axis
  yTheta = yTheta * (360 / (2*M_PI)); // convert rad to deg
  //Serial.print("Y Raw: ");
  //Serial.println(yRaw);
  //Serial.print("Y milli-Gs: ");
  //Serial.println(ymG);
  
  Serial.print("Y Angle: ");
  Serial.println(yTheta);
  if (yTheta >= 10) {
    rightLed();
  } else if (yTheta <= -10) {
    leftLed();
  } else {
    offLed();
  }
}

void leftLed() {
  digitalWrite(ledPins[0], HIGH);
  digitalWrite(ledPins[1], LOW);
}

void rightLed() {
  digitalWrite(ledPins[0], LOW);
  digitalWrite(ledPins[1], HIGH);
}

void offLed() {
  digitalWrite(ledPins[0], LOW);
  digitalWrite(ledPins[1], LOW);
}

int size(int arr[]) {
  int i = 0;
  while(arr[i] != NULL) i++;
  return i;
}