LaserAlarm

// Laser Security Alarm
// BY Stigern, www.stigern.net

int ldr_readings = 0;
int AlarmPin = 10;

void setup()
{
 // Setting up Serial communication!
 // I use this for calibration first, to read what values I
 // get when it got the laser in center, and what value I
 // get when it's not in the center. So that I know what
 // to put in the if statements.
  Serial.begin(9600);
}

void loop()
{
  // Read from the analog 0 and put it into the integer.
  // So that we can use the if statement to ask if it's
  // something blocking the light or now.
  ldr_readings = analogRead(0);

  // Just so we can see the values from the LDR
  // Prints the integer to us via serial. Used
  // for calibration when adjusting 100 and 50.
  Serial.println(ldr_readings);

  // Should we activate the alarm?
  // Yepp, if we get a value higher than 100.
  if (ldr_readings > 100)
  {
     digitalWrite(AlarmPin, HIGH);
  }

  // Or should we deactivate it?
  // Yes if we get a value lower than 50.
  if (ldr_readings < 50)
  {
     digitalWrite(AlarmPin, LOW);
  }
}