// Public domain, by Chad Miller
// Photo of layout at
//   http://picasaweb.google.com/chadmill/Arduino#5563199409956300850
// BETTER VERSION with more asynchronicity and immediate response at
//   http://sandbox.chad.org/arduino-light-excitable-blinker-smarter.pde


// Map pins to color inputs of LED.
int red = 9;
int blue = 10;
int green = 11;

void setup() {                
  pinMode(13, OUTPUT); // pseudo-pin leading to on-board LED
  pinMode(red, OUTPUT);
  pinMode(blue, OUTPUT);
  pinMode(green, OUTPUT);
}

int lightread() {
  int a = constrain(analogRead(0), 0, 900); // delay(d) hates nonpositive
  int lr = 2000 - map(a, 0, 900, 500, 1990);
  return lr;
}

void loop() {
  digitalWrite(13, HIGH);
  digitalWrite(red, HIGH);
  delay(lightread());
  digitalWrite(blue, HIGH);
  delay(lightread());
  digitalWrite(blue, LOW);
  digitalWrite(green, HIGH);
  delay(lightread());
  digitalWrite(red, LOW);
  delay(lightread());
  digitalWrite(red, LOW);
  digitalWrite(blue, LOW);
  digitalWrite(green, LOW);
  digitalWrite(13, LOW);
  delay(lightread());
}