const int sound = 8;
const int photoPin = A0;
int readVal;
int minSense = 1000;
int maxSense = 0;
unsigned long myTime;
void setup() {
  // put your setup code here, to run once:
pinMode (photoPin, INPUT);
pinMode (sound, OUTPUT);
Serial.begin (9600);
calibrate ();


}

void calibrate ()
{
  myTime = millis ();
  while (millis() - myTime < 5000)
  {

  readVal = analogRead (photoPin);
  if (readVal > maxSense)
 {
  maxSense = readVal;

 }
 if (readVal < minSense)
 {
  minSense = readVal;
 }
  }
Serial.print (" max Value ");
Serial.print (maxSense);
Serial.print ("min Value ");
Serial.print (minSense);


  }

void loop()
{
 readVal = analogRead(photoPin);
 readVal = map(readVal, minSense, maxSense, 40, 4000);
readVal = constrain(readVal, 4000, 40);
tone (sound, readVal, 20);
  delay (10);
  noTone (sound);


}