calibrateAnalogIn.ino

// These constants won't change:
const int sensorPin = A7;    // pin that the sensor is attached to
const int ledPin = 2;        // pin that the LED is attached to

// variables:
int sensorValue = 0;         // the sensor value
int sensorMin = 1023;        // minimum sensor value
int sensorMax = 0;           // maximum sensor value


void setup() {
   // open the serial port for communication
  Serial.begin(9600);
    while(!Serial){
    ;; // do nothing until the serial port opens
  }
  Serial.println("calibrating ......");

  // turn on LED to signal the start of the calibration period:
  pinMode(13, OUTPUT);
  digitalWrite(13, HIGH);

  // calibrate during the first ten seconds
  while (millis() < 10000) {
    sensorValue = analogRead(sensorPin);

    // record the maximum sensor value
    if (sensorValue > sensorMax) {
      sensorMax = sensorValue;
    }

    // record the minimum sensor value
    if (sensorValue < sensorMin) {
      sensorMin = sensorValue;
    }
  }

  // signal the end of the calibration period
  digitalWrite(13, LOW);

  // print out some diagnostics to the serial monitor
  Serial.print("sensorMin: ");
  Serial.print(sensorMin);
  Serial.print(", sensorMax: ");
  Serial.println(sensorMax);
}

void loop() {
  // read the sensor:
  sensorValue = analogRead(sensorPin);

  // apply the calibration to the sensor reading
  sensorValue = map(sensorValue, sensorMin, sensorMax, 0, 255);

  // in case the sensor value is outside the range seen during calibration
  sensorValue = constrain(sensorValue, 0, 255);

  // fade the LED using the calibrated value:
  analogWrite(ledPin, sensorValue);
}

LDR.md