const int inputPin = A0;
const int lampPin = 9;

void setup() {
  Serial.begin(115200);
  pinMode(inputPin, INPUT);
  pinMode(lampPin, OUTPUT);
}

#define CMPX(a, b) if (a > b) { t = a; a = b; b = t; }

void loop() {
#if 0
  // might be noisy
  unsigned val = analogRead(inputPin);
#else
  // take median of 4 samples
  unsigned t;
  unsigned smp0 = analogRead(inputPin);
  delay(2);
  unsigned smp1 = analogRead(inputPin);
  delay(2);
  unsigned smp2 = analogRead(inputPin);
  delay(2);
  unsigned smp3 = analogRead(inputPin);
  CMPX(smp0, smp2);
  CMPX(smp1, smp3);
  CMPX(smp0, smp1);
  CMPX(smp2, smp3);
  // CMPX(smp1, smp2);
  unsigned val = (smp1 + smp2) >> 1;
#endif
  analogWrite(lampPin, val >> 2);
  Serial.println(val);
  delay(40);
}