#define SENSORPIN A7
#define OUTPIN 13
#define DELAYMILLIS 50
#define NSAMPLES 20
#define MINCHANGE 13
#define ON HIGH
#define OFF LOW

int samples[NSAMPLES] = {0};
int index;

void setup() {
  pinMode(OUTPIN, OUTPUT);
  Serial.begin(115200);
  index = 0;
}

void loop() {
  samples[index] = analogRead(SENSORPIN);
  index = (index + 1) % NSAMPLES;
  int maxlevel = -1;
  int minlevel = 2000;
  for (int i = 0; i < NSAMPLES; i++) {
    if (samples[i] < minlevel) {
      minlevel = samples[i];
    }
    if (samples[i] > maxlevel) {
      maxlevel = samples[i];
    }
  }
  Serial.println(maxlevel - minlevel);
  digitalWrite(OUTPIN, (maxlevel - minlevel) > MINCHANGE ? ON : OFF);
  delay(DELAYMILLIS);
}