unsigned long read_high;
unsigned long read_low;
unsigned long diff;
unsigned long sum;

int sensorMax = 117000;
int sensorMin = 109000;
int outputMin = 0;
int outputMax = 255;

int N_samples = 1000;

int analog_pin = A0;

void setup() {
pinMode(D1,OUTPUT);
Serial.begin(115200);
}

void loop() {
 sum = 0;

 for (int i = 0; i < N_samples; i++){
   digitalWrite(D1,HIGH);
   read_high = analogRead(analog_pin);
   delayMicroseconds(100);
   digitalWrite(D1,LOW);
   read_low = analogRead(analog_pin);
   diff = read_high - read_low;
   sum += diff;
 }
 
int output = constrain(map(sum, sensorMax, sensorMin, 0, 255), outputMin, outputMax);
Serial.println(output);
delay(100);

}