const int ledPin =  3;
#define sensorPower 7
#define sensorPin A0

int val = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(sensorPower, OUTPUT);
  digitalWrite(sensorPower, LOW);
  Serial.begin(9600);
}

void loop() {
  int level = readSensor();
  if (level > 0) {
    analogWrite(ledPin, map(level,0,1023,0,255));
  }  else {
    digitalWrite(ledPin, LOW);
  }
}

int readSensor() {
  digitalWrite(sensorPower, HIGH);
  delay(10);
  int val = analogRead(sensorPin);
  digitalWrite(sensorPower, LOW);
  return val;
}