int sensor = 0; 
void setup() {
 pinMode(A0, INPUT);
 pinMode(2, OUTPUT);
 pinMode(3, OUTPUT);
 pinMode(4, OUTPUT);
 Serial.begin(9600);
}

void loop() {
  Serial.println(sensor);
  sensor = analogRead(A0);
  if (sensor <= 341)
  {
    digitalWrite(2, HIGH);
    delay(sensor);
    delay(1000);
    digitalWrite(2, LOW);
    delay(sensor);
  }
  else if (sensor <= 682)
  {
    digitalWrite(3, HIGH);
    delay(sensor);
    digitalWrite(3, LOW);
    delay(sensor);
  }
  else
  {
    digitalWrite(4, HIGH);
    delay(sensor);
    digitalWrite(4, LOW);
    delay(sensor);
  }
 delay(500);
}