float voltage;

void setup() {

Serial.begin(9600);
Serial.println("BEGIN");
Serial.println();

pinMode(2, OUTPUT);
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);

}

void loop() {

voltage = analogRead(A0) / 204.6;
Serial.println(voltage);

if (voltage < 1) {
  digitalWrite (2, LOW);
  digitalWrite (3, LOW);
  digitalWrite (4, LOW);
}

if (voltage > 1 &&  voltage < 3.0) {
  digitalWrite (2, HIGH);
  digitalWrite (3, LOW);
  digitalWrite (4, LOW);
}

if (voltage > 3.0 &&  voltage < 4.0) {
  digitalWrite (2, HIGH);
  digitalWrite (3, HIGH);
  digitalWrite (4, LOW);
}

if (voltage > 4.0 &&  voltage < 5.1) {
  digitalWrite (2, HIGH);
  digitalWrite (3, HIGH);
  digitalWrite (4, HIGH);
}

}