int analogPin = 3;
int RdVal = 0;
float Vx = 0.0;
void setup() {
  // put your setup code here, to run once:
  analogReference(DEFAULT); // Arduino 5 V
  Serial.begin(9600);
  Serial.println("Arduino Voltage meter");
  Serial.println(" ");
}

void loop() {
  // put your main code here, to run repeatedly:
  RdVal = analogRead(analogPin);
  Vx = float(5.0)*(float(RdVal)/float(1023));
  delay(2000);
  // Serial.print(RdVal);
  Serial.print(" Tensione letta: ");
  Serial.println(Vx);
}