float voltage = 0.0f; 
void setup()
{ Serial.begin(9600);
  pinMode(A1, INPUT);
}

void loop()
{
  // Convert from 0-1023 range to 0-12V range
  // (.0293255  = 30.0 / 1023)
  voltage = (analogRead(A1) * 0.0293255);
  Serial.print("Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  delay(100); // Wait for 100 millisecond(s)
}