This example shows you how to read an analog input on Pin 0, convert the values from analogRead() into voltage, and print it out to the serial monitor.


https://www.arduino.cc/en/uploads/Tutorial/AnalogReadSerial_BB.png 


/*
  ReadAnalogVoltage
  Reads an analog input on pin 0, converts it to voltage, and prints the result to the serial monitor.
  Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V and ground.

  */


// the setup routine runs once when you press reset:
void setup() {
 
// initialize serial communication at 9600 bits per second:
 
Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
 
// read the input on analog pin 0:
 
int sensorValue = analogRead(A0);
 
// Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 5V):
 
float voltage = sensorValue * (5.0 / 1023.0);
 
// print out the value you read:
 
Serial.println(voltage);
}
  

Download this sketch :