int new_V;
int old_V;
int pin =A0;

void setup() {
  // put your setup code here, to run once:
pinMode(A0, INPUT);
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
new_V = analogRead(pin);

if (new_V != old_V) {
  Serial.println(new_V);
  old_V = new_V;
 }
}