int analogPin = A3; 
                    
int meas = 0;  

void setup() {
  Serial.begin(9600);           //  setup serial
}

void loop() 
  {
 meas = analogRead(analogPin);  // read the input pin
 
  if (Serial.available())
    {
        if (Serial.read() == '1')
        {
  Serial.println(meas);          // debug value
    }
    } 
    }