boolean sendData = false;
void setup() 
{

Serial.begin(9600);
pinMode(A0,INPUT);
Serial.println("Press 'START' to start the ADC");
Serial.println("Press 'STOP' to stop the ADC");


}

void loop() 
{
  // put your main code here, to run repeatedly:
if(Serial.available() >0)
{
String intruction = Serial.readStringUntil('\n');
intruction.trim();
intruction.toUpperCase();
if(intruction == "START")
{
Serial.print("You have pressed : ");
Serial.println(intruction);
sendData = true;
}
else if(intruction == 'STOP')
{
Serial.print("You have pressed : ");
Serial.println(intruction);
sendData = false;
}
}
if(sendData == true)
{
int analog = analogRead(A0);
float voltage = analog * (3.3 / 1023.0);
Serial.print("Analog Value : ");
Serial.print(analog);
Serial.print("\tVoltage: ");
Serial.println(voltage);
}
delay(500);

}