int sensorPin = A0; //KY-038 microphone
int relay = 13; 
int sensorValue = 0;
bool on = false;

void setup () 
{
  pinMode (relay, OUTPUT);
  digitalWrite (relay, LOW);
  Serial.begin (9600);
}
 
void loop () 
{
  sensorValue = analogRead (sensorPin);
  Serial.println (sensorValue, DEC);
  if (sensorValue > 500) {
    /*if (on == true) {
      on = false;
    } else {
      on = true;
    }*/
    on = !on;
  }
  digitalWrite (relay, on);
  delay(100);
}