Serial Control Test

Code

char switchstate;     
void setup()  { 
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() { 
  while(Serial.available() > 0) {       
    switchstate = Serial.read();
    Serial.print(switchstate);
    delay(15);
    if(switchstate == '1') { 
      digitalWrite(LED_BUILTIN, HIGH);
    }
    else if(switchstate == '0') { 
      digitalWrite(LED_BUILTIN, LOW); 
    }
  }
}