       ledState = HIGH;  // Note that this switches the LED *off*
     else
       ledState = LOW;   // Note that this switches the LED *on*
-    digitalWrite(ledPin, ledState);
+    digitalWrite(BUILTIN_LED, ledState);
   }
 }
-

 Blink the blue LED on the ESP-01 module
 Based on the Arduino Blink without Delay example
 This example code is in the public domain
*/

const int ledPin =  1;  // The blue LED on the ESP-01 module is connected to GPIO1 
                        // (which is also the TXD pin; so we cannot use 
                        // Serial.print() at the same time

int ledState = LOW;     


const long interval = 1000;

void setup() {
  pinMode(BUILTIN_LED, OUTPUT);
}

void loop()
