#include <Wire.h>

#define LED D4

void setup() {

  pinMode(LED, OUTPUT);

  Wire.begin(D1, D2, 8);              /* join i2c bus with address 8 */
  Wire.onReceive(receiveEvent); /* register receive event */
  Wire.onRequest(requestEvent); /* register request event */
  Serial.begin(9600);           /* start serial for debug */
}

void loop() {
  digitalWrite(LED, HIGH);

  delay(100);
  digitalWrite(LED, LOW);

}

// function that executes whenever data is received from master
void receiveEvent(int howMany) {
  while (0 < Wire.available()) {
    char c = Wire.read();      /* receive byte as a character */
    Serial.print(c);           /* print the character */
  }
  Serial.println();             /* to newline */
}

// function that executes whenever data is requested from master
void requestEvent() {
  Wire.write("Hello NodeMCU");  /*send string on request */
}