#include <Wire.h>

const int ledPin = D1; // Pin of the LED

void setup() {
  pinMode(ledPin, OUTPUT);
  Wire.begin(0x09); // Slave address
  Wire.onReceive(receiveEvent);
  Serial.begin(9600);
}

void loop() {
  // Nothing to do here
}

void receiveEvent(int howMany) {
  while (Wire.available()) {
    char c = Wire.read();
    if (c == 'L') { // Command to turn on the LED
      digitalWrite(ledPin, HIGH);
    }
  }
}