Master_ESP

#include <Wire.h>
//#define I2C_SLAVE_1_ADDR  1
#define I2C_SLAVE_2_ADDR  2

void setup() {
  Wire.begin(); // join i2c bus (address optional for master)
  Serial.begin(9600);
  Serial.print("Ready");
}

char x = 0;

void loop() {
  if (Serial.available() > 0) {

    x = Serial.read();

    if (x == '0') {
      Wire.beginTransmission(2); // transmit to device #8
      Wire.write('0');              // sends one byte
      Wire.endTransmission();    // stop transmitting
    }
    if (x == '1') {
      Wire.beginTransmission(2); // transmit to device #8
      Wire.write('1');              // sends one byte
      Wire.endTransmission();    // stop transmitting
    }
    if (x == '2') {
      Wire.beginTransmission(2); // transmit to device #8
      Wire.write('2');              // sends one byte
      Wire.endTransmission();    // stop transmitting
    }
    if (x == '3') {
      Wire.beginTransmission(2); // transmit to device #8
      Wire.write('3');              // sends one byte
      Wire.endTransmission();    // stop transmitting
    }
  }
}