#include <Wire.h>

void setup()
{
  Wire.begin(1);   // Begin using Wire in slave mode, where it will respond at "1" when other I2C masters chips initiate communication.

  Wire.onReceive(receiveEvent); // Causes "receiveEvent" to be called when a master device sends data. This only works in slave mode.
  Serial.begin(9600);   //start serial communication
  pinMode(13,OUTPUT);   //LED pin on arduino
}
byte x = 0;
void loop ()
{
 delay(100);
}

//function that executes whenver data is received from master
//this function is registered as an event

void receiveEvent(int howMany){ //howMany contains the amount of bytes of the received data

  while(Wire.available()){
    char c = Wire.read();
    Serial.println(c);

  if (c == 's')
  {digitalWrite (13,HIGH);} //Turn on LED
  else if (c == 'x')
  {digitalWrite (13,LOW);} //Turn off LED
}
}