#include <Wire.h>

const byte slaveId = 1;

void setup()
{
  Serial.begin(9600);
  Wire.begin(slaveId);
  Wire.onReceive(receiveEvent);

  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  digitalWrite(8, LOW);
  digitalWrite(9, LOW);
}

void loop()
{
}

void receiveEvent(int howMany)
{
  char tlacitko1;
  char tlacitko2;

  while(Wire.available() > 0)
  {
    tlacitko1 = Wire.read();
    tlacitko2 = Wire.read();

    if (tlacitko1 == 'a')
    {
      Serial.println("=> Tlacitko1 = zapnuto");
      digitalWrite(8, HIGH);
      delay(1000);
    }
    else if (tlacitko2 == 'b')
    {
      Serial.println("=> Tlacitko2 = zapnuto");
      digitalWrite(9, HIGH);
      delay(1000);
    }
    else {
      digitalWrite(8, LOW);
      digitalWrite(9, LOW);
      delay(100);

    }
  }
}