#include <Wire.h>
byte val = 0;
int BUTTON = 5; // PB4
int mainLED = 0; // PA4
int state = 0;

void setup() {
  pinMode(mainLED, OUTPUT);
  pinMode(BUTTON, INPUT);
  Wire.begin(); // define main board itself
  Serial.begin(9600);
}

void loop() {

  state = digitalRead(BUTTON);

  if (state == 0) {
    digitalWrite(mainLED, HIGH);
    delay(1000);

    Wire.beginTransmission(9); // Turn on secondary #9
    Wire.write(1);
    Wire.endTransmission();

    delay(1000);

    Wire.beginTransmission(10); // Turn on secondary #10
    Wire.write(1);
    Wire.endTransmission();

    delay(1000);

    Wire.beginTransmission(10); // Turn off secondary #10
    Wire.write(0);
    Wire.endTransmission();

    delay(1000);

    Wire.beginTransmission(9); // Turn off secondary #9
    Wire.write(0);
    Wire.endTransmission();

    delay(1000);

    digitalWrite(mainLED, LOW);

    delay(1000);
  }

}