//Original code made by Pablo Nuñez, available at https://hackmd.io/@ihhYfPp3TlKoBY_QfN2kZQ/S13ZXYK9U
//Translated and edited by Jonathan León


//This code is for the master board, connect it to a breadboard with wires on TX, 5V and GND
//on three different lines.
//The slave(s) board(s) uses almost the same connections but using the RX pin instead.
//Connect the LED with the positive leg on the 13 pin and the negative leg on the next pin (GND).
#define BUTTON_PIN   8 //Button
boolean oldState = HIGH; //Initial button state
int     mode     = 0; //Initial mode

void setup() {
Serial.begin (9600); //Starts serial monitor
pinMode(BUTTON_PIN, INPUT_PULLUP); //Sets the button as an input
}

void loop() {
boolean newState = digitalRead(BUTTON_PIN);
if((newState == LOW) && (oldState == HIGH)) {
    delay(20);    // Short delay to debounce button.
    newState = digitalRead(BUTTON_PIN);    // Check if button is still low after debounce.
    if(newState == LOW) {      // Yes, still low
      if(++mode > 1) mode = 0; // Advance to next mode, wrap around after #2
      switch(mode) {           // Start the new animation...
        case 0:
Serial.write('a'); //Calls the slave board ("a")
delay(1000); 
          break;
        case 1:
Serial.write('b'); //Calls the slave board ("b")
delay(1000);
          break;
          //When using more than two slave boards add more Cases and update ++mode > 1 on line 20
      }
      }
    }
      oldState = newState; //Update the button state
}