#define btn 7
#define led 8
#include <SoftwareSerial.h>

SoftwareSerial mySerial(0, 1); // RX, TX
bool pressed = false;

void setup() {
  pinMode(btn, INPUT_PULLUP);
  pinMode(led, OUTPUT);
  mySerial.begin(9600);
}

void loop() {
  if (digitalRead(btn) == LOW && pressed == false)
  {
    pressed = true;
    mySerial.write(byte(0x01));
    delay(100); // debouncing 
  }
  if (digitalRead(btn) == HIGH && pressed == true)
  {
    pressed = false;
    mySerial.write(byte(0x02));
  }
 
  if (mySerial.available())
  {
    byte msg = mySerial.read();
    if (msg == 0x0A) digitalWrite(led, HIGH);
    if (msg == 0x0B) digitalWrite(led, LOW);
  }
}