void sim_bmp() {
  char c = XBee.read();
  if (c == '<') {
    sim_pr = "";
    c = XBee.read();
    while (c != '>') {
      sim_pr += c;
      c = XBee.read();
    }
  }

  int simulated_pressure = sim_pr.toInt();
   
  float sim_alt = bmp.readAltitude(simulated_pressure/100);
  packet += String(sim_alt, 1);
  packet += ",";

  packet += sim_pr;
  packet += ",";

  float sim_temp = bmp.readTemperature();
  packet += String(sim_temp, 1);
  packet += ",";
}