void SDsave(long leftdistance , long frontdistance , char direct) {
  // make a string for assembling the data to log:
  String dataString = "";
  dataString += String(leftdistance);
  dataString += ",";
  dataString += String(frontdistance);
  dataString += ",";
  dataString += direct;
  // read three sensors and append to the string:
  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  File dataFile = SD.open("datalog.csv", FILE_WRITE);     //可以改成.csv變成excel

  // if the file is available, write to it:
  if (dataFile) {
    dataFile.println(dataString);
    dataFile.close();
    }
  // if the file isn't open, pop up an error:
 /* 
  else {
    ;
  }
  */
  
}