Timestamp

String timestamp() {
  int y = year();   // 2003, 2004, 2005, etc.
  int m = month();  // Values from 1 - 12
  int d = day();    // Values from 1 - 31
  int h = hour();   // 2003, 2004, 2005, etc.
  int mi = minute();   // 2003, 2004, 2005, etc.
  int sec = second();
  int mill = millis();

  String val = 
    "_" +
    String.valueOf(y) +  
    String.valueOf(m) +
    String.valueOf(d) + "_" + 
    String.valueOf(h) + "_" + 
    String.valueOf(mi) + "_" +  
    String.valueOf(sec) + "_" + 
    String.valueOf(mill);

  return val;
}