An Arduino function to print a double-precision floating point number via Serial. Not exhaustively tested, use at your own risk.

arduino_print_double.ino

void print_double(double val)
{
  char buf[10];
  int neg = (val < 0);
  int exponent = 0;
  if (val == 0.0) {
    Serial.print("0.0");
    return;
  }
  if (neg)
    val = -val;
  while (val >= 10.0) {
    val *= 0.1;
    exponent++;
  }
  while (val < 1.0) {
    val *= 10.0;
    exponent--;
  }

  if (neg)
    Serial.print("-");
  Serial.print(int(val));
  Serial.print(".");
  sprintf(buf, "%06u",
    (unsigned int) ((val - int(val)) * 1000000));
  Serial.print(buf);
  if (exponent != 0) {
    Serial.print('e');
    Serial.print(exponent);
  }
}