ASCII to Morse Translator

While there are several ASCII to Morse code translators out there, I haven’t seen the encoding used herein. It is slightly denser than most and should work nicely in machines with a tight memory constraint.

The basic translation represents each Morse code character as a single byte. The individual Morse code dots and dashes are the low-order bits as 0s and 1s, respectively. But since Morse codes are different lengths, not all bits are used. To mark the used bits, a 1 bit is to the left of the first Morse code bit.

For example, in Morse code, “E” is a single dot. Encoded in binary here, it is 00000010 where the 1 is the marker and the 0 thereafter is that single dot.

The letter “J” is dot-dash-dash-dash and is encoded (in binary) as 00010111 with the left-most 1 the marker and the 0111 sequence that follows is dot-dash-dash-dash.

Since all Morse code letters, numbers and punctuation marks have six or fewer elements, a maximum of seven bits is needed for the marker plus the Morse code bits.

In the source code, alphanumerics are translated by a look-up table while the less-used punctuation marks are handled in a switch statement.

Here is a fragment of the translation table for the first six letters:

static char a2m_alpha[26] = {
    0x05, /* A */
    0x18, /* B */
    0x1a, /* C */
    0x0c, /* D */
    0x02, /* E */
    0x12, /* F */
    ...
};

The decoding is done by shifting to find the leading 1 marker bit, and then shifting out the remaining Morse code bits. Here is a fragment of that routine:

for (cnt = 0; (!(code & 0x80)) && (cnt <= 7); cnt++ )
    code <<= 1;
for ( ; cnt <= 6; cnt++ ) {
    code <<= 1;
    if (code & 0x80)
        send_dash();
    else
        send_dot();
}

I built and tested this on an Arduino Duemilanove using the default LED so it should be compatible with most of the Arduino boards – but since I was developing on Eclipse, if you’re using the standard Arduino development GUI, you’ll need to save the files as *.ino instead of the *.cpp and *.h I used.

You may download the five (5) source files below, or download ascii2morse.zip file.

1. ascii2morse.cpp - Translates ASCII to Morse, calls send_dot() and send_dash()
2. ascii2morse.h - Prototypes, etc. for above
3. ascii2morse_test.cpp - Test driver - Sends all Morse code characters
4. ascii2morse_send.cpp - Miscellaneous support routines (send_dot(), etc.)
5. ascii2morse_send.h - Prototypes, etc. for above

License is Apache 2.0 – Read the license for details but, in a nutshell:

1. Keep my copyright and license intact, and
2. Put a note in the code if you make any changes.

There are no fees or restrictions other than that.

Enjoy!