An algorithm for decoding Morse code with arduino, some inspiration from this article

 

From wikipedia:

The perfect morse code needs:

1. short mark, dot or 'dit' (·) — 'dot duration' is one unit long
2. longer mark, dash or 'dah' (–) — three units long
3. inter-element gap between the dots and dashes within a character — one dot duration or one unit long
4. short gap (between letters) — three units long
5. medium gap (between words) — seven units long

The real morse code has a dot:dash ratio of 2.5:1 to 3.5:1

Firstly, we need to determine this ratio:

If the inter-element gap length is denoted as Tm and dot as Td:

Use the first ten time lengths to calculate Tm and Td

 

High Level Time=H_TIME [ie not pressing]

Low Level Time=L_TIME [ie key pressing]

blank a dot/dash array

R=H_TIME[n]/Tm

If (R with 0.5 and 1.5) {

      S=L_TIME[n-1]/Td

      if (S within 2.5 and 3.5) {

             dash

      } else {

             dot

      }  

advance to next element in dot/dash array

} else  if R (within 2.5-3.5) {

           we have a letter space hence decode array

}

 

 

Another algorithm obtained from here can be summarised in this diagram