Before generating the waveforms, a time reference is needed. The dot has a period of 50 ms that translates to a duration of 34x50 = 1700 ms for the entire SOS waveform period. Starting from AVR resources, a symmetrical sequence is much easier to implement. To create this symmetry, the period of the reference clock should be half of the dot period (25 ms).
Figure 1. Reference Clock
The process of generating the SOS signal can be split into three parts:
- Generating the waveform for the letters ‘S’
- Generating the waveform for the letter ‘O’
- Combining the waveforms