Improve testability of the DDS DAC
The performance and correctness of soldering of the DAC can't be easily tested with the current design, as the DAC is followed by a zero crossing detector. Two solutions are possible:
- add an UFL connector at the DAC output for factory testing purposes
- add a small 16-bit serial ADC (needs not be fast) at the DAC output. This one will make the DAC self-testable.