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The signal on the picture looks like it has main power (50/60Hz) mixed. It can be non-screened cable or ambient light.
But then, you didn't have the entire signal to verify that claim. I do have that 50Hz signal, but it's only visible when the led isn't blinking, it's around -36 dB whereas my actual signal is ~-9 dB. Zooming out, the "interference" doesn't really look like a steady 50Hz signal, either. Anyway, as you can see
here, it seems that my diode attempts to even out the signal around zero. That's what's making things difficult for the normal adc to handle, so I reprogrammed it to find the extremes of each peak and switch high/low level after exceeding a threshold, compared to the extreme of the last-seen peak. That way, I'll either work my way towards the extreme or towards exceeding that threshold, and it seems to work flawlessly, given the correct "sync-timeout-time". I didn't get ANY sync or crc16 errors for the entire firmware, so it seems to work well
