That definitely looks like uart, it's 5v rather than the 3.3v I expected but your adapter will work!
Just to confirm, you had it wired like this?
GND - Black
0.2V - Green
Fluctuating 2.2V - White
Your 8mhz is more than enough, serial is slooooow. Try increasing the duration of capture to 15s, start the capture and power the box, then zoom out and look for any spikes. Are you using the Saleae Logic software to capture? Ctrl+E to export and I'll gladly take a look.