So I'm running about 400 Neopixels from an Adafruit Trinket Pro, using an ATX Power supply. When I run a strand test (found on this thread: http://forum.arduino.cc/index.php?topic=364208.0). I was getting these intermittent random flashes, like there was a lot of noise coming from the Trinket, or there were power fluctuations or something. Then when I hooked up my scope to the output of the Trinket, the flashes stopped!
Also, I tried putting a 470uF cap between the trinket and the neopixel input, and that sort of helped, but only for the first part of the strandtest when it turns everything red. Weird...
Any idea how to solve the flashing problem, or why the scope would fix it? Any help is appreciated!