@whitequark how bright was the LED and under what environment did you look at it? unless my arduino code is broken, or signal integrity gnomes are visiting my breadboard, i can apparently see 0.5us flashes of a random green LED driven with a 10k resistor and 5v (if i put my eye right next to it. otherwise i can only see up to 2.5us, though i could probably do better in a darker room)