I am not sure what you mean by "buffered LED". I thought you were reading the signal on GPIO 20 the Pico lighting a LED on another GPIO when it determined the signal was present ?Maybe in this case it is a buffered LED, and somehow turning both channels on at once splits the power across both channels such that it does not meet the threshold to turn the LED on.
I can't see that a Pico input, or any other buffer input, would cause significant drop on the signal, nor whatever is on the second channel. You have a scope so the easiest thing to do would be to look at the signal, check what level it shows when working on just one channel, and how it changes when the other is switched on.
Statistics: Posted by hippy — Sat Feb 14, 2026 10:36 pm