So this is happening.
It’s a power issue of some kind, I’m just not sure what the next steps are to diagnose exactly what the problem is.
Seems I had not indeed fried the LM7805 by overheating it trying to desolder it the other day, but adding a capacitor across the output gives me a solid 5V under load. Using a Teensy that doesn’t have its VUSB trace cut (thus powering it and the level shifters from my laptop) gives a much more stable result—some flickering like this, but not nearly as bad.
The LM7805 I’m using is rated for 1A and isn’t getting hot at all, how much current would a fully-loaded Teensy 3.1 and a couple of 74HCT245s pull, anyway?
Could voltage drop on my (4m long, but 1.5mm^2 thick) signal wires be an issue? I don’t have access to a scope so this could be tricky to conclusively diagnose.
I didn’t end up wiring in the big electrolytic caps on the output of the Murata 5V regulators, but this seems to me to be an issue with the signal rather than the strips’ 5V rail sagging on big transients.
