LEDs are incredibly common and incredibly useful debug tools. I've had to work with boards that don't have them and without physical access to the traces for a

LEDs are incredibly common and incredibly useful debug tools. I've had to work with boards that don't have them and without physical access to the traces for a scope, you're out of luck. While some of it is fascinating, I've also had to spend entire days figuring out why a single pin won't toggle on a microcontroller. It sometimes takes herculean effort for the simplest debugging tasks.