As for design patterns, I would never accuse Andy of using them. He was a coding wild man and super impressive, but his real skill was coming up with cool ideas and willing them into existence. Working with him, I always felt he was going through the jungle making paths with a machete and the rest of us had to actually build the roads behind him.
That is, as opposed to using a timer interrupt or a delay routine, arrange instructions so that the processor naturally gets to the instruction to change the output pin at the correct time, within the acceptable tolerance. These processors have no caches or predictors so instruction timing is reliable.
I think people are doing it these days on the Raspberry Pico chips, but any "old school" microcontroller will do.