I don't get it why people pick an Arduino for their electronics projects: they're expensive, fat gadgets in all senses of the word fat: bootloader, IDE, board size, dev environment complexity...

A $5 PIC can do the same things and exposes you properly to what you're doing - preferrably in assembler, not C. Sure, large projects are better coded in C - later on, after you've mastered the low level; until then there's nothing better than assembler for learning how a computer works.