Has been a long time since I watched either of these

Rusty Russell - Advanced C Coding For Fun! - A series of crazy tricks that is quite enlightening. https://www.youtube.com/watch?v=BEQ3sRakIs0

Tridge - Linux powered coffee roaster. Tridge (of Samba and rsync fame) walks through the process he used to reverse engineer a USB thermometer live during the talk. https://www.youtube.com/watch?v=3LQr4At5Z5Q