When taking my summer apprenticeship I got to work with STM32 micro-controllers (ARM architecture), at last something more advanced than AVR! At that time I played a lot with them, but I did not made any project, until... By a lucky coincidence next semester we used the same micros on my university. It was a robotics laboratory, from this was born a line follower! In this project I was mostly responsible for writing software as my friend Tomek was dealing with connecting the cables :D. The hardest part was to build the library for Pololu QTR-8RC Reflectance Sensor Array. This sensor is based on IR diode and phototransistor so really low level stuff analog stuff :D. Just connect it to GPIO of the micro and deal with it... You can find whole project repository on github with my library for this sensor. Also I was proud that whole project was written without any blocking delays, only hardware timers!