Very often, there are message asking for a way to go beyond the Arduino programming.
Tomorrow (January 20 ) is starting the excellent MOOC from Austin University
Embedded Systems - Shape The World
https://www.edx.org/course/embedded-systems-shape-world-utaustinx-ut-6-03x#!This is a series of lectures about microcontroller programming in C, using a professional environment (Keil)
with the TM4C123 Tiva C launchpad Texas Instrument developing card as target. You need to buy this card to do the labs (about 13$).
Everything else is free, apart from a small amount of standard electronics parts.
The course lasts for 16 weeks. At the end, you should know how to program the registers of a IC, do in circuit debugging using professional tools, and program a state machine for a robot.
The very nice thing is the possibility to have your programs and hardware evaluated online through the keil IDE. This is excellent for isolated
people. The forum of the course is also a good place to progress.
If you have nothing in your drawers, you can eventually get a full kit.
http://edx-org-utaustinx.s3.amazonaws.com/UT601x/index.htmlDisclaimer : I have absolutely no interest either in EdX, Austin University, Keil, Ti, but followed most of it last year and found that it was the best combination of lectures/labs I encountered on the Web for self educating.