Here’s a really really great source for circuits for personal use.

On of my favorite websites for electronics circuits is electronicsforu.com.   You will find very good documented circuits that include a detailed explanation of how they work.  I think this archive can provide a great library of circuits to devise your own ideas from.  Or have fun building one as a project on the weekend.   Some are ardunio based, and others could be converted by you for use with your ardunio.

electronicsforu/microcontrollers/