Here are some useful articles on electronics and microcontrollers.
Digital I/O expansion methods.
Switch debounce: Three different ways to debounce input push switches with one amazing method that you can't miss.
How to Easily Use the DS18B20 Maxim One-Wire thermometer with Arduino example code showing external or parasitic power modes.
How to use the BMP280 for weather pressure measurement or altitude change detection.
How to use the TCS230 (/TCS3200) Color detector chip and easily add it to any of your projects.
How to use MC78M05BDTRKG for maximum current without using too large a heatsink pad and how to select the optimum input voltage.
How to use fixed point maths to save microcontroller memory by avoiding use of the floating point library.