Everything from Displays to LCDs. Displays can be created by simple 7-Segment Displays, LEDs or more advanced the LCDs.
The heart of almost every electronics project nowadays. A microcontroller is basically a little computer with all its components integrated. RAM, CPU, BUS everything you need.
I think the trend began when Arduinos became popular. With an Arduino platform you could plug a so called shield on top of the Arduino. With the shields you can add additional functionality like port expander, connection modules like WiFi or RS232.
In this section I describe some of my projects I made over the years.
Sensors are a vital part of a Arduino Project. A Sensor can be a simple end-switch, or an intelligent sensor board which precomputes readings for you. An analog sensor is usually read with an voltage divider. Most sensors relate the physical reading into and change in resistance. Like simple PT100 Temperature Sensors.