The classic "repeat the sequence" memory game translates neatly into an Arduino project — four colored LEDs, four matching buttons, and a growing…
An explanation of how the 74HC595 chip works as a serial-to-parallel converter, wired with just three pins to control eight Arduino outputs.
An explanation of how an LED works via electroluminescence, with the method for calculating the current-limiting resistor it needs.
Program a three-LED traffic light using a simple millis()-based state machine, with realistic timing for each phase.