Mounting the Joystick Shield v2.4 directly onto Arduino, and its components — two analog axes and seven digital buttons.
Building an automatic irrigation system that opens a solenoid valve when soil is dry using the FC-28 sensor and a switching transistor, with a safety note on the protection diode.
An explanation of how the 74HC595 chip works as a serial-to-parallel converter, wired with just three pins to control eight Arduino outputs.
Getting to know membrane keypad types and the matrix principle that saves wiring pins with Arduino.