Build a simple educational fire-alarm system with a flame sensor and three alert levels, with an explicit note against relying on it as a certified detector.
A basic guide to wiring and controlling an SG90 servo motor with the standard Servo library, including smooth sweeping between angles.
Measure water flow rate and total volume using the Hall-effect YF-S201 sensor and Arduino's interrupt-driven pulse counting.
Replace mechanical buttons with a TTP223 capacitive touch sensor working as a toggle with a relay module, with a safety note for mains-voltage loads.