Measure distance with a Sharp infrared sensor based on optical triangulation, as a practical alternative to ultrasonic sensing.
Build an educational Arduino PIR motion alarm, including wiring, warm-up time, sensitivity adjustment, false-trigger reduction, and safe limitations.
Use the TCS3200 sensor to recognize colors by measuring reflected light frequency, showing the result with LEDs.
Automatically detect rainfall with an FC-37 sensor to trigger an alarm or automate closing a window or awning when rain is detected.