I wasn't happy with the way the square waves sound, so I explored using other methods of generating sound waves with Arduino.
A discussion about digital sound synthesis.
A photoresistor can sense the subtle changes in light intensity caused by your blood to detect your heartbeat!
Learn about photoresistors and the process of characterizing their response to light intensity.
An R/C servo can be used to make a gauge to measure the intensity of light.
Exploring the signals behind Arduino's Servo library, and characterizing a servo's response to pulse width.
Set up an RGB LED to phase through the colors of the rainbow, or use twist knobs to make a custom color.
Arduino boards don't have analog outputs. But they do have a function called analogWrite. So what is it doing there?
Using an Arduino to toggle something like an LED light is simple in theory, but buttons don't always behave the way we think.
Characterizing button switching behavior is an important first step for developing effective debounce algorithms in your systems.