He hooked up a microphone and a photodiode to the Arduino, allowing him to use both sound and light to trigger his camera, depending on which mode he selects.

The MozziByte Mozzi Arduino Sonification Sound Synth board measures just 45 x 40 x 10 mm when mounted to the Arduino Pro mini.

While a Raspberry Pi is a full-fledged computer that can do more complex things than an Arduino microcontroller, it's not the best choice for every project.