Just finished putting together Limor’s $22 Wave Shield for Arduino. This shield snaps on top of the Arduino microcontroller board, creating a ridiculously easy way to get audio playback into physical computing prototypes. The Wave Shield will play back uncompressed .wav files of any length from a regular SD card, either over headphones or through a small speaker. Now projects can chant, count, warn, soothe, mumble, moo, cajole, challenge, respond, sob and sing.
Like all of the Adafruit kits, Limor has made the schematic and board files available for download, so once you’ve prototyped with the shield, you can adapt her design into a custom PCB. My favorite story so far is an NYC Resistor guy who combined a light sensor with a prerecorded scream. He made his Arduino afraid of the dark.