Stroboscope
Make a mechanical strobe with a toy motor and construction paper, pair it with a digital SLR camera, and take stunning photographs of objects in motion.
From MAKE:
24: Space page 90
Exclusively in the Maker Shed, this updated Redpark Breakout Pack for Arduino and iOS makes interfacing your iPhone, iPad, or iPod touch with the real world easy! This bundle includes the new RedPark TTL Cable for iOS so a TTL adapter (and soldering) is no longer required.