Persistence-of-Vision LED Wand

Spell words in mid-air. Eight LEDs on a stick, an Arduino, and your wrist do the rest — physics rendering a virtual display.

Difficulty: Breadboard. Estimated build time: about 45 minutes. Estimated parts cost: about US$5.50. 6-part bill of materials with live supplier pricing. A handheld stick of eight LEDs that, when waved back and forth, paints text or a small bitmap in the air.