illusion on technabob...

When not telling time, these clever clocks look like a triangular hunk of wood. But switch them on, and a bright red 7-segment LED display hidden behind the thin wood veneer reveals the current time…

Here’s a cool gadget that lets you send messages using the wheels of your bicycle. By using an optical illusion called persistence of vision, your words are revealed as you pedal your bike.

The Lampex Lex module screws onto the spokes of your bicycle, and produces rapidly flashing sequences of LEDs to display your messages…