Writing on Air
searching for motivating projects for students of the Real-Time
Systems course here at Universitat Politècnica de València, we found a curious device that produces a
fascinating effect. It holds a 12 cm bar from its bottom and makes it
swing, like an upside-down pendulum, at a frequency of nearly 9 Hz.
The free end of the bar holds a row of eight LEDs. With careful and
timely switching of those LEDs, and due to visual persistence, it
creates the illusion of text... floating in the air!