I have been playing with Arduinos for about a year now, and I noticed that none of my projects were really utilizing the speed capabilities of the ATmega328 chips. At 16 MHz, they can do a hell of a lot more than blink LEDs. To improve my appreciation of their capabilities, I wanted to build a project which required very fast and precise timings. That is what motivated me to build a persistence of vision alphanumeric laser projector.
My projector uses a single laser and has only one moving part. 6 mirrors are hot glued to a spinning platform. Each mirror is at a slightly different angle, and each is responsible for 1 of the 6 lines of vertical resolution. One full rotation sweeps the laser across the target 6 times at 6 different heights. An optical sensor detects the start of a rotation and times the laser pulses to produce readable text.