As a leaving present for a coworker, the idea of a ‘laser coaster’ was born. Like an etch-a-sketch, but you’re drawing with an IR laser onto an LED matrix.
A cheap laser pointer was gutted and an IR laser module put in its place, with a 1024Hz oscillator to modulate it too. A 16×16 matrix of LEDs and 15×15 matrix of infrared phototransistors was used, with battery, charger, regulator and MCU all included too.
Fred Temperton 