CNC plotters come in many variations, but most operate by moving a felt-tip pen around a sheet of paper to sketch out a design. This one, however, is a bit more special. It works by using two stepper motors to control the X and Y axes of an old Etch A Sketch. Each turn of the knob moves a stylus inside of the toy that etches away some of the powdered aluminum that was adhered to the glass's surface.
The creator, Steve Turner, notes that the patterns created by his device are entirely random and generated by emulating a classic drawing machine. This is made possible by the program he wrote, which begins by setting a random seed and then positioning the stylus to its new location. Inside of the main loop, the program first rotates its emulated gears slightly and then calculates the new positions of the virtual rods and pen. Once the pen position has been figured out, the actual knobs are then rotated by the stepper motors to draw the line.
The device as a whole works pretty well, but the project's author, Turner, does point out a few flaws in the design that need to be improved. First and foremost, there is quite a bit of slop in the belt drive system, which can lead to lopsided drawings. The system also has a tendency to create less-than-ideal drawings, partially due to how it generates its random seeds. The fact that a user is able to save and reuse numbers they like is very appealing, because that means designs can be shared and recreated by just copying the seed. Turner also made a simple Processing sketch that virtually keeps track of where the stylus is in real-time, which is very useful for debugging.
Overall, this project is an excellent way to put an old Etch A Sketch to use and generate intriguing patterns and designs.