For the final project in my 6.115 embedded systems class, I built a robotic etch-a-sketch. "Sketch-Dude" allowed the user to rotate two knobs (X and Y) to draw shapes on a whiteboard with a two degree-of-freedom robotic arm. The system also used a switch to allow for recording and playback, and it displayed the mode and marker coordinates on an LCD screen. 
 
I used a PSoC (Portable System on Chip) and an 8051 microcontroller to create the device's brains and used servos to actuate the arm. This in part involved incorporating PWM generators, 16-bit ADC's, analog multiplexers, hardware interrupts, and UART comms. I lasercut the links and plates from acrylic, 3D-printed the spacers and mounts in ABS, and CNC-routed the wooden platform after staining and sealing it.