Students of Mechanical Engineering at Carnegie Mellon University make use of a certain servo controller board to simulate loads on their model bridges.
The professor who teaches that class wanted more of these controller boards. Unfortunately the design files and the firmware for these controllers were missing.
I re-designed the circuit and reverse engineered the function of the controller. The video below shows the teaching assistant verifying the function of the first sample. The servo controller includes a microcontroller, potentiometer and a switch.