The goal here was to provide a basic but useful servo driver at very low cost (blank PIC 18F14k22's are under $2, the BOB PCB is $8, couple bucks misc parts) which could replace stepper motors in any standard application, such as 3D printers or CNC machines.
It accepts both serial and step / direction inputs. The serial interface allows for easy tuning of the P.I.D. constants and setting options like the polarity of the output direction signal. The step / direction input allows it's use in any application where a standard stepper driver was intended.
The output is PWM speed and direction which will drive most any standard H-Bridge or other motor driver.
Instructions, PCB, kit, etc... all at:
http://techref.massmind.org/techref/io/SERVO/BOBPID.htm
Quick video of it running from a 3D printer RAMPS/Marlin controller: