This is my second CNC control pendant. 
It was designed to use more available parts
than my origional pendant (which uses an optical encoder 
and a unobtainium keyboard)
This design uses a cdrom motor as a position sensor
There is a circuit to centre the motor votlage around 2.5V
and then feed both halves into different adc channels
this was the system can read from -5V to 5V from the motor

the keyboard is 3d printed. 

see:
  https://www.thingiverse.com/thing:2794690
  https://www.thingiverse.com/thing:2794705
  https://www.thingiverse.com/thing:2794712