The autotester uses a raspberry pi for computation and image processing. Control of the steppers, pump, agitator, solenoid, LEDs is done via a board.
That is assembled as a raspberry pi hat. It sits on top of the raspberry pi. The driving of the steppers and electromagnets are done by A4988 chips (used in 3D printers). The pump and valve are controlled using Mosfets. A general purpose transistor controls the LEDs.
The PCB design for the autotester hat can be found here. The board was designed using Eagle, so the files are in Eagle format.
Power is provided to the unit using the buck converter. There are inputs on the hat for 12v, GND, 5V. Be sure and calibrate the output of the buck converter before connecting it to the hat. 12V straight into the 5V input will likely burn out the raspberry pi. No separate power into the raspberry pi is required as it will draw power from the hat.
The BoM can be found here