[Frank Herrmann] had an interesting idea to turn a geared DC motor into a servo motor assembly ... The Arduino source for this can be found on the project GitHub. Whilst [Frank] mentions that ...

Hobby servos are nifty and useful for a wide range of projects ... together nice and tight. A DC motor is charged with driving the assembly, as with any regular servo motor.

Raspberry Pi HATs offer small, stackable data acquisition with features like analog and digital I/O.