Here are some process pictures from the second jog-dial I converted to USB. This particular device is more complex than the previous jog-dial I worked on. Unlike the previous version, this one uses optical sensors for the up/down/left/right control, and the wheel itself has been fitted inside the knob and is quite similar to how a modern mouse scroll wheel operates. As usual I spent quite a bit of time following traces and trying to use the existing circuits. The problem is not knowing what any of the pin ins and outs are, or how the device interacts with the CAN bus, or how they (those devils in Bavaria) power it, etc. Some of this can be determined with an ohm meter and testing each pin. In the end I isolate the circuits I want to use and cut traces and add my own wiring to get the job done.
I also used a wireless mouse to handle the dial output, converting this directly to mouse scrolling functionality. Everything else is connected to a Makey Makey board which already handles up/down/left/right and has pin inputs for keyboard strokes. I also used a SparkFun Redboard Arduino to do initial testing of my circuits.