Wawa:
Voltage on the two (or three) pot terminals must fall inside the ground and supply range of the MCP41x2.
That generally means that Arduino ground and device ground must be shared.
And again, controller voltage must be lower than VCC of the pot (5volt?).If there is a 10k pot in that controller, then there is probably a transistor (darlington) somewhere to boost current.
Leo..
I'm thinking something along those lines too, which is to say that the controller is just providing a control signal which is used somewhere else to generate the actual power to the slot car tracks. I measured a voltage of ~2.5V over the controller, which is inside the supply range of the MCP41x2. The shared ground isn't a bad idea.
ted:
Handheld controller potentiometer is made from wire (maybe 100 ohms) can cary 1 A or more, 10K digital potentiometer will not work , you can use voltage regulator controlled by arduino or bjt transistor.
Would you happen to have a reference schematic which illustrates how this would need to be wired up?