Ok so I managed to get control of the axis with Linuxcnc and parallel card. The next thing is figuring out these balluff 2 wire numar sensors. these don't switch on or off like a normal switch. They seem to change the resistance inside the sensor. Something quite sensitive like a 200ma difference.

Question is how can I measure the change in current so I can switch a pin on something like an Arduino?

I know people don't bother with these and switch them out for normal sensors. But I'd like to try and get these working.