Thor, or should that be Zeus?

[Neale]

I've been thinking about exactly this problem for my own machine (also using CSMIO). I haven't built the touch probe yet but I was intending to use a simple bit of circuitry to invert one of the signals and then combine them. I'm not sure that you can solve the problem without adding something outside the CSMIO as it only has one input that is suitable for the job.