Proximity switch "contact bounce"

[Neale]

Home position - problem here is that the same switch is home and limit. During homing, Mach3 disables limit function to allow homing to take place (l believe). It homes, and then immediately re-enables limit function and the next "flicker" (random switch operation) trips the limit. I think! Sometimes the z homing does work, and Mach3 starts the XY homing (I home both together). I suspect that gantry vibration then trips the hair-trigger Z limit switch again and it all stops. I could, I suppose, move z away from the home position once it has homed (if it does without tripping a limit) so that subsequent vibration does not cause false triggers, but that's not really fixing the underlying problem.

Pull-ups - IP/M doesn't work that way. A lot of BOBs use some kind of buffer input so you use a pull-up/pull-down resistor to one rail and switch to the other rail. The IP/M input looks rather like an opto-isolator input (with some clever current limiting, etc, to handle a range of input voltages and with both ends brought out to a terminal block) so you take one end to one of the rails and switch to the other. In my case, with open-collector NPN switches, I take one side of each input to the 24V rail and switch the other side to ground. My X and Y axes both have two switches wired in cascade (effectively in series as they are NC); this seemed to work fine testing on the bench and seems to work OK on the machine for limit switch purposes. In any case, the problematic axis at present is Z where there is only one switch anyway!

Sorry if I might come over as teaching anyone to suck eggs but I wanted to explain some of my reasoning to people with less knowledge; sometimes those with less knowledge make fewer assumptions and can see wood for trees

Personally, I still suspect those switches...