I am using hall effect sensors for my limit switches. I use a small button magnet and thus the limit switch is only activated over a short range. If the axis is moving fast you will get a short duration pulse out of the limit switch. It appears that the duration is not long enough for the SmoothStepper to register the limit and thus I can run right past the limit switch. I am not sure at what speed it will work, but I know I have overrun it at 300 ipm.  Slow speed operation, such as when I am homing, works fine. Has anyone else experienced this?

Hall sensors are used for ignition triggers on Radio controlled gas engines and I use them plenty ! What I've found is that they have a low voltage threshold and will not trigger reliably if voltage is not hot enough. Also, the magnet has to be strong enough to make the trigger. I'd test the voltage supply to the hall switch and also test that the magnet is still viable. It should be able to trigger well above 40,000 " min ! That comes from a 2" hub turning at close to 7,000 rpm !

There is a recently discovered problem in the SS plug-in. Mach had a setting called 'Disable Limits' that is no longer used or accessible by the user, but defaults to 'ON' (which is bad). This is causing the SS to not treat a limit as a limit but rather just decelerate the motor to a stop (hence the over run). Greg is working on it now.

OOPS ! I missed the SS part ! or I would have added that too ! This is the recent HOT thread on the OTHER site.