Originally Posted by
patrick31
Thought I would share my limit switch noise solution. I searched here looking for answers a couple years ago when my PM25 CNC conversion kept getting false triggers on the limit switches. I wired in some resistors which helped, but never totally fixed it. I tried shielded wires too but that didn't work.
I kept getting "Limit Switch Triggered" in Mach 3 while cutting, which would freeze the machine. I have a 48V system two large Nema 23's and a Nema 34, all running at 5A's.
Anyways, I researched it and decided to make a better solution.
My limit switch filter board puts a load across the limit switches to reduce voltage spikes, an RC circuit to filter that signal, then a Schmitt trigger to remove jitter and add hysteresis, a level shifter to convert the signal to 5V, and current limiting resistors to protect the output wires from short circuits.
It's been on the machine for the last couple months, and has finally fixed my noise problem!
Pics of the final board and a screenshot of the signals!
Reply with Quote
Posting Permissions
