I recently put limit switches on my machine, and now I continuously get nuisance hard limit alarms. It's got an Arduino controller running GRBL .9. I used shielded wire for the switches, and ran the wires well away from all the power wiring. I first noticed it when an infrared motion light in my garage turned on, I got a hard limit error. So, I put in a good AC power filter on the laptop and control electronics supply. Seemed to correct the problem - for a while. Then, last night I was trying to cut some plates and the dang machine wouldn't run for more than 30 seconds without a hard limit alarm. Seems to be tied to the router being noisy, turning the router on and off will trigger it every time. I tried plugging the router into a different outlet, no luck. Rearrange the cords so they were nowhere near the system, no difference. I added low value (2k ohm) pullup resistors to +5v to the limit switch inputs on the Arduino board. I was thinking if the Arduino just used the internal programmable pullup resistors on the inputs, they may be just a suggestion of a pullup - 100k or so. No difference. I gave up for the day, but I need some ideas to try tomorrow. Should I try some caps to ground on the limit input pins? A tinfoil hat for the router? I notice the router does not have a ground wire, is this an issue? I have the frame of the machine grounded, but somebody once told me to run individual grounds to each axis motor. Is this a good idea? Help?