Pic Interference and Power Filter Question

[Hylan]

So I'm stumped and would appreciate some input. I've got a circuit board with a 18F6520 Pic. I've got a handfull of these and they all test out and work fine. I'm powering the board using a basic meanwell power supply. I found that when I run a small vibratory sander on the same circuit in my home it triggers the pic to do its own thing like turn on an output when the input switch is not closed. I switched circuit boards and tried a couple different set ups and can reproduce the issue pretty consistently with this one piece of equipment. I cannot get it to happen with anything else even welders, saws, routers, drills etc...

I guessing that this one piece of equipment is putting a frequency onto the power line and causing the issue because if I run the circuit board off a battery in the same location it works fine.

So I tried every filter, surge protector, home theater power filter I could buy at Radio Shack and nothing made any impact. I then bought a handfull of different ferrite core filters and tried them, one pass and multipass, again no improvement.

So at this point, I'm rather puzzled and would like to know what else to try.

Thank you!

[J_norrie]

Hi there I have always used an isolated DC supply to power microprocessor stuff, because of the same spike problems. Fit a small DC to DC convertor in between your PSU and the PIC board something like a traco power tmh0505 should be fine.

[sayzer]

Post your schematic;

[BrianT]

Go after the noise at source - often a better approach than to try and clean it up when it gets to your board. Sounds to me like the hand sander has arcing brushes. Try a 47 ohm/0.1 uF suppressor capacitor across the active to neutral inside the sander case if possible. Suppression capacitors have a special winding of the capacitor to make it lossy and they work a treat on most noisy brushes.

HTH
BrianT