Noise help with USB near a switch

Thread Starter

benha

Joined Jan 4, 2011
49
Hello!

I have fabricated a control panel for a hobby CNC mill controlled by a PC that's tucked away safely out of harm's way.

It has:
  • eStop button
  • 2 USB ports connected to the computer's USB system
  • An 1/8" mono jack that's an input for a probe - connected to the breakout board for the machine
  • A momentary button hacked into the computer's power button line so I can turn it on remotely
  • A quarter turn type switch that turns on power to the CNC control box
  • A quarter turn type switch that turns on the coolant pump
It all works swimmingly with one major exception. When I turn OFF the coolant pump it "freaks out" the computer. The monitor blips briefly and the USB system shuts down. I have to unplug the USB cables and plug them back in to get them working again. And rarely the whole computer locks up and I have to force power down.

I've messed around with moving wires to see if it fixes things and it doesn't. My problem is that I'm not really sure what's, specifically, is likely to be happening so it's tough to come up with a remediation.

Anyone have ideas here?

Thanks
-Ben
 

Wolframore

Joined Jan 21, 2019
1,478
Try one then the other then both. All guns blazing. Do you have a fly back diode on the coolant pump? This might be the issue and would be better that squashing the reverse current from a collapsing field from your motor.
 

Thread Starter

benha

Joined Jan 4, 2011
49
Given that I've only got the vaguest recollection of hearing that term somewhere once... No. :)

By the way, thanks for the speedy replies to all this. I neglected that in my first reply!
 

Thread Starter

benha

Joined Jan 4, 2011
49
Ah. Well it's an AC motor. So I don't think that'll help.

I just put ferrites (which I happened to have lying around) on the USB lines and the power line and while it's slightly better it still screws up. Is there any kind of meainingful shielding I could be doing? Is it likely that the fact I bought cheap import switches off Amazon is making a big difference?
 

Wolframore

Joined Jan 21, 2019
1,478
Ahhh it’s AC. Post a schematic or wiring diagram. I still think it’s the motor but we need to figure out where the source of noise is.
 

MrSoftware

Joined Oct 29, 2013
1,606
If you power the coolant pump from entirely outside the rest of the system, does the problem still exist? Can you get a scope on any of the power lines to try to get an idea of what's actually happening?
 
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