Suggestions for how to shield connections to USB breakout?

[macardoso]

Thanks for everyone's suggestions so far - to answer one of the earlier questions, there is a fluorescent light about 15 feet away. The jumpers are about 6 inches long. I've included a photo - my suspicion is that my relatively long, unshielded jumpers with header pin connections are picking up / generating some sort of noise. In the photo you can see the ground wire I've attached to one of the mounting points - I don't think a ground loop is the issue, since the scales aren't currently connected to anything with a ground (they're resting on the tabletop for now).View attachment 356802

Without reading the whole thread, I see one major deficiency in this image. In each of the breakout boards, the GND pin is not connected back to the micro controller power ground. So the metal case of the USB socket isn't grounded, nor are your USB cables themselves. So any shielding on the cable is doing nothing.

Ideally this GND would be tied to earth ground (third leg of your power adapter), but if that isn't possible, then it should be tied to the DC common as close to the source (DC barrel jack) as possible.

 

[btipton]

Without reading the whole thread, I see one major deficiency in this image. In each of the breakout boards, the GND pin is not connected back to the micro controller power ground. So the metal case of the USB socket isn't grounded, nor are your USB cables themselves. So any shielding on the cable is doing nothing.

Ideally this GND would be tied to earth ground (third leg of your power adapter), but if that isn't possible, then it should be tied to the DC common as close to the source (DC barrel jack) as possible.

For the Shahe scales, the USB connectors aren't really USB - they're just using them for the convenience/cost of the connectors. I can't post links yet on the forum, but on the touchdro site, there's a page about the Shahe scales that gives the pinout. The USB GND pin isn't connected. Unfortunately, that makes the USB breakout board a bit harder to work with, but that's half the fun.

 

[btipton]

This particular behavior is pretty uncommon with iGaging scales (although I've heard about it happening). I haven't seen this with the Shahe sales (assuming you are talking about the new Shahe-branded scales, not the old unbranded iGaging DigiMag sacles).
Would you be willing to let me borrow them for a few days so I can hook the setup to a scope and see what is happening? I will cover shipping both ways, of course.
Yuriy

Thanks for the generous offer, but I'm not confident enough that I haven't just done something silly to ask you to pay shipping and spend time on it. Let me take a few days and double-check my work and I'll do some more testing. If I'm still getting unexplained strange results, I may take you up on your offer. Thanks for such a quick reply as well!

 

[btipton]

One of the members at my local makerspace suggested that I make sure the USB shielding was grounded. I tied the shielding pad for each of the usb breakouts together, and connected them to ground on the adapter board as below. After that change, I didn't have any weird issues with the readings, other than a rare case where the display would flash a negative sign, then it would go away immediately. It seems like the USB cable, being so long, would be the most likely wire to pick up any interference, but I couldn't find the shielding connected at either end of the Shahe scales, so I connected it to the adapter.

 

[mksj]

Typical USB connectors use a 5 pin header cable with the shield grounded which was missing until you attached the grounds. Grounding is usually at the source or origin, but varies on application. In addition when using other equipment such as a VFD electrical noise can be a significant issue, the type of cable, shield and using centralized grounding such as a star or buss can significantly effect the electrical noise. Alternative would be to use the ground pin on t each USB header and ground everything to the ground screw. When possible I also try a battery source as opposed to a wall wart to see if the problem goes away. I have electrical noise issues with tachometer installs and ended up needing a line filter and also have tried different grounding setups. Also can be seen with VFD low voltage input controls and remote speed pots.