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First of all, I'm new to all this so I most probably won't understand complicated explanations.

I'm planning to solder a USB-C breakout to my old keyboard's wires, but I'm not entirely sure where to solder the shield cable. I know where I should solder the first 4 cables from checking different posts though.

I've got 4 choices I guess:

  • don't connect the shield to anything
  • remove it entirely by cutting the wire from the base
  • solder it together with the ground
  • solder it to the metal case of the USB C breakout

Could I have some advice for this?

VCC,D-,D+,GND,SGND

enter image description here

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  • \$\begingroup\$ Where is the shield connected now? Why can't it be connected in a matching way that it is now? \$\endgroup\$
    – Justme
    Dec 16, 2020 at 11:28
  • \$\begingroup\$ it's not connected to anything right now. What do you mean by connect it in a matching way? I added another photo of the state of the wires. \$\endgroup\$
    – Zammy
    Dec 16, 2020 at 11:37
  • \$\begingroup\$ I see it is not connected right now. Where was it connected before it became unconnected? \$\endgroup\$
    – Justme
    Dec 16, 2020 at 11:44
  • \$\begingroup\$ It used to be a USB 3.0 cable (i think) attached to the keyboard pcb. (I'll reattach it to the keyboard pcb after soldering) I stripped the cable, and now I'm trying to solder the stripped ends to the USB C break out. I'm just wondering where to solder the shield wire to the usb c breakout specifically. \$\endgroup\$
    – Zammy
    Dec 16, 2020 at 11:47
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    \$\begingroup\$ If it was connected to connector shield before, it should be connected to connector shield now too. You could use a multimeter to check where it was connected. Highly unlikely it was a USB 3 connector though. No keyboard would ever need USB 3, and there is not enough wires for USB 3 either. \$\endgroup\$
    – Justme
    Dec 16, 2020 at 11:53

2 Answers 2

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The cable shield was most likely connected originally to connector metal shell, so it would be best to connect it as it were.

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From the first photo it seems original cable had shield wired to the bottom pin of the connector on the PCB. So I would recommend to check continuity between that shield wire and the shell of the old USB plug, to make sure it was actually connected to anything.

If you find out that the shield wire was not connected to the plug you may as well leave it unconnected at both ends. However better option would be to connect it at least at one side, does not matter which one.

If you find out that the original shield was indeed connected to the shell then you better connect it at both ends, to the bottom pin of the keyboard PCB and to the shell of the USB-C receptacle.

Now, from the second photo it seems you are using Adafruit breakout board. Unfortunately that board does not have the shell broken out. However you can easily solder the wire to one of four shell pins on the bottom (oval through-holes).

enter image description here

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