Connecting USB and VIN at the same time



  • Hello all, I have a quick question. I was trying to debug my Duet3 earlier as I wasn't getting a response from the board. The issue is fixed now but I ended up plugging in the USB on my Duet3 to my computer to get a COM connection while VIN was connected to 24V power. I was wondering after the fact, was this safe for the board, or did I potentially fry something? I was looking at the getting started page for the Duet3 and it has a small section about this but the wording was a little vague.

    Thanks for your time.



  • Also, the Duet3 has its jumper on internal 5V enable so the SBC is powering itself and the Duet is getting power from VIN



  • There are two reasons for avoiding it in general; one is https://duet3d.dozuki.com/Wiki/USB_ground_loops and the other is the potential for to damage the SBC interface if the Duet and Pi are not powered from the same time/5V source (which I think is no longer relevant for the 1.01 revision)

    So if it still works and you don't have a SBC/Raspberry Pi you have nothing to worry about. And if you have a SBC and/or revision 1.01 Duet and it still works you have nothing to worry about. But yes, there is potential for damage so best to avoid unless you're certain your mains wiring is safe and potential SBC connection is safe. If you use a SBC like the Raspberry Pi it would be safer to connect the USB there as the ribbon cable already provides the same interconnections for power, and you can access the serial terminal over SSH.



  • @bearer thanks for the knowledgeable response and helpful link. Very good to be aware of going forward.


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