Joulescope output momentarily toggling off

Hi Folks,

Posting this in case other folks accidently run into this. I was observing the Joulescope output to randomly “cut off” during testing and eventually found out it’s related to the fact that I had too many devices attached to my USB hub. The USB hub is self-powered, but with multiple devices attached seems like it was not able to supply enough current to my joulescope.

In any case, this was the symptom from the joulescope log under “Help”–>“View Logs”… search for “error”

ERROR:2021-08-13 09:26:18, halt 1: EndpointIn WinUsb_GetOverlappedResult fatal: [31] A device attached to the system is not functioning.

Thanks again Matt for the help

Hi @Gary - Thanks for following up here on the forum, and great to hear that you are back up and running.

Even determining your hub’s power needs with compliant USB devices is challenging. You used to be able to say 500 mA @ 5 V per device. The USB power delivery specification and USB battery charging specification make things more complicated.