Anyone else monitoring USB powered devices?

I’m enjoying my new Joulescope. The barrel jacks are great for the lab. However I find myself working with more and more DUTs that are USB powered. So I end up hacking up USB cables so I can monitor/inject power as still maintain comms.

My approach to the Joulescope is no exception:

This is… fine… but it’s finicky and hard to store. I wondered if I made an adaptor that you can just plug USB cables into, whether that would be useful to others?

I’m thinking either a PCB that slots behind the posts, or a replacement front panel. Maybe USB in and USB out in the common form factors. And maybe provision for external supply if that’s useful.

Have you seen the JS220 USB Front Panel? Design files here.

Does this do what you want?

Oh nice! I thought for sure this would be a thing but managed to overlook that. Yeah, that pretty much does the trick. I think I would have connected V+ to I- not I+ to avoid measuring the burden, but I’m not so sure now. Good choice of connectors - pretty universal, although no doubt many devices will be USB-C before long.

So yeah, that’s basically it! I only had in mind a bit more flexibility, like accepting external power, a slot in option if you wanted to leave the standard front panel in, and supporting USB-C and optional Kelvin connection to the load. But that would make it significantly more complex and expensive too.

The design does have a simple trace cut option to switch V+ from I+ to I-, if you want:

Not easily flexible, but possible.

For more flexibility, you may want something like this:

I made my own version a while back, but never got around to open-sourcing it:

I have attached the design in case it’s useful:
usb_power_injector.brd (36.3 KB)
usb_power_injector.sch (32.4 KB)
I release this usb_power_injector design under the Apache 2.0 license.

Also, one of our JS220 customers is making a USB-C front panel, and I think that they plan to open-source it.

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