this post was submitted on 07 Oct 2024
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What’s the easiest way to pull ~30mA from a USB 3 port without getting a warning from Windows? (lemmy.world)
submitted 2 months ago by ch00f@lemmy.world to c/askelectronics@discuss.tchncs.de
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Back in my day, you could usually sip a few mA from a USB2 port without any trouble.

When I try that now, Windows pops up with a “device not recognized” error. I know you can draw up to 150mA before enumeration, but it looks like after some time, Windows will complain that you haven’t enumerated yet.

Is there an easy way to keep from getting this error without having to actually make the device smart?

I’m hoping for something dumb along the lines of USB-PD but facing the other direction. For the record, it has to work on a USB-A port, so USB-C hacks won’t work.

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[–] Darkassassin07@lemmy.ca 4 points 2 months ago (1 children)

Do you get the same issue if you short the data lines? That's usually the indication (to devices) that the port is for charging only; not sure how thats received in the reverse direction.

[–] zurohki@aussie.zone 3 points 2 months ago (1 children)

Looking at the PD spec I got the impression devices are supposed to pull the D+ pin up to a certain voltage, but I got lost partway through.

OP asked for the easiest way and deciphering the spec docs probably isn't it.

[–] Darkassassin07@lemmy.ca 3 points 2 months ago* (last edited 2 months ago)

For power delivery, ie requesting power outside the typical 5v 3a max; yes.

The charger shorting them together usually indicates to the device, it's fixed at 5v 3a.

I think the device shorting them will indicate to the charger/port that you're only requesting power @ 5v 3a max; but I haven't dived into the spec.

I'd give that a try and dig further if it doesn't work.