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USB On-The-Go

(computer.rip)
208 points jnord | 2 comments | 03 Jan 25 12:42 UTC | HN request time: 0.412s | source
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MarkusWandel ◴[07 Jan 25 15:40 UTC] No.42623539[source]▶
USB-C has obfuscated things but I was hoping the following would work:

Buy a Y-cable from Ali Express that has USB-C male to plug into the phone, and both USB-C female and USB-A female sockets. Plug keyboard into the USB-A and the charger into USB-C.

But it doesn't work, and I suspect it's a software limitation at least on my phone (Moto G Play 2023). If the charger is plugged in first, the phone will charge but not use the keyboard. If the keyboard is plugged in first, the phone will use it, but not charge. I think the wires are there to make it all work, but the phone's OS just doesn't support this scenario. Pity.

Needless to say documentation is nonexistent so I don't actually know what's in the cable. For all I know, the two female sockets are just connected in parallel.

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bluGill ◴[07 Jan 25 16:05 UTC] No.42623866[source]▶
USB-C never defined a Y cable and so they never figured out how that would work. If such a cable works anywhere it is either luck, or there is some chip inside that checks for power messages from either end but otherwise looks like a straight through cable. Even then it will be tricky because if the two devices want different voltages from the charger only one can get their way.

I can't blame the USB-C people for not working on this case. It is a lot harder than it seems to make work, and of limited use. Just get a USB-C hub if you need this ability.

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MarkusWandel ◴[07 Jan 25 16:18 UTC] No.42624065[source]▶
Heh, if you want a really atrocious USB power violation... Costco sold some extremely bright flashlights (think car headlight bright, and also usable as a self-defense weapon in the spirit of the old D-cell Maglites) before Christmas, that have an USB charge socket. Needless to say they include a charge cable but no charger.

But this thing wants 1.5A at 5V. And doesn't do any power "negotiation" at all, as far as I can see. It happens to work because modern smartphone chargers can do 5V at 2A by default. But plug it into any older charger and the charger immediately shuts down due to overcurrent.

I have one of those USB passthrough voltage/current meter gadgets. Yes, it draws 1.5A. I guess what it should be doing is slow-charge unless it can negotiate for more power. It's a very decent flashlight otherwise.

Oh, it also has two USB-C sockets. A red one for charging, and a black one for using the flashlight's substantial battery as a power bank. I don't know what would happen if you plugged the charger into the wrong socket and don't have the courage to try.

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1. curiousObject ◴[08 Jan 25 02:40 UTC] No.42630306[source]▶
> extremely bright flashlights (think car headlight bright, and also usable as a self-defense weapon in the spirit of the old D-cell Maglites)

Using a device which is mostly lithium ion batteries as a weapon? Even scarier than you expect, if you puncture a battery

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2. MarkusWandel ◴[08 Jan 25 18:47 UTC] No.42637189[source]▶
First of all these flashlights are very sturdy, and second, if you need a self-defense weapon, I don't think a slight danger of the weapon bursting into flame, post-use, is a high priority concern. The battery pack is a relatively loose fit, slide-out item inside a metal tube. All the charge electronics including connectors are part of it. The flashlight actually comes with an alternative battery pack that takes (a lot of) AA cells.