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USB On-The-Go

(computer.rip)
208 points jnord | 4 comments | 03 Jan 25 12:42 UTC | HN request time: 0s | 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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xg15 ◴[07 Jan 25 16:30 UTC] No.42624228[source]▶
Isn't this exactly what USB-C docks are for?

I've seen plenty of those devices, where you have a female USB-C socket to connect a charger to, a range of other female USB-C, USB-A and other ports for peripherals and a short cable with a male USB-C plug to connect to a laptop. If everything works, the dock will act as a power source for both the peripherals and the laptop, but will act like a hub on the data lines, with the laptop being the host.

I wonder if it would work just the same if you connected a phone instead of a laptop to the "host" cable.

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1. MarkusWandel ◴[07 Jan 25 20:31 UTC] No.42627068[source]▶
Hmmm, it occurred to me, I'm sitting in front of a laptop connected to a (power delivery) USB-C dock. So unplugged the laptop and plugged the cable into my phone instead (very basic, Moto G Play 2023). What happened? Almost nothing! The phone reported an audio output device, but did not charge, and the keyboard and mouse plugged into the dock did not get recognized either. Not encouraging.
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2. MarkusWandel ◴[07 Jan 25 22:09 UTC] No.42628239[source]▶
Well, the Kensington dock at work did not work (for delivering power to the phone and letting keyboard and mouse be used) - in fact it did none of those things. But ordered this cheapie from Ali:

https://vi.aliexpress.com/item/1005007015739540.html

which does claim to work with various smartphones. We'll see.

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3. xg15 ◴[07 Jan 25 22:17 UTC] No.42628322[source]▶
Would be interested to know that as well. Good luck!
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4. MarkusWandel ◴[17 Jan 25 14:50 UTC] No.42738056{3}[source]▶
Dunno if anyone stil sees this but.. the gadget came from Ali.

Phone doesn't charge through it. However, my work laptop does. If this thing is plugged in between its USB-C dock and the laptop, it is powered, but the dock is not otherwise seen. So the USB-C socket is a full power delivery passthrough but that's all it is.

The USB-A port does work; a mouse plugged into it is seen by the laptop. Didn't test the HDMI output.

For the phone: Useless. Obviously this phone does not do USB-PD. It just expects the power adapter to deliver 5V. So a limitation with this phone; I'll never be able to simultaneously power it and also get an OTG USB connection.