USB-C has been game changing for us.
I can now confidently go to any desk or meeting room in the company and be fairly certain that my laptop will just work with whatever’s been installed regardless of brands.
USB-C has been game changing for us.
I can now confidently go to any desk or meeting room in the company and be fairly certain that my laptop will just work with whatever’s been installed regardless of brands.
daveyOsborn@infosec.pub 3 days ago
USB PD is also a shit show. You might want to read this:
goughlui.com/…/tested-usb-c-barrel-connector-adap…
Which shows those USB PD negotiations can get dicey. It chooses voltages thought to be close enough to what’s requested.
I’ve run into a nasty problem where a USB-C appliance needed 9v. Says in the manual something like “only use Kenwood power supplies on this device”. I thought, fuck that, USB PD is a standard for a reason. I’m not going to blow money on a proprietary OEM Kenwood USB-C PSU. Then found that many power supplies actually skip 9v. The USB PD standard makes some voltage steps optional, and some mandatory. IIRC, 9v was one of the required ones, yet it was easy to find USB-C power supplies that skipped 9v but offered 12v (or 15v, I forget). And yet 12v or 15v was one of the voltage steps that’s optional.
cmnybo@discuss.tchncs.de 2 days ago
12V is optional now. It was part of PD revision 1.0 and dropped in later revisions, but many chargers still support it. 9V has been required since PD rev 2.0.
With the device that uses the 9V only USB adapter, I would either glue the plug in or replace it with something else. Its too easy to accidentally fry something with that.
kkj@lemmy.dbzer0.com 2 days ago
I’m getting the sense from your comments that you think that USB-PD will deliver a higher voltage than requested. This is not accurate. A device can request any of the voltages specified by PD, and the power supply will supply that voltage if it is capable of doing so. If not, it will provide 5V. It’s very possible to get a sippy that won’t power your device, but a working, PD-compliant power supply will not damage a working, PD-compliant device.
Obviously, if you get a barrel jack adapter that requests 20V and then plug it into a 5V device, you’re going to let the magic smoke out, but that’s because barrel jacks don’t do negotiation. The power supply correctly supplies 20V as requested, and then you plug that 20V into the wrong thing.
daveyOsborn@infosec.pub 1 day ago
That’s not true. See the experiment I linked.
Of course. Not sure what point you’re trying to make here but the conversation was about whether the barrel adapter is compliant with the standards. Not whether you can misuse it.
kkj@lemmy.dbzer0.com 1 day ago
You’re misreading the blog post. That adapter has 19.5V written on it, but it requests 20V. 19.5V is not a PD voltage.
The latter is pretty much impossible to make to spec, because it can’t negotiate voltage. A barrel jack is single-voltage by necessity.
Respectfully, I’m going to have to disagree. It’s much more interesting when it catches fire, and I’d rather have a protocol that sometimes doesn’t operate in order to avoid the excitement of one that sometimes explodes
No matter what charging standard you use, some idiot could cut off the end, wire it to a stun gun, and send 100,000V into your phone. That doesn’t make the standard bad, it makes the adapter bad.
If you do it correctly, a USB power supply being adapted to a barrel jack won’t destroy any device that can tolerate 5V. It may not operate the device, but as long as nothing breaks, I’d consider it as foolproof as anything reasonably can be.
That’s just how electricity works. You can get 5V devices that use 5.5x2.5 barrel jacks and you can get 20V 5.5x2.5 power supplies. You can get C13 leads that connect to 240V wall outlets and you can get C14 devices that only accept 100V. If someone plugged things in without reading before USB, they broke things and started fires. PD simply doing nothing when incompatible devices are connected is a massive upgrade over that, even if it can be frustrating sometimes.
Onomatopoeia@lemmy.cafe 3 days ago
That’s joy part of USB spec as there’s no way to communcate requirements through the barrel. Hard to blame USB for when we side-step it’s design.
I do stuff like this too, but only for devices that just need power, nothing like a laptop or with circuitry that could get fried by the wrong voltage.
daveyOsborn@infosec.pub 3 days ago
Do you mean the USB PD spec? It does not violate the USB spec which sets a default voltage of 5v. The adapter /would/ violate the USB PD spec if it were to claim to be USB PD compliant. But the shit-show we have is that USB-C does not imply USB PD. And so the market is full of USB-C things that are not USB PD. And often they do not claim to be USB PD as consumers are not wise enough to demand it.
Note as well the adapter I mentioned is quite dumb – just hardwires pins for the situation that the appliance expects 5v without negotiation. But it would be possible to implement a USB PD-compliant adaptor with the smarts to handshake, which would then refuse to complete the handshake in the event that the voltage supplied is not that requested. Of course it would be a bit strange to put that much sophistication into it which would likely drive the cost to that of a whole compliant PSU anyway (thus defeating the purpose). But notice the opposite has been done, whereby the adapter negotiates a voltage on behalf of a barrel device.
IIRC, it’s disputed whether the hanshake negotiation is needed for 5v. Some appliances expect to do a handshake /no matter what/, and some 5v appliances are designed to skip the negotiation entirely. If you are in the camp that says even 5v must have a handshake negotiation, then you would condemn the simple barrel to usb-c adapter (but perhaps not one that is only for a fixed input and the circuitry to do the negotiation).
The blame was not pin-pointed. I pointed out a shit show in the marketplace. There are bits of the standard you can blame, and you can also blame market actors. You can probably also blame regulators for not preventing the shit show that I described.