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Ask HN: Why do laptop chargers have data wires?

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Re: Ask HN: Why do laptop chargers have data wires?

#41

Post by andrei_says_ »

reaperducer wrote: post #27
andrei_says_ wrote: post #10

Earlier quoted context omitted.

“There ain’t such thing as a free lunch” I think? Coined by Heinlein in The Moon is a Harsh Mistress.

Coined by Heinlein in The Moon is a Harsh Mistress. It's far older than that. At least a 150 years old. Bars used to provide free lunches to encourage people to buy more drinks. Often very cheap and salty lunches, like stews or corned beef. This was very common in the 1920's-1940's, decades before Heinlein. It later evolved into just bowls of peanuts or pretzels on bars, though I haven't seen a bar with complimentary…

1. Today I learned ;)

2. I was writing about the abbreviation specifically, which was used in Heinkein’s book.

Re: Ask HN: Why do laptop chargers have data wires?

#42

Post by SAI_Peregrinus »

freehorse wrote: post #38
DanielHB wrote: post #31

Earlier quoted context omitted.

My inlaws were trying to transfer files to a PC from their phones with one of these non-data cables. Even my somewhat tech-savy partner didn't know non-data cables. I taught them the trick about feeling the cable stiffness, I showed them a type-c cable without data vs one with data vs thunderbolt3 type-c. They just couldn't understand why it wasn't working until I showed them there was a physical and tactile differen…

In usb-a cables you can actually see the pins themselves missing looking into the connector from the outside; in usb-c not so much (or at least i could not really see anything there). I could never figure out how to determine a no-data usb-c cable, though I have only even seen one anyway. The problem with stiffness etc is that there is already a lot of variability on usb-c cables, though there could definitely be som…

I just bought a tester from Treedix. It's a small board with a bunch of USB connectors (host side has 3.0 A, 2.0A, C, device side has micro-B, lightning, mini-B, 3.0 micro-B, C, and 3.0 B), a CR2032 coin cell, and a bunch of LEDs that light up when there's continuity for that link. So you can see when a cable has a USB-C connector but only USB-2.0 D+ and D- lines and CC vs one with the extra differential pairs. Faster than trying to mess with a breakout board & a multimeter.

Re: Ask HN: Why do laptop chargers have data wires?

#43

Post by nixosbestos »

acdha wrote: post #40
nixosbestos wrote: post #39

Earlier quoted context omitted.

That's one billion percent not what I meant. Wow. I just can't man, I fucking can't anymore with the Internet and people's need for everything to be spoon fed and assuming that everyone else has lost all information literacy.

So … what did you mean? Going by the plain English words, I pasted the title minus the “ask HN” prefix into Google and got a part-wrong answer. Asking here seems to be inline with practicing information literacy since it’s a community where people are more likely to have actual knowledge than some SEO bot, and there’s both attribution and community voting to help when assessing answers.

You know, the way people used Google and looked things up say a whopping 3 years ago?

> Why do laptop chargers have data wires?

I know, it's crazy to think people would like, research topics, be curious about what PD is, maybe skim the wikipedia for a whole 45 seconds, etc.

But no, apparently just spamming basic questions to reddit and HN is the way we're headed because everyone is used to have these AI-regurgitated crap spoon-fed to them. Or want someone to spell it all out for them because intellectual curiosity is a dying rare thing.

But hey, we're talking about a person who was reading unspecified communities that were apparently promoting cutting open wires to remove data lines, undoubtledly for "freedom" or "privacy", all seemingly without any context or clue about what they were doing.

Re: Ask HN: Why do laptop chargers have data wires?

#44

Post by acdha »

nixosbestos wrote: post #43
acdha wrote: post #40

Earlier quoted context omitted.

So … what did you mean? Going by the plain English words, I pasted the title minus the “ask HN” prefix into Google and got a part-wrong answer. Asking here seems to be inline with practicing information literacy since it’s a community where people are more likely to have actual knowledge than some SEO bot, and there’s both attribution and community voting to help when assessing answers.

You know, the way people used Google and looked things up say a whopping 3 years ago? > Why do laptop chargers have data wires? I know, it's crazy to think people would like, research topics, be curious about what PD is, maybe skim the wikipedia for a whole 45 seconds, etc. But no, apparently just spamming basic questions to reddit and HN is the way we're headed because everyone is used to have these AI-regurgitated…

Maybe this would be a good topic for you to hide and move on.

Re: Ask HN: Why do laptop chargers have data wires?

#45

Post by fuzzfactor »

andrei_says_ wrote: post #41
reaperducer wrote: post #27

Earlier quoted context omitted.

Coined by Heinlein in The Moon is a Harsh Mistress. It's far older than that. At least a 150 years old. Bars used to provide free lunches to encourage people to buy more drinks. Often very cheap and salty lunches, like stews or corned beef. This was very common in the 1920's-1940's, decades before Heinlein. It later evolved into just bowls of peanuts or pretzels on bars, though I haven't seen a bar with complimentary…

1. Today I learned ;) 2. I was writing about the abbreviation specifically, which was used in Heinkein’s book.

I first heard it in person as advice from people who were born in the 1890's and I think it was something that had been explained to them as children themselves.

Seemed to me it probably originated in New York City.

Heinlein was referencing a familiar but cynical saying which is an example that was intended to be kept in mind whether you understood the full implications or not.

Re: Ask HN: Why do laptop chargers have data wires?

#46

Post by aruametello »

qwertytyyuu wrote: post #29

I want to output to my monitor and charge the thing at the same time

you can use a "usb hub with a PD usb C connector"

a random example that has it: https://www.anker.com/products/a8365

you can connect your charger into the PD port, and the hub into your device to charge.

Re: Ask HN: Why do laptop chargers have data wires?

#48

Post by kj4ips »

There's a few cases where this makes sense:

* The laptop supports one or more power supplies, but with different current ratings, and the laptop needs to know how much it can safely draw. (This can be done with passives)

* The charger has dynamic power availability, possibly because it charges multiple devices, and the amount of power available varies with other factors, such as temperature.

* The charger has various output modes available, only some of which align with the device to be charged. Therefore, the two devices must negotiate a common set of parameters.

On the note of USB Condoms, they only interrupt the data lines, USB's power negotiation (nowadays) mostly happens on the power line itself. Though usually, the device's OS (if it has one) has limited/no visiblity to this, and a dedicated port controller handles this interaction, possibly passing higher-level information to the rest of the device.

There are some things that can be done to reduce the threat surface:

* Build the protocol parser as a FSM.

* Formal methods for critical systems.

* Severely restrict the expressiveness of the protocol, particularly any variable-length fields.

Re: Ask HN: Why do laptop chargers have data wires?

#49

Post by dragonwriter »

> Why do laptop chargers have data wires?

Charging cables have data wires because then they can be used as data cables, meaning you can pull the end out of the charger and plug it into some other device, since the USB-C port on the laptop that accepts charge is certain to be a dual-role port. If charging cables didn’t have data wires, you’d have to swap cables in this use case.

> Why don’t the charger manufacturers do this themselves and remove the data wires if there is no purpose for them? It creates an unnecessary security risk by having the data wires.

Because then everyone would have to buy additional USB-C data cables, and then (because it is more convenient) they’d use those with the charger anyway, and the only product would be more e-waste. I mean, the charger already is probably going to last much longer than the supplied cable, and eventually people are going to be using a separate cable with it, using a useless-for-other-purposes cable just accelerates that.

And the security risk is from untrusted chargers. For the charger manufacturer, their charger isn’t untrusted. If the buyer doesn’t trust them, they won’t trust them to supply a safe cable whether or not they actually do, so its not even a useful “secure” sales gimmick. If someone has security concerns about the charger manufacturer, they’ll get a power-only cable from a trusted party and use that, there is no benefit to anyone from the charger manufacturer providing a power-only cable except, I guess, for customers for whom the charger manufacturer is a trusted party, who wants a cable they can use with the original charger and also when they are charging from untrusted other chargers on the road, but compared to people who are better served by dual use cables and people who will use a separately-acquired “safe” cable with any charger, that’s going to be a very small audience.

Re: Ask HN: Why do laptop chargers have data wires?

#50

Post by dragonwriter »

gnabgib wrote: post #3

The USB standard only allows 7.5W (5V @ 1.5A) of power. By negotiating over the data lines, the supplier and consumer can agree to higher amperage and voltage (up to 100W in USB3, 240W in USB3.1) - but you need data lines for this feature. Some USB condoms include a chip to do this negotiation (with the other device) for you - but you still have to trust the chip. You may very well have experienced this with a very b…

> The USB standard only allows 7.5W (5V @ 1.5A) of power. By negotiating over the data lines, the supplier and consumer can agree to higher amperage and voltage (up to 100W in USB3, 240W in USB3.1) - but you need data lines for this feature.

Per the USB 3.1 power delivery spec [0] all communications related to power delivery occurs over the CC wire (with roles chosen according to Vconn), the data wires are not involved.

[0] https://www.usb.org/sites/default/files/USB%20PD%20R3.1%20V1...

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