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How it works (on page 52):

"The TPS25751 supports liquid detection by measuring the voltage level across the SBU pins of the Type-C connector. When a short occurs across the SBU pins to another Type-C pin(s), the TPS25751 takes action to protect the the Type-C port by disabling the power paths and notifies the embedded controller when applicable. Once liquid has been detected, the TPS25751 continuously monitors the SBU voltage. During the SBU voltage monitoring, if the liquid/short is no longer present the TPS25751 takes action to return to normal operation."

In other words, it's not actually detecting "liquids" but more of any conductive short. Non-conductive liquids, like oils and many other petroleum products, won't be detected.

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Dumb question: wouldn't non-conductive liquids be harmless? i.e., the USB port can in theory work even if it is immersed in some non-conductive liquid, no?

Non-conductive liquids still might be corrosive, or might provide enough thermal insulation to cause heat build-up, or might leave some kind of residue that would be problematic, or...

Or dissolve plastics and rubber, maybe delaminate circuit boards, destroy any tape and glue...

Sure, this is the same principle of, eg, the mineral oil cooled PC: https://www.pugetsystems.com/mineral-oil-pc/

Also some companies like 3M actually make a collection of liquids specifically for immersion cooling in data centres, so it's mature enough that people are happy to use it even in a data centre setting.

Very mature, going back to at least 1985 in the Cray-2.

I wonder if any of those coolant varieties survived the recent jihad against fluorochemicals. AFAIK 3M is out of the business entirely at this point.

> Dumb question: wouldn't non-conductive liquids be harmless?

Mostly yes, except for things like concentrated sulfuric acid which is highly corrosive but a bad conductor.

Agree: bad conductor - https://chemistry.stackexchange.com/questions/153107/why-doe...

I'll keep that in mind.

Somewhere, a YouTube content creator scribbles Macbook Pro in concentrated sulphuric acid.

(And I'd probably watch it).

As long as we get a Steve Mould cross-section made from 3D printed parts, I’m on board!

NileRed for HN, paging NileRed for a video about non conductive liquids in USBC PD

NileRed: I turned this MacBook Pro into Cotton Candy!

At least bigstackD can recover the aluminum afterward.

Is Codys Lab ok?

I guess I won't be liquid cooling my setup with concentrated sulfuric acid then

Wise.

This is definitely the next "Cooling Adventures with Alex" video on Linus Tech Tips.

Well, the device can't make heat if the device no longer exists I guess...

But you would need to make sure that the pins still contact though.

Would depend on the nature of the liquids. A harmless liquid can still damage the plastic or be toxic for the owner.

So it's a software visible GFCI circuit. Not super interesting, though sure, if the chip does it the OS should probably listen. The spin in the article about how this is all because of warranty denial revenue is pretty weird though.

Really nitpicky, but not really a GFCI.

The USB connector is detecting a short circuit--a direct connection between the two pins--and cutting power while the condition is present. If you wanted to put this in terms of household electrical, this would be closest to a self-resetting breaker. (And actually, most devices you have already _have_ this. There's usually a self-resetting fuse/PTC thermistor protecting your USB ports from over-current conditions. The only novel thing here seems to be that it's done in software.)

A GFCI, meanwhile, works by detecting in imbalance between the hot and neutral lines. The amount of current flowing through one should match the amount flowing through the other. If power is being drawn through the hot pin but not returning through the neutral, it has to be going _somewhere_ and it's not where we intended it to go. It cuts the power off rather than let it continue to flow out and find a path to ground through your kitchen sink/etc.

Even more nitpicky: that's totally a GFCI. You "detect a short circuit", by definition, by detecting current flowing between pins that shouldn't carry current. GFCI is the same thing, just for the special case of three-wire power delivery where all it needs to do is test one ground line.

Gelman amnesia and all that…

Even more nitpicky: it’s not a GFCI because GFCI does not detect current leakage between pins that shouldn’t carry current. It measures current imbalance between pins that should be carrying current.

The distinction is that a real GFCI (which this USB port is not) does not care whether the imbalance is returning through a third conductor on the power cord or some other path.

If this were a real GFCI, it would be able to detect when current flows out through the case, to your hand, though your body and then back though the puddle of watch you’re standing in.

That’s not what this is doing. It is measuring unexpected current between the pins within the port for the purpose of avoiding galvanic corrosion (the hint is in the daemon name reported by macrumors).

Does the USB-C specification allow that? Can such devices get USB-C certification?

OTOH, I haven't seen any USB certifications on Apple USB cables or devices, so most likely Apple doesn't care.

Although Apple is a board member of USB-IF, at least their cables are indeed not USB-IF certified.

Why would that not be allowed? In isolation, not running power through a short seems like a great safety feature for the hardware.

This is a standard feature of all Smartphones with IPxx certification. It prevents corrosion on the connector contacts.

Yes: because Apple actually got this added to the spec: https://www.usb.org/document-library/usb-type-cr-cable-and-c... which is the real story IMO (I am impressed no one bothered looking at the Type-C spec update after the Type-C iPhone finally came out)

This actually replaced the analog audio mode (good riddance- whoever thought adding analog audio into a port that also does digital audio was a good idea?)

Me with an analog headphone?

The problem is that it's a rather confusing Alt Mode.

Basically, it's only supposed to be used for USB-C-to-3.5mm adapters, and it was only implemented by some smartphones. It's not a reliable way to get audio out of a USB-C port, and because it's using the internal DAC the audio quality isn't going to be good anyways.

The proper solution is to use a USB DAC. This provides the same user experience but it actually works with all USB-C devices. Considering the official Apple USB DAC is available for $9, the Audio Alt Mode really doesn't have a reason to exist.

For an iPhone...

Unless I'm misunderstanding the mode, there could be uses to get audio out of a USB port that don't involve phones...

Why is it confusing or bad? Sure, it sacrifices a data line pair, but the same can be said of DisplayPort Alt Mode - if you want 4K@60Hz on DP 1.2 you need to sacrifice USB3.0.

The ability to make this tradeoff should be up to the user.

Thanks. I didn’t know that that connector actually contained a DAC.

Thanks for posting this. I was curious how they were able to detect liquid in the USB port

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