Adafruit USB Type C CC Resistor Fixer

RRicoElectrico about 4 hours ago 40 commentsRead Article on adafruit.com

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Discussion (40 Comments)Read Original on HackerNews

blacksmith_tb•29 minutes ago

I have a fair number of badly designed / implemented usb-c devices with this problem (not all from fly-by-night companies, my Philips water flosser is a glaring example). I have a couple of small metal-enclosed male C to female C adapters (which don't have an exposed circuit board) that do the same thing as the Adafruit version.

lgeorget•about 3 hours ago

I lost a good two hours the other day on an insufficiently documented device, looking for a way to flash a new firmware onto it.

dmesg was absolutely silent about it when I plugged in or out my C-C USB cable although the device switched on when I was using a simple charger instead. I opened it up to see if there was a special switch or something to put it in firmware flashing mode, to no avail. The little documentation I had only mentioned using one of the USB port.

In the end, out of ideas, I switched cables (even though I knew my cable was perfectly fine). As soon as I plugged in a A-C USB cables, everything worked immediately...

mort96•about 1 hour ago

IMO it's a huge failure of the USB-C standard that to a USB 2 only device, a C-C cable looks different to an A-C cable. It's the cause of so many issues of the kind, "it works when I use a different cable" or "it works with this power supply but not that power supply". I understand why something needs the ability to check, but when not doing anything special to detect USB-C capabilities, they should be identical.

crote•about 1 hour ago

> to a USB 2 only device, a C-C cable looks different to an A-C cable

It does not. The vast majority of sinks have absolutely no knowledge of the cable used.

This is literally device engineers not bothering to read any part of the USB-C spec, or intentionally leaving out a $0.0003 part. And no, that's not a typo - I really do mean "50k unit reel for $15".

mort96•39 minutes ago

I know how cheap resistors are. I design PCBs as a hobby and occasionally semi-professionally.

Leaving off parts should result in behavior which is identical whether you connect an A-C cable or a C-C cable. Detecting the difference between them should require adding parts.

NooneAtAll3•27 minutes ago

if nobody follows the spec, it's the problem in the spec

why tf does it matter what the other side of the cable is connected to?

ianburrell•24 minutes ago

USB-C doesn't provide power by default which is better design than USB-A always providing some power. The device needs to signal that it is a sink with 5.1k ohm resistors so the charger can turn on the power. There is also resistor to signal legacy USB charging to work with USB-A ports.

How is the standard supposed to work with defective devices that don't implement the standard?

seba_dos1•17 minutes ago

> There is also resistor to signal legacy USB charging to work with USB-A ports.

There's no such thing on the device. A power sink with a USB-C receptacle has two 5.1kΩ resistors, one on each CC line. A power sink with a USB-C plug has a single 5.1kΩ resistor. Always. That's it - anything else in on the power source (or cable) side.

You only need to bother with anything more on the sink side once you want to either sense what's the max current provided by the source (which you can do simply by measuring the voltage on CC pins), or implement PD.

criddell•about 2 hours ago

What was the device? Somebody experiencing the same problem might appreciate the tip.

seba_dos1•about 1 hour ago

There's all sorts of cheap devices like that out there that merely have a Type C-shaped receptacle that doesn't actually implement Type C because they couldn't bother to place two resistors on the board.

eknkc•about 2 hours ago

I did not know this was a thing.

I have a couple of devices that do not charge on a usb c source. I have to use a USB A - C cable on their shitty usb-c ports.

Now that I know the probable reason I’m more annoyed.

Cieric•about 1 hour ago

Another thing that it could be is quick charge, since that seems to conflict with some PD chargers as they'll try to negotiate, fail and then reset. My Light L16 camera has this problem so I have to use the charger it came with or find something dumb enough that it doesn't try anything special.

rjh29•about 2 hours ago

While the device is ultimately to blame, many PD chargers will work anyway (by dangerously assuming 5V when there are no CC resistors). My Anker chargers do this.

8cvor6j844qw_d6•about 1 hour ago

Interesting. I thought 5V is a safe default for USB when in doubt and risk of damage is nil even if it's assumed.

seba_dos1•about 1 hour ago

Just grab two of these spec-violating chargers and a C-to-C cable.

I don't think the right solution to problems coming from spec-violating garbage is producing differently spec-violating garbage.

Palomides•about 1 hour ago

are there devices that are damaged by 5V?

megous•about 1 hour ago

There's nothing dangerous about it.

No Type-C receptacle featuring device can assume there will be no Vbus voltage on attachment from the other side, regardless of CC signals.

For a simple reason that USB C-A cable assemblies exist and can be plugged to any old charger or port on the A side, which will not wait or negotiate anything. It will just source Vbus 5V right away.

crote•about 1 hour ago

... which is exactly why a source with a female USB-C port is not supposed to apply VBUS until it detects a sink.

Obvious counterpoint: what's going to happen when two noncompliant "always provide 5V" USB-C wall warts are connected together with a C-C cable? How well does a charger like power being fed into it?

joecool1029•about 2 hours ago

There were some higher profile products that left this out like the original revisions of the raspberry pi 4.

seba_dos1•about 1 hour ago

Raspberry Pi 4 had a slightly different problem - they attempted to get away with using just one resistor instead of two, as it allowed them to simplify their voltage-sensing circuit a bit. At a cost of non-compliance and all the issues that came with it, of course, so not a great bet after all.

rufo•about 2 hours ago

As someone with a bunch of "USB-C" devices that do this, I'd wondered for years why nobody sold these. I recently just found them on Aliexpress in a more finished format (nice-looking case and such), so I'm hopeful they'll start to filter out into the world more. (If you're interested, do a search for "usb c resistor" and you'll find them for ~$2-$4.)

kevin_thibedeau•about 2 hours ago

Are you sure they aren't C-to-C data blockers?

The_SamminAter•about 2 hours ago

Oh, I made one of these not too long ago with those 4-pin solderable aliexpress USB-c pcbs. One side has the resisters, and I just joined them with headers. A few months ago I was looking for something just like this, but couldn’t find anything. I think a pack of 10 male and 10 female ports with CC resistors cost <$10, but I suppose this is a more elegant and accessible solution (plus, may actually pass more lines through).

metaphor•about 1 hour ago

Anyone in test for the domain able to attest that formal USB compliance verification would have detected the design defect that this hack resolves?

crote•about 1 hour ago

It absolutely would. This is an "didn't even read a 5-paragraph AI summary of the spec" level of a design defect.

If you need this fix, it will literally refuse to work with any spec-compliant USB-C device on the other side of a C-C cable. No way to miss it.

8cvor6j844qw_d6•about 1 hour ago

Wonder if there are USB C cable testers that detects this.

In practice, most if not all networking/hardware department carries a ethernet cable tester but somehow not true for USB cables.

Ajedi32•38 minutes ago

It's not the cable that's the problem here; it's the device you're plugging into the cable.

You don't need a cable tester to detect this problem; just plug the device into a spec-compliant USB-C power brick with a USB-C cable and see if it fails to charge.

seba_dos1•43 minutes ago

You don't need a tester to detect this (and it's not about cables).

tbyehl•about 2 hours ago

Hagibis makes one that isn't a bare PCB. B0GLFGTLW9 on Amazon.com, for me today it's showing $6.99 for a 2-pack.

megous•about 1 hour ago

2 connectors and a 0.01c PCB for the price of a complete working charger.

Ajedi32•42 minutes ago

If you need this, it's not the charger that's broken but the device you're plugging into it.

megous•23 minutes ago

Yes, the point is it's extremely expensive for what it is.

rahimnathwani•about 1 hour ago

You can get five of them for less than $4 total here:

https://a.aliexpress.com/_mtW11kT

megous•24 minutes ago

Including a cover, which is $2 extra here.

Congeec•about 2 hours ago

I don't buy and return products that don't charge with a single usb-c cable. How can I expect good quality from a product if the maker saves on ¢1 cent? It's 2026 yet new products still keep people from going all usb-c.

0x457•about 1 hour ago

It's much less than a cent.