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Adafruit USB Type C CC Resistor Fixer
- lgeorget 24d agoI 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...
- criddell 24d agoWhat was the device? Somebody experiencing the same problem might appreciate the tip.
- seba_dos1 24d agoThere'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.
- lgeorget 23d agoIt's the LTS5 from Dragino, a LoRa touchscreen: https://docs.dragino.com/docs/LoRaWAN-End-Node/lora-modules-accessories/lts5/ https://docs.dragino.com/docs/LoRaWAN-End-Node/lora-modules-.... And for the record, I'm extremely happy with all their other products, which are all open-firmware, open-hardware, etc. and excellent quality. Plus they're super responsive. It's just this particular product which has this weird issue.
- mort96 24d agoIMO 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 24d 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 24d agoI 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.
- crote 23d agoThere is nothing to detect on the sink side, for basic operation. All the smarts are in the power source. It's like saying USB cables should still carry 10Gbps data when only the VBUS and GND wires are present, because some AliExpress scammers leave out the data wires: you can't leave out trivial core parts and still expect it to work!
- mort96 23d ago> There is nothing to detect on the sink side, for basic operation. I know. You need the detection for the fancy stuff like PD, not for basic operation. So why does it matter that a resistor is missing on the sink side? It's stupid.
- seba_dos1 23d agoYou already got the answer spelled out several times here in this thread.
- Ajedi32 23d agoIt is needed for basic operation, because unlike with a A-to-B cable, power bricks plugged into a USB-C cable have no way of knowing whether the other side is also a power supply that will short out if you try to feed it power instead of drawing power from it. A couple resistors in the sink is probably the cheapest possible way of signaling this information to the supply. This isn't PD, it's just a basic requirement to allow having the same connector on both ends of the cable.
- genxy 23d agoThe A-C cable is new the mini-usb cable. I keep a couple magic cables in the tool box with a big flag of tape on it so it doesn't disappear into the gyre.
- eknkc 24d agoI 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.
- rjh29 24d agoWhile 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.
- Palomides 24d agoare there devices that are damaged by 5V?
- 8cvor6j844qw_d6 24d agoInteresting. 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 24d agoJust 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.
- megous 24d agoThere'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 24d 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?
- The_SamminAter 24d agoOh, 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).
- rufo 24d agoAs 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 24d agoAre you sure they aren't C-to-C data blockers?
- rufo 23d agoAs positive as I can be without having bought one just yet. The ones I've seen specifically say they "solve the problem that low power devices cannot be powered via C to C", that they support 480Mbps data transmission, and are listed as 5.1K ohm resistor adapters.
- Congeec 24d agoI 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 24d agoIt's much less than a cent.
- tbyehl 24d agoHagibis makes one that isn't a bare PCB. B0GLFGTLW9 on Amazon.com, for me today it's showing $6.99 for a 2-pack.
- joecool1029 24d agoThere were some higher profile products that left this out like the original revisions of the raspberry pi 4.
- seba_dos1 24d agoRaspberry 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.
- nubinetwork 23d agoSo it wouldn't work on a pi then?
- seba_dos1 23d agoIt would, but it would make the Pi not able to check the power capability of the source. Note that the Pi's failure mode is different - it does work with C-to-C cables as long as they don't contain e-markers. They tried to be clever and it backfired.
- metaphor 24d agoAnyone in test for the domain able to attest that formal USB compliance verification would have detected the design defect that this hack resolves?
- 8cvor6j844qw_d6 24d agoWonder 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.
- seba_dos1 24d agoYou don't need a tester to detect this (and it's not about cables).
- Ajedi32 24d agoIt'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.
- crote 24d agoIt 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.
- megous 24d ago2 connectors and a 0.01c PCB for the price of a complete working charger.
- rahimnathwani 24d agoYou can get five of them for less than $4 total here: https://a.aliexpress.com/_mtW11kT https://a.aliexpress.com/_mtW11kT
- megous 23d agoIncluding a cover, which is $2 extra here.
- Ajedi32 24d agoIf you need this, it's not the charger that's broken but the device you're plugging into it.
- megous 23d agoYes, the point is it's extremely expensive for what it is.
- seba_dos1 23d agoYeah, I once had similar (with a different purpose, but very alike) boards of my own design produced and paid $22 total for 5 assembled boards, including shipping from China to Europe and all taxes/customs. Unlike this one it had SuperSpeed passthrough too, so you could probably go cheaper :)
- crote 23d agoThat's the cost of Western retail for you! $0.50 to get it manufactured somewhere in Asia, $4.00 to get it shipped to the US, tested, packaged, put on a shelf, retrieved for your order, and put in a box to ship your way. You're not paying for the PCB, you are paying for an American warehouse worker to do their job without having to pee in a bottle and walk around dead coworkers.
- blacksmith_tb 24d agoI 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.
- m-p-3 23d agoI hate my Powkiddy retro game console because of this. What's the point of a portable console if it's doesn't work with all the USB-C cable I have? I'm so annoyed they cheaped out that I don't even plan on buying anything from them again.
- throwaway89201 23d agoThe Miyoo Flip has the same problem. Great device otherwise for GBA or earlier games.
- summermusic 23d agoI've fixed this issue by using a Micro-USB to USB-C adapter