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by firloop 17 days ago
Some cheaper devices I have (e.g. rechargeable LED light strip) _only_ charge via power-only cables. Was maddening when I realized I had thrown out all but one of the cables that can charge it.
3 comments

More often than not these are usually cheap Chinese devices that are expecting a USB-C to USB-A (power-only) cable, because they're actually USB-A devices, with USB-A circuitry, modified slightly to appear as if they're USB-C.

Basically they skipped out on building power negotiation smarts that are required to support real USB-C charging, and instead just swapped out the physical connector.

They skipped out on literally 2 resistors. That's it, that's all that is required for real USB-C charging.
Yep. The two fucking resistors. All it takes 2 x 5.1K, and yet, somehow, people keep fucking it up.

It's not expensive or complex. It's just that somehow, no one thought to look up "how to add type c to your device" online, or ask an LLM, or put literally any effort into making sure the device works as it should.

Those two resistors cost money. It's not incompetence. It's a deliberate choice.
You're saving a fraction of a cent per device, while banking on customers not sending it back as defective because it didn't charge when they tried it with a random cable.

If it is a deliberate choice, it's a really, really dumb one.

Yup. Buy it, test it, post a review, return it. It's the only message you can send.
If it works (aka enough people buy it) it aint stupid
One of my theories is that there is a deliberate choice happening by people who don't realize it is as simple as a couple of resistors and think they need some fancy PD negotiation chip.

Even over on r/usbchardware it is super common for people to conflate "PD" with this missing resistor issue. Part of the confusion is that the devices that people want to charge with are very likely to be PD power supplies.

It's because they take PCBs spec'ed for micro-usb and just replace the port with USB-C.
I've read countless stories of designs sent out getting backroom-cost-reduced by removing the most ridiculously cheap parts.
Out of interest, is that all that's required for the power negotiation handshake? I would have expected more complexity?
Just two resistors to say ‘I am a device, give me 5V’ - you only need more negotiation = a chip - to get more than 5V
Thanks!
Complexity is cost.
Some manufacturers don't want to do the power negotiation aspect which is the cause of this, I believe.
Not even power negotiation but a simple resistor would be too costly for them to implement.
Thankfully I’ve never encountered one. But I’ll check before discarding if I ever get a device that comes with one, thanks!