Comment by vscode-rest
9 hours ago
At least they’re forward about it - I’ve lost count of how many bike accessories claimed to be USB C, but they only charge when connected to their specialized cable that converts from USB A to C.
9 hours ago
At least they’re forward about it - I’ve lost count of how many bike accessories claimed to be USB C, but they only charge when connected to their specialized cable that converts from USB A to C.
Double-sided USB-C connections require a handshake before sending voltage. USB-A ports can have the 5v line active at all times. Cheap USB C gadgets often don't make the handshake, they just use it as a 5V input, necessitating an A to C cable.
If you add 5.1kΩ pulldown resistors on the CC lines for USB-C, you can get the standard 5V without a handshake although current may be limited by some chargers without negotiation.
I think you're overstating this. The "handshake" is purely 2 simple resistors correctly installed. The problem is a lot of folks do it wrong for various reasons, most likely never testing with anything more than type a to type c cables.
https://people.kernel.org/bleung/how-to-design-a-proper-usb-...
One of the many deficiencies of usb-c (who knows what power your cable supports, charger supports, if you accessory will charge, of it will connect at all)
Interesting. Does UsBC spec/licensing require any sort of notation for products that don’t implement handshake?
There is no handshake, all that's needed are two 5.1 kΩ pulldown resistors. By omitting them the manufacturer saved all of about 0.1c and made their device incompatible with compliant usb-c chargers.
More info: https://hackaday.com/2023/02/07/all-about-usb-c-manufacturer...
Such products shouldn’t exist by spec, they’re just not compliant.