I just went to charge my kitchen scale and it wouldn’t work until I dug out a USB-A -> C cable and plugged it into my desktop…
It just reminded me of how many devices like that I have. This scale, my wife’s sound torc, some car jumperstarters, and I think a one or two more…
I assume it’s because they just slap a usbc port on a dumb 5v circuit that doesn’t have a power negotiation controller. So the cable and the charger cant figure out the power needs of the device are and just never send any.
All of that because they couldn’t be bothered to put two resistors for the detect pin.
Remember, line must go up at any cost.
Bro have you SEEN the price of resistors lately?
……cuz I haven’t and I assume it’s fractions of a penny per.
A fraction of a penny per? Have you seen superman? Office space? How do you think millionaires are made?
I worked on an embedded product, on prototype there were pullup resistors on the RX/TX lines we used to plug a USB FTDI to do some debug. At manufacture they removed them, it created a floating RX that sometimes injected character that broke uboot…
I love stories from hardware / embedded design. Reminds me that black magic is real, and it’s a miracle any of this works.
What is completely incredible, is that there is some simple embedded devices, be it a thermostat, dishwasher, etc, that sold thousands/millions of units, and the firmware is done by one guy, a simple developer, and when it works, it is not touched again.
Proud to be one of those wizards
But wait. Doesn’t this make them both dumb? I’d expect a modern USB-C charger to still support basic 5v low current lazy devices too. If there’s a USB-A to C cable that works, it must also still be possible to send the basic 5v down a C-C cable.
I also think there’s always going to be a balance between how much a device needs to make and/or how much it needs fast charging to make sense to add the charging circuit for PD/PPS. Even $1-2 on top of the cost can ruin margins in the current electronic market.
USB c has active negotiation for power and communication via a cc pin
The usb a to c cable has a pull up resistor that mimics this and says “give 5v”
Some usb c chargers have a fallback 5v mode for this scenario but not all do
PD includes a 5v option, so you’d think that chargers would default to a dumb 5v/4.5w with no other input, but apparently not… It’s probably something to do with the overcharge protection, or to not (further) harm a device with a damaged charge controller.
Or it could be that my PD chargers are pre pandemic and PD 3.1 fixed this.
Well, I’d expect that if they allowed 5v through but with a low current limit (I think the default 5v standard states quite a low current allowance). They could catch anything drawing too much and shut the port off until it detects disconnection/other reset.
I mean, if they’re thinking about protecting a downstream device, adding this logic would make more sense than just not supplying any power unless a negotiation is made.
In any case, since standard USB ports on a computer will output 5v without anything being negotiated, then it’s really no less safe than any other USB port in that regard.
Surface Pro X is the worst about this. It knows you’re trying to charge it via the USB c ports. And tells you to use their stupid charger instead.
