5 ms·

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 w

by mort96 23d 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.

crote 23d ago
There 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 ago
    You already got the answer spelled out several times here in this thread.
  - Ajedi32 23d ago
    It 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.
Ajedi32 23d ago
I don't think you understand the problem. Unlike a USB-A power supply, a USB-C power supply cannot just assume by default that the device you plugged into it is not another power supply. That would risk causing a short and potentially starting things on fire. I suppose that instead of a $0.01 resistor to request power they could have mandated some kind of (probably more expensive) circuit breaker that detects the short and shuts things off before it causes a fire, but I suspect then instead of broken devices having missing resistors you'd get ones with missing circuit breakers... It pretty hard (maybe impossible) to design a spec that still works when manufacturers randomly omit critical components for no reason.

by mort96 23d ago

crote 23d ago

There 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 ago
  You already got the answer spelled out several times here in this thread.
- Ajedi32 23d ago
  It 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.

Ajedi32 23d ago

I don't think you understand the problem. Unlike a USB-A power supply, a USB-C power supply cannot just assume by default that the device you plugged into it is not another power supply. That would risk causing a short and potentially starting things on fire. I suppose that instead of a $0.01 resistor to request power they could have mandated some kind of (probably more expensive) circuit breaker that detects the short and shuts things off before it causes a fire, but I suspect then instead of broken devices having missing resistors you'd get ones with missing circuit breakers... It pretty hard (maybe impossible) to design a spec that still works when manufacturers randomly omit critical components for no reason.