pull-up resistor values + hub issues

[_frank26080115]

I made a circuit similar to http://macetech.com/blog/?q=node/46
with a 1.5k pull-up resistor, it works with my laptop's USB port directly, but with a USB hub, the device fails enumeration
with a 2k pull-up resistor, it works sometimes with a USB hub but never with the laptop's USB port

what resistor value do you recommend? I am thinking about using 1k8 resistors next

[ulao]

I had a similar problem. With no zeners I could not connect to a usb port directly, but on a hub it worked fine. I used 1.5k's as well. When instilling the 3.6 zerners it worked with both hubs and ports. Guessing you of course have the zerners on there?

[_frank26080115]

no zeners, the circuit is just 3 resistors (1k5, 68R, 68R) and one 0.1uF cap, i want something that works with and without a hub by next monday so i'm ordering from 1k8 and 2k2 resistors from digikey tonight

[maxi]

The only way I can make v-usb enummerate on all the PC's I have access to is using 500mW 3V6 Zeners & 1K5 pull-up as per the wiki. However there is one bit I have never quite understood.

And 3.6 V is better than 3.3 V because 3.3 V diodes yield only ca. 2.7 V in conjunction with an 1.5 kΩ (or more exactly 10 kΩ) pull-up resistor.

What is this all about (or more exactly 10 kΩ) ?

[ulao]

Yeah, I dont see how it woudl work without the zeners. Being compatible on hubs and ports that is.

[_frank26080115]

got the 1K8 resistors, works with and without the hub now!

[maxi]

Yeah, I dont see how it woudl work without the zeners. Being compatible on hubs and ports that is.

Right, without the zener diodes there is no level conversion taking place, thus violating the electrical spec for USB.

got the 1K8 resistors, works with and without the hub now!

Some, possibly most, hosts/platforms will tolerate 5V logic levels but I can testify there are those that wont.

[_frank26080115]

Ok I have had problems getting the "no Zener diode" design to work on several computers (notably, they are all large laptops or desktops), while they work on smaller laptops (my 13" laptop and a friend's tablet PC).

I have placed Zener diodes into the design and now they work in all cases.

My 13" laptop's USB port seem to output slightly less than 5V, while my 17" laptop's ports output slightly more than 5V, maybe that affects the I/O voltage on the D+ and D- lines enough to cause the signals to be incompatible with the host.

Anyways I'll be including the Zeners on all future designs.

[Mike J.]

Hello frank,
I create a PCB with 3.3V Voltage regulator for the Controller and a USB connection to my AVR.

If I use a 1.5k PullUp to 3.3V the PC and the Hub does not find the "VOTI- Device"
if I connect the 1.5k Resistor to 5V the device will be found and everything works.

For connecting +D with 3.3V a 1k resistor should be used I think.

PC: ATI/AMD chipset (AMD 690G + ATI SB600) and a USB 1.1 Hub
OS: LinuxMint10

On +5V from ATX Powersupply I measure 4.96V , so it should be okay.