Objective Development Forums

Re: pull-up resistor values + hub issues

2010-12-18T21:39:56+02:00

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.

Statistics: Posted by Mike J. — Sat Dec 18, 2010 9:39 pm

Re: pull-up resistor values + hub issues

2010-10-16T19:36:54+02:00

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.

Statistics: Posted by Guest — Sat Oct 16, 2010 7:36 pm

Re: pull-up resistor values + hub issues

2010-10-15T19:53:49+02:00

ulao wrote: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.

_frank26080115 wrote: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.

Statistics: Posted by maxi — Fri Oct 15, 2010 7:53 pm

Re: pull-up resistor values + hub issues

2010-10-15T07:43:55+02:00

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

Statistics: Posted by Guest — Fri Oct 15, 2010 7:43 am

Re: pull-up resistor values + hub issues

2010-10-15T04:07:32+02:00

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

Statistics: Posted by ulao — Fri Oct 15, 2010 4:07 am

Re: pull-up resistor values + hub issues

2010-10-14T20:24:25+02:00

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.

vusb.wikidot.com/hardware wrote: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) ?

Statistics: Posted by maxi — Thu Oct 14, 2010 8:24 pm

Re: pull-up resistor values + hub issues

2010-10-13T06:11:00+02:00

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

Statistics: Posted by Guest — Wed Oct 13, 2010 6:11 am

Re: pull-up resistor values + hub issues

2010-10-13T05:31:01+02:00

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?

Statistics: Posted by ulao — Wed Oct 13, 2010 5:31 am

pull-up resistor values + hub issues

2010-10-12T23:01:12+02:00

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

Statistics: Posted by Guest — Tue Oct 12, 2010 11:01 pm