When I'm trying to connect a USB device like a USB WiFi dongle or Pendrive with a homegrown USB breakout by soldering 4 wires to them, it's just not working.

I'm running Ubuntu and getting errors like this,

hub 1-1:1.0: unable to enumerate USB device on port 3

Above line is not the exact same error message, I can post them if needed.

But low speed USB devices like a USB AVR programmer is working fine.

The ehci-pci kernel driver is being used for both high-speed and low-speed USB devices.

So what's the problem with high-speed devices ? Is there any way to fix this problem ? Probably extra capacitance and inductance from the DIY breakout is violating high-speed USB specification, am I right ?

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    \$\begingroup\$ That and the impedance mismatch too yes \$\endgroup\$
    – brhans
    Dec 2, 2016 at 14:10
  • \$\begingroup\$ Thanks ! And what kind of impedance mismatch ? If you can make it a bit clear please. \$\endgroup\$
    – Arnab
    Dec 2, 2016 at 14:13
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    \$\begingroup\$ Google "transmission line impedance". USB D+/D- lines should be a twisted pair of the correct impedance. \$\endgroup\$ Dec 2, 2016 at 14:23
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    \$\begingroup\$ Might be worth posting a photo of your setup. USB is 90Ohm differential while Ethernet is 100Ohm. Might work, might not, depends how long the cable is and how sensitive the device is. \$\endgroup\$ Dec 2, 2016 at 14:48
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    \$\begingroup\$ I'm using cat5 cables twisted pairs That cat5 is for Ethernet which is not USB. How long is your cable ? If it is up to 20 cm it might just work. For a longer distance: forget about that, you must use USB cable. Note how in a USB cable the datalines are NOT twisted ! \$\endgroup\$ Dec 2, 2016 at 14:50

1 Answer 1


Probably extra capacitance and inductance from the DIY breakout is violating high-speed USB specification

Nope. The problem is impedance. USB 2.0 is high frequency enough to have signal refections at any point with significant impedance mismatch - and your breakout will have a rather large impedance mismatch.

Remember that impedance largely depends on physical properties like size and distance (to each other and ground), so a "breakout" is never a good idea for any HF transmission lines.

The 6 MHz with USB Full devices may work in some cases with short cables, and some AVR programmers only use USB low speed anyway - those are less sensitive to this problem.


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