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-   -   Long USB cable voltage drop, is there a homemade solution? (http://www.linuxquestions.org/questions/linux-hardware-18/long-usb-cable-voltage-drop-is-there-a-homemade-solution-817090/)

revered 06-29-2010 09:35 PM

Long USB cable voltage drop, is there a homemade solution?
 
I attached a 6mtrs cable into a small usb cable, and now the voltage in the output is 4.7v. I want to use it with a wifi usb adapter, I tested it on windows and it worked fine, I can connect and browser the net without any problem, but in linux (tried on ubuntu 10.04 lts, opensuse 10 and backtrack 4) the device is not recognized, like theres nothing plugged in. I guess is because of the voltage drop (without the cable it works fine), lsusb shows nothing. The light on the device does turn on but it should blink but it just stays on (in windows it does blink).

My question is: Is there any homemade solution for this? (I mean I know I can buy a good cable but since it worked on windows maybe there's a way to make it work on linux also)

This is the wifi device http://www.eusso.com/Models/Wireless...L2454-U2ZA.htm I have been reading in that page but couldn't find any info about the power supply.

John VV 06-30-2010 12:20 AM

homemade ?
i would start with buying a new and GOOD quality cord . A wire with very low resistance

Quote:

I attached a 6mtrs cable into a small usb cable
just how did you attach it ?
wire nut ?
solder ?
twist and tape?

linus.newbert 06-30-2010 01:49 AM

use a hub
 
My suggestion, and anyone else's (electrically speaking) on this matter is this: 5m usb cable (if shielded the better) then a usb hub (if independently powered the better) then one more 5m usb cable. Do not rely on anything on USB after 5m, without a hub. It may work at times but if the peripherals get realy power hungry you might lose conectivity.

tredegar 06-30-2010 02:48 AM

Please see this

fruttenboel 06-30-2010 03:24 AM

No.

revered 06-30-2010 08:16 AM

Quote:

Originally Posted by John VV (Post 4018976)
homemade ?
i would start with buying a new and GOOD quality cord . A wire with very low resistance


just how did you attach it ?
wire nut ?
solder ?
twist and tape?

Twist, solder and tape.

I kwow it should work with a self powered hub, but I was looking for something like building my own external power for the cable.

onebuck 06-30-2010 08:22 AM

Hi,

Why?

A lot easier and safer to use a manufactured self powered hub.

:hattip:

revered 06-30-2010 08:44 AM

Quote:

Originally Posted by onebuck (Post 4019367)
Hi,

Why?

A lot easier and safer to use a manufactured self powered hub.

:hattip:

As I said, I know a self powered hub will work, but the topic is about building a homemade one or a workaround for the voltage drop, I dont know why I want to build it myself, I just want to.

My cable is exactly 7.5mts, if I cut it down to < 5 mts (16.4 ft), could it work? I don't want to lose 2.5mts if it will still need self power.


I found 3 power adapters at home that could be useful for this, 5v - 800mA, 4.9v - 450mA and 5v - 350mA.
Since the usb adapter doesn't work with the long cable (and 4.7v) I assume is a high power device, but I can't find how many mA it will need. Would it be dangerous to use one of those 3 power adapters?

And to add the power adapter to the usb, should I only replace the power cables on the usb or its more complicated than that?

business_kid 06-30-2010 10:06 AM

Don't stick a wall wart onto that usb. If the box goes off, you'll be powering the m/b and results would be unpredictable.
I concur with the (more diplomatically expressed) view here that this is a brainless way of doing things.
Have you heard of crosstalk? With 7.5 Metres, you're going to have lots of crosstalk on the data. That messes up the signal. Try
rmmod -f ehci_hcd
That will slow you down to usb-1.0 speeds, but might help.

revered 06-30-2010 10:40 AM

I dont have ehci_hcd, im using ubuntu 10.04 lts.

I do have vhci-hcd, but couldnt find much info about it. I removed it but still the device is not recognized.

tredegar 06-30-2010 11:12 AM

The link I gave at post #4, to usb.org (who should know about these things) clearly explains why a cable longer than 5meters is NOT going to work:
Code:

Q: I want to build a cable longer than 5 meters,
why won't this work?

A:  Even if you violated the spec, it literally wouldn't get you very
far. Assuming worst-case delay times, a full speed device at the bottom
of 5 hubs and cables has a timeout margin of 280ps. Reducing this margin
to 0ps would only give you an extra 5cm, which is hardly worth the
trouble.

Q: What about using USB signal repeaters to make a cable longer than 5
meters?

A:  Don't bother. The best solution is self-powered hub with a fixed 10m
cable that had a one-port bus powered hub in the middle. The maximum
range will still have to deal with the timeout, so any out of spec
tweaking of the terminations between the two hubs and the timing budget
still won't yield more than 5cm of extra distance. A better solution is
described in the following question.


Q: I really need to put a USB device more than 30 meters away from my PC.
What should I do?

A:  Build a USB bridge that acts as a USB device on one side and has a
USB host controller at the other end. Use a long-haul signaling protocol
like Ethernet or RS-485 in the middle. Using cables or short-haul fiber,
you can get ranges upwards of a kilometer, though there's no reason why
the long-haul link in the middle of the bridge couldn't be a pair of
radio transceivers or satellite modems.

Embedded host solutions capable of doing this already exist. Also, two
PCs connected via USB Ethernet adapters are essentially a slave/slave
version of this master/slave bridge.


Electro 07-02-2010 05:14 PM

Quote:

Originally Posted by revered (Post 4019390)
As I said, I know a self powered hub will work, but the topic is about building a homemade one or a workaround for the voltage drop, I dont know why I want to build it myself, I just want to.

My cable is exactly 7.5mts, if I cut it down to < 5 mts (16.4 ft), could it work? I don't want to lose 2.5mts if it will still need self power.


I found 3 power adapters at home that could be useful for this, 5v - 800mA, 4.9v - 450mA and 5v - 350mA.
Since the usb adapter doesn't work with the long cable (and 4.7v) I assume is a high power device, but I can't find how many mA it will need. Would it be dangerous to use one of those 3 power adapters?

And to add the power adapter to the usb, should I only replace the power cables on the usb or its more complicated than that?

It is more complicated than you think. The power adapters will not be compatible on how you are setting it up. Each one will provide like a feedback to each adapter, so you will need something. This something is a diode. Diodes have a voltage drop of 0.6 volts and they direct DC in one direction. Then you are back to where you started or worst than you started.

If you are seeing a voltage drop with USB and the power is only coming from the computer and not anything else, it is more likely it needs more current. USB wifi NIC requires more power than people think. A USB powered hub is required because not all computers can handle the power requirement. Some computers are under spec for powering USB devices.

It is best to just buy an access point or an Ethernet to WiFi bridge that connects to the Ethernet port of your computer. This will save you a lot of problems.

FahadOnline 05-24-2011 06:36 PM

Take a look at this !

Quote:

4. I really need to put a USB device more than 30 meters away from my PC. What should I do?

A: Build a USB bridge that acts as a USB device on one side and has a USB host controller at the other end. Use a long-haul signaling protocol like Ethernet or RS-485 in the middle. Using cables or short-haul fiber, you can get ranges upwards of a kilometer, though there's no reason why the long-haul link in the middle of the bridge couldn't be a pair of radio transceivers or satellite modems.
Embedded host solutions capable of doing this already exist. Also, two PCs connected via USB Ethernet adapters are essentially a slave/slave version of this master/slave bridge.
Source : http://www.usb.org/developers/usbfaq#cab4


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