Increasing USB ports

[VK4WDM]

This is a very nerdy question, but please don't laugh too loud.

Does a "USB hub" actually increase the number of available USB ports or is really only providing several inputs into the one port? I only have four USB ports on this laptop and the abiity to connect more devices would be useful.

There also appears to be two types of hubs. One that requires an external psu and one that is self powered. Is one better than the other?

73

Wayne VK4WDM

[VK2GOM]

Hi Wayne,

Yes, they really do allow you to use more USB ports.

Powered vs unpowered refers to whether the devices you will be running on them require to be 'powered' or not. ie. devices that draw current from the USB supply. If unsure, it is safer to use a powered hub.

73 - Rob VK2GOM / GW0MOH

[VK4GHZ]

Does a "USB hub" actually increase the number of available USB ports

In a word, yes.

Each device connected to that hub is seen as a separate device.

For instance, this DELL 24" screen has a built in 4-way USB hub.
Into these USB feeds are; the USB to GPIB lead going to the spectrum analyzer, the USB interface to my Behringer audio mixer, and one to a Spyder3 screen calibrator device.
There is one spare USB port.
All these devices plugged into this hub are seen by the puter as separate devices.
This particular screen also has a built-in card reader (handy, I plug my dSLR camera cards into it), and this also goes back to the puter via this one USB feed, and everything appears as separate devices.

There also appears to be two types of hubs. One that requires an external psu and one that is self powered. Is one better than the other?

This depends on your application, and what device you are intending to use!
Like the hubs, some devices are "self-powered" and derive their power from the USB feed itself.
USB ports are typically good for supplying up to 100mA.
Some laptops have a configurable USB port, a "charging port" that can supply up to 500mA.
For card readers and general purpose comms between devices, a self-powered port should be more than adequate.
if you intended to plug in a device that draws it's power from the USB connection, and it is >100mA, I would go for the hub that is externally powered.

[VK4GHZ]

Rob beat me to it, whilst I was typing!

[VK2GOM]

...but your answer was far more detailed Adam! Feel free to edit this forum thread out and remove my message and leave yours for future reference of anyone (any lurkers!) looking for info on USB hubs

73 - Rob VK2GOM / GW0MOH

[VK4WDM]

Thanks for the detailed and very understandable replies.

I have two plane plotter down converters, my digital interface, and a wireless mouse connected to existing ports. None of these draw anywhere near 100mA, but I have just ordered a Signal link interface. I will see how I go with an un-powered hub to start with as I have a horror about the noise potential of small switch mode PSUs.

73

Wayne VK4WDM

[VK2MUS]

This is a very nerdy question, but please don't laugh too loud.

Does a "USB hub" actually increase the number of available USB ports or is really only providing several inputs into the one port? I only have four USB ports on this laptop and the abiity to connect more devices would be useful.

There also appears to be two types of hubs. One that requires an external psu and one that is self powered. Is one better than the other?

73

Wayne VK4WDM

usb unlike serial port can daisy chain usb devices - you are not actually making another usb port

I run a BUXCOMM rascal interfaqce which draws all its power from the usb with no problem
John

[VK5PJ]

Wayne,

Thanks for the detailed and very understandable replies.
I have two plane plotter down converters, my digital interface, and a wireless mouse connected to existing ports. None of these draw anywhere near 100mA, but I have just ordered a Signal link interface. I will see how I go with an un-powered hub to start with as I have a horror about the noise potential of small switch mode PSUs.
73 Wayne VK4WDM

The beauty of a USB HUB is that you plug all your fixed devices into it, then ONE and only one cable to your laptop, then when you need to pick it up and go, you only unplug one USB not many, same goes for return just plug in one USB fromthe HUB and it is all go!

I do this for my desktop in the shack, has three USB serial ports, 1x USB sound. When I want to use my old DELL laptop, just transfer the single uplink USB cable from the HUB to the laptop.

Peter, vk5pj

P.S buy a powered hub if you get a choice, they can generally run in either mode, just leave the plug pack out for unpowered mode

[VK2XSO]

And power your USB soldering iron

[VK3ANZ]

One aspect that has not been mentioned is that each USB controller can address up to 127 devices. (This does NOT take into account the power required for those devices - however powered hubs are recommended anyway). A device is a hub or an actual device (such as a camera, keyboard, radio etc.). Hubs can be used in a tiered manner to provide you with additional sockets to plug your devices into, but the limit of 127 remains. [Actually it is 128 BUT the controller acts as a "root hub" and so leaves you with 127].

However there is the complication that some computers provide multiple USB controllers; this is especially true for those computers that connect their internal keyboards, trackpads etc. up as USB devices and so use multiple controllers to provide enough device addresses to the external USB ports. This means that some computers can actually have more than 127 devices connected as long as they are on different controllers. You will need to look at the USB information your computer provides (each OS has its own way) to see the number of controllers and the devices attached to each.

Therefore my simple rule is "plug it in anyway". For a start you will be going well of you have 127 USB devices already in use and try to add the 128th!

Susan

[VK2AVR]

The main consideration aside from power draw is bandwidth. If you have 4 devices plugged into a hub then they are sharing the bandwidth on the "uplink" from the hub to PC. This isn't a problem if you are using low bandwidth components eg keyboards and mice but may start to become a problem if you have several high bandwidth devices plugged in. An example would be a USB stick used for SDR, a Signalink and especially a removable USB HDD. (not a flash drive, a normal hard drive). If you have several of these used in and are accessing them all at once then your overall performance may drop. That said, it's not usually a big issue you'd have to be a pretty effective multi-tasker to have a problem

Geoff

[VK4MWS]

If you are worried about the intereference from the wall wart power supply, I have 2 x 7 port hubs running lots of things and found that they were 5V. Then I remembered that the molex plugs inside the computer that run hard drives, CD roms etc carried 12V and 5V. So I run wire from the molex plug to the hubs. 2 less wall warts.

[VK4GHZ]

...So I run wire from the molex plug to the hubs. 2 less wall warts.

An excellent idea!
I was inside my PC last week (installing a 3rd HDD), and noticed all the unused power feeds the PSU had available.