Date: Thu, 21 Jul 2011 15:50:17 +0200 From: Uffe Jakobsen <uffe@uffe.org> To: freebsd-usb@freebsd.org Subject: Re: Off-Topic: question about usb-hub power Message-ID: <4E282DCE.2070403@uffe.org> In-Reply-To: <CAOgwaMt9pKNujjiUHhoutBHstLKqCuo=xqNUV24hzyC6t8s1hg@mail.gmail.com> References: <4E280986.8020701@uffe.org> <CAOgwaMt9pKNujjiUHhoutBHstLKqCuo=xqNUV24hzyC6t8s1hg@mail.gmail.com>
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On 2011-07-21 14:55, Mehmet Erol Sanliturk wrote: > > > On Thu, Jul 21, 2011 at 7:12 AM, Uffe Jakobsen <uffe@uffe.org > <mailto:uffe@uffe.org>> wrote: > > Apologies if this is a kind of off-topic for this list - since it > does not have anything to do with FreeBSD. > > The external USB-hubs (v2.0) that I've come across comes in two > categories: > > Some are willing to deliver power (500mA pr. connector) even if the > hub isn't connected to a computer - and some that doesn't do this - > the hubs that I have purchased from Dlink falls into the last category. > > I looking for an USB hub that is willing to deliver power without it > beeing connected to a computer in order to drive some external units > - no it is not a mobile-phone ;-) > > Could anyone give me a hint what specs to look for ? - before I > actually buy another hub - the Dlink ones were not a success... > > > I do not know whether the above answer is correct for you or not . > Hi Mehmet, Thanks for your answer - it has revealed that my initial inquiry was quite inaccurate - my apologies for that. I'll try to fill out the gaps. The product I'm referring to is a Dlink DUB-H7 (http://www.dlink.com/products/?pid=149). A standard USB 2.0 hub with 7 ports that can be powered from an external power supply. I do know how to determine if there is power on an usb connector (pins 1+4) - also I know the math involved in making sure that the hub is not overloaded - but that it not really the issue here. This usb-hub will (apparently like so many other usb-hubs) only apply power to its connectors if it is connected to a computer (that is running) - and that applies even if the external power supply is connected to the usb-hub. Let me give you an example: You want to charge your mobile phone but you haven't brought the charger itself. You've only got the micro-usb cable for the mobile phone and the above mentioned Dlink hub - also you've got no computer at hand. Now connecting the mobile phone to the usb-hub while the usb-hub is connected to the external power supply will not make the mobile phone start charging. This will only happen once you connect the "uplink" usb cable from the usb-hub and to a computer and boot it up. Let me add here that this has nothing to do with the complexity and internal logic of the mobile phone mobile phone and its software - it could be any other device that can drain its power from an usb cable. I've previously owned an usb hub that would deliver power without beeing connected to a running computer - but unfortunately that was lost during relocation - and I do not remember the model/brand. Now I realize that this functionality is a part of the usb standard - and that leads to my original question: It there anyway to determine this habit without unpacking and testing every the usb-hub ? Kind regards Uffe
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