Netbooks with DVD
in [UK Linux]
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From: Daniel James on 17 Dec 2008 09:24 In article news:<gi3itc$1lg$1(a)localhost.localdomain>, Martin Gregorie wrote: > Hmmm, its surprising that nobody has yet made a 'dumb' USB power cord > adapter to fool the socket into supplying 500 mA. It's not a matter of fooling the socket into supplying the higher current. The socket either supplies it or it doesn't, the point is that the device mustn't draw more than 100mA unless and until it has negotiated with the device and been given permission to draw more. You would therefore have to design a 'smart' USB power cord that could perform the required negotiation with the USB host and arrange for the peripheral to draw power at the higher level if negotiation was successful and at the lower power otherwise. Cheers, Daniel.
From: Martin Gregorie on 17 Dec 2008 10:42 On Wed, 17 Dec 2008 14:24:42 +0000, Daniel James wrote: > > You would therefore have to design a 'smart' USB power cord that could > perform the required negotiation with the USB host and arrange for the > peripheral to draw power at the higher level if negotiation was > successful and at the lower power otherwise. > Thats what I meant: I was using 'dumb' as a short-hand for a mini-brick with USB plug on one end and USB socket on the other, IOW no useful function except to supply more than 100 mA via its socket. > Cheers, > Daniel. -- martin@ | Martin Gregorie gregorie. | Essex, UK org |
From: Daniel James on 18 Dec 2008 06:23 In article news:<gib6ka$af8$4(a)localhost.localdomain>, Martin Gregorie wrote: > Thats what I meant: I was using 'dumb' as a short-hand for a > mini-brick with USB plug on one end and USB socket on the other, > IOW no useful function except to supply more than 100 mA via its > socket. IIUYC that still wouldn't help. A correctly-designed USB device will either negotiate for 500mA or will draw only up to 100mA. Any device that can't negotiate should be designed not to draw more than 100mA. If you connect a 'dumb' USB device (one that can't negotiate) via a 'smart' cable (one that can perform the negotiation itself) to a PC which can supply 500mA the PC will happily make 500mA available ... but the device still won't draw more than 100mA because it doesn't know that negotiation has taken place. The secondary power USB cable of the LG "USB Powered" DVD-writer we were discussing doesn't connect to the drive with a USB connector, but with a simple centre-positive push-in barrel connector (marked "DC IN 5V"). Cheers, Daniel.
From: Ian Rawlings on 18 Dec 2008 07:24 On 2008-12-18, Daniel James <wastebasket(a)nospam.aaisp.org> wrote: > In article news:<gib6ka$af8$4(a)localhost.localdomain>, Martin Gregorie > wrote: >> Thats what I meant: I was using 'dumb' as a short-hand for a >> mini-brick with USB plug on one end and USB socket on the other, >> IOW no useful function except to supply more than 100 mA via its >> socket. > > IIUYC that still wouldn't help. > > A correctly-designed USB device will either negotiate for 500mA or will > draw only up to 100mA. Any device that can't negotiate should be > designed not to draw more than 100mA. If you ever find a correctly-designed USB device let us know so we can gather around it and gawp ;-) I have numerous USB recharging cables, just a USB plug on one end and a jack plug on the other, and the two devices at either end are left to sort it out, thankfully it all works well! From the speed of recharging of some of the devices, it looks like it's being supplied with more than 100mA. One of them is a NiMH AA recharger, 4x AA cells being recharged at about 400mA total according to the docs. Thankfully the widescale flouting of the USB regs hasn't resulted in any fried USB ports for me yet! -- Blast off and strike the evil Bydo empire! http://youtube.com/user/tarcus69 http://www.flickr.com/photos/tarcus/sets/
From: Martin Gregorie on 18 Dec 2008 09:15
On Thu, 18 Dec 2008 11:23:14 +0000, Daniel James wrote: > > The secondary power USB cable of the LG "USB Powered" DVD-writer we were > discussing doesn't connect to the drive with a USB connector, but with a > simple centre-positive push-in barrel connector (marked "DC IN 5V"). > I have a Formac 2.5" HDD with two USB plugs, which is the arrangement I thought we were discussing. It communicates with one of them and gets additional power from a USB 1.0 rig via the second, which isn't needed if the PC uses USB 2.0. My hypothetical microbrick would go between the second cable and the PC (if it was a stand-alone) or replace the second plug and would be just bright enough to do the negotiation and then supply power to the device on the first plug. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |