Hello,
I have a D-Link DSB-H7 (7 port, self powered USB 1.x hub.)
http://www.dlink.com/products/usb/dsbh7/
I only want to use it to provide power to long-haul VGA extenders,
which are USB-powered.
The problem is, the DSB-H7 appears to need to be plugged in to a
computer (virtual root hub, whatever) before it will turn on the
power.
I suspect the reason for this was some braniac engineer somewhere
saying, "Well, OBVIOUSLY we don't want to power attached devices if
the computer itself is not on!" Well, duh. It's probably part of the
USB spec.
Solutions I have already tried:
1) Took a 3' USB A to B cable, and cut off the A end. I'm left with
four wires + ground, leading up to a B end. Pluged the B end into the
hub and shorted across all unique pin combinations (data to data,
power to power -- data to power, I didn't care -- hoping that one
combination would trick the hub into providing power. Cons: I
might've shorted out one of my hubs, though at least I doubt that it,
in turn, shorted anything out down the chain. And, of course, it did
not work.
2) Took a radio shack 5V power adapter and tried using that on all pin
combinations; since USB uses 5V, I figured that it might sense power
coming from the upstream computer and trip some solid-state relay for
the power on all of the downstream ports... Cons: if I thought that
shorting the pins to one another was bad, I'm sure this was worse. And
of course, it did not work.
Solutions I have brainstormed but not yet tried:
1) open up the hub and try to modify it, shorting across a solid state
relay (I assume) so that power is always on. The cons are: this would
require that I do this for all of the hubs, and it means I can't ever
re-use the hub for another applications.
2) modify one hub and daisy-chain all of the others to it. Cons: Not
sure if modifying one hub to 'fake it out' will propagate down the
chain.
I don't even know how the heck to search google for this answer
because it's so specific and obscure, requires knowledge of the USB
pinouts and possibly spec.
An acceptable answer could include:
1) Plans for building an inexpensive IC to attach to my hacked cable,
if that's what it requires -- I have to order from digikey soon anyway
for something else;
2) A manufacturer who sells a product for less than $20 which will
solve my problem, and whose solution will (preferably) propagate
through all daisy chained hubs.
Anyone? Anyone.... Bueller?
If you can answer this question, you'll save Christmas! (Well, okay,
you'll make an entire "CyberSpace Gallery" in our Planetarium/Museum
light up in festive cheer. Close enough.)
Tips also available, the neater/more reliable the solution is.
Best,
Thom Brooks
Computer Support Supervisor
Adler Planetarium and Astronomy Museum
Chicago, IL |
Request for Question Clarification by
duncan2-ga
on
17 Dec 2002 21:42 PST
Hi unithom,
Can you tell me a little bit more about the USB-powered VGA extender
you're using? I'm not very familiar with USB/VGA solutions. If the
only reason you need the hub is to provide power to the extender (i.e.
the VGA signal isn't being compressed and passed somehow down the USB
chain), then this seems to be just a 'how can I get power to a
USB-powered device' question--in which case you might be able to
eliminate the hub entirely.
If the extender just needs the 5v/500ma, you might be able to wire a
power supply directly to it, instead of having to worry about USB host
protocols.
On the other hand, if you really do need the hub, then you're going to
need a root hub on the chain, somehow. If a PC isn't a possibility,
then the only thing I can suggest is perhaps some USB test equipment,
like the standalone root hub from RPM Systems Corporation
(http://www.rpmsys.com/ ). It's designed to work with a computer via
RS-232, but the docs seem to suggest that can work alone as well. I
suspect this doesn't meet your $20 limitation though.
Regards,
Duncan2-ga
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Clarification of Question by
unithom-ga
on
17 Dec 2002 22:45 PST
Using a computer: while it might SEEM to be the easiest and most
brainless solution,
I've BEEN using one of the machines as the root hub to drive all of
the other hubs & screens; guess which machine totally fritzed
yesterday? Hint: it prompted me to post this question. So I'm trying
to separate the functionality of a machine providing content (maybe
someone will want it turned off, etc) from the functionality of a
device providing power to these DAs.
Here's a page on the DAs:
http://www.extron.com/product/product.asp?id=p2da1
P/2 DA1 (USB) 60-319-03
Specs are all there, but I'm pretty sure that these are JUST drawing
the power from the hubs. But we already have the hubs, and these
Extrons already have USB ends on them. (And they weren't cheap. Extron
makes good, but pricey, stuff.)
Besides: chopping up 55 already existing USB connectors and wiring
them to a power supply is not my idea of a party! Too much room for
human error and it'd take a while.
Our main reason for going with this 'solution' (the 7 port hubs) was
simply because they were cheaper than the custom (read: way too
expensive) solution offered us by the contractor who built the space.
Another factor: space is at an EXTREME premium here. We are
line-driving approximately 55 computers' VGA and usb HID's to a room
250 feet away. Half go to custom classroom desks (lockable flip-up top
conceals mercury-switch activated flatscreen display, touchpad and
keyboard); the other half have their VGA converted to pigtail (5 wire
BNC) which then go to plasma screens or LCD screens that display
video, slide shows, interactives, and other content.
So, in a space smaller than my clothes closet (which is very small),
we're running an entire computer classroom and a gallery with over 40
screens. (Cool, huh?) But my boss would SCREAM bloody murder if I
wanted to put even one more machine in there, just to keep these hubs
alive.
Therefore: small form factor -> pricier computer. And depending on an
entire computer (read: complicated, involves hard drive, must be
happily booted into some OS probably before ever considering turning
on its USB stuff...) to daisy-chain all of these hubs means that if
one computer dies (for whatEVER reason), half of the screens fail.
During visitor hours we want 5 9's uptime so nobody has a reason to
complain!
I'm asking the impossible, I know -- cheap, easy, fast. Pick one. :)
Did I mention that it's the end of the year and we don't have a
budget? (Stop banging your heads on your desks... ;)
Duncan, you've got the most 'can-do' attitude; I will see if rpm sys'
device would work, and if it's a reasonable solution (pricewise and
does what we want), or if their people are able to help us, it's all
yours.
PS: Omnivorous: thanks! A lot of people get really mad if our camera
is ever unavailable, so we know what a following it has.
Unfortunately, when important people are here for special events,
people in suits and black sunglasses make us turn it off. :)
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