| Jack Erbes 2007-05-30, 10:33 pm |
| Dominic Sexton wrote:
> In article < 135rfi1d41ee19c@corp
.supernews.com>, Dale DePriest
> <Dale@gpsinformation.het> writes
>
> The USB specifications require that USB ports or host controllers and
> powered hubs have in built current limiting to ensure that the port (and
> the host / hub) are not damaged by devices connected to the port
> attempting to draw too much current.
>
> No damage will occur to hardware that adheres to the specifications no
> matter what load is connected to the power supply from the port.
You can buy USB hubs that come with an external DC adapter so that you
can connect heavier loads through a single port. I have one that
converts one USB port to four ports.
The four ports all use the 5VDC from the computer unless I plug the DC
adapter in. Wit the DC adapter plugged in the hub is disconnected from
the computer's 5VDC source and the ports on the hub have a shared 5
Amp source.
Those are a good choice for connecting (via LPT to USB and serial to USB
adapters) older printers and scanners that have a heavy draw. Things
like the HP LaserJet II, III and IV series printers that seem to have a
service life measured in decades, not years.
I'm still using a LaserJet 4L that is dated march 1994, I got it in 2000
(at a yard sale for $2.00), and other than one toner cartridge it has
needed nothing since I got it.
Those printers honored the work ethics of the HP founders, the current
HP stuff has a service life that is about 2 days longer than the
warranty as near as I can tell.
Jack
--
Jack Erbes in Ellsworth, Maine, USA - jackerbes at adelphia dot net
(also receiving email at jacker at midmaine.com)
|