Corrections etc Welcome
Too many (self included) have had or still see USB problems,
I guess too often it gets blamed, on mystical `non USB-2
compliant cables' , which might occasionally even be true, if
perhaps some cables aren't screened too well, or are too
thin, but I think for many things there's a much simpler
explanation: Inadequate power & bad connections.
allows power ratings on devices to be seen with `usbdevs
USB spec. allows devices to draw no more than 0.5 Amps =
But devices such as external disks Lie & say "self
powered", even when no power supply is connected. What this
must mean is "Device is capable of or should be self powered"
- but does not have intelligence to realise currently Not
self powered. ... & sometimes such disks may work, &
sometimes not ... (what's the betting more likely if the hub
power is plugged in ;-)
Power consumption varies. If your computer or hub power
supply is strained, (or cable kinked & some wires
fractured to make a high resistance) not all devices may be
affected the same way.
Example: Some USB memory sticks power ratings from
- 256 M - Celldisk 100 mA
- 512 M - Kingston 100 mA
- 512 M - MyFlash 80 mA (stick now dead & gone)
- 1 Gig - Integral 200 mA (this has a 1.4M pretend floppy
lock/ file system, maybe using more high power logic
- 2 Gig Sony - (Many were Defunct) 100 mA
- 2 Gig SanDisk 100 mA
- Havit USB Keyboard is rated on back as 0.25 Amps
- USB to PS/2 converter "Semi Tech PS/2 Keyboard - PS/2
Mouse" reports with `usbdevs -v` 100 mA, regardless if
mouse & keyboard plugged into it.
- Larger Havit PS/2 keyboard (that I use through a USB to
PS/2 converter is not labelled for power, so no idea what
- A small blue Kensington mouse isn't power labelled, but
`usbdevs -v` reports 100 mA
- A mouse given away as a pharmaceutical promotion
reports: "low speed, power 98 mA, config 1, USB Optical
Mouse(0x00c3)" (nice to see a non round number :-)
- [ I'll solder up a socket to monitor power consumption
- ( Internal mouse pad inside laptop reports 100mA.
Disk: Toshiba MK1403MAV 12.7mm IDE 1.44GB Paper label
say 0.7 A.
- MK6021GAS HDD2183 MQ60kfGG 9.5mm IDE 16 16,383 2 1 60GB
5V 4.7W on startup, 2.6 Watts seeking, 2.3 R/W
Really thin cables in spring loaded rewind drums
I've just confirmed (as expected): That two ultra thin usb
cables, on rewinding drums, wont pass enough power to an
external disk (small laptop disk in small box, not a big
chunky 3.5" disk) to start disk spinning (but will supply
enough power to keep disk spinning if already started), So
external power needs to be supplied direct to disk from
transformer (even though thin cable carries sufficient power
to turn on LED that doubtless works at lower voltage, &
too high a cable resistance to supply enough power than disk
motor & drive & adapter electronics. Confirmed as
when wobbling it, I could not feel disk spinning.
With external power direct to disk, then it works (&
one can feel it spinning too). Reason of course must be cable
is simply too thin for disk power. Same disk works without
direct power, if using a bit thicker USB extension cable to a
The disk was not recognised (no /dev/da* on FreeBSD) unless the
hub was powered up, or external power for the disk
This all at USB-1 speeds, so no mystical speculation about
magic of USB 1 v. USB 2 cables applies ;-)
Of 3 USB power supplies:
- 2 came with 2 port USB 2 card from Belkin.
- 1 Manufacturer DVE is rated 5V 2.4 Amp. Plug is too
short to fit reliably in the Belkin Cardbus (credit card
size) USB adaptor. Plug is far too short (7.5 mm) to do
much more than wobble quite unreliably in drive box garyj@
gave me. Plug was long enough to fit in a Belkin 4 port
USB-1 hub though. I cut off 2 mm of plastic on end of
- Other PSU looks identical shape but labelled Achme
Corp, rated 3.0 Amp & Longer plug, 9.5 mm, which sits
well in Belkin USB cardbus adapter & in garyj@ drive
box. Belkin card has 3 A written on it.
- The transformer of Zediworks 4 port USB2 hub is
labelled 2.1 Amps Zediworks (subd reports an NEC chip) Hub
also falsely reports "self powered" even when no power is
plugged into hub or disc
- All are 5V, positive centre pin, though different size
Small plugs: One should also remember with these smaller than
normal size USB plugs, that they're not as rugged as the full
size ones, if they wobble the power may get interrupted to
the disk, the disk may then reset confusing the Op Systems.
One small USB plug I had was too short: 6mm instead of 7
mm It didn't fit properly into external disk chassis (chassis
from garyj@, with Grey plastic fascia) Of course thus a
potential double problem of failing power & failing USB
signal. Cutting off 1 mm of plastic made it work.
Sometimes the USB hub locks up (crashes). Same solution as
anything else, removing external power & USB cable to
laptop (& drive if powered I guess) seems to reset
A power related problem. Likely it could do similar to other
OS's eg Linux & XP.
Cabling - Pin Outs
On both full size flat (A) plug & square (B) plug, 2 of
the pins (outer 2 on A) are longer to stabilise power before
devices can signal on other 2 wires.
USB port on main boards
|Plug at peripherals.
(B) Plug on cable, from single upstream side of a hub
to a PC.
|Socket (jack) at controller.
(A) As on a PC chassis & 4 outputs of a Hub.
(B) Single Socket on chassis of a 4 port hub
Wire Colour Code Other
||Power, VCC, SVCC, +5V
||P-, Data-, SBD-
||P+, DATA+, SBD+
|Black, Blue, Brown
||Ground, Grnd, Gnd
With a cable (from garyj@), transparent, with: 1 male
flat plug forking to 2 cables:
- 1 long thick cable, plaited screen, to a mini usb
- short thin cable, with simpler spiral (non plaited)
screen going to a combination male + female:
Ohm Meter shows:
- The thick long cable implements all 4 wires end to
- The Male + Female plug implements all 4 wires.
- The short thin cable only implements 2 wires:
- Normal Single Use Configuration: A plug on
thick cable connecting straight to camera or external
- Use just 1 socket to also Charge a 2nd
device connected to the combi. male + female via
thin cable, while simultaneously the standard size
cable A plug connects PC to miniature device eg disk
drive/ camera to be controlled from PC.
- Extra power for non self powered External
Disk (laptop sized) : If no external power supply
is plugged in (or available), & disk perhaps wants
1.0 Amps; 2 USB sockets on your hub/ PC/ laptop could
supply it, even if each limit supply to just the USB
specified 0.5 Amps. (Note if silicon is not identical
one may deliver more than the other [& possibly
overheat or limit at less than 1.0 ?]
- Use just 1 socket to also Charge miniature plug
connected device (eg a camera or phone), while
simultaneously connecting through male + female adapter
to another cable with an A plug.
With a black cable with 1 Full size male plug with 2 black
cables from it
- 1 cable going to mini male plug
- 1 cable going to another full size male plug
It's same electrically as previous cable set: The thinner
of the 2 cables only has 2 power wires, no signal wires.
As is has no female socket, the last of the cases listed
above is not viable.
Grey cable with Male to male type A plugs each end,
Male type A plug adaptor
I'm not clear what the purpose of these is, but ...
With a double socket I've cut off a dead main board I'll
be able to make a male to female current measuring