USB Cable too long?

On 08/30/2018 03:01 PM, Fokke Nauta wrote:

[snip]

Yes, USB hubs do. But my USB switch is a simple switch. Connecting one
wire to the input connector or the other wire.

I remember something about how such a simple switch is "wrong" because
on the impedance mismatch. However, it often works.

Which wire? There are 4 wires in a USB cable.

Fokke

--
Mark Lloyd
http://notstupid.us/

"Death is an experience best avoided, as it makes reliable internet
access difficult to obtain."

On 8/30/2018 12:55 PM, Fokke Nauta wrote:
On 30/08/2018 18:36, NotMe wrote:
On 8/30/2018 8:26 AM, Fokke Nauta wrote:
On 30/08/2018 15:14, Mayayana wrote:
"Fokke Nauta" wrote

| Could it be that total cable length is too much?
| Why is the scanner then working allright with my pc?

* I wouldn't dismiss the other two answers, but I have
found that hardware varies. And some devices will
tell you in their manuals what the length of a cable
can be.

* We have a high-end Epson photo printer and a
budget, everyday printer. (I think the latter may
be HP.) Only one can fit near the computer, so
there's a 12' USB cord for the other. The Epson
simply won't tolerate that cord. The everyday
printer doesn't mind at all.

* So it could be the ports, the switch, the systems....
But it's also possible that you've set it up at the
high end of the cable length it will tolerate. On the
bright side, all of the ideas presented so far are easy
to test.




If the scanner is the problem, that it can't handle the length of the
USB cables, it would be a problem with my pc as well. Same type of
cables, same length. But my system works well with the scanner.
Tried different USB inputs on my wwife's pc. Didn't make a difference.
Motherboard perhaps? Too old? USB 2.0 inputs, whereas my pc has USB
3.0 inputs.
Should this make the difference?

Fokke
USB 3 puts out more power than USB 2, get a powered USB hub.

To my knowledge an USB hub is to connect multiple USB devices to one pc.
What I'm doing, is to connect one USB-device with two pc's. Not
simultaneously, but either one or the other. One can't use a hub for that.

Fokke
Can you set up the device on one computer and then share it with the
other computer, wireless or Ethernet?

On 30/08/2018 23:50, Paul wrote:
Ken Blake wrote:
On Thu, 30 Aug 2018 19:55:11 +0200, Fokke Nauta
wrote:

To my knowledge an USB hub is to connect multiple USB devices to one pc.


Yes.


What I'm doing, is to connect one USB-device with two pc's. Not
simultaneously, but either one or the other. One can't use a hub for
that.


Have you tried using a hub for that, reversing its connections? I'm
not saying that it will work, since I don't know and I also doubt it,
but it might be worth a try.

Let me ask why you want to do that. I sometimes move a thumb drive
from a USB port of my computer to one on my wife's. It's easy enough
to do that, so I've never the need for something like what you're
talking about.

A "hub" has active regeneration in the path. The upstream
is the host, the downstream is the peripheral.

Upstream
|
|
packet regeneration
| | | |
Down Down Down Down
Stream Stream Stream Stream

A "mechanical switch", doesn't need anything.
This could also be implemented with QuickSwitches
or transmission gates or something similar.
The total cable on either side ("path length")
cannot exceed 15 feet. If you put 15 feet of cable
on upstream, 15 feet on downstream, that's 30 feet total
and too long. Only if the switch happened to have
digital regeneration (effectively, be a switch with
a 1-port hub built into each path), could you
support 15 foot cables on either side. I've not
seen a photo of what's in these things, to know,
but the price suggests a cheesy mechanical switch.

Upstream1 Upstream2
| | | |
D+ D- D+ D-
| | | |
\ \ / /
\ \ / /
Mech
Switch A-B
| |
D+ D-
Downstream
| |
To USB Printer

That's my interpretation, and the above
assumes USB2. I don't know how or if,
all the same solutions exist for USB3.

USB3 has TX+ TX- GND RX+ RX- === 5GHz interface USB3 rate

+5V D+ D- GND === 480Mbit/sec USB2 interface

and the 5GHz part is similar in design to
PCI Express or SATA differential signaling.

The USB2 four pin interface is not nearly
the same quality. In its lowest speed modes,
it runs single-ended and the wiring is
also half-duplex, which doesn't help matters.

The nice thing about USB3, is it's full duplex,
you can TX and RX at the same time, and the role
and function of each pin is more fixed (the RX pair
can have a 100 ohm resistor permanently affixed
as flyby termination, that sort of idea).

Paul

Thanks, Paul.
This makes things clear.

Fokke

On 31/08/2018 03:30, NotMe wrote:
On 8/30/2018 12:55 PM, Fokke Nauta wrote:
On 30/08/2018 18:36, NotMe wrote:
On 8/30/2018 8:26 AM, Fokke Nauta wrote:
On 30/08/2018 15:14, Mayayana wrote:
"Fokke Nauta" wrote

| Could it be that total cable length is too much?
| Why is the scanner then working allright with my pc?

I wouldn't dismiss the other two answers, but I have
found that hardware varies. And some devices will
tell you in their manuals what the length of a cable
can be.

We have a high-end Epson photo printer and a
budget, everyday printer. (I think the latter may
be HP.) Only one can fit near the computer, so
there's a 12' USB cord for the other. The Epson
simply won't tolerate that cord. The everyday
printer doesn't mind at all.

So it could be the ports, the switch, the systems....
But it's also possible that you've set it up at the
high end of the cable length it will tolerate. On the
bright side, all of the ideas presented so far are easy
to test.




If the scanner is the problem, that it can't handle the length of the
USB cables, it would be a problem with my pc as well. Same type of
cables, same length. But my system works well with the scanner.
Tried different USB inputs on my wwife's pc. Didn't make a difference.
Motherboard perhaps? Too old? USB 2.0 inputs, whereas my pc has USB
3.0 inputs.
Should this make the difference?

Fokke
USB 3 puts out more power than USB 2, get a powered USB hub.

To my knowledge an USB hub is to connect multiple USB devices to one
pc. What I'm doing, is to connect one USB-device with two pc's. Not
simultaneously, but either one or the other. One can't use a hub for
that.

Fokke
Can you set up the device on one computer and then share it with the
other computer, wireless or Ethernet?

No, I'm afraid not.

Fokke

On 31/08/2018 01:38, Mark Lloyd wrote:
On 08/30/2018 03:01 PM, Fokke Nauta wrote:

[snip]

Yes, USB hubs do. But my USB switch is a simple switch. Connecting one
wire to the input connector or the other wire.

I remember something about how such a simple switch is "wrong" because
on the impedance mismatch. However, it often works.

Which wire? There are 4 wires in a USB cable.

Fokke


Sorry - I meant cable.

Fokke

On 30/08/2018 22:15, Zaidy036 wrote:
On 8/30/2018 8:00 AM, Fokke Nauta wrote:
Hi all,

We have an Epson flatbed scanner, V600 Photo. It is connected to an
USB switch by a cable of 1 meter. One output of the switch is
connected with my pc by a cable of 1.8 meter. Scanner works fine. The
other output of the switch is connected to the pc of my wife (W7 Pro
64b, mobo: ASUS P7P55D). This cable is also 1.8 meter. On this pc the
scanner is recognized, the system bleeps when the scanner is turned
on. Scanning is impossible, it gets stuck, the led on the scanner
keeps flashing, and nothing further happens. Doesn't make a difference
when I use Photoshop or the Epson utility for scanning.
When I connect the scanner straight away to my wife's pc with a cable
of 1 meter, it works fine.
I use Belkin USB cables, thought they are good quality. The USB switch
is König, passsive.

Could it be that total cable length is too much? Why is the scanner
then working allright with my pc?
What type of cable should I order to make sure the scanner works
allright with my wife's pc?

Fokke

Exchange PC connections on switch and observe if that exchanges which PC
works.


I already did that. No difference.

Fokke

On 31/08/2018 00:41, VanguardLH wrote:
Fokke Nauta wrote:

We have an Epson flatbed scanner, V600 Photo. It is connected to an USB
switch by a cable of 1 meter. One output of the switch is connected with
my pc by a cable of 1.8 meter. Scanner works fine. The other output of
the switch is connected to the pc of my wife (W7 Pro 64b, mobo: ASUS
P7P55D). This cable is also 1.8 meter. On this pc the scanner is
recognized, the system bleeps when the scanner is turned on. Scanning is
impossible, it gets stuck, the led on the scanner keeps flashing, and
nothing further happens. Doesn't make a difference when I use Photoshop
or the Epson utility for scanning.
When I connect the scanner straight away to my wife's pc with a cable of
1 meter, it works fine.
I use Belkin USB cables, thought they are good quality. The USB switch
is König, passsive.

Could it be that total cable length is too much? Why is the scanner then
working allright with my pc?
What type of cable should I order to make sure the scanner works
allright with my wife's pc?

Is it actually a USB switch or is it a USB hub?

It's an USB switch, mechanically.

https://www.allekabels.nl/usb-schake...BoCZnEQAvD_BwE

(In Dutch, though. Couldn't find an English one)

Are there switches
(mechanical or software-controlled) as to which ONE output of the USB
switch will currently be connected to the USB port on the PC to which
that USB switch is connected? That is, can only one USB device be used
at a time with the USB "switch"?

If only one USB device on the output side of the USB switch can be used
at a time then it is a switch. There would be some means of selection
which output port got connected to the input port of the switch, and the
other output ports are disconnected. If all USB devices are [expected
to be] concurrently accessible that are connected to the output of the
"switch" then it really is a USB hub. Is it really a hub and there are
multiple switches on it to simply disable/unpower the individual output
ports?

Got a model of the USB switch? You mentioned "Konig" but they've had
several different models of USB switches some of which are discontinued.
At Konig's site, the only one that I found they currently produce is:

https://www.konigelectronic.com/comp...h-black-795543
which warns:
This switch is not compatible with devices that requires a constant
connection to a computer. Usually these are devices like
multifunctionals or laser printers.

That is used to share a USB device (printer, scanner, etc) to 2
computers. That is, its input port goes to the USB device and its
output ports go to the USB ports on 2 different computers. That way,
when you press the toggle button, the one USB device gets toggled
between the two computers' USB ports.

That USB switch itself requires no drivers. It merely mechanical (well,
electronically) performs a change in pathing between the one input port
from the USB device to the two output ports to the computers. I'm not
sure the switchover of the 5V power (coming from the PC's USB port)
would be smooth. Which PC's USB port would be supplying the 5V power
during a switch? Does it have some electronics to smooth out the power
switch when changing which PC to which the USB device is connected
(which means it would need a capacitor to maintain power during the
glitch at the time of the switch). That momentary loss of 5V power
during the switch could force the USB device to initialize again.

The Epson V600 scanner has its own A/C power supply, so it doesn't need
and probably doesn't use the 5V from the USB connection. However, it's
possible the USB 5V power is used when the USB device goes into sleep
mode (to power the sensing logic in the USB device to know when it
should wake up).

The total length of the USB connection would be from the USB device's
USB port through the length of USB cable connected to it to the USB
switch, the pathing internal to the USB switch, and then the length of
USB cable from the USB switch to whichever PC the switch was currently
configured to connect.

USB device (scanner) - 1 meter USB cable - USB switch - 1.8 meter USB
cable - computer's USB port. That's just a tiny bit over 2.8 meters.
The maximum length for a USB2 cable is 5 meters for full-speed USB
devices, 3 meters for low-speed USB devices. To go further means you
need to insert an active USB extender aka repeater (amplifies and cleans
up the signal and ensures 5V gets to the USB device - cheap ones don't
do the latter, they may recondition the signal but pass on the power
as-is). USB 3 has a max length of 3 meters. According the Konig's
specs, their 2-port USB switch only handles USB 2.

There is also the issue with handshake timing; see:
https://superuser.com/a/1105099

If the switch between computer's for the 5V power isn't smooth or the
switch provides its own power to the USB device, a glitch could result
in the device reinitializing which will be a hell of lot longer than the
link failure timeout. The Konig switch has no A/C power adapter, so it
must switch the 5V power from the USB cable to one computer to the 5V
power from the USB cable to the other cable but without dropping the
power. I don't know what your USB device(s) has(have) to cover very
short power glitches (outages). Konig's specs are minimal, so no
information on how they smooth the 5V power switchover. Their "support"
page, after entering "CMP-USBSW2" and selecting their USB switch, just
dumps me back to their product page which tells me nothing about HOW
that switch operates. Back in the mechanical switch era, you needed a
make-before-break switch to ensure no disruption in power. All they
note is the statement that I commented under the link above for their
product page.

Besides the issue of switching the power to the device from the two
computers, how about USB enumeration? When you toggle, the same device
will now appear as a new connect to the computer to which you toggled.
Handshaking takes some time and there isn't an instantaneous bong-bing
tone notifying you the device has sent its presentation data and becomes
recognized. That's probably why Konig mentions their switch won't work
with devices that require a constant connection (once connected). Those
devices don't tolerate disconnects without having to reinitialize again.

They dis-recommend you using their USB switch with multifunctional (MFC)
and laser printers. Is a scanner that different, especially if it
expects to use 2-way communication to report status of the device? They
provide a passive USB switch. I've seen powered USB switches that claim
"Stable connection: USB 2.0 sharing switch with a separate micro female
port for optional power, optimizing its compatibility with more devices,
such as ...", noted at:

https://www.amazon.com/UGREEN-Select.../dp/B01MXXQKGM
(but you have to provide the power adapter that has a micro USB
connector)

By providing their own power to the USB device(s), they don't encounter
glitches in the source USB's 5V power during the switch. That one
happens to be a USB3-capable switch.

Have you tried powering down the scanner BEFORE using the USB switch to
toggle between PCs. PCs are up, power down the scanner, press the
toggle button on the USB switch, power up the scanner. Else, it looks
like you need to use a powered USB switch (not USB powered but line
powered). Alternatively, add a powered USB hub between the USB switch
and the USB device (scanner). I've seen those sell new for under $10
but that's on the low-end, like:

https://www.newegg.com/Product/Produ...9SIA6SY2B99168
No spec on the adapter to know how much load it can handle across all 7
ports, and it's too small to handle a full load on all of them.

https://www.newegg.com/Product/Produ...82E16817111402
They give a 3A rating for their power adapter to spread across all USB
device ports.

https://www.newegg.com/Product/Produ...82E16817182057
Although the same price as the Dlink, their adapter puts out only 2A.

I think I've seen powered USB hubs that had a 48W power converter
(probably for 4-port USB3 powered hub with a 2.4A charging port) but
that's a large brick sitting in the middle of the cord, not a walwart
hanging from an outlet.

Sorry - my previous post was accidentally sent prematurely.

On 31/08/2018 00:41, VanguardLH wrote:
Fokke Nauta wrote:

We have an Epson flatbed scanner, V600 Photo. It is connected to an USB
switch by a cable of 1 meter. One output of the switch is connected with
my pc by a cable of 1.8 meter. Scanner works fine. The other output of
the switch is connected to the pc of my wife (W7 Pro 64b, mobo: ASUS
P7P55D). This cable is also 1.8 meter. On this pc the scanner is
recognized, the system bleeps when the scanner is turned on. Scanning is
impossible, it gets stuck, the led on the scanner keeps flashing, and
nothing further happens. Doesn't make a difference when I use Photoshop
or the Epson utility for scanning.
When I connect the scanner straight away to my wife's pc with a cable of
1 meter, it works fine.
I use Belkin USB cables, thought they are good quality. The USB switch
is König, passsive.

Could it be that total cable length is too much? Why is the scanner then
working allright with my pc?
What type of cable should I order to make sure the scanner works
allright with my wife's pc?

Is it actually a USB switch or is it a USB hub?

It's an USB switch, mechanically.

https://www.allekabels.nl/usb-schake...BoCZnEQAvD_BwE

(In Dutch, though. Couldn't find an English one)

Are there switches
(mechanical or software-controlled) as to which ONE output of the USB
switch will currently be connected to the USB port on the PC to which
that USB switch is connected? That is, can only one USB device be used
at a time with the USB "switch"?

Yes, correct. The USB device is connected to only one of the pc's.

If only one USB device on the output side of the USB switch can be used
at a time then it is a switch. There would be some means of selection
which output port got connected to the input port of the switch, and the
other output ports are disconnected. If all USB devices are [expected
to be] concurrently accessible that are connected to the output of the
"switch" then it really is a USB hub. Is it really a hub and there are
multiple switches on it to simply disable/unpower the individual output
ports?

No, it's a switch.

Got a model of the USB switch? You mentioned "Konig" but they've had
several different models of USB switches some of which are discontinued.
At Konig's site, the only one that I found they currently produce is:

https://www.konigelectronic.com/comp...h-black-795543

No, that's not the one. See my url above

which warns:
This switch is not compatible with devices that requires a constant
connection to a computer. Usually these are devices like
multifunctionals or laser printers.

Yes, that's correct, but:
It's just a switch. When you set it to a pc, and whitch the USB device
on, and don't toggle the switch any more, it should just work.

That is used to share a USB device (printer, scanner, etc) to 2
computers. That is, its input port goes to the USB device and its
output ports go to the USB ports on 2 different computers. That way,
when you press the toggle button, the one USB device gets toggled
between the two computers' USB ports.

Correct. But you should not toggle it when the usb device is on.

That USB switch itself requires no drivers. It merely mechanical (well,
electronically) performs a change in pathing between the one input port
from the USB device to the two output ports to the computers. I'm not
sure the switchover of the 5V power (coming from the PC's USB port)
would be smooth. Which PC's USB port would be supplying the 5V power
during a switch? Does it have some electronics to smooth out the power
switch when changing which PC to which the USB device is connected
(which means it would need a capacitor to maintain power during the
glitch at the time of the switch). That momentary loss of 5V power
during the switch could force the USB device to initialize again.

The Epson V600 scanner has its own A/C power supply, so it doesn't need
and probably doesn't use the 5V from the USB connection.

Correct

However, it's
possible the USB 5V power is used when the USB device goes into sleep
mode (to power the sensing logic in the USB device to know when it
should wake up).

No, the scanner doesn't get into sleep mode. And as you said, it has its
own power supply.

The total length of the USB connection would be from the USB device's
USB port through the length of USB cable connected to it to the USB
switch, the pathing internal to the USB switch, and then the length of
USB cable from the USB switch to whichever PC the switch was currently
configured to connect.

USB device (scanner) - 1 meter USB cable - USB switch - 1.8 meter USB
cable - computer's USB port. That's just a tiny bit over 2.8 meters.
The maximum length for a USB2 cable is 5 meters for full-speed USB
devices, 3 meters for low-speed USB devices. To go further means you
need to insert an active USB extender aka repeater (amplifies and cleans
up the signal and ensures 5V gets to the USB device - cheap ones don't
do the latter, they may recondition the signal but pass on the power
as-is). USB 3 has a max length of 3 meters. According the Konig's
specs, their 2-port USB switch only handles USB 2.

There is also the issue with handshake timing; see:
https://superuser.com/a/1105099

If the switch between computer's for the 5V power isn't smooth or the
switch provides its own power to the USB device,

No, it doesn't. It's just a simple mechanical switch.

a glitch could result
in the device reinitializing which will be a hell of lot longer than the
link failure timeout. The Konig switch has no A/C power adapter, so it
must switch the 5V power from the USB cable to one computer to the 5V
power from the USB cable to the other cable but without dropping the
power.

I don't think so. When toggling the existing connections will be cut off
before the other connections will be made. But it should not be toggled
when the scanner is on.

I don't know what your USB device(s) has(have) to cover very
short power glitches (outages). Konig's specs are minimal, so no
information on how they smooth the 5V power switchover. Their "support"
page, after entering "CMP-USBSW2" and selecting their USB switch, just
dumps me back to their product page which tells me nothing about HOW
that switch operates. Back in the mechanical switch era, you needed a
make-before-break switch to ensure no disruption in power. All they
note is the statement that I commented under the link above for their
product page.

I assume it's break before make.

Besides the issue of switching the power to the device from the two
computers, how about USB enumeration? When you toggle, the same device
will now appear as a new connect to the computer to which you toggled.
Handshaking takes some time and there isn't an instantaneous bong-bing
tone notifying you the device has sent its presentation data and becomes
recognized. That's probably why Konig mentions their switch won't work
with devices that require a constant connection (once connected). Those
devices don't tolerate disconnects without having to reinitialize again.

They dis-recommend you using their USB switch with multifunctional (MFC)
and laser printers. Is a scanner that different, especially if it
expects to use 2-way communication to report status of the device? They
provide a passive USB switch. I've seen powered USB switches that claim
"Stable connection: USB 2.0 sharing switch with a separate micro female
port for optional power, optimizing its compatibility with more devices,
such as ...", noted at:

https://www.amazon.com/UGREEN-Select.../dp/B01MXXQKGM
(but you have to provide the power adapter that has a micro USB
connector)

Perhaps this may do the trick?

By providing their own power to the USB device(s), they don't encounter
glitches in the source USB's 5V power during the switch. That one
happens to be a USB3-capable switch.

Have you tried powering down the scanner BEFORE using the USB switch to
toggle between PCs.

Ofcourse. I toggle the swwitch only when the scanner is off.

PCs are up, power down the scanner, press the
toggle button on the USB switch, power up the scanner. Else, it looks
like you need to use a powered USB switch (not USB powered but line
powered). Alternatively, add a powered USB hub between the USB switch
and the USB device (scanner). I've seen those sell new for under $10
but that's on the low-end, like:

https://www.newegg.com/Product/Produ...9SIA6SY2B99168
No spec on the adapter to know how much load it can handle across all 7
ports, and it's too small to handle a full load on all of them.

Could't find this one

https://www.newegg.com/Product/Produ...82E16817111402
They give a 3A rating for their power adapter to spread across all USB
device ports.

It's a hub, not a switch

https://www.newegg.com/Product/Produ...82E16817182057
Although the same price as the Dlink, their adapter puts out only 2A.

A hub as well

I think I've seen powered USB hubs that had a 48W power converter
(probably for 4-port USB3 powered hub with a 2.4A charging port) but
that's a large brick sitting in the middle of the cord, not a walwart
hanging from an outlet.


Fokke

Fokke Nauta wrote:

It's an USB switch, mechanically.
https://www.allekabels.nl/usb-schake...BoCZnEQAvD_BwE
(In Dutch, though. Couldn't find an English one)

After trying several different searches, finally I happened upon one
that led me to:

https://www.konigelectronic.com/comp...lack-550510836

Konig says:

Please note that the switch only works with USB devices that do not
require constant contact with a PC, such as most printers, scanners,
cameras, joysticks, PDAs, MP3 players and iPod docking stations.

Although they mention printers and scanners should work, that is if they
don't keep constant communication with the PC (where something is
monitoring the status of the USB device). Nowadays, most printers and
scanners report their status to their driver or ancilliary software
running on the PC. In fact, I had a MFC printer that went bad, wouldn't
communicate with the software on the PC, so I couldn't print to it (the
software couldn't tell if the printer was reachable and ready).

I doubt that it is purely a mechanical switch. The pushbuttons might go
to slide switches but the inside should have a PCB with the logic to do
the path switching. If it is truly and only a mechanical switch, it
needs to make-before-break the USB 5V during the switch. For self-
powered USB devices, like your scanner, they detect a disconnect by
monitoring the VBUS (+5V) wire. If the mechanical or electronic USB
switch had a glitch when changing to different power sources (the PCs)
then the USB device figures it got disconnected from the PC. Upon
seeing a connect due to VBUS reappearing after switching to the other
PC, the USB device reinitializes by sending its presentation data during
the new handshake for the new connection (which could be to the same or
different PC).

https://www.st.com/resource/en/appli...cd00004193.pdf

USB VBUS disconnect might not work on some USB devices due to ESD
protection. See:

http://www.keil.com/support/docs/3837.htm

Got a spare line-powered USB hub collecting dust in a drawer just to
make sure it isn't a USB 5-volt power switch problem? That is, when you
switch the USB device from computer #1 to computer #2, they're also
switching the power source. If you add a powered USB hub after the USB
switch, the VBUS won't be interrupted to the USB device during a switch.
You'd think they'd use the equivalent of a make-before-break switch but
maybe not in a $5 switch box. Plus if it is really a mechanical switch
then those parts wear and the switchbox might be defective.

Correct. But you should not toggle it when the usb device is on.

So, just to be sure, you powered off the scanner before switching?

It's just a simple mechanical switch.

The switch box won't know if you have a self-powered or USB-powered
device attached to it. I've had scanners that used line power. I've
had scanners that only need the USB power. That switchbox doesn't just
change the path for the signal lines. It also has to switch to the
other computer as the power source (USB 5-volt).

When toggling the existing connections will be cut off
before the other connections will be made. But it should not be toggled
when the scanner is on.

If the switch worked as you described, the USB device would always see a
disconnect during the switch. VBUS would get yanked away from one host
before VBUS was restored from the other host. USB devices have to
initialize when they connect. I would think it would make for a
smoother switch if VBUS remained present during the switch whether it
came from PC #1 or PC #2. The USB device wouldn't have to reinitialize.
Of course, if you're powering off the USB device before the switch, do
the switch, and then power up the USB device then it obviously must
reinitialize.

I had assumed you left the scanner powered on during the switch.
Doesn't having to power off the scanner before the switch and power in
on after the switch slow down using the scanner since those devices
often take awhile to get ready?

Because you are powering up the USB device (scanner) after making the
switch and having to wait for it to get ready but the handshake only
fails with one PC, I was thinking there could be a USB enumeration
problem in the Windows registry. Every USB device sends presentation
data which gets recorded under the Enum key when the device is first
discovered, and that enumeration data gets reused on subsequent
reconnects. If that data is corrupt or invalid, Windows uses the
incorrect or invalid enumeration data to identify and manage the device.
However, you said if you make a direct connect (no USB switch between
the problematic PC to the scanner, the scanner works okay with that PC.

Have you tried changing the cabling for the PCs to the USB switchbox?
That is, if PC #1 went to input #1 of the switchbox and PC #2 went to
the input #2 of the switchbox but you're having problems with the
scanner working through the switchbox to PC #2, see what happens when
you change PC #1 to input #2 and PC #2 to input #1. Also move the
cables: PC #1's cable gets used on PC #2 and visa versa. If the problem
moves over to the other PC, you've got a bad switch or cable.

[https://www.newegg.com/Product/Produ...2E16817111402]

It's a hub, not a switch

Yep, which means the USB device (scanner) won't see a loss of VBUS
during the switch. Again, I had assumed you were leaving the scanner
powered on during the switch. The idea was to use the hub AFTER the
switch so the device wouldn't lose VBUS. Since you are powering off
during the switch, keeping VBUS available during the switch is not an
issue. I wasn't suggesting to replace the switch with a hub. I was
suggesting to ADD the hub after the switch (between switch and device).
That's moot if you're powering off during the switch - and then having
to wait until the scanner initializes to get ready.

When you power up the Epson V600, how long does the blue light keep
flashing (which means the unit is initializing)?

When you power off the scanner, switch to the problematic PC, and power
on the scanner, and after it finishes initialize, is its orange LED
blinking which represents the unit issued an error?

After you do the switch, see if Nirsoft's USBDeview shows that PC can
find the scanner through the switch.

You mentioned your wife's PC uses Windows 7. That could be why you
posted here. We don't really know what OS you are using on the other PC
connected to the USB switch. Also Windows 7 so something else, like
Windows 10?

https://www.drivereasy.com/knowledge...on-windows-10/
(Just read the info. Don't get drivers from there.)

When I went to Epson's site to look for downloads, they have "Scanner
Driver and Epson Scan Utility v3.920" for the V600 under Windows 7.
That download is 46.63 MB in size and dated 7/29/13. I selected
different versions and bitwidths of Windows but they offered the same
software download, so it is probably a universal installer that decides
what to inject depending under which OS it is ran.

You said your wife's PC has an ASUS P7P55D motherboard. That has only
USB2.0/1.1 support. I'm assuming further that there isn't a USB3
daughtercard plugged into a PCI-e slot to which you connected the USB
switch. The V600 scanner has a USB2 port and the USB switchbox only has
USB2 support, so it's not an issue of mixing USB3 and USB2.

My guess is you have a bad USB switchbox or USB cables. Since the
scanner works when it is directly connected to her PC, you've eliminated
the USB switch which points a heavy finger at the USB switch. The
scanner works when directly connected to either PC. The scanner works
with only one PC through the switchbox. Try flipping the PCs and their
cables to the other inputs of the switchbox to see if the problem moves
over.

Also try different USB ports on the PCs. I currently have one that is
flaky but it took awhile to narrow down the problems to that USB port.
I put some black self-stick velcro tape over that port to keep me from
using it again. The other USB ports work just fine with by USB flash
drives and USB HDD. Moving to another port (that hasn't been used
before for the USB device) forces new enumeration data for the device
get recorded in a new enum key in the registry.

On 31/08/2018 12:37, VanguardLH wrote:
Fokke Nauta wrote:

It's an USB switch, mechanically.
https://www.allekabels.nl/usb-schake...BoCZnEQAvD_BwE
(In Dutch, though. Couldn't find an English one)

After trying several different searches, finally I happened upon one
that led me to:

https://www.konigelectronic.com/comp...lack-550510836

Yeah, that's the one.

Konig says:

Please note that the switch only works with USB devices that do not
require constant contact with a PC, such as most printers, scanners,
cameras, joysticks, PDAs, MP3 players and iPod docking stations.

Although they mention printers and scanners should work, that is if they
don't keep constant communication with the PC (where something is
monitoring the status of the USB device). Nowadays, most printers and
scanners report their status to their driver or ancilliary software
running on the PC. In fact, I had a MFC printer that went bad, wouldn't
communicate with the software on the PC, so I couldn't print to it (the
software couldn't tell if the printer was reachable and ready).

OK, but when I do not toggle the switch when the scanner is connected to
a pc, it wouldn't metter, would it? I use the switch to select either of
the pc's, and then I turn on the scanner. It sould work with the pc the
switch connects it to.

And both of the pc's recognize the scanner, but my wife's pc can't scan.

I doubt that it is purely a mechanical switch. The pushbuttons might go
to slide switches but the inside should have a PCB with the logic to do
the path switching. If it is truly and only a mechanical switch, it
needs to make-before-break the USB 5V during the switch.

I opened it - it is a pure and simple mechanical switch. And I doubt
whether is is a make-before-break type. Why should it? Isn't it enough
to make the decision which pc to select and then turn the USB device on?
There is no need for a make-before-break contact and a break-before-make
is from a mechanical and electronical point of view more robust.

For self-
powered USB devices, like your scanner, they detect a disconnect by
monitoring the VBUS (+5V) wire. If the mechanical or electronic USB
switch had a glitch when changing to different power sources (the PCs)
then the USB device figures it got disconnected from the PC. Upon
seeing a connect due to VBUS reappearing after switching to the other
PC, the USB device reinitializes by sending its presentation data during
the new handshake for the new connection (which could be to the same or
different PC).

https://www.st.com/resource/en/appli...cd00004193.pdf

USB VBUS disconnect might not work on some USB devices due to ESD
protection. See:

http://www.keil.com/support/docs/3837.htm

But there is no disconnect as I won't use the switch since the scanner
is on.

Got a spare line-powered USB hub collecting dust in a drawer just to
make sure it isn't a USB 5-volt power switch problem?

No, unfortunately not.

That is, when you
switch the USB device from computer #1 to computer #2, they're also
switching the power source. If you add a powered USB hub after the USB
switch, the VBUS won't be interrupted to the USB device during a switch.
You'd think they'd use the equivalent of a make-before-break switch but
maybe not in a $5 switch box. Plus if it is really a mechanical switch
then those parts wear and the switchbox might be defective.

Correct. But you should not toggle it when the usb device is on.

So, just to be sure, you powered off the scanner before switching?

Yes. I first set the switch to the desired pc, and then I turn the
scanner on. I don't use the switch as long as the scanner is on.

It's just a simple mechanical switch.

The switch box won't know if you have a self-powered or USB-powered
device attached to it. I've had scanners that used line power. I've
had scanners that only need the USB power. That switchbox doesn't just
change the path for the signal lines. It also has to switch to the
other computer as the power source (USB 5-volt).

When toggling the existing connections will be cut off
before the other connections will be made. But it should not be toggled
when the scanner is on.

If the switch worked as you described, the USB device would always see a
disconnect during the switch.

Yes, I think so.

VBUS would get yanked away from one host
before VBUS was restored from the other host. USB devices have to
initialize when they connect. I would think it would make for a
smoother switch if VBUS remained present during the switch whether it
came from PC #1 or PC #2. The USB device wouldn't have to reinitialize.
Of course, if you're powering off the USB device before the switch, do
the switch, and then power up the USB device then it obviously must
reinitialize.

I had assumed you left the scanner powered on during the switch.
Doesn't having to power off the scanner before the switch and power in
on after the switch slow down using the scanner since those devices
often take awhile to get ready?

Well, I can use the switch whilst the scanner is on, and when I switch
it to my pc it works.
But to do it properly, I first set the switch and then turn the scanner on.


Because you are powering up the USB device (scanner) after making the
switch and having to wait for it to get ready but the handshake only
fails with one PC, I was thinking there could be a USB enumeration
problem in the Windows registry. Every USB device sends presentation
data which gets recorded under the Enum key when the device is first
discovered, and that enumeration data gets reused on subsequent
reconnects. If that data is corrupt or invalid, Windows uses the
incorrect or invalid enumeration data to identify and manage the device.
However, you said if you make a direct connect (no USB switch between
the problematic PC to the scanner, the scanner works okay with that PC.

Have you tried changing the cabling for the PCs to the USB switchbox?
That is, if PC #1 went to input #1 of the switchbox and PC #2 went to
the input #2 of the switchbox but you're having problems with the
scanner working through the switchbox to PC #2, see what happens when
you change PC #1 to input #2 and PC #2 to input #1. Also move the
cables: PC #1's cable gets used on PC #2 and visa versa. If the problem
moves over to the other PC, you've got a bad switch or cable.

Yes, I changed the cables. Even ordered new cables, shielded, with a
better quality. Didn't make a difference.

[https://www.newegg.com/Product/Produ...2E16817111402]

It's a hub, not a switch

Yep, which means the USB device (scanner) won't see a loss of VBUS
during the switch. Again, I had assumed you were leaving the scanner
powered on during the switch. The idea was to use the hub AFTER the
switch so the device wouldn't lose VBUS.

I wasn't aware you mentioned this option.

Since you are powering off
during the switch, keeping VBUS available during the switch is not an
issue. I wasn't suggesting to replace the switch with a hub. I was
suggesting to ADD the hub after the switch (between switch and device).
That's moot if you're powering off during the switch - and then having
to wait until the scanner initializes to get ready.

When you power up the Epson V600, how long does the blue light keep
flashing (which means the unit is initializing)?

For my pc: 25 sec
For my wife's pc: 30 sec


When you power off the scanner, switch to the problematic PC, and power
on the scanner, and after it finishes initialize, is its orange LED
blinking which represents the unit issued an error?

No

After you do the switch, see if Nirsoft's USBDeview shows that PC can
find the scanner through the switch.

Interesting tool!
On my pc: yes
On my wife's pc: Yes!


You mentioned your wife's PC uses Windows 7. That could be why you
posted here.

Correct

We don't really know what OS you are using on the other PC
connected to the USB switch. Also Windows 7 so something else, like
Windows 10?

Indeed, W10 Pro x64, mobo: ASUS PRIME H270-PRO. Using an USB 3.0 port.

https://www.drivereasy.com/knowledge...on-windows-10/
(Just read the info. Don't get drivers from there.)

When I went to Epson's site to look for downloads, they have "Scanner
Driver and Epson Scan Utility v3.920" for the V600 under Windows 7.
That download is 46.63 MB in size and dated 7/29/13. I selected
different versions and bitwidths of Windows but they offered the same
software download, so it is probably a universal installer that decides
what to inject depending under which OS it is ran.

You said your wife's PC has an ASUS P7P55D motherboard. That has only
USB2.0/1.1 support.

Correct

I'm assuming further that there isn't a USB3
daughtercard plugged into a PCI-e slot to which you connected the USB
switch.

No. Would that help?

The V600 scanner has a USB2 port and the USB switchbox only has
USB2 support, so it's not an issue of mixing USB3 and USB2.

Correct

My guess is you have a bad USB switchbox or USB cables. Since the
scanner works when it is directly connected to her PC, you've eliminated
the USB switch which points a heavy finger at the USB switch. The
scanner works when directly connected to either PC. The scanner works
with only one PC through the switchbox. Try flipping the PCs and their
cables to the other inputs of the switchbox to see if the problem moves
over.

I already used different cables, and used different outputs on the
switch. Whatever I do, on my pc it works, and on my wife's pc it doesn't.

Different pc? Different wife? :-)

Also try different USB ports on the PCs. I currently have one that is
flaky but it took awhile to narrow down the problems to that USB port.
I put some black self-stick velcro tape over that port to keep me from
using it again. The other USB ports work just fine with by USB flash
drives and USB HDD. Moving to another port (that hasn't been used
before for the USB device) forces new enumeration data for the device
get recorded in a new enum key in the registry.

I already tried. Didn't make a difference.

A difficult one, this ?

Fokke

On Thu, 30 Aug 2018 20:56:18 +0200, Fokke Nauta
wrote:

On 30/08/2018 20:32, Ken Blake wrote:
On Thu, 30 Aug 2018 19:55:11 +0200, Fokke Nauta
wrote:

To my knowledge an USB hub is to connect multiple USB devices to one pc.


Yes.


What I'm doing, is to connect one USB-device with two pc's. Not
simultaneously, but either one or the other. One can't use a hub for that.


Have you tried using a hub for that, reversing its connections? I'm
not saying that it will work, since I don't know and I also doubt it,
but it might be worth a try.

No. How about the connecors, which need to be reversed as well?


You should be able to buy inexpensive reversing adapters. A quick
glance at amazon.com shows one for $5.99; there might be others for
even less.



Let me ask why you want to do that. I sometimes move a thumb drive
from a USB port of my computer to one on my wife's. It's easy enough
to do that, so I've never the need for something like what you're
talking about.


We have one scanner and two pc's. We both want to use the scanner.

Fokke

On Thu, 30 Aug 2018 14:00:32 +0200, Fokke Nauta
wrote:

Hi all,

We have an Epson flatbed scanner, V600 Photo. It is connected to an USB
switch by a cable of 1 meter. One output of the switch is connected with
my pc by a cable of 1.8 meter. Scanner works fine. The other output of
the switch is connected to the pc of my wife (W7 Pro 64b, mobo: ASUS
P7P55D). This cable is also 1.8 meter. On this pc the scanner is
recognized, the system bleeps when the scanner is turned on. Scanning is
impossible, it gets stuck, the led on the scanner keeps flashing, and
nothing further happens. Doesn't make a difference when I use Photoshop
or the Epson utility for scanning.
When I connect the scanner straight away to my wife's pc with a cable of
1 meter, it works fine.
I use Belkin USB cables, thought they are good quality. The USB switch
is König, passsive.

Could it be that automatic USB-switches generally are ****? We had one
delivered together with some lab equipment. One printer was shared
between two PCs with a USB-switch. It worked sometimes, but often did
not, so it really was a pain. Changed to network connectd printer, and
no more problems.
--
Jesper Kaas -

On 31/08/2018 18:07, Jesper Kaas wrote:
On Thu, 30 Aug 2018 14:00:32 +0200, Fokke Nauta
wrote:

Hi all,

We have an Epson flatbed scanner, V600 Photo. It is connected to an USB
switch by a cable of 1 meter. One output of the switch is connected with
my pc by a cable of 1.8 meter. Scanner works fine. The other output of
the switch is connected to the pc of my wife (W7 Pro 64b, mobo: ASUS
P7P55D). This cable is also 1.8 meter. On this pc the scanner is
recognized, the system bleeps when the scanner is turned on. Scanning is
impossible, it gets stuck, the led on the scanner keeps flashing, and
nothing further happens. Doesn't make a difference when I use Photoshop
or the Epson utility for scanning.
When I connect the scanner straight away to my wife's pc with a cable of
1 meter, it works fine.
I use Belkin USB cables, thought they are good quality. The USB switch
is König, passsive.

Could it be that automatic USB-switches generally are ****? We had one
delivered together with some lab equipment. One printer was shared
between two PCs with a USB-switch. It worked sometimes, but often did
not, so it really was a pain. Changed to network connectd printer, and
no more problems.


It was not an automatic switch, but a simpel manual one. Mechanically.
It simply connects one or the other cable to the output.

And if your printer has a network port, that's the best way to use it.

Fokke

Fokke Nauta wrote:
On 31/08/2018 00:41, VanguardLH wrote:
Fokke Nauta wrote:

We have an Epson flatbed scanner, V600 Photo. It is connected to an USB
switch by a cable of 1 meter. One output of the switch is connected with
my pc by a cable of 1.8 meter. Scanner works fine. The other output of
the switch is connected to the pc of my wife (W7 Pro 64b, mobo: ASUS
P7P55D). This cable is also 1.8 meter. On this pc the scanner is
recognized, the system bleeps when the scanner is turned on. Scanning is
impossible, it gets stuck, the led on the scanner keeps flashing, and
nothing further happens. Doesn't make a difference when I use Photoshop
or the Epson utility for scanning.
When I connect the scanner straight away to my wife's pc with a cable of
1 meter, it works fine.
I use Belkin USB cables, thought they are good quality. The USB switch
is König, passsive.

Could it be that total cable length is too much? Why is the scanner then
working allright with my pc?
What type of cable should I order to make sure the scanner works
allright with my wife's pc?

Is it actually a USB switch or is it a USB hub?

It's an USB switch, mechanically.

https://www.allekabels.nl/usb-schake...BoCZnEQAvD_BwE

I notice on the same page, for twice the price,
there's one that looks electronic rather than mechanical.

https://www.allekabels.nl/aten/4906/...laar-aten.html

https://assets.aten.com/product/manual/us_221_421.pdf

It can be switched with software.

Paul

On 31/08/2018 20:44, Paul wrote:
Fokke Nauta wrote:
On 31/08/2018 00:41, VanguardLH wrote:
Fokke Nauta wrote:

We have an Epson flatbed scanner, V600 Photo. It is connected to an USB
switch by a cable of 1 meter. One output of the switch is connected
with
my pc by a cable of 1.8 meter. Scanner works fine. The other output of
the switch is connected to the pc of my wife (W7 Pro 64b, mobo: ASUS
P7P55D). This cable is also 1.8 meter. On this pc the scanner is
recognized, the system bleeps when the scanner is turned on.
Scanning is
impossible, it gets stuck, the led on the scanner keeps flashing, and
nothing further happens. Doesn't make a difference when I use Photoshop
or the Epson utility for scanning.
When I connect the scanner straight away to my wife's pc with a
cable of
1 meter, it works fine.
I use Belkin USB cables, thought they are good quality. The USB switch
is König, passsive.

Could it be that total cable length is too much? Why is the scanner
then
working allright with my pc?
What type of cable should I order to make sure the scanner works
allright with my wife's pc?

Is it actually a USB switch or is it a USB hub?

It's an USB switch, mechanically.

https://www.allekabels.nl/usb-schake...BoCZnEQAvD_BwE


I notice on the same page, for twice the price,
there's one that looks electronic rather than mechanical.

https://www.allekabels.nl/aten/4906/...laar-aten.html


https://assets.aten.com/product/manual/us_221_421.pdf

It can be switched with software.

Paul

Thanks!
Wow, this is great! I will order this one, perhaps it will do the trick!
And, BTW, where did you learn Dutch?

Fokke