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KVM switches

 
 
SCCC
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      07-05-2005
I want to use a 4 port electronic KVM switch to switch only the VGA
signals. A number of models have pushbutton switches fitted on the front
panel to select which input is required.

The keyboard and mouse connectors will not be used in this instance as
we want them to remain connected to the primary computer. The use in
this case is to act as a multi input switch for VGA video routed to a
projector.

If the KVM switch has its own power supply, is there any reason why it
shouldn't work properly without connection to keyboard and mouse ports
on any computers? Some units derive their power from the keyboard port,
which is why I specified that it have a separate power supply.

Models by Novaview and others appear to meet these specs. There is
little need for the autoscan features most of these devices have when no
keyboard or mouse will ever be connected.
 
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SNOman
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      07-05-2005
SCCC wrote:
> I want to use a 4 port electronic KVM switch to switch only the VGA
> signals. A number of models have pushbutton switches fitted on the front
> panel to select which input is required.
>
> The keyboard and mouse connectors will not be used in this instance as
> we want them to remain connected to the primary computer. The use in
> this case is to act as a multi input switch for VGA video routed to a
> projector.
>
> If the KVM switch has its own power supply, is there any reason why it
> shouldn't work properly without connection to keyboard and mouse ports
> on any computers? Some units derive their power from the keyboard port,
> which is why I specified that it have a separate power supply.
>
> Models by Novaview and others appear to meet these specs. There is
> little need for the autoscan features most of these devices have when no
> keyboard or mouse will ever be connected.


I'm in the process of trying to do exactly the same thing at this moment
for two notebooks to a projector. Have found that kvm type switch will
not work for this. You need a good old fashioned manual 15 pin vga
switchbox ala
http://www.sicom.co.nz/xurl/function...or-switch.html
 
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Harry
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      07-05-2005
SCCC wrote:

> I want to use a 4 port electronic KVM switch to switch only the VGA
> signals. A number of models have pushbutton switches fitted on the front
> panel to select which input is required.
>
> The keyboard and mouse connectors will not be used in this instance as
> we want them to remain connected to the primary computer. The use in
> this case is to act as a multi input switch for VGA video routed to a
> projector.
>
> If the KVM switch has its own power supply, is there any reason why it
> shouldn't work properly without connection to keyboard and mouse ports
> on any computers? Some units derive their power from the keyboard port,
> which is why I specified that it have a separate power supply.
>
> Models by Novaview and others appear to meet these specs. There is
> little need for the autoscan features most of these devices have when no
> keyboard or mouse will ever be connected.


You could create a special keyboard cable which just has the power supply.
Or you could even connect to USB power supply with a special cable.
You would have to make the cable yourself.

You can also jumper the one keyboard power supply to multiple inputs
using diodes if necessary (depends on model of KVM).

 
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Ewen McNeill
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      07-05-2005
In article <vYkye.12857$(E-Mail Removed)>,
SCCC <(E-Mail Removed)> wrote:
>I want to use a 4 port electronic KVM switch to switch only the VGA
>signals. [....] If the KVM switch has its own power supply, is there
>any reason why it shouldn't work properly without connection to
>keyboard and mouse ports on any computers?


I would expect it to work like that providing there was a separate power
source for the KVM switch. The Novaview KVM switches I have will power
up if either (a) there is at least one machine with a keyboard port
plugged in _or_ (b) the supplied power supply is plugged in. And they'll
definitely let you switch to a port which doesn't have the keyboard signal
connected/active (the port button will not show as green, but you can
still select it and see the video signal).

If you have no keyboard lines connected them obviously "keyboard switching"
and the autoscan features won't work, but switching through the push
buttons on the front should still work.

As someone else pointed out you could also use one of the manual
KVM switches (with a bit rotary knob) as they require no power. But
beware that the manual ones have a lot less video bandwidth than electronic
KVM switches like the NovaView so you'll get ghosting, etc, if you
use a high screen resolution or refresh speed.

Ewen
 
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SCCC
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      07-05-2005
Yes I have noticed that the Novaviews and the like offer 2048x15..
resolution support.
The rotary ones are not available in more than 2 ports commonly. Plus they
do not use any special components internally, they have a two position
switch with a huge number of poles and just plain wires running from the
terminals to each pole. Not using the proper kind of wires would generate
all sorts of problems with connected stuff and the switch is probably just a
plain old one. VGA uses 75 ohm coax so if the wiring and switch do not match
there are bound to be problems.

The other issue I want to resolve if possible is the loss of sync signals
when switching on a manual switch unit. This causes the picture to blink a
lot and connected projectors can lose custom settings as they reset
themselves to a default configuration.

I wondered what the autoscan feature was, obviously I don't want any feature
that might cause the switch to switch displays by itself.

I see Novaview are doing DVI now. But as our application requires signal
boosting as well I can't see how we could go to DVI unless signal boosting
for long cables becomes available.


"Ewen McNeill" <(E-Mail Removed)> wrote in message
news:dactck$737$(E-Mail Removed)...
> In article <vYkye.12857$(E-Mail Removed)>,
> SCCC <(E-Mail Removed)> wrote:
>>I want to use a 4 port electronic KVM switch to switch only the VGA
>>signals. [....] If the KVM switch has its own power supply, is there
>>any reason why it shouldn't work properly without connection to
>>keyboard and mouse ports on any computers?

>
> I would expect it to work like that providing there was a separate power
> source for the KVM switch. The Novaview KVM switches I have will power
> up if either (a) there is at least one machine with a keyboard port
> plugged in _or_ (b) the supplied power supply is plugged in. And they'll
> definitely let you switch to a port which doesn't have the keyboard signal
> connected/active (the port button will not show as green, but you can
> still select it and see the video signal).
>
> If you have no keyboard lines connected them obviously "keyboard
> switching"
> and the autoscan features won't work, but switching through the push
> buttons on the front should still work.
>
> As someone else pointed out you could also use one of the manual
> KVM switches (with a bit rotary knob) as they require no power. But
> beware that the manual ones have a lot less video bandwidth than
> electronic
> KVM switches like the NovaView so you'll get ghosting, etc, if you
> use a high screen resolution or refresh speed.
>
> Ewen



 
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Ewen McNeill
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      07-05-2005
In article <dad1pa$619$(E-Mail Removed)>, SCCC <(E-Mail Removed)> wrote:
>Yes I have noticed that the Novaviews and the like offer 2048x15..
>resolution support.


FWIW, about all that means is that the cables will be the limiting factor
rather than the KVM switch itself. Ie, with very short, well shielded
cables you might be able to do that. With longer cables, or lower quality
cables, expect the usable resolution to be lower. That said, I've run
800x600 @ 60Hz over a 10M cable through one of my NovaViews and it's
quite usuable; with some other KVM switches I've tried it wasn't really
readable.

>The rotary ones are not available in more than 2 ports commonly.


I've often seen 4 port rotary switches (I even own a couple of them).
But possibly they're not available any longer since the electronic ones
have come down in price. (When I got them the rotary 4-port switches
were about $100 with cheap cables, and the electronic ones were several
hundred, plus cables.)

But yes, you're right they're just a multi-pole switch internally, and
cause all sorts of interesting effects when switching. (It was particularly
bad with keyboards.)

>The other issue I want to resolve if possible is the loss of sync signals
>when switching on a manual switch unit.


Right. An electronic unit should be much better for that. The monitor
will resync on the signal change if the video frequency is different, but
there's not the dramatic discontinuity that happens with a manual switch.
Hopefully if all the display frequencies are the same/similar you shouldn't
see enough switching change to disturb a projector, etc.

>I wondered what the autoscan feature was, obviously I don't want any feature
>that might cause the switch to switch displays by itself.


From memory you have to manually enable the auto-scan (by pushing a pair
of buttons) and what it does is cycle through the "active" (detected
by keyboard signal) ports in some time cycle. I guess it's intended
for some sort of monitoring/security environment. I've never used it.
As I said, it probably won't work for you, but that's probably no loss.

Anyway hope that's of some help. I'm definitely pleased with my Novaview
KVM switches, and the ability to cascade them is also handy. Hopefully
they'll work for your application too.

Ewen
 
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Bling-Bling
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      07-05-2005
On Tue, 05 Jul 2005 13:00:08 +1200, SCCC wrote:

> If the KVM switch has its own power supply, is there any reason why it
> shouldn't work properly without connection to keyboard and mouse ports
> on any computers?


No - no reason at all.

I have an electronic four-port KVM switch to connect the video output of
two computers in my server room to one monitor. Only one of those
computers has the keyboard and mouse connected to the KVM switch - and
that was purely because I didn't want a wallwart sticking out where the
servers were plugged in to the power.


Bling Bling

--
IBM: "Linux is not just another operating system. It represents a
collaboration of the best programmers in the industry coming together to
create an operating system that works on any hardware platform."

 
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SCCC
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Posts: n/a
 
      07-06-2005
Bling-Bling wrote:
> On Tue, 05 Jul 2005 13:00:08 +1200, SCCC wrote:
>
>
>>If the KVM switch has its own power supply, is there any reason why it
>>shouldn't work properly without connection to keyboard and mouse ports
>>on any computers?

>
>
> No - no reason at all.
>
> I have an electronic four-port KVM switch to connect the video output of
> two computers in my server room to one monitor. Only one of those
> computers has the keyboard and mouse connected to the KVM switch - and
> that was purely because I didn't want a wallwart sticking out where the
> servers were plugged in to the power.
>
>
> Bling Bling
>


Is there no actual keyboard or mouse plugged into the ports on the KVM?
 
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Bling-Bling
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      07-06-2005
On Wed, 06 Jul 2005 16:49:14 +1200, SCCC wrote:

>>>If the KVM switch has its own power supply, is there any reason why it
>>>shouldn't work properly without connection to keyboard and mouse ports
>>>on any computers?

>>
>>
>> No - no reason at all.
>>
>> I have an electronic four-port KVM switch to connect the video output of
>> two computers in my server room to one monitor. Only one of those
>> computers has the keyboard and mouse connected to the KVM switch - and
>> that was purely because I didn't want a wallwart sticking out where the
>> servers were plugged in to the power.

>
> Is there no actual keyboard or mouse plugged into the ports on the KVM?


Go back and read again what I typed!


Bling Bling

--
The above reply is in response to a person who can be only described as
blind!

 
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SCCC
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      07-07-2005

"Bling-Bling" <(E-Mail Removed)> wrote in message
newsan.2005.07.06.11.55.16.494956@TRACKER...
> On Wed, 06 Jul 2005 16:49:14 +1200, SCCC wrote:
>
>>>>If the KVM switch has its own power supply, is there any reason why it
>>>>shouldn't work properly without connection to keyboard and mouse ports
>>>>on any computers?
>>>
>>>
>>> No - no reason at all.
>>>
>>> I have an electronic four-port KVM switch to connect the video output of
>>> two computers in my server room to one monitor. Only one of those
>>> computers has the keyboard and mouse connected to the KVM switch - and
>>> that was purely because I didn't want a wallwart sticking out where the
>>> servers were plugged in to the power.

>>
>> Is there no actual keyboard or mouse plugged into the ports on the KVM?

>
> Go back and read again what I typed!


It would have taken you less time to reply than to write rubbish like that.

The KVM has both ports for your computer's keyboard and mouse inputs, and
ports for the actual keyboard and mouse themselves.

Now, think about that for a minute, and then try answering my question
again.


 
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