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VGA signal fading

C

Coyoteboy

Jan 1, 1970
0
I'm looking to create a VGA fader - I have a projector that takes a VGA
signal from a PC, but I want to be able to fade that signal down to black
between projections, manually using a slider. I know there are production
items out there but they are in the region of upper hundreds and over-spec'd
for what I need. I just need to be able to fade in and out one input.

I cant find, on a brief hunt, the VGA signal spec but I would guess its got
a sync line and 3 AC signals for pixel brightness. I hear it may be ~0.7v
p-p but i dont have that confirmed. Would it be fairly simple to create a
variable gain amp to maintain 1:1 or lower gain to fade the signals to black
without losing sync with the projector (it pops up a blue screen when the
cable is unplugged). Obvioulsly one amp on each analogue line.

Any hints/pointers would be of great help!

J
 
C

Charles

Jan 1, 1970
0
Coyoteboy said:
I'm looking to create a VGA fader - I have a projector that takes a VGA
signal from a PC, but I want to be able to fade that signal down to black
between projections, manually using a slider. I know there are production
items out there but they are in the region of upper hundreds and
over-spec'd for what I need. I just need to be able to fade in and out one
input.

I cant find, on a brief hunt, the VGA signal spec but I would guess its
got a sync line and 3 AC signals for pixel brightness. I hear it may be
~0.7v p-p but i dont have that confirmed. Would it be fairly simple to
create a variable gain amp to maintain 1:1 or lower gain to fade the
signals to black without losing sync with the projector (it pops up a blue
screen when the cable is unplugged). Obvioulsly one amp on each analogue
line.

I don't think you can gracefully fade a digital signal.
 
C

Charles

Jan 1, 1970
0
Brian Gregory said:
VGA is analog.

Yes it is. But how about the synch pulses? Decreasing amplitude might
reduce contrast to a point, but then synchronization will be lost.
 
P

PeterD

Jan 1, 1970
0
I don't think you can gracefully fade a digital signal.

Standard VGA is analog, not digital.

A quick version would require a triple ganged pot, perhaps 150 ohms
each (one for each color signal). I guess three sliders with some sort
of homemade handle to gang 'em together might do just fine.
 
C

Charles

Jan 1, 1970
0
Standard VGA is analog, not digital.

A quick version would require a triple ganged pot, perhaps 150 ohms
each (one for each color signal). I guess three sliders with some sort
of homemade handle to gang 'em together might do just fine.

That makes sense.
 
B

Brian Gregory [UK]

Jan 1, 1970
0
Charles said:
Yes it is. But how about the synch pulses? Decreasing amplitude might
reduce contrast to a point, but then synchronization will be lost.

Why would one even think about fading the sync pulses?
They're on separate lines in the VGA connector.
 
C

Coyoteboy

Jan 1, 1970
0
Charles said:
That makes sense.

I'm concerned about shorting the signals to ground. I'll experiment with a
cheap video card and see what is required to pull the signal low without a
full short. It'd be fairly easy to set this up with a set of digital pots
too, is my thinking, and enjoy the lack of mechanical failures (as a
version2).
 
H

Hachiroku $B%O%A%m%/(B

Jan 1, 1970
0
I'm looking to create a VGA fader - I have a projector that takes a VGA
signal from a PC, but I want to be able to fade that signal down to black
between projections, manually using a slider. I know there are production
items out there but they are in the region of upper hundreds and
over-spec'd for what I need. I just need to be able to fade in and out one
input.

Where are you?!?!
 

Cliff Woodcraft

Jan 18, 2011
1
Joined
Jan 18, 2011
Messages
1
I have made a VGA fader, which works quite well because nobody seems to make one. I am wondering whether to go into production for the benefit of anyone else in a similar predicament
 
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