Analog VGA RGB

[Ervin Bovine]

Well, I asked a question here before and I got some great advice which
has gotten me very far with my project...

I'm trying to build a device which outputs 1 frame of pure white to
the monitor whenever triggered. I've programmed an Altera CPLD to
handle the trigger event and to act as a universal blanking interval
generator, I've decided to go with Fairchild's FSAV330 analog switch:
http://www.fairchildsemi.com/ds/FS/FSAV330.pdf

which seems to work fine (except it starts to get fuzzy at the higher
resolutions > 1024x768... but that's not a problem for me)

The one thing I just can't seem to figure out is how to generate the
white signals for my red green and blue. I think the proper signal
should be 0.7 volts pp. I need to convert that from 5 volts DC
(pulled from the USB port -- which also powers the rest of my
circuitry). The signals are terminated at the monitor end by 75 ohms,
and I have no idea how I'm supposed to match the impedance.

I truly appreciate any guidance you can offer

 

[James Meyer]

The one thing I just can't seem to figure out is how to generate the
white signals for my red green and blue. I think the proper signal
should be 0.7 volts pp. I need to convert that from 5 volts DC
(pulled from the USB port -- which also powers the rest of my
circuitry). The signals are terminated at the monitor end by 75 ohms,
and I have no idea how I'm supposed to match the impedance.

I truly appreciate any guidance you can offer

Put a 3 500 Ohm potentiometers, wired to act like rheostats, in series
with the 5 volt supply and individually connected to the inputs of each section
of the switch that handle the red, blue, and green video.

That will allow you to set each video output to a wide range of levels
so that you can get the right intensity of white and adjust the tint at the same
time.

Forget the 75 Ohm requirement. The monitor will take care of that
automatically.

Jim