Suggestions: a circuit which converts digital video signals from a DVI for output on a display medium (such as a CRT).

Jul 27, 2005 7 Replies

I would like the hear others' views regarding such a design. It works something like this: since a normal DVI for our purpose consists of



25-pins (24 pins representing a pixel being 24-bpp with 8-bits per color plus one extra pin for clock) each pixel can be seperated by channel (RGB) and fed as a sample into three consequitive DACs during the scanning of a frame. When the value of the three 8-bit colors is fed into the three DACs repectively, the analogue signal that is produced from the outputs of the three DACs is then sent through the three seperate RGB guns in a CRT while scanning a frame. With good timing considerations, a good picture will be produced in time.

A diagram has also been demonstrated below:



___ / |


24-pin DVI + 1 CLK / | _ / | | \\ RED CHANNEL +===== R --- |

- | o-- ------- | +== G | CRT |



- |======== . . . . . o--| 8-bit | | | +=B --- |



- |======== . . . . . o--| |----O ====== | | \\ |



- | o--| DAC | | | \\ | | / o-- ------- | | \\___| - | | GREEN CHANNEL | | o-- ------- | | o--| | | | INPUT ==>> o--| |----O ========+ | o--| | | o-- ------- | | BLUE CHANNEL | o-- ------- | o--| | | o--| |----O =========+ o--| | o-- ------- o = Digital Input O = Analogue Output ... = Trail



Suggestions are appreciated alongside any considerations that must be taken account of for a design such as the above.



You're quite correct. In fact, I'm looking at one right now. It's called (Rich, did I use the apostrophe correctly?) a video card. The DVI connector is simply a means to move the digital data off board to another. All video cards with a VGA connector have RGB DACs on board (with a little longer cable than you imagine in your description). With good coax cable and properly interfaced in the analog world, you would not be able to see the difference.

Now for a DLP or LCD, the digital data is converted to PWM to get variable (analog) intensity but does the same task as the DAC to CRT.

Sorry to rain on your parade. It's been done.

GG

[snip]

It can't be that tricky. Apple sells their mini Mac with only a DVI output. They give you a little DVI to VGA dongle that is a little over an inch long and just wide and high enough for the connectors on either end.

Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ The opinions stated herein are the sole property of the author. All rights reserved. Void where prohibited. For external use only. Standard disclaimers apply. If irritation, rash or swelling occurs, discontinue use immediately and consult a physician.

My Apple video converter is somewhat larger, having about a 4" cable to a head which outputs composite video and audio. In my opinion the video quality is very poor. Obviously another Apple "Think Different," and think cheap.

Don

Don

Yup. :-)

a video card. The

Cheers! Rich Grise, Self-Appointed Chief, Apostrophe Police

On the DVI connectors, some of the pins are dedicated to analog output. So the DVI out has both anolog and digital. You 'dongle' is just a few wires to connect the good pins to the VGA connector.

That's right, it IS on or off, but to get the variable brightness, you have to mimic the analog world. SO, the PWM. I stand by my comment that the PWM does the same task as a DAC in this instance. That's all.

GG

A DLP is digital all the way to the mirror: the light is either on or off.

Thomas

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