Frequency doubling

Too radical an idea ?

....... Phil

No, where's the fun in that? :-)

I was thinking of building one myself. Not quite sure what's the best approach, tho.. that's why I'm fishing for ideas here. My first thought was ADC->Some microcontroller fast enough to repeat signal twice->DAC (with 8-bit quality on the converters) but maybe that's a bit overkill for such a trivial task.

Stian

I think you need even more for this task. So you have an FBAS signal and you want to display it on a VGA monitor? Just doubling the frequency doesn't work, your idea reading it and repeating it twice per frame is good. But you have to convert it from FBAS to RGB, too. And microcontrollers fast enough for a 50MHz pixel clock may be expensive. You should consider using a FPGA.

On a sunny day (Fri, 30 Nov 2007 04:43:06 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

I have done it in FPGA. This has been discussed here some year(s?) ago. IF you have YCrBb you can read in a line and write it back at double speed. lowpass - ADC - blockram - DAC -lowpass, but you can sample CrCb half at half the frequency, as color is less detail (note sign, CrCb can be negative). If you have composite, a good PAL or NTSC decoder in FPGA is not trivial, use an analog one perhaps to get to YCrCb.

Also somebody found some links with really cheap converters. Probably cheaper then one mcan make them oneself. Personally I would not bother, all will go digital soon, and old analog TVtronics will be gone.

Steps.

1. Get a good PC
2. Get a good video capture board.
3. Install same in PC
4. Run 15.625 (???) video into the capture board.
5. Connect VGA monitor into the computer's video output
6. Watch your TV!

How simple do you want it? Or are you looking for a passive solution?

A Frame buffer.

Rene

First is the conversion clock, or "dot" clock which should be synchronous with the line rate. This means a PLL to lock to the Hz rate. You'll need ADC(s) of 10 bits minimum. Is your input composite? Then you'll need a composite-to-YUV decoder in the FPGA firmware. You might be able to find this on open cores, but I've implemented this from scratch, and like Jan said, it's not trivial.

Not wanting to discourage the DIY approach, but in case you give up:

Frank

On a sunny day (Fri, 30 Nov 2007 14:46:27 +0100) it happened Rene Tschaggelar wrote in :

You do not need to store a whole frame, one line is enough.

Just buy a converter box. Like Phil said, YOU asked for the easiest approach. Or buy a LCD TV. Doing this yourself is not as trivial as it seems. You can look into the AL250 chips, I tried making a RGBI to VGA converter with one, and all I ended up with was a purple mess and a bad clock recovery system. This isn't so trivial as you think, it's a bit more involved than just doubling the sync signals. Converter boxes are available at any computer store and are pretty cheap.

...aaaaand "ignore". There.

Stian

I know, I just expected something a bit more exciting from the sci.electronics.design than "buy a box."

Ok, I see. Maybe we're on the same boat, as my signal is RGBI as well. Sorry I didn't have the chance to mention that earlier.

Maybe you've been playing with the Amiga's RGB as well?

Stian

Electronics is heavily commoditized now, often you're better off speccing than designing.

Nah, I was fooling around with the C128 RGBI. I don't remember if the Amiga gave you RGBI, I have a vague memory of a db-23 video connector with analog RGB on it. Maybe there was RGBI to use cheaper monitors?

If you want I can tell you more about my AL250 project. It's dead now. Too boring, and too much work. How do you plan on getting the pixel clock? If you design an internal card for the 2000, you're golden.