Supergun Transcoder?

[Sectorseven]

I know there are various circuits you can buy/make that will convert the arcade RGB video into S-Video and the like for your TV, but I'm a little confused as to whether or not any of them actually carry over the 15khz frequency and original resolution. Is this possible (and practical)?

[MonMotha]

Pretty much anything you can build will not alter video timings, just color space and chroma encoding.  The timings (i.e. resolution) are maintained and must be compatible with TV timings in the first place.  Fortunately, CGA arcade video (15kHz scanrate) is generally within the liking range of most televisions.  Pure colorspace transcoders and most "RGB to s-video adapters" fall into this category.

Altering the video timings (e.g. to display CGA timed video on a VGA monitor) requires a scaler of some sort, and that's pretty much universally done digitally.  If it has RAM, then it's probably got a scaler and will alter video timings.  Most devices that fall into this category advertise the scaling as a feature since it lets you display video signals on incompatible monitors.

[Sectorseven]

Pretty much anything you can build will not alter video timings, just color space and chroma encoding.  The timings (i.e. resolution) are maintained and must be compatible with TV timings in the first place.  Fortunately, CGA arcade video (15kHz scanrate) is generally within the liking range of most televisions.  Pure colorspace transcoders and most "RGB to s-video adapters" fall into this category.

Altering the video timings (e.g. to display CGA timed video on a VGA monitor) requires a scaler of some sort, and that's pretty much universally done digitally.  If it has RAM, then it's probably got a scaler and will alter video timings.  Most devices that fall into this category advertise the scaling as a feature since it lets you display video signals on incompatible monitors.

If I deciphered your post correctly (sorry, it was a little over my head) , that's a "yes" for most TVs and "no" for computer monitors. The only reason I ask is I don't see these "features" advertised on any of the adapters. Are these things that the manufacturers usually just take for granted, or if it's not advertised is it really not a true transcoder?

[MonMotha]

Well, you just have to be careful what kind of device you're purchasing as there are two kinds out there.

Some devices are pure transcoders (colorspace conveters).  These are some "RGB to Component" and "RGB to S-Video" adapters.  These generally just change the colorspace from RGB (arcade video) to something your TV can handle (YPbPr component, S-Video, or Composite).  They don't do any scaling, and they don't alter video timings, so they maintain all the original resolution and scanrates.  These are devices that require a 15kHz input signal.

Some devices are pixel mashers.  They do whatever it takes to display whatever you feed it on whatever you've got it hooked up to.  These generally cost a little more (though they can be had for as little as $50 or so).  These are things like "RGB to VGA" adapters, but some also have component outputs.  These will let you do things like display medium res (25kHz/EGA) on a standard res (15kHz/CGA) or VGA (31kHz) monitor, but they won't maintain the video timings or resolution.


http://www.arcademvs.com/ARCADE_ACESSERIOR.htm has both types listed (just as an example - I'm not endorsing this seller).

A-22 (RGB CGA to TV and Video Composite converter) is an example of the former: it simply converts RGB to S-Video/Composite, and it leaves the timings and resolution alone.  You get out whatever you put in.  If what you put in isn't TV compatible, then it won't work.  Fortunately, standard res 15kHz arcade video is TV compatible.

A-24 (RGBS CGA/EGA/YUV TO 2 VGA CONVERTER) is an example of the latter: it takes just about anything you feed it and attempts to convert it to whatever you tell it to on the output.  It looks like this one only has VGA/RGB outputs, but I've seen them with YPbPr component, S-Video, etc.


Both types have their uses.  It sounds like you want the former.  I've not used the exact device that arcademvs has, though I know many who have and say it works well.  It's the same board that Wei-Ya and others sell just with different markings.  I built a similar device with a different chip a few years back with outstanding results.  On a good TV (tested with a Sony Wega), results were almost (though not quite) indistinguishable from an arcade monitor.

If you're interested in building something yourself, only the former type (no scaling) is really feasible for hand construction.  There are several circuits out there, or I might be able to get you the schematic for my design.

[Sectorseven]

Thanks for clearing that up for me. If you get the chance, I'd be interested in seeing your schematic. I've built some very basic circuits and I'd like to see if yours is within my skill level.