C128 80 clumn RGB to S-Video...

airship · December 01, 2009, 01:02 AM

I believe this is an RGBA converter, not an RGBI converter. Right? So it wouldn't work with the C128.

Hydrophilic · December 01, 2009, 03:25 PM

Good point. As shown, I don't think the circuit would work. But with a few tweeks I think it would.

Although I know virtually nothing of the ST's I/O specs, the acrticle points out that its R,G,B outputs are 1.8 Vp-p with a 1.2 Vdc bias. It also says the caps and resistors in the schematic are used to remove the dc bias and provide 1.0 Vp-p for the MC1377 converter.

So this should work with a C128 by changing the resistor values on the R,G,B lines. I'm thinking that about 0.2 mA goes through each 4K resistor to produce the 0.8 V drop (from 1.8 to 1.0). So maybe using 20k resistors will drop the TTL voltages of the C128 down to 1.0V for that chip?

Other than that, there is the issue of the syncs. If the VDC syncs are active high (I'm thinking this but not sure), the AND gate would need to be replaced by a NOR gate. This is a relatively minor change and can be changed in software too, via register 37 of 8568 equiped C128 D[CR]s (so I've read, I got a flat C128 with 8563 so I can't confirm).

Hmm, I wonder if inverters would be needed on the R,G,B lines? The VDC outputs are active high for R,G,B (I've tested).

I won't try building it, but I think it could work with a few tweaks like mentioned above. Of course it will produce only 8 colors without adding circuitry for Intensity. Also note that composite color video is not very pretty in the best case and the author says the color-filter circuit is not great.

The circuit might be made simpler because the author also states the chip can produce the color-burst itself without an external oscilator as shown.

Edit
I just noticed that the pre-fabricated RGB to S-Video board I bought (I think RobertB has the same one) is available on eBay for only $29.99. I am extremely happy with mine. Please note it only provides 8 of the 16 colors without additional circuitry. However the required circuit is much simpler than the one discussed above; review previous posts in this topic for more details.

Maybe this should go under eBay auctions? It ends in just a few hours and is buy-it-now, so probably not. Anyway, this guy seems to sell them often, so check back later if you missed it.
/Edit

airship · December 09, 2009, 02:36 AM

Only $24.99 & $12 shpg. now. Poster says he has 'more than 10' to sell at that price.

redrumloa · January 31, 2010, 11:43 AM

This is great, I just ordered a board. My 128T is using the RGB to SVGA adapter, but it doesn't do interlace mode. I guess the trick will be finding a TV with "game mode" for flicker fixing?

redrumloa · January 31, 2010, 12:17 PM

The next step I am thinking is to convert from composite to SVGA suitable for use with a standard LCD monitor, but it must display good on LCD and interlace modes. Here are the 2 on my radar.

http://www.buy.com/retail/product.asp?sku=206778928&listingid=22031194

This one says it has the most recent de-interlace technology. And then there is this one.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120395398191&ssPageName=STRK:MEWAX:IT

Which is unclear how it will treat interlace, but has multiple inputs to switch between.

Anyone have thoughts on this? My 40 col ntsc to SVGA adapter leaves some to be desired. It looks o-k on crt monitors, but terrible on LCDs.

Hydrophilic · February 01, 2010, 02:00 PM

I have to dis-recommend the second unit on eBay because it does not support S-Video, only Composite input. Composite output results in a very distorted (blurry) picture due to the limited color bandwidth. If you look on my webpage, you can find Composite and S-Video shots to compare. Unfortunately they're not side-by-side... sorry! The best S-Video shot is to the right of the last schematic, and the equivalent Composite screen shot is on the left below the schematic.

Anyway, it should be obvious from those photos that the Composite is much more blurry. Imagine taking a blurry picture and turning into VGA and then possibly doing de-interlace and I bet it would look terrible on any type of display...

The first unit on Buy.com doesn't offer the multiple inputs, but it says it has S-Video input (however no S-Video connector is visible in photos).

As for de-interlace, I can't say because I'm using a CRT television. VGA monitors (at least my old CRT unit) can support interlace. So if using an LCD VGA monitor, it may support de-interlace already... I guess you won't know until you try...

I'm also assuming you have an existing LCD VGA monitor you want to use. If you are buying a new one, I would recommend a monitor that has S-Video input already! These almost always support some type of de-interlace / gaming mode function... and if it doesn't just return it!

Have fun!

redrumloa · March 14, 2010, 11:14 AM

@Hydrophilic

I finally got around to testing this on my bedroom TV. This TV sucks bad, but it works!

http://i41.tinypic.com/21411ea.jpg

My USB TV tuner for the peecee? Not so good, no picture in interlace and even distorted in standard 80 column. Oh well. I am curious how a better TV would look.

airship · March 15, 2010, 01:59 AM

Quote from: redrumloa on March 14, 2010, 11:14 AM
I finally got around to testing this on my bedroom TV. This TV sucks bad, but it works!

Actually, compensating mentally for the fact that photos of TVs usually look worse than the actual real-life screen, I think it looks pretty good! I'm almost tempted...

redrumloa · March 30, 2010, 01:55 AM

Out of curiosity, this weekend I hooked my 128 with this adapter to my 50" Toshiba DLP TV. The results were very poor in standard 80 column, with parts of the screen being cut off. In interlace mode the picture was worthless.

It is doubtful anyone would want to use a 50" DLP TV with their 128, but I figured I'd put it out there.

On a related note, I am on the market for a 17-19 inch LCD for future every day use with my 128T. The LCD TV I used for testing in the picture a few posts ago in this thread works fine, but the TV itself has a poor picture. I know it is not the adapter, it is the TV. This model TV is crap. Anyone using a TV in this size range with a rock solid picture? If so, please post the make and model number.

BloodyCactus · March 30, 2010, 09:51 AM

does anyone know if the "Arcade RGBS CGA/EGA/YUV TO 2 VGA CONVERTER(NEW)" works? (Its the guys site who sells the RGB converter) http://www.arcademvs.com/ARCADE_ACESSERIOR.htm

would that also do it?

I'm electronically inept so, while I understand "add resistors" I don't get the "how" to add part :/

redrumloa · March 30, 2010, 01:08 PM

@BloodyCactus

It looks very similar to another board that others here (magelore iirc) discovered worked with the small resistor and diode mod. I currently have one in my 128 Tower. It does a pretty good job with CRT monitors, but leaves a little to be desired with LCD monitors. It does not handle interlace modes, but honestly there is almost zero software that supports interlace mode.

In a week, give or take, I plan on gutting both my VGA adapters out of my 128T and selling them. The RGB->SVGA adapter already has the modification for 16 colors and with the composite -> adapter, I have it set up to switch between 40/80 column on the fly. If you are interested, we can speak when I get back in town ~Friday. It would need a few small mods to be used externally, and you may want to put it in a project case to be clean. If not interested, no problem just throwing it out there thinking out loud. It should be a pretty quick sale on eBay.

crazyegg · May 04, 2010, 02:30 AM

Hi All,

Just a quick thanks to everyone here and Hydrophilic for the cool intensity hack!

I just finished this hack over the weekend and it works great. I can't wait to get rid of my 1902A monitor now...

Anybody know of any cool 80 column games other than the ones by Infocom?

PS: I didn't have a 9V or 12V adapter handy so I am using a 15V one. The specs say that 15V is OK so I hope I don't burn the board...

Regards,
ed...

airship · May 05, 2010, 04:30 AM

No games to recommend here, but if you don't have BASIC 8 yet, get a copy. You should also get BigDumbDinosaur's 80-column Manager. It's pretty awesome.

RobertB · May 05, 2010, 05:04 PM

Quote from: crazyegg on May 04, 2010, 02:30 AMAnybody know of any cool 80 column games other than the ones by Infocom?

Not commercial but homebrew 80-column games can be found at

http://cbmfiles.com/genie/C128GamesListing.php

Truly,
Robert Bernardo
Fresno Commodore User Group
http://videocam.net.au/fcug
July 24-25 Commodore Vegas Expo 2010 - http://www.commodore.ca/forum
and click on ComVEX

Hydrophilic · May 06, 2010, 05:38 PM

@redrumloa, I have to agree with airship, that the image doesn't look bad in your photo. It looks like you are using S-Video connector in the photo. Interlace looks good on my 36 inch CRT TV (there is some flicker), but the highest resolutions of ZED also get cutoff at the top. Also note that ZED does not use correct NTSC settings, so that might be a problem. What kind of board did you use in your C128 tower? I've read that it has s-video for 80-columns with some modification. (By the way, your C128 tower if f*king awesome)

@BloodyCactus, I haven't tried the board you mentioned; it sounds like what redrumloa used?

@crazyegg, I'm glad the Intensity hack works for you; Rest In Peace 1902 (I wonder if you could sell it on eBay?); I hope 15V is safe too, please let us know if it burns up...

I tried a variation on my Pull-Both method which uses more common resistor values AND looks better than the original. I've attached schematic. It uses 3 resistors of 1.0k and 1 resistor of 1.2k. Note for a slight penalty in color "crispness" you can use all 1.0k Ohm resistors... you can't get more common than that!

crazyegg · May 11, 2010, 05:43 AM

Hi All,

Thanks for the 80 Col program recommendations. There are quite a few indeed...

Of note, for those of you also using SVIDEO on the 40 column output of the C128, you will need to plug that output to a different SVIDEO input of the TV or use a SVIDEO box changer. I tried originally using a cheap SVIDEO Y-adapter (for both 40 col and 80 col) and it was causing interference.

Also, its a shame that most of the new LCDs that are out don't even have any SVIDEO inputs! But those that do only sport one SVIDEO input...

PS: I am currently using the revised schematic of Hydrophilic and it is working great on my LCD. So far so good on the 15V AC adapter. I remember I was using an 18V AC adapter for the longest time on my Nintendo 8 bit machine (rated at 9V or so) with no ill effect!

Regards,
ed...

redrumloa · May 11, 2010, 06:04 AM

Quote from: Hydrophilic on May 06, 2010, 05:38 PM
@redrumloa, I have to agree with airship, that the image doesn't look bad in your photo. It looks like you are using S-Video connector in the photo. Interlace looks good on my 36 inch CRT TV (there is some flicker), but the highest resolutions of ZED also get cutoff at the top. Also note that ZED does not use correct NTSC settings, so that might be a problem. What kind of board did you use in your C128 tower? I've read that it has s-video for 80-columns with some modification. (By the way, your C128 tower if f*king awesome)

Thanks for the compliment. That image earlier in this thread was when I was testing out on a flat 128 with a Viewsonic LCD TV. The remark was about the TV itself, it is a poor TV. The adapter has since been installed in the 128T and I bought a new Broksonic LCD TV, which has a fantastic picture. The 128T does indeed use only S-Video output for both 40 & 80 column.