I've been looking for an adapter, or combination of adapters, that can be used to view the RGB monitor output of an Apple IIgs on a modern VGA/SVGA monitor. (I already have a dual monitor setup on my Macintosh G3, one being an SVGA monitor and one being a Macintosh-style Dsub 15 monitor, and just don't have any more space to add a third.) I've hoped and dreamed for a Second Sight card, but no one on earth seems to want to sell theirs (presumably for good reason). The adapter in question would need to be able to input the RGB signal from the IIgs as separate red/green/blue component signals, use double-scan conversion to convert the 15.75 kHz horizontal scan rate (matching the NTSC standard) of the GS RGB output to at least 31.5 kHz to work on a VGA monitor, and output VGA-compatible video. (Sure, I could use the GS composite video out port and use a composite-to-VGA converter, which I've seen many of on the Web, but then I'd be limited to composite video quality.) So far, this is the only thing I've found that's sparked my mind as having a chance to do the job: AV converter 4 in 1 box Ypbpr in RGB Monitor http://www.bryce-max.com.hk/AV%20converter%204%20in%201%20box.htm Would something like this work? According to the description of this product on the page, I gather that it can input component video matching the NTSC standard in YPbPr format. The best definition of YPbPr I've been able to find is: ---begin YPbPr A component analog video signal containing one luma and two chroma components. Often referred to loosely as YUV or Y, B-Y, R-Y. YUV In the general sense, any form of color-difference video signal containing one luma and two chroma components. Technically, YUV is applicable only to the process of encoding component video into composite video. See YCbCr and YPbPr. ---end I'd like a better definition of YPbPr to know if it would work. I am hoping that I could possibly construct a cable that connects to the GS RGB port via the Dsub-15 connector, and feeds the necessary signals individually into the coaxial RCA jacks on the converter box. Would this work with no additional signal manipulation required? ------------------------------------------------- As an addendum, I've included the IIGS monitor port pinout from R023PINOUTS.TXT and the specs of the original monitor from the Apple II MONITOR FAQ: 026- What are the specs and pin-out for the GS RGB monitor? Max Resolution: 640 Horizontal dots x 200 Vertical dots/lines Dot Pitch: .37mm CRT Size: 12"/ 11.5" viewable Video Bandwidth: 6.5MHz (+/- 1.5DB) Scanning Frequencies 60Hz model 50Hz model Horizontal: 15.734kHz 15.696kHz Vertical: 60Hz 50Hz ___________________________ IIGS RGB Connector Note: "Not used" indicates signals not used by the IIgs RGB monitor. Dsub-15 (female) socket at back of IIgs ,--------------------------------. \ 08 07 06 05 04 03 02 01 / \ 15 14 13 12 11 10 09 / `----------------------------' | | pin # signal | | shell system ground 1 ground (for red) 2 red analog video 3 composite sync 4 (not used) 5 green analog video 6 ground (for green) 7 -5 V (not used) 8 +12 V (not used) 9 blue analog video 10 (not used) 11 audio output (not used) 12 composite video (not used) 13 ground (for blue) 14 (not used) 15 (not used) ____________________________ -- <> Email: mailto:ToasterKing@SPLATbigfoot.com Visit ToasterKingdom at http://SPLATtoasterking.tripod.com/ ToasterKing wrote: >So far, this is the only thing I've found that's sparked my mind as >having a chance to do the job: > >AV converter 4 in 1 box Ypbpr in RGB Monitor >http://www.bryce-max.com.hk/AV%20converter%204%20in%201%20box.htm > >Would something like this work? According to the description of this >product on the page, I gather that it can input component video >matching the NTSC standard in YPbPr format. The best definition of >YPbPr I've been able to find is: > >---begin >YPbPr >A component analog video signal containing one luma and two chroma >components. Often referred to loosely as YUV or Y, B-Y, R-Y. > >YUV >In the general sense, any form of color-difference video signal >containing one luma and two chroma components. Technically, YUV is >applicable only to the process of encoding component video into >composite video. See YCbCr and YPbPr. >---end > >I'd like a better definition of YPbPr to know if it would work. I am >hoping that I could possibly construct a cable that connects to the GS >RGB port via the Dsub-15 connector, and feeds the necessary signals >individually into the coaxial RCA jacks on the converter box. Would >this work with no additional signal manipulation required? Some signal processing is required, but perhaps only simple analog addition and subtraction. There are quad video op-amps available that will certainly do the job of generating YPbPr from RGB, but you'll have to get some power to them, since they drive 75 ohm loads. The Y signal is a weighted sum of R, G, and B signals, where the weights are a standard. Pb is B minus Y and Pr is R minus Y. All signals have standard polarities and peak-to-peak amplitudes. -michael Check out amazing quality 8-bit Apple sound on my Home page: http://members.aol.com/MJMahon/ ToasterKing replied: >In article <20030512180919.24954.00000344@mb-m06.aol.com>, Michael J. >Mahon wrote: > >> Some signal processing is required, but perhaps only simple >> analog addition and subtraction. >> >> There are quad video op-amps available that will certainly >> do the job of generating YPbPr from RGB, but you'll have >> to get some power to them, since they drive 75 ohm loads. >> >> The Y signal is a weighted sum of R, G, and B signals, >> where the weights are a standard. Pb is B minus Y and >> Pr is R minus Y. All signals have standard polarities and >> peak-to-peak amplitudes. >> >> -michael >> >> Check out amazing quality 8-bit Apple sound on my >> Home page: http://members.aol.com/MJMahon/ > >That sounds like possible a little more complex design than I was >hoping for, especially since my circuit design skills are a little >rusty. Since I don't know exactly what the specifications of YPbPr >call for, and how to manipulate the signal from RGB, I'm not really >sure where to start here. If you happen to have any of this knowledge, >could you possibly point me in the right direction? Otherwise, can you >think of any other easily-achievable design that's a little more >elegant than conversion to first YPbPr, then to VGA? There's a Linear Technology Application Note that has a circuit for converting RGB to YPbPr: http://www.linear-tech.com/pdf/13989f.pdf It requires two dual video op amps and some resistors. It does not show adding composite sync to the Y signal. That will require another op amp between the Y output shown in the diagram and the real Y output, to add (or subtract--I couldn't quickly confirm the IIgs sync polarity) the composite sync to the Y signal in the right proportion (about 1/4 of the Y peak-to-peak amplitude). The circuit assumes +5v and -5v supplies, which is a bit awkward. The circuit could probably be adapted to work from a single-ended supply, since I believe all the signal components are positive(?), but levels would have to be shifted some to keep the video linear. Assuming that 75 ohm impedances are used throughout, the current requirement from each supply should be less than 100ma, so, though it's not a power hog, it will need access to "real" power. The reason that this "transcoding" is so simple is that we need not do anything to change the timing of the signals, only the mixing of the components. -michael Check out amazing quality 8-bit Apple sound on my Home page: http://members.aol.com/MJMahon/ I agree with your statement about converting SVideo or composite signals into RGB, tit is quite disappointing. But the video cheesebox may yet have the answer in it's digital processign chip,the AL250. Per our previous discussion, I will try bypassing the pre processor (SAA7111) that does the analog to digital conversion. Patching the RGB binary wighted signals from the IIgs graphics chip into the AL250 directly and wire it for RGB565 processing. Granted the graphics chip in the IIgs only puts out 4-4-4, but we can experiment by tying the extra inputs high and low to get the best results. If I ever get the time ot do this, I at least now have all the pieces. It may end up being my K-fest hack project. Reference previous discussion: http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&th=85bc3022f0c0078a&rnum=1 Michael J. Mahon wrote: > I tried a "Video Cheese Box" (Yes, really ;-) and was quite disappointed with the quality of the conversion of lowly composite video to VGA. The composite format, like the S-Video format, is fundamentally incapable of carrying the information to make a crisp IIgs display, so our hopes must be pinned on direct RGB or component video.