External RGB to S-video schematic

[TmEE]

The RGB lines from VDP are 0 to 5V, and ones after CXA are around 1V. The RGB on CXA inputs should be at right level.

[Drakon]

Yes it's a double sided pcb there's nothing fooked about it. Sync goes through a lm1881n circuit. Tiido he's trying to make something that you can wire into the rgb output of the cxa1145 so *shrug*. I honestly don't care about making this encoder work with the genesis it still gets jailbars just like any other encoder.

[MEGADRIVE Jeroi]

I did now md2 mb3514 rgb encoder, the pin2 : red input, pin3: green, pin4: blue input and they have all 2,7voltage. So this is too big for ad724. Going to add resitors to divide voltage down to 0,7 for input of ad724. So getting input signal from various genesis or megadrive versions with various chips is error. Only doaple situation is to divide 5v to 0,7 or output rgb to 0,7v. For general rule, all the vdp's output 5volt so I am going to use 5 volt as input. It seems 470 in series and 75 to gnd does reduce voltage to 0,63volts so I will do this setup. Also we need input ncaps again to stabilize the input.

For sync, we dont need 1881 to separate sync signal. The neogeo circuit did that just to separate sync out of composhit. How ever, AD724 accepts FSB sync, 4*FSB sync and combosite sync or Hsync and Vsync. So there is no need for 1881 circuit for megadrives to get ad724 to work. We just take sync singla from megadrive cxa input pin and voila.

[Drakon]

I did now md2 mb3514 rgb encoder, the pin2 : red input, pin3: green, pin4: blue input and they have all 2,7voltage. So this is too big for ad724. GOin to add resitors to divide voltage down to 0,7 for input of ad724.

Thanks I'm interested in learning how to bring voltage down and I'll happily test it out. Are you testing the voltage at the rgb inputs or the outputs of the encoder? The outputs are what connect to the av port so you'd be better off setting the resistance for the voltage at the av port.

[MEGADRIVE Jeroi]

Well plaah. I did mistake, the input pins has 0,2-1.2Vpp where the chip in md2 max 1Vpp. So the inputs are good enought for ad724 also. How ever, for enabling maximum console modification circuit, there is absolutely need for either drop down from 5vpp to 0,7vpp or then use console output pin voltages and divide them to working voltage for ad724. If divider where developed for different voltage inputs for RGB which might be 640*480 resolution support, then it is obivious that voltages are too hight for AD724 and would make colors behave like Dragons photo. So I see only doable universal method is to use VDP output level which is 5volts output, then divide that to working voltage and it would be universal for different machines. How ever, changing Vpp is matter of capacitor in series with coils to rpoduce lesser wave. If there is no cap to lowdown the AC voltage then only DC voltage is reduced by resistors. This why Sega cxa has one resistor in series, one cap and resistors to gnd.

Here is my detailed measurements and resistors plus caps what are in rgb lines:



So it seems sega adds more voltage to rgb lines in order to get the near zero voltage output to little higher voltage with 0.3Vpp inputs. As you can see from this diagram you can get directly RGB from encoders input to AD724 inputs with no problems as AD724 wants maximum of 0.7Vpp RGB inputs. How ever voltage cannot take from encoder output as the ac is buffed in sony to 1.3Vpp.

Dragon: If you did take rgb from output to Neogeo it surely wont work then.

[Drakon]

*sigh* my ad724 circuit works great on my neogeo mvs. It doesn't work on the rgb out from the cxa1145 in the genesis.

[Joe Redifer]

Yes. The Genesis is funky. I have an external RGB-to-s-video box that works great on the Neo Geo and on the TurboGrafx-16, but it comes up as false colors on the Genesis. A few games will play in real colors, however, like Barver Battle Saga. Very, very odd.

[Drakon]

Yes. The Genesis is funky. I have an external RGB-to-s-video box that works great on the Neo Geo and on the TurboGrafx-16, but it comes up as false colors on the Genesis. A few games will play in real colors, however, like Barver Battle Saga. Very, very odd.

Thankyou sir maybe now people will finally believe me when I say I wired it right! Apparently the genesis has the most arcade cabinet friendly rgb to come out a console from what I've heard....but I can't verify that. I will say this....pumping the rgb from the av port through a jrok component encoder (and probably any other component encoder) with vdp pin 50 lifted is the g@ddamn sex....it's as good looking as my 32x s-video mod but without the very mild rainbow banding.

I really think we should abandon trying to use the ad724. I mean even though the colours are insane I get nice big happy jailbars showing up on the picture you can't miss them. I'm pretty sure jailbars aren't caused by the encoder but they're fixable by tweaking the video circuit to filter them away, just like what I did with the cxa1145 s-video circuit. I really don't know what the source of the jailbars is, if it were simply the colour subcarrier then driving an encoder off of its own crystal oscillator would get rid of the jailbars but instead it makes them start scrolling.

Or you can go the route of component video grab a properly wired rgb cord disconnect vdp pin 50 and say bye-bye to both jailbars and rainbow banding forever. Unless your tv is over-sensitive? I really wish I had a flatscreen tv that takes component video or a component video capture card just to see because on my crt the component video was nothing but pixel perfection.

Also joe there's even some systems that screw up on even the most forgiving video encoders out there. My official street fighter 2 world warrior arcade pcb only works right on my bh7236af encoder board. On other boards world warrior either has screwed up colours or is too dark. Surprisingly street fighter 2 champion edition / turbo boards don't have the same problem....only world warrior. I also have an official mercs arcade pcb and between stages it always screws up...on any encoder. I did a web search and apparently mercs pcbs are like that they were designed for a really obscure arcade moniter and output very non standard rgb. My mercs pcb also screws up for a split second when I hit the bomb button but otherwise it's okay. Strangely enough my capture card does a better job handling the s-video than my tv but even my capture card goes dark looking in between stages....weird.

I think the funniest was when I borrowed a raiden dx (raiden 2 special edition) arcade pcb. It worked great on my supergun....except one row of pixels didn't fit onto my screen. I could literally fly my ship off the screen and there was just enough space for the ship to fit off the screen before it hit the invisible barrier haha. Oh also my dragon breed pcb the bottom row gets clipped off but it's only score and stats so it's no big deal. Really though the most forgiving encoder I've found is the bh7236af circuit....the only problem is with this circuit the colour encoding is quite a limited pallette. In the rgb nes once I switched to sony encoders suddenly buildings that used to all be the same colour were showing up as slightly different colours.

Anyway I could rant on all day about which encoder is best for what purpose but you get the idea.....I know what I'm talking about when I say which encoder is best for the job when it comes to s-video. Component encoding isn't nearly as tricky luckily.

[Joe Redifer]

Arcades are funky as well because they all run at their own bizarre refresh rate (57.34Hz, anyone?). There's no standard whatsoever which kind of sucks, especially for recording the video.

But I'm still wondering why a few Genesis games will work with my generic RGB-to-S-video box in the correct colors whereas most will not. Is there something different that game (Barver Battle Saga) is doing with its video output?

[Drakon]

Arcades are funky as well because they all run at their own bizarre refresh rate (57.34Hz, anyone?). There's no standard whatsoever which kind of sucks, especially for recording the video.

But I'm still wondering why a few Genesis games will work with my generic RGB-to-S-video box in the correct colors whereas most will not. Is there something different that game (Barver Battle Saga) is doing with its video output?

Beats me. I don't know THAT much about the genesis hardware such as how many video modes it has....all I know is from the experience of buying / building and testing most common s-video encoders I know which ones work on which systems. If you could tell me what encoder your s-video box uses that would be helpful. Then we could look up the datasheet and come up with endless theories about what's going on.

Maybe the colours that game uses are in a certain range that are okay with the encoder? Maybe that game uses a video mode that somehow effects the rgb in a way the encoder is okay with encoding? I'm going to guess it has to do with colour strength. With my street fighter 2 world warrior arcade board after it shows the high scores the picture slowly fades to dark. During the fading process when it gets dark enough suddenly it goes from f#ked up colours to the actual correct colours. Although with the ad724 on the genesis it's non-stop insanity. I could spend all day trying to make these things work but when I have another encoder circuit sitting right there that works fine then there's no point. If I wire up an encoder that doesn't like the signal but I can still see the same interference I was getting from the encoder that likes the signal....then there's no point in trying to figure out a solution.

[MEGADRIVE Jeroi]

This tread is to develop simple ad724 circuit for internal usage for genesis. Just because the others did not work, so stop speaking some other circuit that is needed to PAY. This is DIYcircuit development thread, not buy some already developed circuit thread. SO dragon please stop speaking commercial products as this thread is for devlopment. If you know how ever some other chip rather than CXA to output s-video easilly out of rgb then please do post it to make it consedered to switched to. Again this is not thread to speak about existing products that cost money and there is stil needed some soldering to make it work. This thread is DIY circuit development. DYI from start to finish. If we make decent circuit for genny to produce outstanding image for s-video, it is up to you to build it yourself. So it's not needed for ranting external products in this thread, exept if you now what chips it uses to make good s-video. So Dragon please read what the trhead is, think, then post.

And do please consider to stop talking in this thread, as I am happy that you have a external s-video converter that works. It seems this thread is not for you.

I really think we should abandon trying to use the ad724.

Nope, I just ordered 10 ad724 samples and will continue to develop this. It's funny tho, you think "WE" as it seems that you were never even interested in this development. You just rant how stupid this is and so on. This beats me but makes me laugh. You're just so funny guy.

*sigh* my ad724 circuit works great on my neogeo mvs. It doesn't work on the rgb out from the cxa1145 in the genesis.

Yes it's because cxa outputs are 1.3VPP which is not standard RGB outputs Vpp. Stnadart is 0.7Vpp. AD724 works up to 0.7Vpp signal. So AD724 can only be taken from CXA input pins.

Any more news is that I ordered full scale resisitor series assortment, full scale transistor assortment, full scale op-amp assortment, full scale voltage regulators assortment also L version of 7805 and 7905, full scale diodes assortment, full scale Zener assortment, all the chips to make CCAM, RGBtoS-video devel, RGBtoComponent devel, some chips I ordered also as smd versions, as if some chip is only smd I will then use only smd chips while resistors and such could be thrue hole. BK precision True RMS meter, 10 more Soldererless Breadboards and Banana input connectors for DIY circuit board development panel, where I going to use 250W computer powersource to add my own circuit for generatin +5 and +12 and -1to -16 voltage wiht pot and 1-16voltage with pot to banan plugs. How ever as I have used switchable 1.3to9volt power adapor until now, I ordered also 2 0-16volt benchtop voltage sources. Also going to add 4ohm speaker to board, and 10k, 100K, 1000K potentiometers and ON-ON switch, ON-OFF-ON switch, ON-ON-ON switch and more. ONly thing what I dont add is Logic controls and function generator. I will buy function generator separately. How ever voltage supply is nice DIY project for my development board.

[omp]

So you spent some money then? Well done hope you have fun with your experiments!

[Drakon]

I DIY made a cxa2075 it works a lot better than the ad724. There's nothing wrong with the cxa chip. I already said the ad724 has the same jailbars as the cxa chip so I don't see the point in using a non sony encoder. What I'm looking for is a reason why you're tyring to use an ad724 when a cxa2075 will work tapping rgb from anywhere. Is there some advantage of the ad724 that I'm not aware of?

[MEGADRIVE Jeroi]

Price tag for an example. Also your ad724 is wired with comboshit coming from cxa. Ofcourse it has jailbars then. ROFL.

[Drakon]

Price tag for an example. Also your ad724 is wired with comboshit coming from cxa. Ofcourse it has jailbars then. ROFL.

What? My ad724 isn't using composite it's using just rgb and sync. And it outputs s-video. I never used composite video. I got a bunch of cxa2075 encoders for pretty cheap but....okay whatever.