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RGB/YPbPr Intellivision Thoughts


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I have a programmable Intellivision mod kit and need to know what is most important to other people.

  1. Selection between RGB or YPbPr (CRT ONLY).
  2. Selection between 2 palettes.
  3. Color accuracy.


I am currently doing #1 and #2. Specifically, I have selection between two simple palettes (that don't change much at all) and a toggle for RGB or YPbPr out.

Because of limitations in the amount of code I can load into this thing I can only do variable amounts of those things.

So please pick any one or two and I will use that to guide what I do.



Anyway, here is Pitfall! with a gameboy palette as an example of random nonsense: https://i.imgur.com/2QjCBQT.jpg

Pacman as well: https://i.imgur.com/GVdSL5f.jpg


Ill get screenshots of the normal palettes in a few.

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Colour accuracy is important.  Here's a discussion on intellivision colours.  You could do an NTSC palette and a pal palette.



S-video out would be good too.


Is your kit for ntsc intellivisions or pal intellivisions?


Edited by mr_me
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4 minutes ago, mr_me said:

Colour accuracy is important.  Here's a discussion on intellivision colours.



S-video out would be good too.


Thanks for letting me know,. So accuracy.

I have seen that page. I have read through a ton of pages referring to Intellivision palettes (on atari age).

I have actually been loading various palettes and trying them out this whole week.


I think so far I have liked @intvnut's palette the most. The problem is if the goal is accuracy then what is the accurate color ? Out of all the palettes which is the 'correct' one ?


I hadn't considered this but I can actually mix YPbPr, composite, and S-video all from the RGB outputs. I think there is probably a little lost in transit. 

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Thanks for all the input. This has been helpful.


here was the palette I was using (by randomly selecting values):



here is the same picture but using IMBerzerk's palette:



IMBerzerk's palette on motocross:



These are just pictures taken on my TV. Darkgreen and brown do look different to my eyes but through the camera they look the same. The brick mortar looks alot whiter on camera as well.


Anyway, I may have room for another palette so that is what I will be working on.

Then I will maybe get some game play recorded.


As a random note I added sync pulses to VSYNC but am not sure if this will make it work with the OSSC.


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YPbPR (CRT) screenshots:







All this was using IMBerzerk's palette.

I fat fingered cyan into gray when converting these values; It's fixed now.

That drop shadow effect is probably specific to that CRT I will look into it. The effect is most likely not caused from a mod/code error. Other aberrations if present are probably related to capacitors/power supply/voltage regulators (I haven't changed any).


I currently have RGB/YPbPr toggle-able while using IMBerzerk's palette.

The only thing we have lost is the ability to toggle multiple palettes. There may be room however to change 1 or 2 colors.

So if anyone can think of some aesthetic changes to a color let me know. Personally, I like having tan closer to yellow or more of a 'dirt' color.


This setup as it is now would be the basic setup to the board.

Alternatively if using RGB with the addition of some circuitry I can split RGB output and convert RGB to YPbPr, S-Video, and composite. The benefit of doing this would be that you could play over component/s-vid/composite and record RGB or whatever with no need to toggle anything.


I will be working on board design/testing for the foreseeable future. Please point out if I have missed anything.

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On 9/27/2020 at 10:42 PM, mr_me said:

I've seen palettes where red and pink/magenta are too close, hard to tell the difference. Others to watch out for are cyan and light blue, brown and green.  Brown can look a little green but shouldn't be too green.  The important thing is all the colours are distinguishable.

Here is a comparison of the two palettes I have tried so far:

Left is IMBerzerk right is mthomson





I hope you guys can see the problem in trying to match these colors.


So far I like mthomson's palette the best. I think it is a decent balance between color accuracy and refining the colors for differentiation. Except I might tweak Pitfall Harry's shirt color a smidge.


If someone has a palette they consider the gold standard go ahead an recommend it but I can't match NSTC RF exactly; and if I did it would look worse. My yellow doesn't even seem to show up over RF.


In my opinion the closest colors to RF would be washed out representations of what they SHOULD be.



Edited by the_crayon_king
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2 minutes ago, mr_me said:

I vote for imberzerk's palette.

Thanks for the input.


Looking back imberzerk's version of Harry's shirt looks a lot easier to distinguish.

I like imberzerk's for everthing except its tan color. Gray could also be a smidge darker.



Left is mthomson right is imberzerk.



I can put in a toggle to switch between two different 'tans'., leaving the white looking color as the default and the toggle will change tan to mthomson's version. I hate that white looking tan so it's a must to be able to change it.


mthomson's BG color (what color is that anyway ?!) on the Pitfall! startup screen clearly matches what I am seeing on RF better than imberzerk's. I'd like opinions on what to do there.


Am I the only one who converts all their consoles to YPbPr so I can play on a CRT ?


I could always scrap YPbPr and then have two completely different palettes. The trade off is that people wanting YPbPr would need additional circuitry/costs. I mean I could do that and the additional board could put out YPbPr, S-Video, and composite.




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Here is a rom I wrote while designing my rgb mod. It's a simple color bar program that helped me dial in my palettes. Hopefully you have a flashcart or some means of using it.





Why not just cherry pick your favorite colors from IMBerzerk, mthompson, and other palettes and make your own? No matter what palette you decide on someone else will want it different so I say do what works best for you. You are the developer after all! I would add a program header to your board so the end user can define their own palette, assuming they have the necessary equipment.


In regard to the RGB->YPbPr circuit, I suggest making that a separate product all together. That way people can use it not only with your mods but any console that supports rgb. Having to buy rgb mods + separate converter boards for the quantity of consoles you intend to make this mod for would be quite upsetting to all but the most serious of rgb gamers I would think.

Edited by emerson
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@emerson I still don't have a flash cart for the intellivision. I will keep adjusting and see what I can fit while still fitting YPbPr.

I will make minor changes so that my screen better reflects what RF looks like on my intellivisions.



I have a model 1 intellivision that should be here any day now. I need to take some physical measurements to see if I can make a board that works across both the 1 and 2 models. (so far I have been using the 2)


Anyway, I already have the schematic and the code isn't going to change much.

Assuming I don't make errors when creating the board then I should have everything needed by the end of the month.


I already have dev boards that work more or less the same as the finished product will but I assumed people want to socket these ?

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1 hour ago, Icelvlan said:

Do you have a picture of the install? What do you think will be changed with board surface mount components and size? Isen't only 1 small IC that need to be connected? I don't see why this can't be none-mounted?

I thought I posted a picture of the install (whoops).


I installed "the dev board" like this https://i.imgur.com/ZDewwTz.jpg

Pictured is a very temporary install on the bottom of the motherboard of an intellivision model 2.


Anyway, with a specific board design you could either mount it with the header pin setup or stick it someplace like I am currently doing with the dev board. So you kind of get both options just by changing the design a bit.


The dev board is about 2x1.5 inches and the revision I have made but not printed yet is about 2x2 inches. So either way it is pretty small. The circuit/code won't change at all; it is functionally the same thing (minus that red bodge wire).


I am waiting for a model 1. If I can make the same socketable board work on both then I will do that. Otherwise I will probably revert back to the dev board thing.

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On 10/6/2020 at 9:20 AM, Icelvlan said:

Understood. Will the board be open source or are you selling as a whole?

I will be selling these., they wont be open source for a long time.
There is a lot of time and money invested in this goofy little project.


I just got the model 1 in the mail and it is unfeasible to make a socketable kit for it. :(

I guess I can just go back to the old design and just make breakouts to make the wiring cleaner.


I should probably mention this board works on other consoles as well I just wanted to start with the Intellivision.


I just need to incorporate a clock buffer into the "dev board" design and this will be done.

The Intellivision doesn't need its clock buffered but some of these other consoles do.

I'm just doing some minor research on how to buffer a clock with something that doesn't cost more than 2$.


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1 hour ago, Icelvlan said:

What other consoles will it be compatible with? What do you think your cost will be?

Arcadia 2001, Magnavox O2, Mattel Aquarius, and Fairchild Channel F.

Any console that has 6 or less digital bits for video can interface with this.

Those consoles are the only ones I know of.

The code/clock buffer is the only thing that changes between any of those versions.

Someone would still need multiple boards for multiple consoles.


I have tested all of those except the Chan F and the Aquarius.

I think my Channel F is broken and my Aquarius has a clock with a 12V DC offset (thus the need for a clock buffer).


How much will this cost ? I don't know yet.

It will certainly costs somewhere between 30 and 60$.

It really depends...


Paypal fees are X amount, shipping is X amount, all the parts are X amount, and my time per board is worth X amount. I have to go though and figure that out. If I could invest enough money in a reflow oven and stencils I could possibly reduce the price. Demand will dictate if I can afford to do that.


Right now I need to finish developing the new dev board and then get some tests done with the old version in the interim. For now I just want to concentrate on the Intellivision then move on to those other ones.

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  • 2 weeks later...
1 hour ago, Icelvlan said:

How is the mod coming along?

I tweaked a few colors as I discussed previously.:

  • I am using IMBerzerk's palette for most colors.
  • IMBerzerk's tan (khaki) is the default tan but this tan can be toggled to mthompson's tan (yellowish). Anyway, this is the one and only color that can be toggled.
  • IMBerzerk's grey was too bright (coming off as white) so I am using mthompson's grey there.
  • Lastly, I am using mthompson's brown color since that color (super dark green) looks closer to what I see over RF on all 4 of my intellivisions.

I made some changes to the code that restores hsync pulses inside of vsync,. which has a very small chance of allowing this to work with an OSSC. If this code doesn't help with the OSSC then I will remove it and allocate those resources to adding another color or two to the palette toggle function.

I mean I am working with binary and the code is so full right now changing a single 0 to a 1 puts me over budget as far as available space.


Sadly, most mod developing is sitting around waiting for boards/components to arrive (which is what I am doing right now). I will have at least 10 of these put together by the end of the month. It will take some time after to restock some of these components (the CPLD and DAC). Once I validate the design I won't have a problem buying a larger amount.

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