Add RGB to that old CRT

bentendo64

Active Member
This is a guid-ish sort of thing, I guess. Not really. I was gonna post this in the "Screens" section, but I guess that's gone now....

Anyway, down to business.

I picked up an old crt for free from a hotel that was upgrading. The original plan was to drive the deflection coils with an audio amp and graph parametrics. As it turns out, you need a pretty good amp for a tube of this size to do that, so something else had to be done with it.

RGB video input seemed like a good idea. I have a Super Nintendo that can output it, and the N64 can, too with a bit of modification.

So I cracked open the TV, and guessed at which wires coming off of the video amp/CRT connector would be for the individual color signals. It's pretty easy to tell, because most of the time they're labelled. But mine weren't. I made an educated guess at the three wires that I traced back to three identical circuits on the board containing a transistor.

8mDnNPa.jpg


And then I cut and soldered RCA jacks to the wires.

3dj6LhY.jpg


First test:

rPPjTZL.jpg


The wires weren't labelled as to which were red, green, and blue, so I had to guess. I just mixed up the green and blue signals.
Oh, and before I forget, for syncing, I just connected composite to the composite input on the TV. I don't know if it will work with the actual composite sync signal, because it didn't for me. That might just be because of my cable, though. I don't think that part of it was grounded, I can't remember exactly how I built my cable.

Anyway, all normal now:

eXWhfdV.jpg


And don't forget the proper labels!

286RdvX.jpg
 
Kickback said:
You.. opened a CRT?

Isnt that incredibly dangerous?

Maybe so, but it looks like the end result was worth it. Since you guys have SCART, you'll never know our pain.
 
Zero said:
Kickback said:
You.. opened a CRT?

Isnt that incredibly dangerous?

Maybe so, but it looks like the end result was worth it. Since you guys have SCART, you'll never know our pain.

Haha yeah, godknows why you guys got trapped with composite.

I'm just saying, i've heard opening a CRT can actually kill you if you aren't careful.

Good work though! That picture looks really clean.
 
Yeah KB is right, you are supposed to wait a few days after it's been off iirc or your radiation level will increase
 
I've heard that every time you open a CRT, 63 puppies are corrupted by the devil and then sent to torment you.
 
Haha, I don't think it's too terribly dangerous. I only touch the things I need to and leave everything else alone. I always unplug it while it's on when I'm gonna be working on it. Also, if I'm planning on working around the HV stuff at all, I just touch a grounded (and insulated) wire underneath the suction cup-looking thing on the tube. Normally there's a zap.
 
I mean madam Curie didn't feel the radiation either; doesn't mean it isn't there
 
Also, the puppies are in like... Mexico. They'll take a minute or two to get to you.
 
Oh, that explains why they aren't here yet. Also maybe because we aren't supposed to have pets in the dorms here, so they would have been stopped at the door.
And if you're really worried about the radiation, that's part of the reason the tubes are glass. ;)

ProgMetalMan said:
Can RGB be converted passively to the component color space?

I think so, but I'm not sure how difficult it is. I think component is more closely related to composite and S-video, though. You have the luma signal, which is the same as S-video luma (brightness+sync, if you connect this to a composite input, you will just see the greyscale picture). The other two signals are the difference between green and blue and the difference between green and red or something like that.
 
I was just kidding; there's 4 pounds of lead in them for a reason :) You are correct; component and composite use the YUV color space rather than RGB colors
 
bentendo64 said:
Oh, that explains why they aren't here yet. Also maybe because we aren't supposed to have pets in the dorms here, so they would have been stopped at the door.
And if you're really worried about the radiation, that's part of the reason the tubes are glass. ;)

ProgMetalMan said:
Can RGB be converted passively to the component color space?

I think so, but I'm not sure how difficult it is. I think component is more closely related to composite and S-video, though. You have the luma signal, which is the same as S-video luma (brightness+sync, if you connect this to a composite input, you will just see the greyscale picture). The other two signals are the difference between green and blue and the difference between green and red or something like that.
Component (or more precisely, YPbPr) does indeed have a Luma signal (Y), but the other two signals are [B-Y] and [R-Y], but I wouldn't really feel comfortable saying it's more like composite and S-video just because it uses Luma. You can convert between RGB and YPbPr without any real loss in data, but you can't really say the same about S-video and composite (hence why we are looking for ways around using them).

I'm actually about to start working on a project that will involve converting an image from the RGB color-space to the YIQ colorspace in order to isolate the Luma signal, where I'll perform some functions on it to equalize and then convert the signal back to RGB to display out through VGA.

If that goes well, I may look into an more interesting project involving converting YCbCr into RGB.
 
Interesting.... So when you convert it to YIQ, will it be pretty easy to convert that to YPbPr?
Also, wasn't Marshall or someone working on a component video upscalar for N64?

I guess I should also mention resolution. With my mod, I don't think something like a Gamecube would work (I think the Gamecube has RGB output, someone correct me if I'm wrong). This is because NTSC TV's have a resolution of something like 320 colums by 240 lines. The SNES works and most N64 games will work because they output 240p. The Gamecube outputs 480i (for composite/S-video) and 480p for component and RGB. So if you hook up a Gamecube like this, unless for some reason it outputs in interlaced mode for RGB, you will see the top half of the screen one frame and the bottom half the next (or is it quarters of the screen? I'm not sure).
 
bentendo64 said:
Interesting.... So when you convert it to YIQ, will it be pretty easy to convert that to YPbPr?
Also, wasn't Marshall or someone working on a component video upscalar for N64?

I guess I should also mention resolution. With my mod, I don't think something like a Gamecube would work (I think the Gamecube has RGB output, someone correct me if I'm wrong). This is because NTSC TV's have a resolution of something like 320 colums by 240 lines. The SNES works and most N64 games will work because they output 240p. The Gamecube outputs 480i (for composite/S-video) and 480p for component and RGB. So if you hook up a Gamecube like this, unless for some reason it outputs in interlaced mode for RGB, you will see the top half of the screen one frame and the bottom half the next (or is it quarters of the screen? I'm not sure).
If I wanted to convert to YPbPr, then I wouldn't need to go YIQ first. I believe the steps for YPbPr would be to convert to YCbCr and then pass it through a DAC to make it analog.

As for NTSC, the resolution is 640x480. I just finished up a terrible pacman clone for which I had to create my own VGA driver. All of the timings were based off of a screen at 640x480 (actually 800x525, but the extra pixels/lines have to do with blanking time and aren't actually visible).
 
YPbPr can be converted to RGB and vice versa with simple (ish) analog circuitry. I haven't done it, but it's fairly well documented. This is for plain 480i/240p signals; once you start dealing with progressive scan it gets a lot more complicated IIRC.
 
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