Turning these video signals into VGA

[miguelvp]

Wrong upscaler.  The retro arcade machine community has upscalers that can handle their medium rez. (25KHz Hscan, 60Hz Vscan) consoles.  Google: 25KHz JAMMA converter VGA If you can find the 3 bit digital signal responsible for those brightness levels, you could remap it into RGB and tweak the pallete to your own tastes.    I'm thinking a fast 3 to 8 line decoder driving analog switches to select from a bank of 24 presets to provide an analog RGB colour to replace each brightness level.   

Actually the price of those is not too bad, but with that humongous back porch I wonder if it will work:
http://www.ebay.com/itm/Gonbes-GBS-8200-CGA-15kHz-EGA-25kHz-Arcade-JAMMA-PCB-to-VGA-Video-Converter-/111462780792

[macboy]

Wrong upscaler.  The retro arcade machine community has upscalers that can handle their medium rez. (25KHz Hscan, 60Hz Vscan) consoles.  Google: 25KHz JAMMA converter VGA If you can find the 3 bit digital signal responsible for those brightness levels, you could remap it into RGB and tweak the pallete to your own tastes.    I'm thinking a fast 3 to 8 line decoder driving analog switches to select from a bank of 24 presets to provide an analog RGB colour to replace each brightness level.   

Actually the price of those is not too bad, but with that humongous back porch I wonder if it will work:
http://www.ebay.com/itm/Gonbes-GBS-8200-CGA-15kHz-EGA-25kHz-Arcade-JAMMA-PCB-to-VGA-Video-Converter-/111462780792

It "Supports image position control & image zoom control", so in theory you can adjust for different porch durations. Whether the range of those controls is sufficient is unknown. Hopefully when combined with the monitor's own image postion and size adjustments, it can be dialed in.

[miguelvp]

@OP

Is there a possibility you could take a scope capture of the VSync with respect of the HSync so I can fine try to replicate the vertical front,back porch and pulse?

With that information I can replicate your signal and see what can be done to lock it.

Also be careful when the time comes to replace the tube and it's power supply, but for the sound of things it seems you are aware of the HV dangers in there, but never hurts to point it out for others reading the thread.

[MattHollands]

I'll get a VSYNC and HSYNC picture tonight! Sorry, had a very busy couple of days!

[miguelvp]

Take your time, wife is taking me out for dinner, or is it the other way around? I'm never sure 

[MattHollands]

Ok I've taken images of the VSYNC and HSYNC together.

I've taken images at multiple time-bases so you can see it on different scales. The timebase is included in the name of the file. Of course blue is VSYNC and red is HSYNC.

Have a good evening!

[miguelvp]

Thanks, it seems the video is interlaced so you have even and odd fields.

I'll take a look at them tomorrow in more detail.

Edit: not interlaced, not sure why I thought that, I guess I'm not too used to white wine

[miguelvp]

I don't know what I was thinking.

The HSync vs VSync doesn't give us nothing new other than the vertical pulse, sorry for asking that and wasting your time.

What it would be useful to find the vertical front and back porch, would be showing the video signal versus the VSync as this:



That shows the front porch to be 2 lines, the sync as 3 lines (which is what you showed) and the back porch to be 12 lines.

[MattHollands]

No worries, it doesn't take long to capture some waveforms!

Here is VSYNC-VIDEO at a few timebases.

[miguelvp]

Well, at least I think I have your video reproduced, well as close as I could get since I can't get the exact pixel clock.

Here is my result based on your VSync vs Video:


Your signal is:
Screen refresh rate: 60Hz (Edit: correction the refresh rate is really 59.952 Hz)
Vertical refresh: 25.000kHz
Pixel freq: 14.550 MHz

Horizontal timing (line):
Polarity of horizontal sync pulse is negative
Visible area: 456 pixels
Front porch: 16 pixels
Sync pulse: 46 pixels
Back porch: 64 pixels
Whole line: 582 pixels

Vertical timing (frame):
Polarity of vertical sync pulse is negative
Visible area: 378 lines
Front porch: 11 lines
Sync pulse: 3 lines
Back porch: 25 lines
Whole frame: 417 lines

Here are the settings for my programable module:


I'm going to try to hook it up to my TV that has VGA input (you shouldn't do that because the voltage of your video signal is way beyond 0.7v)
Edit: my thought is that TVs do support legacy NTSC signals so there are higher chances that it would sync.

Also I'm going to try if like Richard mentioned earlier if I can make a composite signal out of this, maybe based on an Analog Devices RGB to NTSC/PAL Encoder AD724 if I can find one out on ebay since I would think it's obsolete, but there are plenty of VGA to composite adapters out there available for very cheap.

I know composite is not ideal but since you are really just doing black and white it might be not too bad and finding an LCD that takes composite in is easy.

Also I have co-workers that have old cabinets and they might have that JAMA converter, I'll ask around to see what it makes out of this signal.

I'm surprised the visible resolution is just 456x378, can you confirm those values?

[miguelvp]

I just noticed the pixel clock is very close to NTSC 14.318180 MHz

I'm going to see what horizontal values will be needed for that pixel clock frequency to stay at 25kHz and leave the vertical alone.
It's more likely to be that frequency than the 14.550 MHz I measured visually.

Edit: Nah, that gives me 572 pixels for the whole horizontal line or just 456 visible pixels, so I think the 14.550 MHz is the right pixel clock.

[miguelvp]

Well, I did hook it up to the TV VGA input and:



That's my little board on the lower left of the image.

It doesn't give me resolution information and I'm just displaying white at the moment.
Tomorrow I'll see if I can put a more advanced version of my project with these values and some text to see if there is any distortion or glitching.

The good thing is that at least a small LCD TV might do the job for you as long as you can divide your video input signal by 2 so is within tolerance.

Edit: at least on a US LCD TV, but maybe they all support PAL/NTSC/SECAM as far as timing signals go via the VGA connector.

[miguelvp]

More on the 456x378 visible resolution.

If the device character set uses 8x9 glyph sprites, it will yield to a text resolution of exactly 57 by 42 characters, which seems to be consistent with the picture you posted if you zoom in:


Edit: It seems the sprites are 6x9 that will be 76 by 42 characters, I think that is more likely, but the 456x378 resolution seems to hold.

[miguelvp]

So I did use a version of my code that displays the character set and keeps on inverting one character every frame, so it inverts 60 characters per second.

I'm using some graphic sprites to separate the characters but those take a full 8x16 block of pixels the same as the characters do.
On the vertical i'm dividing the full resolution by 2 so in essence every character takes an 8x16 pixel

On the horizontal it's using 8 pixels per character so we expect 57 of them for the full 456 visible pixels, and we do get those.
On the vertical however I was expecting 378/16 or 23.625 characters, but I'm only seeing 22. I can go through the TV menu and change the vertical position and I can see the 26 missing pixels, but my TV doesn't let me adjust the height to see all the frame.

In short, out of the 456x378 visible in the signal, I can only get 456x352 to display on my particular TV as seen here:


If I was using the original signal, it will mean that 3 lines of text would be missing since your characters are 9 pixels high, but maybe your TV can adjust the horizontal scaling of a VGA signal or you can change the horizontal scaling on your HP 1662As Logic Analyzer/Oscilloscope.

But the good news is that your signal locks into an LCD TV, now to find one that matches your screen dimensions not the 40" I'm using
Also consider the Composite conversion, there are a lot of LCD panels for back-up camera systems that take Composite and they are up to 8 inch LCD panels diagonally.

What is the diagonal dimension of your screen?

Edit: also if you have a small LCD TV around  that has VGA input and a VGA cable and you just wire the Ground, HSync and VSync but not the video you should be able to see if that TV will lock into the signal.
Then you can use a resistor divider with 75ohm termination of your video signal and connect that to all three RGB inputs of the VGA connector and you should be able to see the screen.

[miguelvp]

@MattHollands

Do you think using an LCD TV would be enough for your needs or do you want me to test this signal with converting it to composite (just some resistors and a electrolytic cap) will do.
Also I can look to see if anyone around work has a JAMA converter and test it.

Also did you try to put the HSync, VSync with no video to an LCD TV to see if you get it to sync?

And the diagonal dimension of your CRT and aspect ratio (probably 4:3) to look for a suitable panel.

[MattHollands]

Great to see that the signal is working for you!

I actually would like to mount the screen inside the original case, where the CRT currently is. Ideally I would also add a "VGA out" port where I could attach an external monitor too.

I assume it's pretty easy to get a composite to VGA converter? In which case I could convert it to composite and then convert that to VGA which could drive any screen?

I did put the HSYNC, VSYNC signals without Video into a PC monitor, but not a TV.

[miguelvp]

I assumed you wanted it inside, that's why I was asking for the diagonal  size of the CRT in inches.

There are some options:

1) Find a small LCD TV that has VGA input and that fits inside and bring the voltage of the video signal so it doesn't go over 0.7V with a 75Ohm termination this won't allow for an external VGA connector unless it's hooked into a larger LCD TV that has VGA input.

2) Find a small LCD monitor that fits inside that takes Composite as an input (like the cheap rear view camera kit that they sell
for backing up your car). You'll have to find the right value resistors and electrolytic cap so that the Composite signal is compliant.This won't allow an external VGA monitor either unless it's an LCD TV that has Composite input.

3) Use the JAMA board to scan convert your signal (after bringing the video voltage down to 0.7V) Then you can find an LCD panel with VGA controller that will fit where the CRT is and allows to put a VGA output that will work on any VGA LCD monitor. That is if the JAMA board can lock into your signal and upconvert properly.

The cheaper options are the LCD TV with VGA or Composite inputs that matches the dimensions of your CRT.

[MattHollands]

Sorry, I missed that part of your response. The display is currently ~9", however I would be happy with 9, 8 or 7" because I plan to make some modifications to the case too.

I'm tempted by the Jamma board because it seems very flexible. It's also not a huge expenditure, so perhaps I'll give it a shot. Seeing as your LCD TV managed to lock onto the signal, it seems quite probable to me that the Jamma board will be able to lock on, seeing as it's designed to be flexible with the input signal.

I'll probably order it tomorrow unless I change my mind before then.

[miguelvp]

Cool, let me know how it goes

Edit: still take care of that video voltage of yours 1.3V might be outside of the JAMA board specs.

[MattHollands]

Just looking at the datasheet, it appears that the board requires 2A, which is a lot and I'm not totally certain if I will be able to extract that from the oscilloscope power supply.

Perhaps I should try the composite signal first.

Just going back to your original option 2 posts ago: Isn't option 1 the same as what I tried with my monitor where I connected the VSYNC and HSYNC signals and it didn't lcok? Are you suggesting I search for a monitor that will lock onto these signals?

[TheSteve]

I have been able to use one of those jamma boards to convert the video out from an HP8921A service monitor to VGA. It uses something like 300mAh when running, I've never seen anything close to 2 amps. The HP8921A has a 19 kHz video out on a single connector so I also use an LM1881 to separate the sync signal.

[miguelvp]

Option 1 would be looking for a 9" LCD "TV" with VGA input, not a computer monitor.
Apparently TVs have the hardware for NTSC like signals so chances are that they will lock.

Option 2 is one of those back-up car rear cameras and displays I'll look around but usually the LCD part of the system takes Composite video that the rear camera supplies. Since your signal is black and white, you don't need to care much about producing a color burst on the composite video.

I'll look for a schematic on how to get composite from this signal.

[miguelvp]

For option 2 here is a simple diagram of VGA to Composite B&W
http://www.geocities.ws/podernixie/htpc/cables-en.html#vgavideo

Since you don't have RGB at 0.7V you need to bring that 1.3V value to the Composite level.

I'm not too familiar with the Composite signal but I think the max voltage is about 1V so you'll need a voltage divider to bring it within that 1V.

Someone please step in if I get this wrong.

Since the video signal has to be 75 Ohm terminated I would use a 75 Ohm resistor from your video signal to ground after passing the signal through a 25 Ohm resistor. I think that will put you in the 1.0 volt range.

If it was for VGA I would use a 75 Ohm resistor to ground after passing the signal through a 75 Ohm resistor halving your video voltage.

As for the LCD Composite monitors is a gamble if they will work but there are plenty on Ebay:

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=9+inch+backup+camera+system&_sop=15

Those are full systems with the camera, remote etc, but you just want the display that takes Composite in.

I'll search if I can find an LCD TV with VGA input that is just 9 inches for option 1.

Option 1 is probably a gamble too:
I don't know if this little car monitors can deal with NTSC signals:
http://www.dx.com/p/9-digital-car-monitor-displayer-w-touch-keys-vga-hdmi-av-black-411613#.VrBN7xUrKUk

http://www.ebay.com/itm/Portable-8-inch-TFT-LCD-4-3-Color-Monitor-Screen-Display-VGA-BNC-AV-Fo-PC-CCTV/271308397540

There are a trillion of them those are just two examples, but hard to tell if they will lock into your signal via the VGA or Composite connectors. But both will work with the JAMA board I would think.

[MattHollands]

Ok thanks for all of that miguelvp!

Based off of TheSteve's input I've gone ahead and ordered the Jamma board from ebay. Should arrive on the 9th of feb!

[miguelvp]

I'm thinking on getting one myself for my older video game consoles.

Btw people are hacking at it to improve it:
http://shmups.system11.org/viewtopic.php?f=6&t=52172
Lots of datasheets on that link.

Other links:
https://ianstedman.wordpress.com/gbs-82xx-experiments/
https://ianstedman.wordpress.com/2015/01/25/gbs-82xx-experiments-part-2/

BTW I can't take credit for that board, it was Ian.M that suggested it.
I would have tried the SCART to HDMI but it seems this one is more flexible.

Did you get the GBS-8220? that has dual VGA outputs.

Edit: but if you didn't it doesn't matter, it has a VGA connector and associated pins as well, maybe with some transistors you can duplicate the output anyways without loosing driver power to either screen. The linear regulator on the 8220 has less ripple too, but not sure how bad the switching supply could be.

Other than that they are both identical.