Weekend home digging project - "Finding VGA666"

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Weekend home digging project - "Finding VGA666"

Post by tobetter »

It's been a couple of months since my new home project is started, that is to support VGA666 from ODROID-N2Plus.

I've been asked many times why ODROID-N2Plus does not support VGA666 and a composite video out is not good, they all asked me about it were a retro game player and all they have old CRT displays. Actually the request were when ODROID-N2 is released, I didn't realize how it is to support VGA666 is great and important since I am not a fan of playing a game. I did have an idea of VGA666 support but it requires an additional hardware that made me hesitate to do experimental test and finally I made some.

The 1st experimetal version to support VGA output.
Image

Then 2nd version became a bit larger with a TV encoder for RGBS/COMPOSITE/S-VIDEO.
Image

They work but not playable since supported resolution is not yet 480i or 240p, made some progress yesterday to have 640x480 and 640x240 and here is the output in 640x480 from ODROID-N2 through RGB cable.
Image
Image

There would be a more points in hardware to improve it, so I made a PCB which is coming in a week. Two boards for one solution, originally it was in a single board but splitted in order to place all video connectors to rear side.
HDMI.png
HDMI.png (167.85 KiB) Viewed 770 times
RGB.png
RGB.png (150.5 KiB) Viewed 770 times
It also requires a kernel changes for the display timing which is not supported yet, specifically 480i and 240p for retro games. It made me keep changing the kernel source every weekend and tested with CRT displays that I purchased in the 2nd market - Samsung 14" CRT TV and Sony PVM-14M2MDE. Not perfect yet, at lest it shows a picture and it would be a bit better when I use a PCB? :) Actually wanted to share my project tonight KST after doing some improvement but why I am writing this earlier than I expected is my 2 weeks old PMV-14M2MDE is burned out. :( It was actually not in a good shape and I fully acknowledged when I purchase it. But paid for it since it's only $80. Now it's gone... :D :oops:

Since I paid a lot for displays, components and PCB as well as my time so far, I would not stop right now...at least I will finish my PCB on next weekend and will see if I can improve it more.

So.......agonizing to purchase another one I found in the 2nd market that I can pick up today itself.
So...stay tuned...

Buy me a coffee if you like my project.
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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

Whoa :O

That board sure got more complex than VGA 666, as the baseline design is just a bunch of resistors. I assume this is because you stretched your goals beyond a simple VGA output.

Yes please, I want to know more! Especially how did you convince GPIO to bitbang (?) an actual image data out.
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Re: Weekend home digging project - "Finding VGA666"

Post by rooted »

The color output to that professional Sony RGB display is beautiful, I've been searching for one but they are far too expensive.

It's an awesome project.

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Re: Weekend home digging project -

Post by tobetter »

rooted wrote:
Sun Aug 07, 2022 9:23 pm
The color output to that professional Sony RGB display is beautiful, I've been searching for one but they are far too expensive.

It's an awesome project.
True, it's not budget hardware at all... :D

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Re: Weekend home digging project - "Finding VGA666"

Post by tobetter »

mctom wrote:
Sun Aug 07, 2022 6:20 pm
Whoa :O

That board sure got more complex than VGA 666, as the baseline design is just a bunch of resistors. I assume this is because you stretched your goals beyond a simple VGA output.

Yes please, I want to know more! Especially how did you convince GPIO to bitbang (?) an actual image data out.
Thanks.
It does not use GPIO for video since its bandwidth very poor for the video. Tried SPI as well but still bandwidth for 30 fps was not possible.

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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

So what you're doing is going to be quite universal - a HDMI to (analog video) converter, as long as the OS is able to output such a low resolution through HDMI. Or am I still missing something?
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Re: Weekend home digging project - "Finding VGA666"

Post by tobetter »

mctom wrote:
Sun Aug 07, 2022 11:28 pm
So what you're doing is going to be quite universal - a HDMI to (analog video) converter, as long as the OS is able to output such a low resolution through HDMI. Or am I still missing something?
Correct, actually the design could be universal and it can work for any hardware/OS if it supports required resolution and video timing.

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Re: Weekend home digging project - "Finding VGA666"

Post by mad_ady »

That's quite a laborious project! Have you drawn inspiration from https://youtu.be/l7rce6IQDWs?

Wasn't there a composite (or s-video) pin output on C2? I guess it didn't carry over to N2...

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Re: Weekend home digging project -

Post by tobetter »

mad_ady wrote:
Mon Aug 08, 2022 3:56 am
That's quite a laborious project! Have you drawn inspiration from https://youtu.be/l7rce6IQDWs?

Wasn't there a composite (or s-video) pin output on C2? I guess it didn't carry over to N2...
I've watched the video several times but this project is not inspired from there. Probably if N2 is capable to extend the memory bus, I would try the one to add an additional frame buffer.
ODROID-C2/N2 can carries the composite signal through the ear jack but the problem is it only support 480P or 576P.

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Re: Weekend home digging project - "Finding VGA666"

Post by mad_ady »

Oh, I never thought there are analog TVs that don't support 480p. That's such a niche market!
Wouldn't it be easier to create a circuit to start with 480p and half the rows? It would look bad, but 240p is supposed to look bad...

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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

I was thinking the same. If the actual video source (a game emulator) outputs 240p, it may be upscaled by software to 480p, that probably is no problem.
Removing every second row from analog signal not only sounds like a a non-trivial task, but also would probably not be recognized by a TV.

Fun fact, TMDS link used by HDMI standard has a minimum rate of 25 Msps. Anything slower requires pixel doubling, which is then to be handled by the HDMI sink.
640x480x60 = 18.4M, so pixel doubling is mandatory.

I never got the answer how is 640x240 @ 60fps handled - that's roughly 9.2Msps, and even with pixel doubling on it's less than minimum 25Msps. I never got the answer if such low resolutions are even supported by HDMI, as I wanted to drive a really small display with it.
So I wonder how you managed to get it to work at 640x240.
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Re: Weekend home digging project - "Finding VGA666"

Post by tobetter »

So...finally I got the PCB and 2 of them are assembled, no major issues on PCB except several silk screens and it works after all. But unfortunately, I got only a black and white screen over CVBS and tilt screen over RGB, no picture over S-VIDEO. After spending a day for debugging and found that the problem is caused by H-Sync, eventually that's because I've ordered wrong part. So...made another order... :(

It does look like this when putting on top of N2/N2Plus.
IMG_20220815_1635437.jpg
IMG_20220815_1635437.jpg (157.79 KiB) Viewed 640 times
IMG_20220815_1635133.jpg
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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

Looks awesome!

I see you're not a fan of SMD components :)
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Re: Weekend home digging project - "Finding VGA666"

Post by rooted »

I like it big and chunky where even a novice can solder the components ;)

It's also fitting being analog with large jacks where no real point in compactness.

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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

It's weird to see chunky electrolytic capacitors that pass analog signals.. But that's how it used to be done, so I can't complain. :)
These days 100uF 10V ceramics can be found in 1206 packages. Two of these would probably take just as much board space :D
rooted wrote:
Tue Aug 16, 2022 2:02 am
I like it big and chunky where even a novice can solder the components ;)
Reminds me when I wanted to buy some 0402 components back in college days, at the local shop. The guy told me they don't sell components that are impossible to solder by hand :roll:
Or was it even 0603?
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Re: Weekend home digging project - "Finding VGA666"

Post by tobetter »

mctom wrote:
Mon Aug 15, 2022 11:45 pm
Looks awesome!

I see you're not a fan of SMD components :)
Thanks. The board have a plenty of space and bulky component with colors in resistors make it look like retro board. :)

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Re: Weekend home digging project - "Finding VGA666"

Post by rooted »

tobetter wrote:
mctom wrote:
Mon Aug 15, 2022 11:45 pm
Looks awesome!

I see you're not a fan of SMD components :)
Thanks. The board have a plenty of space and bulky component with colors in resistors make it look like retro board. :)
It really does, reminds me a bit of an old soundcard.
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Re: Weekend home digging project - "Finding VGA666"

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I sent some time to debug the boards and burned a main component at the first power up since I soldered it as rotated. :D
Then found why the screen comes in black&white, not colour, with the board. So...now I have coloured Super Mario and tried to change the resolution as well as the video timing for 480i and 240p. Since there is no documented information about the display registers to customize the video timing, specifically for the lower resolution and interlaced video timing, I had to try a lot of times after changing a number in the kernel source and keep rebooting. And eventually, I got the picture below which does look liiiiiiiiike 480i as well as liiiiiiike 240p.

480iish picture.
480i1.jpg
480i1.jpg (600.45 KiB) Viewed 545 times
240pish picture.
240p1.jpg
240p1.jpg (605.24 KiB) Viewed 545 times
In composite signal, they shows different wave form that 480i shows two different type of VSYNC for ODD and EVEN field whilest 240p shows one type of VSYNC in every 60Hz.

In 480i mode, both pictures are from the 1st and 2nd fields and they show the different form of VSYNC.
480i-1.png
480i-1.png (65.09 KiB) Viewed 545 times
480i-2.png
480i-2.png (64.64 KiB) Viewed 545 times
In 240p mode, only one VSYNC form in every 260~ lines.
240p.png
240p.png (63.97 KiB) Viewed 545 times
Technically, they look like 480i and 240p but I am not sure if the picture is correct or not since I have no experience with real CRT game playing for sometime. I do remember the picture playing Don King Kong and Bubble Bubble and I do likely remember the shape of pixels of a game screen how they look like, but not sure the picture quality through my board on ODROID when an emulator is running and the picture quality is acceptable apart from the video format.

So...moving forward...
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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

tobetter wrote:
Wed Aug 24, 2022 12:58 am
I sent some time to debug the boards and burned a main component at the first power up since I soldered it as rotated. :D
Oof.. I assume it's that BH7236AF chip. Yeah the marking is not entirely clear on this one. I did exactly the same mistake on my Eng thesis project, learned my lesson to check the datasheet if in doubt.
tobetter wrote:
Wed Aug 24, 2022 12:58 am
Technically, they look like 480i and 240p but I am not sure if the picture is correct or not since I have no experience with real CRT game playing for sometime.
Can't help you with that, but if you have a reliable way of displaying full screen graphics, perhaps some sort of pixel-perfect test patterns would help?
I found that resource on the topic, but the graphics themselves appear to be for demonstration purposes only (various dimensions?):
https://junkerhq.net/xrgb/index.php?tit ... test_suite
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Re: Weekend home digging project - "Finding VGA666"

Post by tobetter »

mctom wrote:
Wed Aug 24, 2022 3:23 am
tobetter wrote:
Wed Aug 24, 2022 12:58 am
I sent some time to debug the boards and burned a main component at the first power up since I soldered it as rotated. :D
Oof.. I assume it's that BH7236AF chip. Yeah the marking is not entirely clear on this one. I did exactly the same mistake on my Eng thesis project, learned my lesson to check the datasheet if in doubt.
Not really, I had no issue with BH7236AF. Had an issue with another main chipset in QFP100 package and I didn't put the index mark properly and confused when soldering.
tobetter wrote:
Wed Aug 24, 2022 12:58 am
Technically, they look like 480i and 240p but I am not sure if the picture is correct or not since I have no experience with real CRT game playing for sometime.
Can't help you with that, but if you have a reliable way of displaying full screen graphics, perhaps some sort of pixel-perfect test patterns would help?
I found that resource on the topic, but the graphics themselves appear to be for demonstration purposes only (various dimensions?):
https://junkerhq.net/xrgb/index.php?tit ... test_suite
I used to run this 240P Test Suite already when testing built-in CVBS, before this project. Since I am integrating the video timing on Ubuntu, not an emulator OS yet, I will run this again. :)

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Re: Weekend home digging project - "Finding VGA666"

Post by odroid »

I really love that interlaced 480i output on the CRT. :D

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Re: Weekend home digging project - "Finding VGA666"

Post by tobetter »

I spent some time to port the change I made for 480i and 240p, gratefully success to EmuELEC kernel and it works. It shows a very wrong screen that says "Life is not easy".
Image

This made me spent my Sunday to figure out. Eventually, it's been fixed after fixing the code in Amlogic code that wrongly stream the video in the interlace mode.
Image

But still wrong in 240p. :(
Image

It's being progressed anyway. :D

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Re: Weekend home digging project - "Finding VGA666"

Post by rooted »

That 480i picture looks great!

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Re: Weekend home digging project - "Finding VGA666"

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Ok....so...my Chuseok holiday went over with the board debugging for a display issue, the wavy live moves slowly over the screen from here to there or there to here. Originally, I struggled to figure out the problem while changing the video timing for 480i, the issue only happens in 480i and 240p is almost perfect.
Image

After digging a lot of things in the code, my approach is changed to check CSYNC maybe it's not clean like I can see it in the scope, several resistors and capacitors are challenged as well as a couple of TTL gates...but no luck. So my plan B is started with another TV encoder which is designed in the same board.

But...unfortunately, new TV encoder leads me to another problem that more noisy screen, almost everywhere. :( Then after half day debugging, I realize that I missed one pin that is not routed and this pin is involved to colour conversion and need to routed to an external 0.1uF. Then...WoW...way better...way better. Very hard to wire to the chip with my old eyes, it almost took 20 minutes. LoL
Image

After adding a capacitor the picture becomes more clean, better than before but still a bit noisy. :(
BUT...by accident, screen becomes a bit better when I touched a ground with a capacitor and this convince me to checked the schematic and the PCB file. I found that the chip has two analog grounds and both are connected with only 10 mil route in my design, this made a weak signal. After adding big capacitor 220uF to the grounds....BOOM!! My CRT shows different picture after adding the capacitor, it's most clean screen I ever seen in this project.
Image

Since I am not familiar to such game screen, I am not able to judge how it's good so I pack the board right away to ship it to one of N2Plus user who willing to have this board. Then he tested over this weekend, he said it's likely or more than RPi VGA666 since RPi cannot play 480i better than N2. This sounds very promising and started to change the design, added more capacitors and ferrite beads also ground patterns for analog and digital are separated. Now new boards are ordered just now.
Image
Image

So...this project is moving forward and we will see the next board after two weeks. LoL

Buy me a coffee if you like my project.
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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

tobetter wrote:
Mon Sep 19, 2022 12:01 am
I realize that I missed one pin that is not routed and this pin is involved to colour conversion and need to routed to an external 0.1uF.
That one could have been avoided if you ran ERC in KiCad (Electrical Rule Check?).
Don't worry, I don't do that in hobby projects either. ;)
tobetter wrote:
Mon Sep 19, 2022 12:01 am
After adding big capacitor 220uF to the grounds....BOOM!!
Oh no! :o
tobetter wrote:
Mon Sep 19, 2022 12:01 am
My CRT shows different picture after adding the capacitor, it's most clean screen I ever seen in this project.
Phew :?
tobetter wrote:
Mon Sep 19, 2022 12:01 am
also ground patterns for analog and digital are separated.
I hope they eventually get connected somewhere... right? Should not be completely isolated from each other.

Anyway, the project looks amazing, and I admire you for your dedication.
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Re: Weekend home digging project - "Finding VGA666"

Post by tobetter »

mctom wrote:
Mon Sep 19, 2022 2:48 am
tobetter wrote:
Mon Sep 19, 2022 12:01 am
also ground patterns for analog and digital are separated.
I hope they eventually get connected somewhere... right? Should not be completely isolated from each other.
Obviously, both grounds are connected via a ferrite bead and analog ground copper is on the bottom only, digital and ground coppers are not overlapped. It's basic design rule that I understand for mixed signal.
Anyway, the project looks amazing, and I admire you for your dedication.
Thanks, will see if this board will work or not. :D

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Re: Weekend home digging project - "Finding VGA666"

Post by mctom »

tobetter wrote:
Mon Sep 19, 2022 4:29 pm
Obviously, both grounds are connected via a ferrite bead and analog ground copper is on the bottom only, digital and ground coppers are not overlapped. It's basic design rule that I understand for mixed signal.
There are a few schools of thought here. Even engineers at my company often debate it and never reached the consensus which one is ultimately the best.
I represent the view that there always shall be a single solid ground for everything, and the component layout should assure that digital currents will not flow through analog parts and vice versa.

But both schools actually work in the end, and I've seen both in commercial products.
I'm sure your design will be much better than the last one with this measures applied.
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