VOGONS


First post, by RayeR

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Hi,
I'm thinking about buying a new 4k monitor and as I browsed the portolio I was disappointed that all new monitors dropped the analog VGA/DVI-I input to be able to connect an old computer. I simply don't have enough space on the table for 2 monitors so I'd like to use one for all with some converter. I found some cheap VGA2HDMI adapters but I got some user experiences that are not much positive about them (some resolutions/refresh rates are not supported or cannot operate with some monitors). Here's one that could be better from cheap ones: https://www.amazon.de/gp/product/B00IJBOMN8/r … sc=1&pldnSite=1
but still some problems reported.
On the opposite side there are well known scalers like OSSC and Framemeister that use expensive FPGA chips so the price is high. And they seems to be primary aimed on consoles and low-res 8bit computers. I even cannot found what is the maximum resolution of VGA input on OSSC.
Currently I don't need more than one VGA input. So I was thinking how about to reuse a control board from an old LCD monitor - the price is 0 as they are lying tons on scrapyards. I have one from BenQ FP73G (17" 1280 x 1024) with DVI+VGA. It's based on Realtek RTD2523B that is well documented: https://datasheetspdf.com/pdf/721071/Realtek/RTD2523B/1
I cannot find the schematics of FP73G but found a similar one FP92W with the same chip
http://elektrotanya.com/benq_q9w5_fp92w_9j.l2 … p/download.html
I just need to know where to connect a power supply and control buttons to swith it on.
The output is LVDS for flat panel. So I try to make a simple converter board from LVDS to HDMI with chip ITE IT6263FN. It can be bought on ebay/ali for a few $. The documentation is worse. I have only 16-pages brief datasheet without registers and programming description. It is available only on CSDN: https://download.csdn.net/download/liangzuoyang/11268290 - anybody can download from there?
Fortunately there's some Linux driver that documents a lof of registers (the chip is used on some iMX8 dev.boards).
So if all will go the rigth way I could be connect it to HDMI monitor and it should behave the same as original BenQ monitor from VGA side - should accept all common VGA/SVGA resolutions. Then I could replace Realtek RTD2523B with a kind better RTD2660 that has also composite video input as a bonus and make it on one compact board. I'd like if someone could share experiences with such video chips - it's quite new topic for me...

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    LVDS2HDMI with IT6263FN experimental board
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    BenQ FP73G with Realtek RTD2523B LCD ctrl board
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Reply 1 of 12, by Tiido

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Only concern I have with this approach is latency, you combine latency of the LCD board and then more latency from scaler of the target monitor (since it will not feed native resolution). It should still be sub-frame, at least on the first stage side but both combined may reach half a frame and that starts to become noticable.

Another possible problem is bit depth, you're most probably going to have 18bit temporal dithered signal going to the HDMI chip as LCD panels that actually were 24bit didn't become common until recently (like last 5 years). The Realtek chip does support 24bit output and maybe the HDMI chip can do too so there's one less headache if the firmware can be programmed to enable it.

Things like OSSC etc. are indeed only for low resolution 15KHz RGB from old consoles with bypass for 31KHz RGB (lowest VGA resolution / highest game device resolution). It definitely cannot handle any higher resolutions and it isn't even meant to. Their only job is to turn the unsupported low res video into something higher resolution for PC inputs on newer display devices so that you can actually use things and bypass stuff like deinterlacing that is usually imposed on TV inputs.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 2 of 12, by Tiido

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However you can use the frontend chip of OSSC and combine it with HDMI transmitter and MCU and create a analog to HDMI/DVI converter, bypassing that FPGA from design as you don't need the scaling. MCU has to program in resolution specific info to get correctly digitized image which is the primary headache with all the cheap converters.

TVP7002 has all of its documentation available and it should be good up to 1920x1080 with reduced blanking, to be within the normal single link HDMI/DVI things 165MHz limit. The ITE HDMI chip can be reused too, though its documentation is less available.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 3 of 12, by RayeR

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The latency - maybe... It may help to set 1:1 on side of RTD or target monitor
Bit depth - yes, probably BenQ panel was 6bpp, I don't know where the dithering is done if in RTD or LCD panel itself. But the chip could be reprogrammed to TrueColor output. This would be next step after making LVDS2HDMI working.

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Reply 4 of 12, by Tiido

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Dithering is done in the realtek chip, there are several settings for it even wen I skimmed through the datasheet.

I'm not familiar with the chip to know if it can just act as a digitizer without scaler, if it could then this would be even better as (dumb) ADC is what you primarly will need.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 5 of 12, by RayeR

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Common LCD panels have OSD option to scale image to whole screen or keep 1:1. I don't know about this, I have no longer the LCD panel so I cannot test it now.

BTW how about HDMI lines AC coupling? I have seen some designs like nVidia Jetson where HDMI was AC coupled but other designs and HDMI spec itself claims "DC coupled TDMS..."

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Reply 6 of 12, by Tiido

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that kind of "1:1" I have only seen in laptops, never on a desktop monitor. This won't help here, all the empty pixels are still written (it is not possible to drive arbitrary part on a panel), just different scaling method applied.

HDMI is supposed to be DC coupled but it depends on transmitter. It needs to be able to supply right amount of current to maintain signal integrity and if the transmitter calls for AC coupling you do it that way, otherwise no. This is one place where you exactly follow what datasheet says, there is no room for your own ideas there whatsoever.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 7 of 12, by darry

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The OSSC can digitize and pass through resolutions above 640x480 up to (and including) at least 1600x1200@60Hz (upper limit is probably TVP7002's max capability) .
It just can't line multiply any input resolution greater than 640x480 .

I use an OSSC with my Voodoo 3 and 1920x1200 LCD monitor (which I use in 4:3 mode as if it was 1600x1200).

EDIT : see here Re: VGA Capture Thread for some examples

Reply 8 of 12, by RayeR

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Aha, OK thanks for info. Just to be clear what you mean by "pass through" - the VGA signal is only digitized and passed out pixel by pixel without any further transformations and processing so no delay introduced... 1600x1200 is good enoug but for my purpose OSSC is quite expansive and I don't utilize FPGA in this case...

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Reply 9 of 12, by darry

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RayeR wrote on 2022-02-07, 18:27:

Aha, OK thanks for info. Just to be clear what you mean by "pass through" - the VGA signal is only digitized and passed out pixel by pixel without any further transformations and processing so no delay introduced... 1600x1200 is good enoug but for my purpose OSSC is quite expansive and I don't utilize FPGA in this case...

Yes, I mean digitized with no processing or delay (or a minimal one).

If you don't need the line multiplication, etc, OSSC is indeed overkill .

Reply 10 of 12, by agent_x007

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When I bought my 4k screen (I own LG 27GP950 monitor since June 2021), I thought VGA to DP would be better.
So I bought VC160A and Delock 62596 (in short : VGA => DVI => DP with optional VGA => DVI => HDMI [through passive adapter]).
Also, I recommend getting a two port switcher for ease of use between main PC, and test platform (type depends on needs HDMI/DP).

I use VGA to HDMI as backup (Delock 62408), here's how it looks inside :

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Last edited by agent_x007 on 2022-02-07, 20:08. Edited 6 times in total.

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Reply 11 of 12, by agent_x007

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PS. Here's my Aten VC160A :

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^I can recommend this little thing (I bought it used)

Hope this helps 😀

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Reply 12 of 12, by RayeR

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>agent_x007
Thanks for hi-res photos of those devices. The price of Aten VC160A is similar to OSSC and Delock 62596 still x-times higher than cheap adapters - it's out of my scope. But it's good to see on what chips are they besed on. Not much magic there. IT6613 is HDMI transmitter with parallel RGB input - I already found TFP410 from TI that should do the same. It's paired with some video ADC with parallel RGB output and chained together. My choice of IT6263 was because it takes LVDS input that is much more common in LCD monitors than parallel RGB so I could re-use a half of the circuit.

Gigabyte GA-P67-DS3-B3, Core i7-2600K @4,5GHz, 4GB DDR3, 128GB SSD, GTX670(GF7900GT), SB Audigy + YMF724F + DreamBlaster combo