Hi guys,

Did anyone try to build the transcoder from the first page of this thread ?

Click to view attachment

How good are your colors ?

I did and I seem to have image quality issues... The luminance seems much too high AND overall colors are a little on pink side.

Although I may have a connection problem somewhere, I can't seem to find it.

But I'm also concerned about the circuit itself. Going back to the books, I tried to understand how the circuit works and I think I have it nailed down. I haven't calculated all the equations from it but I have simulated it on a spice simulator. The results are not quite what one would expect but could explain my quality issues.

So back to the question, did anybody try this circuit with the resistor values specified in the design ?

I built one and had none of the problems you are experiencing. As far as the luminance being too high, check that R3, R10, R14 are exactly 2K.

There are alot of NON standard resistor values in that design above.

typically things are designed so that standard values can be used, just above every resistor im seeing above isnt a normal value, which means you either need alot of resistors in parallel, you have to find/buy non standard value resistors, or your using a bunch of POTs. All which drive the cost up, how much have you guys spent for all the parts?

The resistors are all standard 1% tolerance values. Since all resistor values should directly affect the mathematical equations designed in the circuit, I'm assuming that it's really important to get them precise.

I found some of them at my local electronic store but I had to measure and combine resistors for all others. I measured them to have it as close as possible to the design. I found a few on-line distributors that do have them relatively cheap.

For the total price, I'm guessing that it cost me around 10$ .

Hey Bine, I have a small question. Are you still going to build a transoder with the National LMH1251 chip, or only with the schematics posted on this thread?

Cheers.

http://www.x2vga.com/

Neoya Ltd. announced a new version of the X2VGA.
Here's the official product description:
[QUOTE]
The X2VGA 2 has been officially released! The X2VGA 2 High Definition VGA Transcoder by Neoya is designed to work with any gaming console or video device that has a standard component video output, such as the Playstation2, Xbox, GameCube, and Xbox 360, etc. With the X2VGA 2 and a standard VGA monitor, users can play their favorite games at 480p, 720p, or 1080i resolutions - over double that of a standard TV! The X2VGA 2 makes games come alive, delivering the sharpest, most realistic visuals available. Furthermore, the exceptional 480i EasyView and Input AutoSelect features provided by the X2VGA 2 make it easy for users to fully enjoy the mind-blowing audio and visual effects.
Comparing with the former X2VGA , the X2VGA 2 is compatible with various gaming consoles and video devices, and presents you with the perfect visual performance by its brand-new design of video processing circuits. Moreover, the newly integrated two sets of video inputs and PC pass-through function on the X2VGA 2 even allow a quick switch between your gaming consoles and PC.

In order to express our gratitude for your supports, we provide special offer during the first selling of the X2VGA 2:
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I will probably do both. This week I made my first PCB with the original design but I'm waiting for my samples to arrive for the lmh1251 and friends. I want to try out both designs since they so cheap to build. Here's a shot of my first PCB...

Great. I'm looking forward to the results.
PS. Nice PCB

davehtr: It seems that this new version is preety good. It doesn't use the LMH1251 chip though (but I don't know which one's better so it doesn't matter anyway ).
Do you know if any site has reviewed it?

Cheers.

For the sake of completion, here's my final PCB and almost finished circuit.





The picture quality is much better than my first try. I'm pretty happy with it.

Look really nice, Bine. I am looking forward to the result.

Hi I want to build a transcoder and have put 2 days research in it. Whitout getting closer to an
answer
I need to build a transcoder with a s-video input to vga because my home theater system only outputs
EuroScart and S-Video.
I found out that national semiconducturs had made a new chip
the LMH1981.
It think it does the same thing as the old LM1881.
My question is do i need a second ic to pass the video?

Can anyone design or have a link to a diy circut with support for composite\s-video in
to vga?
All help will be very appreciated Thanks in advance

Cheers,
PJ Viking

PJ Viking, these transcoders only convert component to VGA.
You need a video processor (such as Avermedia's TVbox series).

Thanks for the Answer
In the data sheet of the LMH1981 it says: Features
n Standard analog video sync separation for NTSC, PAL,
SECAM, 480i/p, 576i/p, 720p, 1080i/p, and RGsB from
composite (CVBS), S-Video (Y/C), component (YPBPR),
and computer video interfaces.

Doesn't that mean that it can handle composite\S-video?

The LMH1981 is merely a sync separator, nothing more. I imagine you could use it in a multi-input video processor design, but the sync seperator would only be a small part of the circuit.

The conversion of composite or S-video is not the same as the conversion of component. I've seen S-video and composite to VGA circuits out there, but you could probably buy one for much cheaper than you could build one (I didn't save the links to them though).

Thank you for another informative answer, Chad N.

I guess I just have to sell my little 5.1 home cinema. I will use my pc as a htpc. And maybe buying a
proper reciver when I have saved some money. And then build my own sepakers
The DIY bug has got me

I just recently finished my Ken Gasper Comp->VGA converter. I bought all the components from Mouser (minus free samples from the vendors) with a grand total of ~$25 including a pcb and housing to put the circuit in. The only thing I didn't buy was the power supply stuff (regular, brick, etc) because I found one laying around the apartment. I bought the *exact* resistor values at 1% tolerance and my balance of color looks great, I really can't tell a difference between the same source coming from my PC (VGA) or my progressive scan DVD player (Comp->VGA via converter).

An important note is that most LCDs (from my google-ing) won't support 480i, however, some CRTs may (again, this isn't coming from my personal testing). If you want to view 480i on your LCD (projector) you'll need to come up with a line doubler (also called scalar, maybe...not sure). I highly recommend Ken's design as it seems to work very well. I'm contemplating creating a 4 input component switch box with VGA and Comp vid output a la the MAX4141... we'll see if my college fun gives me the free time to take care of that (meh, I should face the fact and accept electrical engineering doesn't allow for too much spare time...but I can keep my hopes up).

As far as the debate about the LMH1251, I don't really think there's going to be much difference between the output of this device versus Ken's design. I had actually ordered and received samples of this chip prior to finding Ken's design, but could never find a TSSOP to DIP converter at a decent price (I don't have the nifty access to make a pcb and I'm too lazy/cheap to pursue the differenct possibilities). Not to mention, I wasn't in the mood to try to come up with something new when the other design had been tested and known to work. I presume the main benefit is that it would be an all-in-one solution...if anyone sucessfully gets this working, please post as I'd like to know how it performs.

One big fat warning. When I ordered the 4383 chip I ended up getting 4382 (not sure if this was my mistake or theirs - can't find the order confirmation information). But to make a long story short, double check the part number once you get the chips to ensure you're using what you think you're using. Fortunantly for me I was just driving the disable lines so I didn't release any of that magic smoke, but it caused a decent bit of aggrivation for a week or so.

The resistor value (340/680k) on the LM1881 is apparently a debated topic from other websites I've visited on the subject. I actually changed mine back and forth and never saw a differences. According to one site I visited this resistor value adjusts the frequency of the composite sync. Meh, I don't know, didn't seem to change much on my end.

Again, a highly recommended device to build for anyone wanting to display >480P on your VGA projector. Good luck to all who venture down this path.

Hey pmiles, do you know if this transcoder converts the component input to the full range of RGB colours? (a component video signal outputs black at digital level 16, and white at 235, but normal PC monitors use from 0 to 255).

Cheers.

I can't tell you yes or no because I've not used anything to measure the values (nor would I really know how to), but I can tell you that as I was testing this morning I actually noted to myself how amazed I was at the black levels. I know some people have mentioned that the N6 ends up making many blacks look brown, but this circuit has very black looking blacks and very white looking whites. I'd venture to guess that no digital to analog conversion is really happening in this chip...but again, I have nothing to really back this up. Again, I know I'm not really answering your question, but let it suffice to say that I've been very happy with the results and I am a very hard person please.

Hope this helps.

If black looks black on a monitor and not dark grey, it must 'expand' the colours to the full RGB range.
Thanks (that does answer my question really ).
Is the transcoded image centred on the screen (I have a VERY cheap transcoder that displays the video on the left)?

By the way. I've found some adapters for the other chip (if you're still interested).
http://www.epboard.com/eproducts/protoadap...SOPtoDIPAdapter

Cheers.

I have a Viewera 152 monitor and when I play xbox or a progressive scan dvd (both 480P, not tried any 720p games as of yet) the LCD does scale the image to fit the full screen. I think there may be a very slight "squish" from left to right. I think this may be the case because when I watch the lightening THX clip the sphere is ever so slightly elongated from top to bottom, however, unless you're specifically looking for this, I don't think you'd really notice (my roommates pick on how particular I am about all my audio/video equipment). I think this may be due to the fact that the standard resolution for 480p isn't exactly 640x480 (or at least I think that's the case).

It might look squished because that monitor has a 5:4 ratio (ie. not normal 4:3 or widescreen).
Do you notice any 'clipped' blacks or whites?
Got some pics?

Thanks for your answers.

Nah, it's a 4:3 ratio, and like I said, it's really not noticeable unless you're looking especially hard at an object that you know should be a certain shape.

I'll post some pics (both of the device itself and the output) after I finish soldering it down on a project board - an experience all of it's own. After I upload my pics you'll understand, but this experience of laying out the circuit for Ken's circuit on a generic project board from rad shack with PTH components has me wanting something a little more tidy looking. If I had access to etched PCB and surface mount resistors/capacitors, it wouldn't be so bad. However, since I don't, I'm going to pursue the use of LMH1521s, my order of samples should be in sometime this week, however, I'll be out of town so I probably won't get a chance to work on it for a few weeks, but I'll be sure to start a thread or at least throw some stuff on here about it. I figure it should be relatively straight foward since the test circuit in the data sheet has all the recommended resistor values and such for implementing it. I have a feeling this is the same device the Vdigi uses considering the vdigi supports vga passthrough, though, I'd be really interested in their figuring out how they implemented adjustments for brightness and the like.

And lastly, what do you mean by "clipped" blacks or whites? Is this similar to the previous question of whether blacks look black or just dark grey?

Vdigi's device uses the 1881. I opened mine up to see what the circuit looked like. I still don't know what the brightness pot goes to because I couldn't get the rear cover off to look at the back side of the board.

To see what clipped blacks and whites look like, see my post HERE.

The 1st panda pic is normal. The 2nd shows crushed blacks, and the 3rd is an example of clipped whites.
Most PC monitors (LCD or CRT) tend to crush blacks when fed a picture originaly meant for a TV.

Couldn't have explained it better .

hi
I have been following this thread. its interesting but there is a lot for a new user to build one from the schematics. few questions i have if someone can answer them.
first i went to maxin website to order the sample. there are quite a few max4383 with different endings. but there is no max4383/48 there on the website. so i picked couple of them with different endings. so question is that is it okay to use those ones?
second same with lm1881. on their website for samples they have lm1881 with x in the end and maybe n in the end. so which one to get.
third, what would be voltage for the capacitors. diagram doesnt tell that.
fourth, what kind of power adaptor we have to use for this transcoder. meaning ac to dc? and how many amps should it have?
if some one can answer these questions, i would appreciate it..
thanks

videotalk19: I believe you can also use the LMH1981 chip. You can only order samples for the LMH1981MT, and I think its performance has improved...
About the max chip... I have no idea

thanks hrlslcbr for feedback
i checked the new sync separator you told me and it looks a lot better than the old one. still I have a little info about all what I am talking about. looking more help regarding capacitors voltage, power adaptor, and max4283.

Can someone post a picture of the completed project? (Not neccesarily the case but the board?) On the origional (first post) schematic etc I'm a little confused. It has the red green blue inputs from the xbox (which I now realize is probably direct from whatever connector plug that the xbox uses.) I assume this can also be modified and just have the 3 phono red, green, blue plugs to connect things such as a dvd player. I'm not sure though. Also, On the block diagram schematic, it shows "composite video" input going through the sync seperator (the LM1881 chip.) The rest of the it implies that this is the green component input. Is there any slight modification that can be made to accept either a red/blue/green 3 phono jack input, or a standard video phono (RCA) jack that is carrying all of the signals? Thanks

Composite video connects to Y input of the MAX4383 schematic (Y, Pr,and Pb).

I GOT THE LM1881 SYNC SEPERATOR FROM THE MANUFACTURAR. THERE WERE TWO DIFFERENT ONES. I ORDERED BOTH, ONE WAS LM1881M AND THE OTHER WAS LM1881N. NOW THAT I GOT THEM BUT THEY BOTH ARE SO DIFFERENT IN SIZE. ONE IS ALMOST DOUBLE THAN THE OTHER IN SIZE. SO PLEASE CAN SOMEONE HELP ME WHICH ONE TO USE?
THANKS

I have beeen using the LM 1881N version for many years. It can be plugged into a standard 8 pin DIP socket which makes the PCB design and assembly much easier.
By the way, the standard resistor value for the vertical sync separator is 680k. It is not critical, the circuit used to time out and disable the sync separator if the vertical interval is not present for a certain number of milliseconds.

Does anybody have a list of LCD monitors that support 720p from a transcoder? (or know of any cheap ones)

Thanks.

who invented the term "transcoder" for this? I always thought the little LM1881 thingy that you use to get Sync-on-green signals to VGA was called a sync separator. I've built a number of them for people to connect consoles to VGA monitors (usually in addition to software hacks that put the console in a VGA compatible mode). Never heard it called a transcoder before - in fact, it doesn't transcode anything, it only separates sync! They're plenty useful though for this sort of stuff - I almost always play my PS2 games in my monitor now (and soon in my projector once I get around to building it!), since I have one of those PS2 mods that also include VGA output mode. It doesn't have full scaling support, so the (originally 640x512 image) simply shows up as a box inside a 800x600 screen mode, but the borders are not too thick, and the width _is_ scaled (on the PS2 via the hack, not the sync separator of course)

Devices that convert YCbCr, YPbPr to RGB (VGA) and vice versa are known in the video world as transcoders. I don't know how the term was created.

Oh, so we've got two things here - transcoder and sync separator. Sorry, I live in europe where we use RGB for component TV instead of YPbPr, so I sometimes forget that you have to convert YPbPr

hi chad n.
it would be great if you help us here real time. and make a beginner illustrated guide , how to make this transcoder. because its still out of our grip. I remember long time ago when satellite dish rom cards were popular and one could alter their old atmega recievers. People who knew how to do that and had done before, really help others by writing real time beginners guide even with pictures step by step. I know its really hard work but you will get really appreciated doing that. and you are the one who started here and I think we need a little more of your expertise. Personally i couldnt make one and now I am trying to find some sort of electronic expert who could help me build this.
so if you could spare sometime and put something together for all of us that would be awesome.
thanks
bye

Chad N.
Just in case you don't read my post at AVSforum, check this. It seems to be built with the National LMH1251 chip, because the features of this new box and the national chip are almost the same.

www.play-asia.com sells it for 49.90, and I think they ship worldwide. Not expensive if it's as good as National claims it is

Are there any video experts out there that know for sure if the lack of colorspace conversion between YPbPr and RGBHV would significantly contribute to black crush? I have a theory that if you feed a VGA monitor the YPbPr colorspace range of 16-235 instead of the RGB (VGA) colorspace of 0-255, the result is diminished black detail. I also think most cheap video processors and cheap transcoders do no colorspace conversion between the 2 formats.
However, the LMH1251 does perform a YPbPr to RGB colorspace conversion. If this lack of conversion does indeed contribute to black crush, LMH1251 based transcoders may be the only (cheap) way to go for those of us that demand perfect detail in the darks. Anybody know for sure?



videotalk19, if the design only involved a few components, then a step by step guide for anybody would make sense. However, since the transcoder involves many components, you really need a basic electronics background to know how to read the schematics, and arrange/solder the parts to a board. For those that don't have this background, this project is probably over their head. A kit consisting of an etched circuit board and the components would be ideal, but I really don't have the time or desire to put something like that together and offer it for sale.

hrlslcbr, I just e-mailed Mayflash and asked them if it does a colorspace conversion.

I just bought a vdigi USED and dam if I can't make it work at all on my 15" lcd projector. At first I tried it with the old xbox and it states it was out of range. Next I tried a progressive scan dvd recorder with cable in and out and still it says out of range. Played with the dip switches and I get lost signal to out of range. Appreciate some help from you transcoder guru's out there cause I'm beginning to think this might have been a $$ loss here. BTW, it didn't come with any manual

I am at work right now or I would tell you what dip switch settings I am using. I did notice though that my desktop Viewsonic VG700 was a lot more picky with the vdigi than my Samsung 512N is. Another cool thing I found out is the 512N will actually display interlaced content. It looks like crap and isnt centered but it still does it.

There is a .pdf manual that you can download from vdigi that explains what settings to have the vdigi on for it to work with different components.

Here are the dip switch settings straight from the manual complete with broken English. Normal type is from v3 of the manual, and bold is from v3.3. If you can't get it to work with the dip switch settings info, then your unit is more than likely defective.

switch 1,2: To use RGBHV, turn 1 OFF and switch 2 ON; for RGBs, turn 1 ON and switch 2 OFF. By default, RGBHV is used.
Switch 1, 2, and 3: To use RGBHV, turn switch 1, 3 OFF and switch 2 ON; for RGBs, turn switch 2, 3 OFF and switch 1 ON. Switch 3 ON and switch 1 and switch 2 OFF (RGBHV Alternative) is used if the display position is not in the correct position.

switch 3: Turn it on, you can get a bright screen than normal, especially for GC / PS2.

switch 4: If you find there are any abnormal display, for example, under 720P or 1080i, the screen is too dark, or distortion of the pictures, you may choose the mode 2 (switch 4 ON) in order to fix the problem.
Adjust the brightness though the brightness screw when switch 4 is on and switch 5 is off.

switch 5: Choose between XBOX mode and gamecube / PS2 mode.
Brightness screw is disabled when switch 4 is off and switch 5 is on. (This is the factory default setting, you are only need to adjust the brightness if you want to set your own preference)

switch 6: *480i Setup mode allows you to set your dashboard from your monitor directly instead of to set your console from TV.
If you find that the 720P / 1080i picture is not correctly display, you may set switch 6 to on for mode 2. For HDTV cable receiver, it is recommend turn on to mode 2 for 1080i.

do u have 2 feed it 5vdc? any easy way to get this?

Is it common or uncommon for 1024x786 15" screens to downscale 16:9 720p signals?

Cheers.
B

Uncommon. 15" screens don't typically accept 720p signals directly... the use of a scaler is required.

cheers,
gs

Hello.BINE,i am a new guy here，come from CHINA, have you finish test the LMH1251 yet？ I WANT TO DIY IT MYSELF.could you give me a PCB file？XIEXIE !!:)

I have been working on a transcoder using the LMH1251 chip for the last few days as I would like to get a Nintendo Wii working with my projector. A couple of things to note, you also need an LMH6738/LMH6739 to amplify the output signal as it is not designed for driving VGA cables, it is designed for input into preamps inside monitors, If you read the datasheet for the 1251 it mentions it and says you need a gain of +2, which it quite easy to achieve with the LMH6738.

I'll post some pictures when I finally get it working, I'm stuck (until I can get some more capacitors/resistors) with an amplifier that works, but the Sync signals are all broken and the monitor can only lock on for a second or so every 10 seconds approximatly, I think this is just because I'm using too high a capacitor for the sync signals.

I'll let you lot know how it progresses because I think this could come out quite well, components have cost about £6 (about $12), so far, although that doesn't include a pcb yet.

Alex

What voltage capacitors are needed because it doesnt say ?

There haven't been any posts on here for almost a year. I just wanted anyone still watching this thread to know that I'm getting ready to build one to schematic, with LMH1881 and the MAX438. I will be making my own board via UV reactive method and making a case out of clear plastic with some cool leds for indicators and maybe a brightness mod (dip) well I will post updates and pictures soon. I'm ordering samples as I speak. Later all.

Well here’s an up date on what’s going on.....
I decided to use the LMH1251 Instead of the 1881 Gets rid of some of
the nasty setup and adds an RGB pass-through buffer which I was going to
add anyway! So now I’ve got the parts coming and have my sample from
maxim I am going to use those buffers to hook the 1251 up to the output.
So, I’ll post over the holiday with board designs if anyone is watching
and I guess I may move this to a new thread since it is a new design
that I am making and I have plans to incorporate this into a wonder unit
with scalar and composite/s-video HDMI/DVI HDCP support ECT. So I look
forward to ongoing progress thanks:))

Ok, This is my first post... But I've been following everyone's comments and ideas so far. At present I've managed to get samples of both the LMH1981MT Sync Seperator, the LMH6739MQ Very Wideband, Low Distortion Triple Video Buffer but have not been able to get any samples of the LMH1251.

It's been several years since I've designed / made an etched pcb but I'm anxious to get started again.

Can anyone post a comprehensive component list / pcb layout file etc. for me to review? Since it see that National.com is no longer giving out free samples of the LMH1251 chip I'll most likely have to purchase 2 or 3 of them for testing in my design.

Thanks