Topic: Vga Box For Xbox (Read 465 times)

ryn_o · « **Reply #30 on:** July 12, 2005, 10:48:00 PM »

FYI to everyone looking to buy/build a convertor. I have been following a project that has been shown to give better results than the x2vga+. It has been in development for over 2 years and is approaching the final product. It will do resolutions up to 1080p and have adjustable gain and such. Looks very promising but somewhat complicated. It will properly conver the Component Signal of anything to vga/RGB. Will keep you posted if i hear anythig else.

Jameson42 · « **Reply #31 on:** July 13, 2005, 06:50:00 AM »

rfguy,

There is no way that this will hurt your monitor. Once you connect the YPbPr to the inputs, and actually have a signal, RGB will output in AC. They will never give you more than 5V, which is perfectly safe for your monitor.

JaredC01 · « **Reply #32 on:** July 16, 2005, 02:06:00 PM »

QUOTE(Jameson42 @ Jul 13 2005, 08:01 AM)

rfguy,

DarkLegion · « **Reply #33 on:** July 17, 2005, 10:16:00 PM »

QUOTE(rfguy @ Jul 17 2005, 04:19 PM)

However, there is also a diode before each cap. I don't know what that is for. Maybe a protection or level clamp.

Most likely it is a black level clamp.

Chad N. · « **Reply #34 on:** July 18, 2005, 04:47:00 AM »

rfguy, it looks like I may have the same problem as you. My monitor comes up with an error message: "out of range", then tells me the horizontal sync is at 37.3 kHz and the vertical sync is 249 Hz.

The input specs for my monitor are 30-95 kHz for horizontal and 50-160 Hz vertical. Looks like the 1881 is outputting too high of a vertical frequency.
I am using an Intersil 1881 vs National's 1881, but that shouldn't make a difference.

You might try reading the horizontal and vertical syncs from your circuit on the oscilloscope, and finding exactly what frequency they are outputting at. (I don't have an oscilloscope at home).

If they are outside your monitor's specs, the next question is: how to change the horizontal/vertical sync output independantly of each other.

rfguy · « **Reply #35 on:** July 19, 2005, 02:01:00 AM »

First of all I am not very familiar with video signals. So let me tell you what I observed and than you guys can tell me if it makes sense.

I think the problem is on the horizontal sync. On the pin 1 of LM1881 I measured horizontal sync along with a whole bunch of other signals. My scope is old analog so I cannot do a single shot or storage. Now when I read the data sheet it makes sense to me. Pin 1 is the "composite sync", so it is the combination of horiziontal and vertical sync and some other junk. However, the monitor VGA input is expecting a pure horizontal sync. I verified it by measure what's coming out of my computer video card. So using pin 1 of LM1881 will not work.

I think the LM1881 should be replaced by EL4583 which is similar to LM1881 but it also has a dedicated pure horizontal sync out. What do you think?

Chad N. · « **Reply #36 on:** July 19, 2005, 06:01:00 AM »

I got the circuit to work....somewhat. After reading the 1881 datasheet, I discovered the vertical sync frequency is controlled by the resistor value at reset (pin 6). The value used on Ken's schematic is 340Kohms, while the 1881 datasheet tells you to use 680K for NTSC.

The lower the resistor value, the higher the vert sync freq is. I used the recommended 680K and it worked. According to the datasheet, 340K would output a frequency far outside all monitor's range.
For unmodified schematics to work, you would have to have a monitor capable of at least a 250 Hz refresh rate.

Now for the problems:
There are faint green horizontal bands slowly moving up the screen.
Also, 480P is the only resolution to work. With 720P and 1080i, the sync frequencies get outside the monitor's range again.

The good:
Ignoring the green bands, the 480P picture is perfect!!!! A far cry from the crap Viewsonic N6 video processor I have.

Were those of you that got it to work using LCD monitors? LCDs handle refresh rates differently, but I forgot how. I have a suspicion that this won't work well with CRTs.....only LCDs.

rfguy · « **Reply #37 on:** July 19, 2005, 02:10:00 PM »

Chad, this is good news. So you followed the schematic except the 340K? I think I'll try that, but I still don't understand the composite sync thing. I hope something can explain that to me. BTW, can you do me a favor and measure the R,G,B output without anything in the input? I just want to verify that the DC voltage a thte output is normal even though it is AC coupled. Thanks.

greengiant · « **Reply #38 on:** July 20, 2005, 03:35:00 AM »

I also have the problems posted, excpet I do get video but with the red haze as previously noted. I will be trying to use the different resistor for the LM1881 but dont expect my results to change, as I have tried to feed the monitor a variety of different frequencys with a signal generator, and the video goes thru the range but the problems still persist.

As someone pointed out before, the 2nd op amp idea is USED in a commercially available product..... the x2vga.
Ive decomposed it to the last piece, except for 2 ic's.
I know exactly how the device works, its very neat how they did it, im guessing its an improvement upon the 3rd (private) revision of Ken Gasper.

Essentially, they have the 2 max's (op amps) to do proper conversion of the video, the sync signals are either send from the LM to the monitor un changed, or when u enable the 'quick view' thingy, it passes it thru 2 ic's that double the sync so that the monitor is able to see the video (crappy, but see it)
such as 480i 15khz is doubled to 30khz. One ic does the conversion/pass-thru and the other controls the first ic, and the led.
What the part number on these ic's are, i dont know. One IC uses a clock (the control IC) so Im guessing its a MCU (possibly a microchip 16f) but the 1st ic that does the doubling of the synch i have no clue.

Well if anyone has the x2vga they should be able to decompose it better, or gather more intel. As for legality, its based on Ken Gaspers design so in theory is public domain.

Enjoy !

Jameson42 · « **Reply #39 on:** July 20, 2005, 09:48:00 AM »

QUOTE

With nothing on the input, red reads .75V / green: 1.9 / blue: .45
I don't understand the composite sync thing either, or why the vertical sync jumps up out of range when 720P or 1080i is enabled.

I'm guessing your monitor doesn't support those resolutions. 720p = 1280x720. Kinda an exotic resolution for most monitors. The composite sync should still be readable by your monitor as a proper vertical sync signal.

QUOTE

I did solve my green horizontal band problem: the AC to DC converter I was using for the 5v power supply was poor quality and letting some 60Hz through.

You can get your 5V supply through the xbox's AV port... check out JaredC01's A/V guide for some more info.

Chad N. · « **Reply #40 on:** July 25, 2005, 11:09:00 AM »

Rfguy, what about an EL1883? It is very similar to the 1881, but also has horizontal output. It is an 8 pin just like the 1881, but I think they only come as surface mount. Digikey has them for $3.

You might try this one instead to see how it works.

By the way what LCD monitor did you try it on? I tried mine on a CMV-520D LCD and it didn't work either.

rfguy · « **Reply #41 on:** July 25, 2005, 12:57:00 PM »

Chad, thanks for checking out EL1883. I believe EL1883 should work. Let me check the data sheet later tonight. The problem with digikey is that I don't want to buy a $3 item and pay $5 for shipping and handling. I usually wait until I have $25 or more worth of stuff and then order. I always prefer to grab parts from local surplus stores in the silicon valley.

My LCD is a real cheap one. I bought it used and it is a MAG 14 inches old model. I don't have the model number but I can look it up when I get home tonight. Anyway, you can check the manual of you lcd. Sometims it will tell you what the sync requirements are. However, mine doesn't have that information in the manual.

BTW, if you are interested go to this website
http://www.epanorama...vgamonitor.html
It mentions the LM1881 composite sync. There is a simple circuit the author claims that should be able to extract the Hsync from composite sync. I built it and it did not work at all. Actually I ran throught the logic and it didn't make sense to me.

Chad N. · « **Reply #42 on:** July 27, 2005, 07:47:00 AM »

Thanks for the link! From it I learned to disconnect the vertical sync signal out to vga. It worked! Apparently my LCD only needs a horizontal sync.....it won't lock on with horizontal AND vertical. I'll put a switch in line with the vertical sync out:
closed for CRT and open for LCDs.

Now to fix problems with resolutions higher than 480P:
I think the problem with higher resolutions is, the horizontal sync increases as resolution goes up. 720P and 1080i have a frequency outside many monitor's range.

With another CRT I logged horizontal sync frequency with each resolution:
640x480: 37 kHz
800x600: 46 kHz
1024x768: 60 kHz
1280x1024: 80 kHz
1600x1200: 94 kHz

720 is 1280x720 so you need a monitor that can handle H sync of at least 80 kHz

1080 is 1920x1080, so I am guessing you need at least 100 kHz for that

Now the question becomes how can you change the H sync out so it is low enough to be within your particular monitor's range?

massive_hair · « **Reply #43 on:** July 29, 2005, 10:56:00 AM »

Heya. As I live in the UK getting hold of the MAX4383 is a nightmare. The best op amps I can get are for audio applications - the LM837N is a quad op-amp, or the NE5534AN is a single op amp (both from www.maplin.co.uk - datasheets available). Are there likely to be any major headaches from using these?
Sadly I can't get hold of a EL4583 either but I think my monitor will take composite sync... fingers crossed!
Cheers
Chris

rfguy · « **Reply #44 on:** July 29, 2005, 01:06:00 PM »

Try www.digikey.com. They have almost everything and I believe they ship international. NE5534 or anything in the audio band are not acceptable because of the low bandwidth. You need amplifier design for video with high bandwidth and slew rate.

You can also try this website

http://translate.goo...l=e...6lr=&sa=N

This is the equivalent of Ken Gasper design and use a different amplifier IC. You should be able to get it from digikey. I know it's hard to read the translation, but you should be able to read the circuit diagram.

You can also get the EL1883 from digikey too!

By the way, I have not ordered the EL1883 for my board yet, but I was doing some experiment with my current board. What I did was to add a monostable (74HC123) at the output of the LM1881 pin1. Everytime the composite sync goes low a pulse (length adjustable in my case) is generated at the monostable output. I just adjust the pulse width with the oscilloscope to get about 27usec. This pulse becomes the Hsync for the LCD, and I use the pin3 of LM1881 as Vsync for the LCD. It works for a while but sometimes it will lose sync. Anyway, I'll play with it later on today. This is just some experiments before I get the EL1883.

Author Topic: Vga Box For Xbox (Read 465 times)