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[gerzand]

Im a bit confused on some wiring of the LM1881. If you have some knowledge feel free to share please!


Im planning on using a MS HD pack to function as both Y Pr Pb and VGA all in one. I will be mounting a VGA jack inside the HD Pack in addition to the RGB.

My main objective is to make this work without opening up the AVIP plug on the end of the HD pack's cable.

I have just ordered a LM1881 chip to split the V/H signals off of the Green(Y) signal inside the HD Pack, and I pretty much understand the wiring of this chip except for a few things.

The guide here (click) shows the input voltage to the chip coming from an unknown location (would this be from AVIP pin #1?)

If the voltage does come from there, which wire in the MS HD Pack is carrying the Voltage? The only possible wires I can think of would be one of those that feed the SPDIF jack. What do you think?

Also, why does the drawing show pin # 1 (the DC out) of the AVIP going to Pin# 8 of the VGA? I thought pin #8 was used for the Blue(Pb) gnd. Where does the Blue ground go then?

One last thing.. The are 2 grounds on the LM1881. Does it matter if I  connected both of them to the same pin, for instance Green's gnd Pin ?

THANX SO MUCH TO ALL THOSE WHO CAN HELP.           Gerzand

[gerzand]

bump..?

[spillage]

Couple of things I too am confused about here too. VGA is RGBHV, i.e. 5 wire RGB NOT component video! How does the HD pack provide RGB to allow VGA once the LM1881 is installed along with a VGA bios? RGB and component video are not the same type of signal so I would be interested to know if the HD pack cab be made to do proper RGB, something I doubt cause you yanks use component, whereas us brits run RGB.

There is only one ground on my LM1881N, pin 4. The ground for the colour components are not necessarily the same, quite often the are not. Pin 1 from the AVIP cannot possibly go to the blue component ground.

Habs69M seems to have done a great job extracting maximum potential from his HD pack to boot retail then swap to VGA. Your HD pack is Y,YPr,YPb right? How does you monitor work with component when it wants RGB? If you plug a component device into an RGB input you only get green.

You cannot feed the LM1881 from the source for the SPDIF o/p. and I would wager that the sinking current of pin 1 of the AVIP is minimal and used just for HD pack etc. Use the 12v supply for your HDD etc.

I am building my sync stripper using this diagram, which I have just drawn to show you the layout from the manufacturer. I will post back to say if it works or not.

Incidentally I tried to FTP the VGA bios into my box the other day but FTP keeps failing. Any ideas?  

[gerzand]

ACCIDENTAL POST  

[gerzand]

Spillage,

I think youre confused about video types by what you said about component not being the same as RGB.

RGB  and Component video are both the same but different people referr to them by different names. This is true because:  

1) They both use the same color connectors Red, Green, and Blue
                                                                                                 
2) The R(red)  G(green) B(blue) in RGB correspond to the same signals in component. R = Pr,     G = Y   ,   B =  Pb  (the lowercase r  and   b  indicate red and blue)

3) Us "yanks" us often COMPOSITE video when not dealing with HD TV sets (not component RGB) which is the Yellow, White, and Red audio and video combined.

***Do a search on google.com for Composite video, RGB video, and component video. You'll see that RGB and Component are the same thing!

NOW HERE IS HOW A NORMAL RGB/COMPONENT SIGNAL IS MADE INTO A MAKESHIFT VGA SIGNAL ON XBOX
---------------------------------------------------------------------------------------------------------------------------------------
In order to make the xbox output a MAKESHIFT VGA signal, you MUST still open up the AVIP connector on the HD Pack and unsolder the jumper between pins 11 & 12, and move it to pins 9 & 10. This lets the xbox know that you want "mode 2" output. Although "mode 2" is called VGA, it is actually not true VGA b/c the H and V only run at 31khz.. This is why you must split them off of the Y(Green) signal using a LM1881N chip to make it compatible with most computer monitors. If you wanted to hook up one of these cables to a PROJECTOR, you wouldnt need the LM1881N, or to change jumpers because PROJECTORS can determine that the signal coming through the VGA cable is actually COMPONENT/RGB, as where MOST computer monitors that are not "sync on green" cannot.

I now know that its not possible for the HD back to operate correctly AND at the same time have it outputting VGA unless you make switches between pins 9 & 10 , and 11& 12 that you can turn on and off for different modes.

                                                                                               


But i am still confused on the wiring of the LM1881N. How much voltage does the DC out (avip pin #1) actually carry? When I touched the 2 red(+) and green(-) pins together inside the HD pack that power the SPDIF, they sparked. SO it must be some voltage.

Spillage, if you get the  lm1881 post how you wired it.

ANYONE ELSE THAT CAN FOLLOW THIS, POST YOUR INPUT!

[spillage]

Quersand,

The word ‘component’, is this context, is used to denote a primary colour. Both RGB and Y/YCr/YCb - Y/YPr/YPb are forms of ‘component video’.

Contrary to what you may believe, Component video whether digital (Y, YCr,YCb) or analogue (Y,YPr,YPb) are not the same as RGB at all. Firstly sync pulses for component video are on the ‘Y’ luminance component. RGB can have sync on green (RGsB upto tri-level) on a separate carrier ©, as a full composite video signal or as H and V. There is even a six wire system I know very little about.

PC video signals use the RGBHV format, i.e. five connections (full bandwidth), three carrying the
primary colours and the others carrying horizontal and vertical sync. The
video is progressive.

VGA is broadly equivalent to the progressive format 480p, i.e. 480 active
picture lines per 525-line frame with a line frequency of approx. 31kHz.

SCART uses the interlaced format RGBCs, i.e. RGB signals with a separate
video-level composite sync signal (on most RGBS sources the sync is actually a full colour composite video signal (example the yellow connector)).

DVD picture information is encoded in a component video format.
The CbCr / PbPr colour difference signals are sampled at half the rate of
the Y (luminance) signal - the eye has greater sensitivity to brightness
than colour. Turn down or off the colour control on any display device and you will be surprised at how much detail you can still see. As luck would have it, one can take advantage this, and save a lot of space (bandwidth). In an RGB signal, all three primaries must be sampled at the same rate. The eye is less sensitive to colour variations than brightness variations, hence the reduced bandwidth of colour information is not noticed.

The analogue YPbPr signals are mathematically related to/and derived from RGB signals but not the same as.

To derive a VGA-compatible signal from interlaced YPbPr you would first need to de-interlace, then carry out the YPbPr to RGB matrix conversion or transcoding and strip the sync from ‘Y’. Then use a sync separator like the LM1881N to generate the H and V syncs.

I see where you are coming from but the fact the plugs are the same colour is of no relevance.

I used the term 'yanks' cause I am too lazy to type Americans. If you're offended, I apologise.

[gerzand]

Alright,  
well on the non-technical side of things (thanx for that Spillage  but it caused me to have a brain fart   ), I got my lm1881 chips in the mail today and hooked one up to my HD pack/VGA cable. It works great! Great quality on my LCD. I recommend using the Linux guide to wiring it up, not lee's that is in the xbox-scene vga tutorial. If you have any questions, feel free to ask. Thanx for help all!  peace!  Gerzand

The SPDIF wire (aka AVIP Pin #1) does give enough voltage to power the Lm1881. It can power both the SPDIF and the chip at the same time. Give it a try!