MystX
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Re: LVDS Interface

Tue Dec 13, 2011 5:26 am

Er, I'll try =P (anyone please chime in if I'm wrong).
The EDID stores a screens info (resolutions, framerates etc), and will come on the controller board inside any LCD panels that take a digital signal - I know that HDMI and DVI at least have a clock pin and a serial data pin for the EDID.Since the board you provided is basically the controller for whatever panel you plug it into, it needs to provide this info to the video source (R-Pi in this case). Apparently that particular EEPROM chip will do the job after being programmed, and I notice that it's write control pin is held high through a resistor - I think you'd need to ground this pin before trying to write to the EEPROM, but he doesnt mention it. So maybe not?

Anyway, he says to use Phoenix EDID Designer to produce the actual data to go onto the EEPROM - so you would pick some resolutions that would fit on the LCD you planned to use (I'm not sure how much detail you need to go into for this). Then, it's just a matter of plugging the board into a DVI cable and a power source, and then using PowerStrip to write the EDID data. After that, the R-Pi (or anything else you plug in) will be able to query the supported pixel rates/refresh rates/resolutions of your LCD panel and all will be well.. I hope.

^I still have some data sheets to read, and more studying of that schematic needs to be done. For example, I still dont know what most of the jumpers he has on there are for =P
I'm off to order all of the other components though - I already have the two signal conversion chips. Very excited =D

na1pir
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Re: LVDS Interface

Tue Dec 13, 2011 9:09 am

Just out of curiosity; what would be cost of materials for such lvds interface.

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abishur
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Re: LVDS Interface

Tue Dec 13, 2011 3:17 pm

Well cost I know of so far

PCB Etchant: $10 Radio Shack 16 Oz (assuming you're willing to make the board yourself)
Glass container specifically for holding etchant: $3 Walmart (just a note here, the link is to a 10 dollar product, I don't know why the website shows it so expensively, but that's the sort of thing I got in the store. You have to get a unique container because one you put the etchant in it you CANNOT use it again for cooking. EVER
Cost of double sided copper board: $3ish on Amazon
Two chips required from TI... Well I got some samples so nothing, but if you want to make a lot of these it's $10 for the TFP401A on digikey and around $7 for the sn75lvds83b.

As for the rest here's a list that I took straight from the pcb file he sent me

I list what it is, what rating it is, the footprint listed, and the quantity needed

Capacitor 100n - CC1608-0603 x 23
Capacitor 100uF/5v -TC7343-2917 x 4
Capacitor 20uF - CC5750-2220 x 1
Diode Schottky, SOD123 x 1
Diode 27V, DSO-C2/G1.6 x 1
3 pin jumper x 8
DVI connector x 1
28 (2x14) pin header - HDR2X14 x 1
Inductor 20uH - CC5125-2010 x 1
3 (1x3) pin header - HDR1X3 x 2
14 (2x7) pin header - HDR2X7 x 1
2 (1x2) pin header - HDR1X2 x 1
Resistor 5.2K - CR1608-0603 x 1
Resistor 47K - CR1608-0603 x 3
Resistor WC - CR1608-0603 x 1
SN75LVDS84A - TSSO12x8 x 1
TFP401A - F-QFP14x14 x 1
EEPROM M24C01BN6 - PSDIP8A x 1
Regulator 5V to 3v3 - ZZ311 x 1
Boost Converter LM2733 - SO-G5/X.5 x 1

I can't be certain on the cost of all that (minus the TFP and SN5 that I already listed) but my guess is somewhere in the 20 dollar range.

So it's around a 20 dollar build (assuming you have the PCB stuff already, otherwise I think it would cost around 10 dollars to get the board made by someone else)? That's a seriously rough guess, if someone is a little more experienced with purchasing these items and can give a better estimate that would be nice :)

Now at that price, it's a hard sell to not spend a few bucks more and buy one of the pre-made devices off eBay, but then you don't get the bragging rights of having built it yourself :)
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MystX
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Re: LVDS Interface

Tue Dec 13, 2011 6:58 pm

Abishur: I see some stuff on there that's not shown in that schematic you posted. Is there any way to get one that has all of those parts, or at least which component numbers they refer to (D1, J1 etc)?

Also where the heck does one get surface mount jumpers?

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abishur
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Re: LVDS Interface

Tue Dec 20, 2011 8:23 pm

Sorry I missed your post :P I just grabbed the info straight off the pcb file, and the gerber is made off the pcb file so everything *should* be there. It is a two layered board so it might be hidden on the bottom layer?
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MystX
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Re: LVDS Interface

Wed Dec 21, 2011 2:30 am

Yeah everything is in order in the gerbers. Im talking abou the schematic you posted in that .pdf (the very first file you posted). Some of the components aren't in that schematic, so I'm a little confused about what goes where for some parts (20uF cap, 5.2k res. There's also a 100R resistor in the schematic that isn't in your list =\).
I'll have another look at the pcb file to see if I get the same list as you when i get home.

P.S. do you know what value R WC is? I suspect that a 0R will be fine in that position, but I'm not 100% sure.

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abishur
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Re: LVDS Interface

Wed Dec 21, 2011 4:29 am

Oh, I'm not very trustful of the pdf. I'm working off whatever the pcb and gerber files say, since that's the actual mask that the PCB will be made from. I'm not sure what the wc resistor is either :? it could be a typo or maybe someone more experienced can chime in ;)
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JoeStrout
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Re: LVDS Interface

Sun Jan 01, 2012 10:12 pm

I'm chiming in late here, and as a software guy, I too have trouble following much of this thread (especially page 3!).

But I do think an LVDS interface would be a great accessory to the RPi!  I just discovered that iPad replacement screens are available for $65; that's great for a very bright, 10" 1024x768 display with extremely wide viewing angles in all directions.  But it's an LVDS interface.

It seems there are at least a couple of people here who understand this stuff... should I be looking for some off-the-shelf driver board, or is there a good chance we (the R-Pi community) could homebrew something to do the job?

JoeStrout
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Re: LVDS Interface

Sun Jan 01, 2012 10:14 pm

Abishur said:


I"ve seen a possible solution on eBay. You"d hook the r-pi up to it via a hdmi->DVI cable and then hook the LVDS cable to the board. The only draw back here is that it"s $30 (more than the r-pi itself!)


I'm OK with $30... can you provide more details about this board?

Bluemerlin
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Re: LVDS Interface

Tue Jan 03, 2012 2:23 am

I can't seem to see in this post what the DSI port can be connected to, or even if it's still part of the board.

It was mentioned early on but it switched to a HDMI-LVDS convertor.

MystX
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Re: LVDS Interface

Mon Jan 09, 2012 5:10 am

I got my boards back from batchPCB the other day. Here are some pics:

http://i.imgur.com/TFZH9.jpg

http://i.imgur.com/EJDhJ.jpg

For size reference, there's my Return key behind the board, and the connector at the top on the second image is a standard size DVI connector.

I just ordered all of the components last night, cant wait till they get here!

EDIT: For some reason they sent me 10 boards instead of 5. So I have 5 spare boards here That I could sell for $10 USD each if anyone wants one. Unfortunately I'm in New Zealand, so I'm not sure how much shipping will be.

EiNSTeiN_
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Re: LVDS Interface

Fri Jan 20, 2012 3:54 pm


EDIT: For some reason they sent me 10 boards instead of 5. So I have 5 spare boards here That I could sell for $10 USD each if anyone wants one.


Next time you can possibly have a look at SeeedStudio or ITead Studio to have your PCB produced. They are much cheaper than BatchPCB, especially for small boards. Yours appear to be less than 5mm x 5mm which would cost you 10$ for 10 boards (1$/board).

EiN'

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abishur
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Re: LVDS Interface

Fri Jan 20, 2012 4:12 pm

JoeStrout said:


Abishur said:


I"ve seen a possible solution on eBay. You"d hook the r-pi up to it via a hdmi->DVI cable and then hook the LVDS cable to the board. The only draw back here is that it"s $30 (more than the r-pi itself!)


I'm OK with $30... can you provide more details about this board?



The Seller is NJYTouch on eBay, they're called LCD Controller boards.  When selecting a board you need to search his list and make sure that your LCD screen model # is supported by that controller card.  The 30 dollar boards come with the power supply and OSD adjuster I think.

Bluemerlin said:


I can't seem to see in this post what the DSI port can be connected to, or even if it's still part of the board.

It was mentioned early on but it switched to a HDMI-LVDS convertor.



The DSI port is still there (Check FAQ pic, they're south of the GPIO pins and opposite the SD card)  I personally haven't run into anything that uses this, but I think some cell phone screens make use of it and possibly other displays.

@MystX - I can't wait to see your boards up and running!
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MystX
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Re: LVDS Interface

Sun Jan 22, 2012 9:16 am

@Abishur

Unfortunately the first board I've populated is a dud so far. PowerStrip cannot read/recognise the EEPROM chip. I've checked it's power supply and its data and clock connectivity to the dvi connector though =(

Originally I thought that this may be because I didnt have a LCD panel connected. I thought that maybe the graphics card needed some communication with the TI chips before it would try to read the EDID or enable that output at all, but connecting an LCD didnt help. I'm going to populate a new board in a few days and try again - I spent quite a lot of time with the iron on those small ICs with the first board, I may have fried one (I dont see why this would stop the EDID being seen by PowerStrip though).

Can you please ask the board's designer what the 1x2 pin header labeled "LED" is for? I suspect it is a source of power for a CCFL backlight (It has 12V across it), but I want to make sure before connecting something.

Thanks

lokiji
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Re: LVDS Interface

Fri Feb 17, 2012 10:15 am

guys, may I ask you, does this design work? have u tried it?

sam82
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Re: LVDS Interface

Fri Feb 17, 2012 5:59 pm

am confuse ...someone told me that LVDS is used to transfer lots of information very fast ...so its the LVDS for displays(images,videos) or is it for overall data ?

Thanks

jamesh
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Re: LVDS Interface

Fri Feb 17, 2012 7:25 pm

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BertM
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Re: LVDS Interface

Fri Feb 17, 2012 9:08 pm

sammy585 said:


am confuse ...someone told me that LVDS is used to transfer lots of information very fast ...so its the LVDS for displays(images,videos) or is it for overall data ?


LVDS stands for 'Low-voltage differential signaling' and is indeed an electronic way to transfer information. However, when most people say LVDS, they actually mean FPD-Link (Flat Panel Display Link), which is a often-used technology using LVDS (actually, it was one of the first).

So yes, the LVDS we are talking about here is actually FPD-Link and can only transfer 'images' to your screen.

sam82
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Re: LVDS Interface

Fri Feb 17, 2012 10:20 pm

@JamesH... thanks for the link

@BertM......"Yet multimedia and supercomputer users, both of which needed to move large amounts of data over links several meters (from a disk drive to a workstation, for instance) maintained a widespread interest in LVDS"

Thats what I have in mind, was looking to try to send lots data for my project .....

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