first design for an hdmi to lvds adapter


74 posts   Page 3 of 3   1, 2, 3
by kordsi » Thu Jan 10, 2013 2:16 pm
Did anyone get it working yet? I've been searching for a solution for a long time but I didn't find anything except from here.
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by Wire » Thu Jan 10, 2013 9:01 pm
I have a pile of LCDs and all the converter chips sitting on my bench at home. Just need time to sit down and design a PCB for them.
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by ceteras » Fri Jan 11, 2013 1:32 pm
I've been working on this project last year, but unfortunately I've lost all my files in a crashed hard-drive.
The only copies I have are some older versions of it and I don't know when will I have time to work on this.

@Wire: what kind of lcd controllers do you have?
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by Wire » Fri Jan 11, 2013 3:14 pm
I "Think" they are the TI chipset. At work right now but will go check when I get home.

I am using a Unipac 8.4" touch screen model UB084S01-2 (data sheet on the web)
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by Wire » Sat Jan 12, 2013 6:39 pm
Chipset I am going to use is TI SN75LVDS83BDGG and TFP401APZP

http://www.ti.com/lit/ds/symlink/sn75lvds83b.pdf
http://www.ti.com/lit/ds/symlink/tfp401a.pdf
http://www.mikrocontroller.net/attachme ... 4S01-2.pdf

I have the chips and LCD in hand but still need to deign a circuit board. Before I can do that I need to do some more investigation on the I2C bus and what is needed for it to advertise the correct format of the LCD resolution. Would also like to piggy back on that I2C bus for touch screen data but not sure if you can use it as a general I2C bus from the PI (would be great if you could. One cable solution for both display and control/touch input)

My LCD is a 18 bit device but there is no reason why I cannot support 24 bit as well. It will just not be used in my application. BUT... apparently there are 2 ways 24 bit displays are normally wired. either the MSB 2 bits are on the 4th channel for each color or the LSB2 bits are. Anyone happen to know which format is more common?

If I get home at a reasonable time tonight I may fire up eagle and start entering package footprints and start the logics.
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by ceteras » Sat Jan 12, 2013 8:41 pm
What do you need I2C for?
It seems to me that TFP401 does not need it, the chip is configured with dedicated input pins, tied either low or high. Jumpers would do.
I have this board with TFP401 and it works standalone.
Good luck!


Edit: About the MSB bits, the datasheet says that the majority are sent for each color on the 4th line, so I think it's safe to design for this case. I've never dealt with an lcd in the second format.
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by ceteras » Sat Jan 12, 2013 9:08 pm
I've been looking at the board pictures more closely and I believe I've found exactly what you need to do.
Find pin number 5 of IR3Y29 chip, and follow where it goes.
We need the chip to accept composite, and for this, pin 5 should be tied to ground. If pin 5 goes to a connector (perhaps the bigger, 12pins one), then you need to cut its wire too in the same way (as the video in wire) and solder the end that goes to the driver board - to the ground.

I strongly believe that you can skip the other checks before doing this. If the pin 5 is not tied to the ground you will not get a color image with this chip from the raspi.
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by Wire » Sat Jan 12, 2013 9:23 pm
The I2C bus contains either a micro or a eeprom that tells the PI (or other host) what resolutions, refresh rates, ect the LCD can display. In my case it would be just one since I don't have a video processor in line with the LCD. I want to be able to use this on a small server as well and would be nice if the desktop self configured to the LCD.

Here is a high level review of it over on wikipedia
http://en.wikipedia.org/wiki/Display_Data_Channel
more useful details
http://media.blackhat.com/bh-eu-12/Davi ... DMI-WP.pdf
http://nouveau.freedesktop.org/wiki/DDC
http://electronix.ru/forum/index.php?ac ... t&id=24646
http://ddccontrol.sourceforge.net/doc/d ... ol-0.1.pdf
http://www.instructables.com/id/Worlds- ... DC-is-I2C/

and just to make thing messier HDMI also supports CEC data path but not sure if the PI does or not.
http://www.ti.com/lit/an/slaa377/slaa377.pdf

But need to digest and possibly find more details so I can at least put the hardware in to support it in the future.
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by ceteras » Sat Jan 12, 2013 9:33 pm
I see. You can use an I2C memory chip to store the EDID for the resolutions. Most monitors have these chips on the boards. You can download EDID editors from the internet and generate your data for the memory chips. At least that's how I'd do it.
As for CEC, I believe it doesn't work with TFP401, because it is a DVI chip.
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by 3dit » Wed Jan 23, 2013 12:43 am
Hi Ein'

I can look at it and design the PCB if required.

I'll have a look at the files you have once I get to my Altium workstation.
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by 3dit » Wed Jan 23, 2013 10:53 am
EiNSTeiN_ wrote:hello forum,

I have a significant number of LCD panels from old laptops, so I was disappointed when I saw that the r-pi didn't have an lvds output. Given the fact that we don't (and probably won't) have access to the gpu docs or drivers source code, I have doubts on just how straightforward it will be to use the onboard DSI connector.

So I made this today, it's an hdmi to lvds adapter: http://g3nius.org/hdmi-to-lvds.tar.gz

This is an early board design, there are a couple things I haven't worked out, so it will definitely change before I have it produced. I wanted to share this sooner rather than later. It would be great if anyone with electronics knowledge could review the schematics. I made this in an afternoon so more pair of eyes won't hurt.

It works using 2 ICs, the first one is a hdmi receiver and the other one is an LVDS transmitter. between them there is 3 x 8-bit color channels, or 24 bit total. The LVDS transmitter has several modes, the one I used will be compatible with 18-bit displays aswell as [some] 24 bit displays. According to the datasheet, it will be compatible with only a minority of 24-bit capable displays but this is fine since I mostly have 18-bit LCD displays available.

The current BOM should cost in the area of 25$ for a single unit. The main IC on there is the ADV7611 which cost 15$ at digikey. It may be possible to sample the other IC from Texas Instrument and save 7$.

EiN'

Hi Ein' Tried to open the schematics, but Altium doesn't appear to recognize them.

Any chance you could export to Altium, P-CAD or CircuitMaker?

Thanks
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by ceteras » Wed Jan 23, 2013 11:20 am
Those are eagle CAD files, I think. The free version can open them.
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by tncat » Wed Jan 23, 2013 9:24 pm
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by ceteras » Wed Jan 23, 2013 10:57 pm
tncat wrote:http://www.chalk-elec.com/?page_id=1280#!/~/product/category=3094861&id=14647633

Found this...


Looks good, but "Out of stock", also check comments, it looks like hard to get (expensive shipping).
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by rhm1 » Sun May 05, 2013 9:20 pm
The route that I chose was to buy a cheap 15 inch LCD monitor at a car boot sale which had a DVI as well as a VGA input and the display works very well with my Raspberry Pi. I found that this was the cheapest option and less hassle than buying a separate controller board for one of my ex laptop display panels.
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by rhm1 » Tue May 07, 2013 1:41 pm
Has anybody tried to take a HDMI / VGA to LVDS circuit board from a LCD TV that has a broken LCD and hook this up to a laptop display?
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by ceteras » Tue May 07, 2013 6:34 pm
rhm1 wrote:Has anybody tried to take a HDMI / VGA to LVDS circuit board from a LCD TV that has a broken LCD and hook this up to a laptop display?


I actually did something along these lines, but it's hardly reproductible. It was a sort of "scrapheap challenge" project for me.
I use an HDMI input board from a Sony lcd TV, something like this, 15$ from ebay.
Image
It has a SII9993 chip that outputs YPrPb for video and stereo I2S for sound, from an HDMI input.
I2S is converted to audio by a Crystal CS4335 audio dac. Running "tvservice -s" reports 48kHz, 24bit for this board.
My board came without the onboard 3.3V regulator so I had to add one. I also needed 9V for it and 5V for other circuits.

I use a LMH1251 to convert YPrPb to RGB graphics, then an RGB buffer is needed to drive a VGA cable, but I just put 3 transistors on a small board (common collector config). Also an old LS04 was needed for syncs to have the right polarity.

I'm not very pleased with the end result on the VGA part, more careful work is needed for that to perform. A really fast RGB video buffer is needed, such as the recommended LMH6734. Also sync signals were not clean enough, so blanking would occur from time to time on the LCD monitor.
The YPrPb signals looked far better when directly connected to an LCD TV, but I didn't want that.

The sound is good, and the I2S interface can be hacked to another dac instead of the 4335 for better results.

In the end, my experiment looks like this:
Image

I might try to rebuild a cleaner version when I have the time. If I can fix the sync signals quality issue, it might worth converting it to LVDS after all.
Also if somebody has one of these boards, I can help with getting it to work.
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by rhm1 » Wed May 08, 2013 11:40 am
It looks as though you have put a lot of time and effort into this. One big problem that may occur with a project like this is matching up the right lcd to what the controller can handle.
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by ceteras » Wed May 08, 2013 12:43 pm
rhm1 wrote:It looks as though you have put a lot of time and effort into this. One big problem that may occur with a project like this is matching up the right lcd to what the controller can handle.


Yes, it took many hours, but it was fun. I will keep hacking it from time to time until I get a reasonable solution. Then, I estimate a week should be enough to rebuild it in a better looking shape.
I bought it for the on-board DAC, then tried to get the video working.
The SII9993 hdmi receiver on the board supports the following resolutions: 480i/576i/480p/576p/720p/1080i, according to its poor 2-pages documentation available online.

Other HDMI boards can be found on ebay, but none are hack-friendly enough for me.
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by Wire » Sun Mar 16, 2014 3:16 am
Took better part of a year but progress:

Image

Now on to the side band / inverter control card.
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by uberdaff » Wed Mar 26, 2014 12:05 pm
Nice!

Does it work?
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by uberdaff » Wed Mar 26, 2014 12:08 pm
I was in contact with systemation-inc.com about their DVI to LVDS board. It turns out they want 200$ for it, that is in my opinion a quite ridiculous price.
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by Wire » Wed Mar 26, 2014 7:25 pm
uberdaff wrote:Nice!

Does it work?


Not sure yet...

That card is just the high speed devices that required a 4 layer raw card to build. I still need to make a daughter card that holds the voltage regulator, back light control, Touch screen control (want to see if I can run the touch screen over the HDMI I2C bus), and HDMI eeprom. (misc slow stuff that can be done in 2 layers)

As for cost up to around ~$35 for that sub card (all pricing for single pieces no bulk discounts)
~$10 for the raw card from OSH (4 layers are expensive)
HDMI to parallel LCD chip ~$10
parallel to serial chip ~$6
delta in caps and connectors.

I am hopping to be under $75 when all said and done but need to figure out exactly what I need on the second card first. (already have feature creep adding 8-15V in to 3.3V and 5V so I can plug the pi in as well. This is due to the back light inverter needing 8-15V else would have powered everything off of 5V. Currently looking at a dual output switching reg @2A each output.)

$200 for a finished board (depending on the features and support) does not sound unreasonable for one off builds. But for a low end adapter built in mass it seems excessive.

Just as I finished reflowing my cards I got my new issue of make magazine and someone made a Pi tablet. Not a ton of details but looks like someone out there is already making a similar adapter. So may be a little late to the party. Oh well it's a hobby so it's more about the process then the end result.
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by subhagato » Sat Apr 05, 2014 5:10 am
Hi Einstein,

You made a great design using the ADV7611 HDMI Receiver. Did you make it? Is it working? I need to make one such circuit, but in my case, I need just ADV7611 and make an interface to FPGA. I just want to confirm, is your design working? So that I will reuse your design, and modify accordingly.

Thanks,
Subhagato
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