aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Sat Aug 17, 2019 7:31 am

With wrong timings you can have everything: random data to no display at all.

You have a timing chart, so start working from this.

Raquena
Posts: 11
Joined: Wed Aug 14, 2019 11:11 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Mon Aug 19, 2019 2:24 pm

aBUGSworstnightmare wrote:
Sat Aug 17, 2019 7:31 am
With wrong timings you can have everything: random data to no display at all.

You have a timing chart, so start working from this.
Hello again,

I finally got the thing (almost) running!
I still have some problems with the colours
dpi_lvds_colors.jpg
dpi_lvds_colors.jpg (83.43 KiB) Viewed 4179 times
My guess is that there's an LVDS signal that isn't working properly, not sure though.

Could it be wrong RGB configuration?
Could be due to some LVDS signal missing?

Thanks for your help!

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Mon Aug 19, 2019 5:10 pm

1. Check your LVDS data mapping is correct
2. Check if rbg_order in dpi_output_format is matching your HW connections

My guess is 1.

Raquena
Posts: 11
Joined: Wed Aug 14, 2019 11:11 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Tue Aug 20, 2019 10:47 pm

aBUGSworstnightmare wrote:
Mon Aug 19, 2019 5:10 pm
1. Check your LVDS data mapping is correct
2. Check if rbg_order in dpi_output_format is matching your HW connections

My guess is 1.
Hello again,
My guess is also 1, couldn't verify it yet though.
By the way, this raises another question:
I've been using MichaR's schematic as a guide for my desig, but reading the datasheet of the DS90C387, where the configuration for dual LVDS
is described, and the pinout doesn't seem to match.
ds90_schematic1.jpg
ds90_schematic1.jpg (79.26 KiB) Viewed 4114 times
ds90_pinout1.jpg
ds90_pinout1.jpg (121.55 KiB) Viewed 4114 times
ds90_pinout2.jpg
ds90_pinout2.jpg (192.04 KiB) Viewed 4114 times
It seems the schematic was initially planned for 6 bits per color resolution, and when changing to 8 bits, and then changed to 8 bits
without realizing the (weird indeed) new order in the pinning.

Does this sound some sort of coherent with the guess of the wrong mapping on the LVDS (in this case DPI)?
would be great if MichaR is still around and can reply directly in reference tho this ;)

Thanks for your help !!!

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Wed Aug 21, 2019 4:13 am

Search the web for JEIDA and for VESA data mapping in LVDS.
Your LVDS transmitter is not able to switch between the two standard mappings as LVDS data mapping is defined by HW connections

EDIT: VESA mapping is the first picture in this post https://www.raspberrypi.org/forums/view ... 9#p1023780 and JEIDA is the second mapping picture.
Compare to your displays mapping!

pbisiac
Posts: 13
Joined: Wed Nov 13, 2013 5:22 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Wed Aug 28, 2019 3:08 pm

Hello, perhaps this question has already been answered...If I need LVDS + SPI on GPIO09+10+11, shall I use RGB MODE3 (565) and free these pins ? I did not find this in documentation....Thanks

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Thu Aug 29, 2019 4:39 am

pbisiac wrote:
Wed Aug 28, 2019 3:08 pm
Hello, perhaps this question has already been answered...If I need LVDS + SPI on GPIO09+10+11, shall I use RGB MODE3 (565) and free these pins ? I did not find this in documentation....Thanks
the compute module data sheet is a good source of information, even on a standard Pi.

There is no LVDS on a Pi, only DPI and DSI. If you want to use SPI + DPI you can't use a normal PI as there is no mode which allows for both.
Refer to https://www.raspberrypi.org/documentati ... /README.md for info on DPI.
SPI is on GPIO 9 to 11 (SPI0) or GPIO 19 to 21.
There is no DPI mode which has them unused.

Raquena
Posts: 11
Joined: Wed Aug 14, 2019 11:11 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Thu Aug 29, 2019 12:38 pm

aBUGSworstnightmare wrote:
Wed Aug 21, 2019 4:13 am
Search the web for JEIDA and for VESA data mapping in LVDS.
Your LVDS transmitter is not able to switch between the two standard mappings as LVDS data mapping is defined by HW connections

EDIT: VESA mapping is the first picture in this post https://www.raspberrypi.org/forums/view ... 9#p1023780 and JEIDA is the second mapping picture.
Compare to your displays mapping!
As far as I understand (and I think you already commented in other posts) I think my mapping is VESA:
Image

With a redesign in the pin assignment, fitting what the ds90 datasheet dual LVDS application describes, I get this results:
lvds_newcolors.jpg
result
lvds_newcolors.jpg (160.92 KiB) Viewed 3364 times
testchart.jpg
test chart from screen
testchart.jpg (143.19 KiB) Viewed 3364 times
in comparison with the original chart:

Which are slightly better than last time, but still not right (in the pictures of the previous board, it seems there were quite big problems to display red colours)

Still didn't find the proper configuration...
Currently it's like this (which is what the datasheet states for DPI to dual LVDS converter)
pinout.jpg
Pinout for the LVDS adapter
pinout.jpg (118.62 KiB) Viewed 3364 times
I can't see where the error is, so I'll be glad if somebody guides me to it ;)

Besides that, on this iteration of the board, the screen started switching on and off quite often, and I have a guess about why, but
I'd like to hear also about other people's experiences.

Did anybody have a similar problem?

Cheers, and Thanks!

Raquena
Posts: 11
Joined: Wed Aug 14, 2019 11:11 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Thu Aug 29, 2019 12:39 pm

Raquena wrote:
Thu Aug 29, 2019 12:38 pm
aBUGSworstnightmare wrote:
Wed Aug 21, 2019 4:13 am
Search the web for JEIDA and for VESA data mapping in LVDS.
Your LVDS transmitter is not able to switch between the two standard mappings as LVDS data mapping is defined by HW connections

EDIT: VESA mapping is the first picture in this post https://www.raspberrypi.org/forums/view ... 9#p1023780 and JEIDA is the second mapping picture.
Compare to your displays mapping!
As far as I understand (and I think you already commented in other posts) I think my mapping is VESA:
Image

With a redesign in the pin assignment, fitting what the ds90 datasheet dual LVDS application describes, I get this results:
lvds_newcolors.jpg
testchart.jpg
in comparison with the original chart:

Which are slightly better than last time, but still not right (in the pictures of the previous board, it seems there were quite big problems to display red colours)

Still didn't find the proper configuration...
Currently it's like this (which is what the datasheet states for DPI to dual LVDS converter)
pinout.jpg

I can't see where the error is, so I'll be glad if somebody guides me to it ;)

Besides that, on this iteration of the board, the screen started switching on and off quite often, and I have a guess about why, but
I'd like to hear also about other people's experiences.

Did anybody have a similar problem?

Cheers, and Thanks!
P.D:
This is the original test chart:
testchart_good.jpg
testchart_good.jpg (103.1 KiB) Viewed 3364 times

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Thu Aug 29, 2019 6:05 pm

Change rgb_order in dpi_output_format and post the results (mentioning which order is used).
Or post how dpi is connected on your Pi

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Fri Aug 30, 2019 4:44 am

aBUGSworstnightmare wrote:
Thu Aug 29, 2019 6:05 pm
Change rgb_order in dpi_output_format and post the results (mentioning which order is used).
Or post how dpi is connected on your Pi
have you checked the transmitter data sheet and do you unterstand it?
Or have you simply copied from the existig schematic?

I've took the time to check your transmitter connections and I see this:
- your display has VESA mapping (R0 is tranmitted in Y0 signal)
- figure 17 in the transmitter data sheet shows you the data inputs mapped to LVDS outputs
- your display has VESA mapping, so the bit R10 (figure 17) needs to be equal to R0 (red0 DPI bit)
- table no 2 in transmitter data sheet schows you that for 24bit TFT the transmitter input pin name R16 equals R0 (red0 DPI bit).

--> look at the position of R16 in the LVDS data mapping! You will see that the bit isn't transmitted where you need it --> compare to my post which shows JEiDA compared to LVDS mapping.
The data sheet shows connections for a display following JEIDA standard as R10 is LSB in Y0 and connected to red2 (table 2)

Conclusion: your hardware wiring of DPI interface to transmitter inputs is wrong!

Look here for a good read on the topic https://www.google.com/url?sa=t&source= ... 1UlY34sHXf

Do you see the error now?

Raquena
Posts: 11
Joined: Wed Aug 14, 2019 11:11 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Fri Aug 30, 2019 12:37 pm

aBUGSworstnightmare wrote:
Fri Aug 30, 2019 4:44 am
aBUGSworstnightmare wrote:
Thu Aug 29, 2019 6:05 pm
Change rgb_order in dpi_output_format and post the results (mentioning which order is used).
Or post how dpi is connected on your Pi
have you checked the transmitter data sheet and do you unterstand it?
Or have you simply copied from the existig schematic?

I've took the time to check your transmitter connections and I see this:
- your display has VESA mapping (R0 is tranmitted in Y0 signal)
- figure 17 in the transmitter data sheet shows you the data inputs mapped to LVDS outputs
- your display has VESA mapping, so the bit R10 (figure 17) needs to be equal to R0 (red0 DPI bit)
- table no 2 in transmitter data sheet schows you that for 24bit TFT the transmitter input pin name R16 equals R0 (red0 DPI bit).

--> look at the position of R16 in the LVDS data mapping! You will see that the bit isn't transmitted where you need it --> compare to my post which shows JEiDA compared to LVDS mapping.
The data sheet shows connections for a display following JEIDA standard as R10 is LSB in Y0 and connected to red2 (table 2)

Conclusion: your hardware wiring of DPI interface to transmitter inputs is wrong!

Look here for a good read on the topic https://www.google.com/url?sa=t&source= ... 1UlY34sHXf

Do you see the error now?
Casually, yesterday I also found by myself exactly that document, which after reading for a while make me feel I didn't understand at all the topic :)

First of all, I've been reading as much documentation as I could to get to understand how all this LVDS thing works, not just copied the schematic and that's it, this doesn't mean I've understood right what did I have to do though! hahaha

I'll check the document in dept, and try to get to the same point you're describing, if not, I think I may ask again...

Thanks for everything!
Cheers!

BalajiNarasimhan
Posts: 3
Joined: Sun Sep 01, 2019 7:20 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Sun Sep 01, 2019 7:38 am

Hello Everyone.
i have made a lvds addon board with sn75lvds83bdggr. total cost per piece is 3$ inclusive of components,pcb + shipping. yes i used discount coupons. display model used is M185B1-L01 .Resolution 1366x768. works on pi 3 and pi zero. lcd was taked from acer x193hq monitor.

Image
Image
Image

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Sun Sep 01, 2019 2:23 pm

BalajiNarasimhan wrote:
Sun Sep 01, 2019 7:38 am
Hello Everyone.
i have made a lvds addon board with sn75lvds83bdggr. total cost per piece is 3$ inclusive of components,pcb + shipping. yes i used discount coupons. display model used is M185B1-L01 .Resolution 1366x768. works on pi 3 and pi zero. lcd was taked from acer x193hq monitor.
congrats!
Wow $3 for the whole assembled board is cheap as the LVDS transmitter is $3.65 when you buy 1000 pcs.
https://www.digikey.com/product-detail/ ... ND/2071148

BalajiNarasimhan
Posts: 3
Joined: Sun Sep 01, 2019 7:20 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Mon Sep 02, 2019 12:20 pm

aBUGSworstnightmare wrote:
Sun Sep 01, 2019 2:23 pm
BalajiNarasimhan wrote:
Sun Sep 01, 2019 7:38 am
Hello Everyone.
i have made a lvds addon board with sn75lvds83bdggr. total cost per piece is 3$ inclusive of components,pcb + shipping. yes i used discount coupons. display model used is M185B1-L01 .Resolution 1366x768. works on pi 3 and pi zero. lcd was taked from acer x193hq monitor.
congrats!
Wow $3 for the whole assembled board is cheap as the LVDS transmitter is $3.65 when you buy 1000 pcs.
https://www.digikey.com/product-detail/ ... ND/2071148
Yes i used the first time user coupon for the pcb with free shipping plus i sourced the lvds transmitter directly from china for 1.9$ per piece. and 3$ for 5 pcbs and the passives are very cheap. usually the chips are made in china and sent to the brand and then shipped to distributors. which add to the price. the chinese guys sell the same thing for half the price. since it was sent via a post i incurred no customs. ( my luck :D ) for the connectors i soldered them direclty on the pi headers and used berg strips for the lvds.. the female lvds connectors were from a old arduino with lvds soldered and hot glue applied :D .. really couldnt wait for the connectors to arrive..
Last edited by BalajiNarasimhan on Wed Sep 04, 2019 1:55 am, edited 3 times in total.

BalajiNarasimhan
Posts: 3
Joined: Sun Sep 01, 2019 7:20 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Mon Sep 02, 2019 12:29 pm

Raquena wrote:
Thu Aug 29, 2019 12:38 pm
aBUGSworstnightmare wrote:
Wed Aug 21, 2019 4:13 am
Search the web for JEIDA and for VESA data mapping in LVDS.
Your LVDS transmitter is not able to switch between the two standard mappings as LVDS data mapping is defined by HW connections

EDIT: VESA mapping is the first picture in this post https://www.raspberrypi.org/forums/view ... 9#p1023780 and JEIDA is the second mapping picture.
Compare to your displays mapping!
As far as I understand (and I think you already commented in other posts) I think my mapping is VESA:
Image

With a redesign in the pin assignment, fitting what the ds90 datasheet dual LVDS application describes, I get this results:
lvds_newcolors.jpg
testchart.jpg
in comparison with the original chart:

Which are slightly better than last time, but still not right (in the pictures of the previous board, it seems there were quite big problems to display red colours)

Still didn't find the proper configuration...
Currently it's like this (which is what the datasheet states for DPI to dual LVDS converter)
pinout.jpg

I can't see where the error is, so I'll be glad if somebody guides me to it ;)

Besides that, on this iteration of the board, the screen started switching on and off quite often, and I have a guess about why, but
I'd like to hear also about other people's experiences.

Did anybody have a similar problem?

Cheers, and Thanks!

Hi, i faced the same problem when trying for the correct hdmi timings settings for my lcd panel. well mine is a single channel 8 bit one. but i had the same dark hue screen when i tried settings with high clock frequency like 85 hz and 120 hz like in this page

https://www.raspberrypi.org/documentati ... t/video.md

Hdmi group 2 mode options 25 and 26. i got purple ish screen with lines ... and then i finially found the correct resoltuion of mine 1366x768 at 81 and 86 .. yet they had red and green pixel dots around the object shapes in the screen saver. like dots around clouds and mountains... then i found to make a custom hdmi mode and timings and i added 1 for deinterlace. and the problem was gone. i hope it helps you in a way. the usual modes listed on the page doesnt need to work all the time. try your own settings.

FUNcation
Posts: 6
Joined: Mon Dec 11, 2017 12:01 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Sat Sep 21, 2019 8:39 pm

BalajiNarasimhan wrote:
Sun Sep 01, 2019 7:38 am
Hello Everyone.
i have made a lvds addon board with sn75lvds83bdggr. total cost per piece is 3$ inclusive of components,pcb + shipping. yes i used discount coupons. display model used is M185B1-L01 .Resolution 1366x768. works on pi 3 and pi zero. lcd was taked from acer x193hq monitor.
Awesome, Balaji! :D Can you sell me couple boards? Send me email to serg97 at seductive dot com Subj "LVDS for Pi"
I have Samsung LTM220MT09
Thanks in advance

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Sun Sep 22, 2019 6:07 am

FUNcation wrote:
Sat Sep 21, 2019 8:39 pm
BalajiNarasimhan wrote:
Sun Sep 01, 2019 7:38 am
Hello Everyone.
i have made a lvds addon board with sn75lvds83bdggr. total cost per piece is 3$ inclusive of components,pcb + shipping. yes i used discount coupons. display model used is M185B1-L01 .Resolution 1366x768. works on pi 3 and pi zero. lcd was taked from acer x193hq monitor.
Awesome, Balaji! :D Can you sell me couple boards? Send me email to serg97 at seductive dot com Subj "LVDS for Pi"
I have Samsung LTM220MT09
Thanks in advance
are you sure you want to buy the board?
Well go ahead doing so, but maybe you should have a look at the modules data sheet first! It is 1920x1200pixels resolution and needs dual channel LVDS.
The board shown by Balaji is single channel only (max possible resolution is 1366x768 pixels (typ limit of single channel LVDS)

FUNcation
Posts: 6
Joined: Mon Dec 11, 2017 12:01 am

Re: LVDS add-on for Raspberry models with 40pin GPIO

Wed Sep 25, 2019 2:19 am

Thanks for heads up. Can I use 2 LVDS chips or do I need another dual chip?
aBUGSworstnightmare wrote:
Sun Sep 22, 2019 6:07 am

are you sure you want to buy the board?
Well go ahead doing so, but maybe you should have a look at the modules data sheet first! It is 1920x1200pixels resolution and needs dual channel LVDS.

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Sat Sep 28, 2019 7:21 am

You need to use a 48-bit (dual-pixel per clock) TX

bird2000
Posts: 3
Joined: Wed Nov 27, 2019 9:19 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Wed Nov 27, 2019 9:29 pm

Hello @aBUGSworstnightmare, if available I would to buy one or two of the LVDS4PI boards.
best regards
Birgitt

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Thu Nov 28, 2019 4:10 pm

bird2000 wrote: Hello @aBUGSworstnightmare, if available I would to buy one or two of the LVDS4PI boards.
best regards
Birgitt
Hi Birgitt,
sorry, but all boards are gone already (for quite some time).
Anyhow, I've also needed some more and decided to design a successor which will solve some issues:
- one board which support VESA and JEIDA mapping
- single and dual channel displays will be supported --> up to FHD from DPI interface
- cheaper components and only dual-layer PCB cuts cost (NOT: I'm not building a commercial dirt-cheap product, my main goal is functionality. That's why cost is a minor topic. But compared to the LVDS4Pi cost it's way cheaper).

As I'm still testing it i will not disclose further details atm. Once everything is confirmed working I will post here and upload a new video to youtube.

bird2000
Posts: 3
Joined: Wed Nov 27, 2019 9:19 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Fri Nov 29, 2019 2:05 am

Hi, cheaper sounds well, but only two layers ? MichaR is the meaning that this will result in a poor signal! Do you have a ETA of release ? Where are you located because of shipping cost ?

aBUGSworstnightmare
Posts: 1512
Joined: Tue Jun 30, 2015 1:35 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Fri Nov 29, 2019 5:38 am

bird2000 wrote:
Fri Nov 29, 2019 2:05 am
Hi, cheaper sounds well, but only two layers ? MichaR is the meaning that this will result in a poor signal! Do you have a ETA of release ? Where are you located because of shipping cost ?
MichaR's comment is in another context.

What is proven working here https://www.raspberrypi.org/forums/view ... 0#p1385429 will work well again ..

This is not a finished product; I'm running no business! All this here is my personal development where I give others tahe possibility to use it by selling off surplus PCBs at cost.

bird2000
Posts: 3
Joined: Wed Nov 27, 2019 9:19 pm

Re: LVDS add-on for Raspberry models with 40pin GPIO

Sun Dec 01, 2019 12:19 pm

Thx, than the explanations and the way offered by Peter are correct and MichaRs comments targets to a other context. But the main questions about the new PCB you haven't answered - ETA and location?

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