Build your own small VGA

LoopyByteloose

Has anyone looked into salvaging the screens out a dead netbook for use with the Propeller? My netbook just reached the end of its useful life, but it has quite a few interesting parts. I can get a WiFi card and an SDcard slot, and a few other things.

But that screen looks the most appealing. It seems that if this is possibly, there are tons of these on EBay as the first generation of netbooks is about 3 years old.

W9GFO

I remember this question being asked before - for laptop screens. The answer, as I remember, is no. The reason was that the screens connect to specialized hardware on the laptops, there is no standard. It's not like you can just feed VGA signals into the screen.

Maybe netbooks are different?

Rich H

LoopyByteloose

What a pity. They happen to be very nice little screens.

Oldbitcollector (Jeff)

In an ideal world.... this would be perfect..


There is hope however.. I'm told by a friend who does laptop repair that there are some standards emerging in laptop screens. This means there is possibility for someone to design (a redesgn) an interface to talk to these.

Perhaps the answer will be different soon, but for now.. Afraid not.

OBC

LoopyByteloose

And now I wonder if the little camera can be salvaged. There are a lot of goodies in this chassis.

schill

The camera should be a standard usb camera. All you should need to do is figure out which wire is which.

Based on another thread, I expect you are talking about an old Asus EEE (7" ?). There should be old threads on www.eeeuser.com with the pinout since a lot of people were modding these and adding additional usb-based stuff internally.

RickB

The real trick is to find the complete data sheet for the lcd. Then look on the board for a separate controller chip, if there is one. If so, find the data sheet for the controller. The problem is that the controller may be part of a large asic for which the is no documentation. There are many documented controllers with frame buffers (ram) that could be used with the lcd if the lcd docs can be found. At that point, (pcb and fine pitch connectors aside) the interface to the micro of your choice is straight forward. Here is an example of one controller.

http://www.rapidonline.com/productinfo.aspx?tier1=Electronic+Components&tier2=Optoelectronics&tier3=LCDs+And+Accessories&tier4=LCD+Graphics+controller&moduleno=75869

Rick

LoopyByteloose

It is indeed a 7" EEEpc 701-4g.

One hint is that the computer is all Intel chips, including video. And there is a VGA plug to the outside. That has to lead somewhere. Internally, it is capable of switching between the internal screen and the external VGA plug.

kwinn

I was part of an earlier discussion of using notebook screens as standalone monitors with the prop or other micros. Being curious I removed the displays from several dead laptops and searched out the data sheets. I found the displays all required a vertical sync, horizontal sync, 4 to 8 bits of RGB (total of 12-24 bits), and a clock signal to latch the RGB bits. Ideally the clock and RGB signal timing should match the resolution of the display, but it is possible to use at lower resolutions with some loss of clarity.
I concluded it is a difficult but not impossible task to repurpose notebook screens.

LoopyByteloose

That seems close to the Propeller's ability.

kwinn

The major problem I see is producing and synchronizing the clock signal with the RGB video output bits from the prop. It may be possible, but I do not have the level of expertise with the prop video and counters to know for sure. Perhaps someone at Parallax or on the forum knows if it is possible.

LoopyByteloose

Hi again,
The pin outs are in the ballpark. But it becomes essentially a low level programing task in Propeller Assembler. At this point, I've too many other things to think about. But I suspect that some limitations can be imposed on the video quality and it can get done by who-knows-who.

LoopyByteloose

This looks promising for salvaging a laptop screen.

http://www.harbaum.org/till/dvi2par/index.shtml

One might both save some costs and be able to get the 7" or 9" screens from an old EEEpc for Propeller projects.

Clock Loop

kwinn wrote: »

Being curious I removed the displays from several dead laptops and searched out the data sheets. I found the displays all required a vertical sync, horizontal sync, 4 to 8 bits of RGB (total of 12-24 bits), and a clock signal to latch the RGB bits.

If you can't find the datasheet on the lcd, and control chips, then its a worthless lcd.



There is always "reverse engineering" using many logic channels on a scope, if the lcd is operational.

Capt. Quirk

A helpfull site http://www.beyondinfinite.com/library.html

LoopyByteloose

At least take a good look at the link. Waiting for a web site to post pin out info is a bit absurd, reverse engineering can do quite a bit.

http://www.youritronics.com/laptop-lcd-display-to-vga-interface-project/ Here is somebody that is getting somewhere.

For instance, I used to by old HP terminals for $5 broken and repair them without schematics. In some cases, I could just swap things to make them work. But buy carefully examining the power pins of the CPU chips, it because very obvious that they were using an 8080 cpu with HP markings. Eventually, more and more things became clear and more and more units were sold as refurbished for $150-200 USD.

I do have the interface with the LCD on the EEEpc motherboard and I can back-track the context. These days it is getting harder and harder to find anything informative on the internet - search engines are more and more into positioning advertisement than really providing thorough searches.

The two things that came up with the most recent link I posted are AND are why I posted it:

1. One doesn't have to use all 24 bit of the color inputs that are offered. The Propeller provides what seems like 2 bits of scale per color for a total of 6, rather than the 8 bits per color for a total of 24. It looks as though some of the pins can just be pulled high or low. Standards beyond 24 bits of color (ala M$ are about transparency and not really in hardware).

2. The chip posted does provide substantial clues to what an LCD is looking for in i/o and and the chip itself is still available from TI. So this may well be a good interface example between a 'raw' LCD and the Propeller.

BTW, Back-lighting for the LCD may be entirely separate.

LoopyByteloose

http://www.techeblog.com/index.php/tech-gadget/laptop-lcd-with-a-vga-connector

More DIYers

Capt. Quirk

After disassembling a monitor to repair, and my old Toshiba lap top (that used a Sharp tft-lcd Monitor), I found that many pdf's were just additions (size info mainly) to the original data sheet. Scattered through that site are the original data sheets with 40 or 30 pin protocols.

Also I found (but I haven't read yet) an app note for connecting micro-controllers to a Sharp lcd monitor.

LoopyByteloose

Thanks, if that is all there is to the interface, it seems that the Propeller can easily do it.
What I really need is a good oscilloscope to verify pins. I have been getting by on using a 'sound card' software scope that is up to about 40Khz.

I suspect that getting the RGB pins mixed up may not do much harm to the LCD and can be later sorted out by trial and error (the highest bits are most important), but one does have to locate the Vdd, Vss, and the Hsync and the Vsync.

Vdd and Vss are usually no brainers. A Propeller Scope might just assist with finding the syncs. Engineers being what they are, the colors are likely to be grouped together is groups of 8 and in RGB order.

I guess it is time for me to see if I can really do some reverse engineering on the EEEpc as the video is working. And I need to read the Propeller Hardware PDF again in detail. Also the VGA driver. These really decide how directly I can drive it all.a

Of course, there is the option to write another Propeller video driver for a lower level of interface,

Humanoido

More sources.

http://www.google.com/search?hl=en&source=hp&q=USING+OLD+LAPTOP+SCREEN&aq=o&aqi=&aql=&oq=&gs_rfai=

LoopyByteloose

I really have to do more hands-on work with my EEEpc. At the least, I need to count the number of pins in the interface. It would help to begin to trace where some of them go.

One point of interest is that hackers have put the EEEpc 900 LCD in an EEEpc-701. That means that they are the same pinout even though they differ in real estate.

http://jkkmobile.blogspot.com/2008/05/asus-eee-pc-900-screen-on-701.html

I suppose that a database of which screens require what would be in order.

And, there are two goals:
1. Retrofit a generic VGA interface
2. Fit to a specific Propeller driver if this is any easier.

LoopyByteloose

More DIY details on a success.
http://www.adwiens.com/projects/electronics/11/index.html

Here is a pin layout i found ...

EEE-PC LCD Pin-outs
1 lvdsvcc
2 ??? 0.1v
3 ??? 0.3v
4 ??? 2.2v
5 ??? 0v
6 ??? 2.25v
7 lvds ground
8 a0-
9 a0+
10 a1-
11 a1+
12 lvds ground
13 a2-
14 a2+
15 clock-
16 clock+
17 back light ground
18 back light adj
19 back light on/off
20 back light vcc

kwinn

This link "Interfacing LCD Panels to Microcontrollers.pdf" posted by Capt. Quirk gives an excellent description of the drive signals for LCD panels. Must reading for anyone contemplating re-purposing a laptop LCD panel.

BTW - all of the LCD panels I looked at from old laptops conform to the signal description in the above PDF. The oldest panel from a 486 was 6 BPP (262,144 color), the rest were 8 BPP (16,777,216).

LoopyByteloose

I will return to that. On the EEEpc, I am daunted by the LVDS (Low-voltage diffrential signalling) that is referred to the above pin outs.