Force LCD monitor "white"/"black"

All black is easy, just cut the power.

All white is a little more difficult, and need a little bit of electronics. It depends on the panel, but usually, 8 to 10 data bits, plus hsync, vsync and dot clock.

You can definitely do it with a small uC, even with some simple display test patterns.

No, when I refer to having just the "panel", I mean "just the glass"

You might be able to tie all rows together and all columns together, and drive the rows and columns with antiphase square waves. The hard part will be to find the proper voltage levels.

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Tauno Voipio

Hi Don, Knowing almost nothing, I'd guess there are some different technologies. I certainly remember a prof who did liquid Xtal stuff back at Uni. He used an electric field which caused the crystals to line up or not line up and this resulted in more or less scattering of the light.

So the short answer is maybe an electric field. Perhaps you can "scuff up" some high voltage on a carpet and put your finger near an lcd.

(Why the question.. and why not start at wiki?)

George H.

Without controller, the glass is just 1000x800 (typical) dot matrix. Typical connection pads are in (sub)micron.

logies.

e up and this resulted in more or less scattering of the light.

from here,

rystals

"Scientists and engineers are able to use liquid crystals in a variety of a pplications because external perturbation can cause significant changes in the macroscopic properties of the liquid crystal system. Both electric and magnetic fields can be used to induce these changes. The magnitude of the f ields, as well as the speed at which the molecules align are important char acteristics industry deals with. Special surface treatments can be used in liquid crystal devices to force specific orientations of the director."

Making connections are more of a problem. Unless you have a custom glass p anel, all the H & V lines are routed to a small chip area, typically with < .1mm pitch. You can't attach PCB directly to them. The controller interf ace pads are usually bigger, for PCB attachment.

Basically, unless you are making your own custom controller. It will be di fficult to connect properly.

Not as easy as you would think, it is NOT a CRT. There is a board called th e Tcon for "Tin=ming Control" because they could never have enough wires to address alll the pixels. They are done sequentially. the Tcon isn't even the last thing in the chain, there is also either logic roght in th epanel y os possibly COFs (Chip On Film) before it gets to the actual pixels. Only way to do it. Plasma is similar but since there is no variable twist to mo dulate the light, the brighhtness of each pixel is controlled by PWM. the l onger it is fired, the brighter.

If you look at the lines going to the Tcon from the main board, there are p airs opeertated in LVDS, which is Low Voltage Differential Signal. You cna actually see the video on a scope on those, though unless you use different ial probes/V.amps you don't really get a good signal. All the ones I've see n are still synch negative. Frequently there are more than three pairs, it is not necessarily one pair per color, it superimposes OSD and all that, do es half blanking or whaver the engoneer decided that day with the extras. T here are technical resons for all that but it doesn't matter right now.

The Tcon, even though there is no deflection in the conventional sense, doe s need synch to operate. You could most likely find a way to fake it out. A ll you owuld need is one signal connected to all of them since you want whi te. If you want different colors you will have to separate them of course.

But first, you could try to get a manual for it and se if it has a test mod e. Some of them do have a function just like that for servicing. /usually i t is a jumper on the man board, though I am pretty sure it could be put on the Tcon instead, so some models might have it there.

There are online resources for getting these manuals. I am not all that fam iliar with them because when I was doin alot of that servuice I was a membe r of a website whe I could hget all that. But i thknk if you join Encompass ' website (they sell parts)you can get downloads there. There is also somet hing like electrotanys or something like that I've used a couple of times.

would be a shame to kludge something together to do this and find out all y ou needed was a clip lead.

Most of the light from the backlight DOESN'T show up when the screen is 'white', because your LCD display has a mask, color filters, and polarizer all blocking off some of the light.

Photochromic glass, and the skin of cuttlefish, are better light switches. There are liquid crystal solutions, too, but more of the transparent/milky sort than transparent/black, and those use completely different materials (which are nonetheless still liquid crystals, just not twisted-nematic).

Sorry, I had that "basic" understanding. I've used "simple" LCD displays (single backplane) and very small (7x95) multiplexed glass. Driving the former is easy -- drive the backplane with an AC signal and invert the signal for any segments/indicators that you want to "light". The latter was much more complicated and involved multi (voltage) level drive to ensure the columns in the "selected" row were driven properly while NOT driving any of the dots in the unselected rows (which, obviously, saw the same column drives that were being presented to the selected row!).

[IIRC, Hughes made some devices that did this.]

My question was intended to elicit how much *larger* panels are driven -- presumably more complex than the small multiplexed glass I had used.

I would suspect that would work on "dumb glass" (i.e., where the rows and columns were just electrodes screened on the glass).

But, I thought larger panels had some active components *in* (on) the glass to effectively treat the display as a storage device that is "refreshed" with new data, periodically (?)

The "normal" state of the monitor should somehow be set to turn OFF all the pixels so that they act transparent. This is called the NW (normally white) mode for TN (twisted nematic) panels. Then, just turn on and off the backlighting. If it's a CCFL inverter, it's the control wire. If it's an LED panel, you'll need to supply a panel number which should lead to a connection diagram.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

For monochrome panels, the usual chip was KS0083. It is a 80 bit shift register with LCD output level shifters.

For a 320 by 240 display, there were 4 KS0083's for columns and

3 chips for rows. The data was fed serially to the column chips, with the rows clocked once for each full row. I used a refresh rate of 14400 row/s, giving 60 frames/s.

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-Tauno

For color LCD panels, you have to generate something like the old-time video signals (timing-wise), but with digital data for the RGB.

As well as the (possibly) active matrix there are active (silicon chip) drivers in the panel that have huge numbers of connections.

I think Jim has designed some of the driver chip things (Solomon?).

--sp

yes for some LCD panels is is just a clk, hsync,vsync and a number of digital pins per color, but many newer panel those signals are encoded serially onto a couple of lvds pairs

-Lasse

Cool. So basically the same signals but with another layer of timing on top?

--sp

Den fredag den 11. juli 2014 19.28.45 UTC+2 skrev Spehro Pefhany:

yep, just saves on wiring. You can get converters

DVI/HDMI is similar it just uses a fancier parallel to serial encoding

-Lasse

So get a LCD to do just that. Simple drive. A small cell phone 320 by 240 color display requires thousands of connections with complex driver ICs.

No, i do not know where to get them off the top of my head.

?-)

Rather hellishly so. There are about 2 million full color pixels in a standard HD display (1920 by 1080) so figure maybe 10 million connections to the glass (unless there is a lot more smarts in the glass) minimum.

Of course if you want to drive something like that in an "on-off" mode a fast AVR or PIC could do the job of creating the analog or DVI video signal.

?-)