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Force LCD monitor "white"/"black"

Started by Don Y July 10, 2014
Hi George,

On 7/10/2014 1:04 PM, George Herold wrote:
> On Thursday, July 10, 2014 3:52:55 PM UTC-4, Don Y wrote:
>> No, when I refer to having just the "panel", I mean "just the >> glass" > > 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?)
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.
Hi Tauno,

On 7/10/2014 1:02 PM, Tauno Voipio wrote:
> On 10.7.14 22:52, Don Y wrote: >> On 7/10/2014 12:32 PM, edward.ming.lee@gmail.com wrote: >>>> Anyone know how the drive to an LCD panel works? Specifically, how >>>> one can force the display to appear "all white" or "all black" >>>> WITHOUT relying on the electronics already present in the monitor? >>> >>> All black is easy, just cut the power. >> >> <grin> >> >>> 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. >> >> No, when I refer to having just the "panel", I mean "just the glass" >> >>> You can definitely do it with a small uC, even with some simple >>> display test patterns. > > 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.
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 (?)
On Thu, 10 Jul 2014 12:16:28 -0700, Don Y <this@is.not.me.com> wrote:

>Anyone know how the drive to an LCD panel works? Specifically, >how one can force the display to appear "all white" or "all >black" WITHOUT relying on the electronics already present >in the monitor? > >E.g., imagine having *just* the LCD panel and being able to >operate it as a "light gate" (full on, full off).
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. <http://www.personal.kent.edu/~mgu/LCD/tn.htm> 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
On 11.7.14 03:56, Don Y wrote:
> Hi Tauno, > > On 7/10/2014 1:02 PM, Tauno Voipio wrote: >> On 10.7.14 22:52, Don Y wrote: >>> On 7/10/2014 12:32 PM, edward.ming.lee@gmail.com wrote: >>>>> Anyone know how the drive to an LCD panel works? Specifically, how >>>>> one can force the display to appear "all white" or "all black" >>>>> WITHOUT relying on the electronics already present in the monitor? >>>> >>>> All black is easy, just cut the power. >>> >>> <grin> >>> >>>> 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. >>> >>> No, when I refer to having just the "panel", I mean "just the glass" >>> >>>> You can definitely do it with a small uC, even with some simple >>>> display test patterns. >> >> 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. > > 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 (?)
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. -- -Tauno
On Thu, 10 Jul 2014 12:16:28 -0700, Don Y <this@is.not.me.com> wrote:

>Hi, > >Anyone know how the drive to an LCD panel works? Specifically, >how one can force the display to appear "all white" or "all >black" WITHOUT relying on the electronics already present >in the monitor? > >E.g., imagine having *just* the LCD panel and being able to >operate it as a "light gate" (full on, full off). > >Thx!
For color LCD panels, you have to generate something like the old-time video signals (timing-wise), but with digital data for the RGB. http://www.nxp.com/wcm_documents/techzones/microcontrollers-techzone/Presentations/graphics.lcd.technologies.pdf 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
Den fredag den 11. juli 2014 14.52.07 UTC+2 skrev Spehro Pefhany:
> On Thu, 10 Jul 2014 12:16:28 -0700, Don Y <this@is.not.me.com> wrote: > > > > >Hi, > > > > > >Anyone know how the drive to an LCD panel works? Specifically, > > >how one can force the display to appear "all white" or "all > > >black" WITHOUT relying on the electronics already present > > >in the monitor? > > > > > >E.g., imagine having *just* the LCD panel and being able to > > >operate it as a "light gate" (full on, full off). > > > > > >Thx! > > > > For color LCD panels, you have to generate something like the old-time > > video signals (timing-wise), but with digital data for the RGB.
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
On Fri, 11 Jul 2014 06:33:25 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>Den fredag den 11. juli 2014 14.52.07 UTC+2 skrev Spehro Pefhany: >> On Thu, 10 Jul 2014 12:16:28 -0700, Don Y <this@is.not.me.com> wrote: >> >> >> >> >Hi, >> >> > >> >> >Anyone know how the drive to an LCD panel works? Specifically, >> >> >how one can force the display to appear "all white" or "all >> >> >black" WITHOUT relying on the electronics already present >> >> >in the monitor? >> >> > >> >> >E.g., imagine having *just* the LCD panel and being able to >> >> >operate it as a "light gate" (full on, full off). >> >> > >> >> >Thx! >> >> >> >> For color LCD panels, you have to generate something like the old-time >> >> video signals (timing-wise), but with digital data for the RGB. > >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:
> On Fri, 11 Jul 2014 06:33:25 -0700 (PDT), Lasse Langwadt Christensen > > <langwadt@fonz.dk> wrote: > > > > >Den fredag den 11. juli 2014 14.52.07 UTC+2 skrev Spehro Pefhany: > > >> On Thu, 10 Jul 2014 12:16:28 -0700, Don Y <this@is.not.me.com> wrote: > > >> > > >> > > >> > > >> >Hi, > > >> > > >> > > > >> > > >> >Anyone know how the drive to an LCD panel works? Specifically, > > >> > > >> >how one can force the display to appear "all white" or "all > > >> > > >> >black" WITHOUT relying on the electronics already present > > >> > > >> >in the monitor? > > >> > > >> > > > >> > > >> >E.g., imagine having *just* the LCD panel and being able to > > >> > > >> >operate it as a "light gate" (full on, full off). > > >> > > >> > > > >> > > >> >Thx! > > >> > > >> > > >> > > >> For color LCD panels, you have to generate something like the old-time > > >> > > >> video signals (timing-wise), but with digital data for the RGB. > > > > > >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? >
yep, just saves on wiring. You can get converters http://www.ti.com/lit/ds/symlink/ds90cf384.pdf DVI/HDMI is similar it just uses a fancier parallel to serial encoding -Lasse
On Thu, 10 Jul 2014 12:16:28 -0700, Don Y <this@is.not.me.com> wrote:

>Hi, > >Anyone know how the drive to an LCD panel works? Specifically, >how one can force the display to appear "all white" or "all >black" WITHOUT relying on the electronics already present >in the monitor? > >E.g., imagine having *just* the LCD panel and being able to >operate it as a "light gate" (full on, full off). > >Thx!
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. ?-) =20
On Thu, 10 Jul 2014 17:53:13 -0700, Don Y <this@is.not.me.com> wrote:

>Hi George, > >On 7/10/2014 1:04 PM, George Herold wrote: >> On Thursday, July 10, 2014 3:52:55 PM UTC-4, Don Y wrote: > >>> No, when I refer to having just the "panel", I mean "just the >>> glass" >> >> 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?) > >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.
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. ?-) =20