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Driving an lcd panel

Discussion in 'General Electronics Discussion' started by Dicko101, Mar 10, 2015.

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  1. Dicko101

    Dicko101

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    Mar 10, 2015
    Does anyone know if its possible to drive the lcd panel out of a computer monitor with some basic circuitry or an arduino or something? Either to display solid colors or maybe an image or anything at all? I have some projects in mind that I would like to use just the lcd panel without the backlight and I need as simple a setup as possible, the only other way I have found is to connect it to a vga or dvi source such as a computer or raspberry pi etc, but that is overkill for what I need, any ideas?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I believe someone wrote some code to bitbang vga out of an arduino, but maybe I misremember.

    Driving the panel is theoretically possible but you would have to get datasheets for the chips in the monitor and hope that the analogue and digital are not combined.
     
  3. Gryd3

    Gryd3

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    That was certainly done with a Raspi -> http://hackaday.com/2015/03/05/using-cheap-displays-with-the-raspberry-pi/

    Short answer is certainly yes, if you are willing to invest the time.
    Easy answer, no, buy a driver and you can simply use the driver to convert HDMI, DVI, RGB, Composite, etc to the signal required for the display.
     
  4. Dicko101

    Dicko101

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    Mar 10, 2015
    Ok, more what I'm getting at is driving individual pixels, but all together, to basically turn the entire display into a big RGB light. The pixels ultimately have to be controlled by a simple current going through them right? So where the LCD control boards ribbons exit to the panel itself there must be a way to apply a current there directly across a pixel and turn it on, what I want to do is link all of the red, green and blue cells together respectively and apply a current across each group to control the display as one single unit with a range of colors, would this be at all possible or not?
     
  5. Gryd3

    Gryd3

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    I think you would have much better luck dealing with a standard video protocol that DSI, VGA, DVI, or HDMI deal with...
    Other than that, it sounds like you want to bypass the controller and directly control the pixels... but this means you will need to identify the appropriate lines required for each pixel, and the driving characteristics... LCD is not like an LED panel, as each pixel is made up of 3 sub-pixels, and each sub-pixel is a small crystalline structure that reacts with electricity to alter the polarization of light travelling through it.
     
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  6. shumifan50

    shumifan50

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    Jan 16, 2014
    You are aware that LCDs do not generate light, they filter light, which is why they are backlit. The backlighting provide the light and the LCD pixels filter to the required colour.
    This means it is not possible to 'turn the display into an RGB light'.

    It seems that what you want to do can best be done using LED technology (if you really want to make a light).
     
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  7. Dicko101

    Dicko101

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    Mar 10, 2015
    Thanks for the responses, I'm probably not explaining exactly what I'm trying to do very well. Yeah I'm aware of the basics of how LCD displays work, each pixel is comprised of three liquid crystal cells that twist the polarised light from the back layer such that it passes through the front layer and color filter polarised at 90° to the back layer. The light source doesn't really matter as the projects I have in mind use light passing through the panel in other ways, I just want to know how to supply whatever signal I need directly to the cells to manipulate the liquid crystals for all of the red cells, blue cells and green cells as groups to pass light through the panel in a range of colors. For example, if all of the cells have a positive and a negative (just for examples sake) I want to tie all of the positives together, and all of the negatives together for all of the red cells and manipulate them together as a single color filter for the whole panel, and the same for blue and green, to pass light through in whatever color I need. Its not only for display purposes but also for light color filtering for other projects.
     
  8. Gryd3

    Gryd3

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    I'm certain this can be done, but would require some in-depth knowledge of the panel you are going to be using.
    Because of the sheer number of pixels in a display, they will be multiplexed... if you want to treat the display as one giant pixel, they don't really need to be multiplexed any more. With that said, I do not have the experience required to tell you what you will need to directly control an LCD sub-pixel. This could be complicated further by running more than one cell in parallel.
    To take on this task, I would encourage you to grab a multi-meter, and oscilloscope and begin poking and prodding the control board.
    I'm certain you will have better luck 'hi-jacking' the control board to trick it into displaying one color than to bypass it and attempt to drive all of the cells yourself.
    I would still very much like to encourage learning and using a display communication standard... some very basic VGA code can be transmitted to send all red, or all green (or any variation) to the display. The on-board driver will worry about all the other details.

    *Note that even when buying an LCD screen for projects or development, it is rare that the cells are directly driven. You are usually presented with a driver that accepts a specific or set of specific communication protocols.
    This is like trying to build your own control unit for a car engine. Sure it can be done, and lots of people have done so, but unless you want to invest that kind of time into it, it's simpler to use an existing ECU and simply push the gas peddle down with a solenoid.

    I wish you the best of luck on your project, and hope that when you crack apart a display to attempt this on that you do your best to keep the drivers in good condition just in case you run into a road block.



    Some questions you will need answered to drive the display your way.
    - Are all the sub-pixels in the display connected in a common cathode or anode setup? (This makes multi-plexing incredibly easy... but there are alternative driving methods like charlieplexing which could make your proposed solution a huge hassle)
    - Are the sub-pixels supposed to be voltage or current driven? (If you are unsure on the differences... you should visit the 'How to drive an LED' resource. You could easily damage a cell, a row or cells, or a group by driving them incorrectly)
    - What are the specifications at which I should drive the cells at? (Regardless of driving method, there will be a specific rating that should not be exceeded)
    - Are the sub-pixel intensities directly proportional to the control voltage/current or PWM %? If you want 30% green, will you need to build a circuit to compensate for any non-linear responses? (Commonly, running something at 50% does not always appear to be running at half-brightness, or half-volume.)
     
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