LCD pixels

Discussion in 'General Electronics Chat' started by Dicko101, Mar 29, 2015.

  1. Dicko101

    Thread Starter New Member

    Mar 29, 2015
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    Hi everyone, I have a heap of old LCD computer monitors and I have come up with a lot of projects I want to do with them, a lot involving the lease amount of components and power possible. I'm wondering if its possible to drive lcd pixels directly without any kind of driver board. 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, similar to how an RGB LED might work but obviously on a larger scale, would this be at all possible or not?
    Thanks for any advice.
     
  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,652
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    Hola D,

    Be careful in trying to skip all chips managing the display and replace them with discrete components because, most probably, at the end of your journey, even if you can control those pixels of interest (could you?) you could be using a unreasonable amount of parts.

    The few times I did reverse engineering of a comercial product I took advantage of learning with much detail as possible the control signals I needed to provide to the existing cicuitry. In the case of an Epson LX850 I simply discarded the micro in charge and a custom made chip (decoder + glue logic) and replaced the whole with a 18F452 micro that made good use of the steppers and limit sensors.

    Additional suggestion: if in that heap you got two or more of the same model, reserve the best in working condition and do your first attempts on a similar one. Nothing better that the circuit, service manual and a working unit. Or being friend of the designer... :) :p

    Buena suerte.
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    LCD displays will almost certainly be damaged by any sort of DC waveform applied. This tends to happen when batteries die and oscillators stop beating up and down. They require constantly changing AC waveforms. It is literally mind bending to comprehend what you need to to to run a monochrome LCD, never mind the color kind. But maybe you're one of those rare idiot-savants who can visualize the whole process without even thinking about it. If so you should have a blast in such a target rich environment.
     
  4. Dicko101

    Thread Starter New Member

    Mar 29, 2015
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    Thanks for the responses guys, I do have some understanding of how an lcd addresses pixels, but as far as I understood at the most basic level a pixel only needs a voltage applied across it to make the liquid crystal twist (I would have thought this would be DC to determine the direction of the twist) and allow light to pass through that cell and on through the color filter, and the amount of current/voltage determined the amount of twist thus the amount of light allowed past, surely I can program an arduino or the like and modify a basic RGB LED cycling code and adapt it through some transistors etc to provide only what the display needs to allow light through? I just need to determine where the voltage has to be applied to the panel and how much right? I know I'm oversimplifying things but I don't need to address pixels in a timed, logic controlled manner, I don't need to display an image or text or anything, just fade the whole display through a range of colors. I would just use laptop parts or a pi or anything to just drive a panel normally but I want the lease user input possible, maybe just some buttons to cycle through colors and a button for an automatic cycle, which would be simple to program for an arduino if there was no logic between it and the lcd panel. Unless anyone knows if arduino or pic can drive a basic slow color shift like that through vga? But I have read vga is very difficult on such limited hardware. But if i just feed it vga then I need to power the whole monitor circuitry, I really just want to run off of battery power. Sorry for the long message, and for my lack of knowledge in this area, I probably have this all wrong, and thanks again for your help.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    I'm pretty sure that you need constantly changing AC voltages on both sides of a pixel. Constant DC voltages are death to pixels.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    MCU88 and Dicko101 like this.
  7. Dicko101

    Thread Starter New Member

    Mar 29, 2015
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    That looks like it could do what I want MrChips, and ironically the display you use in your example is exactly the same as the one I was experimenting with last night lol, do you think that arrangement could smoothly transition the whole screen through a decent range of colors? The only problem with that is it doesn't eliminate the external power. You're probably right Papabravo, even still, it would be just as easy to feed an AC signal to the pixels if it is possible to manipulate them directly, which I would still prefer in the long run, it seems like overkill to have a simple signal coming from a chip, pass it through another couple of chips to complicate it for no reason, then arrive at the pixels as basic AC signals, it just seems redundant for my needs.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Start off with a 31.5kHz horizontal sync signal.
    Divide this by 525 to give a 60Hz vertical sync signal
    After you've done that, the RGB signals are at your command.
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    I apologize, I misunderstood the following from the original post

    "drive lcd pixels directly without any kind of driver board"
    Driving a VGA controller does not fall within the bounds of that statement IMHO.
     
  10. MCU88

    Member

    Mar 12, 2015
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    Damm straight Mr.Chips I am impressed ;) Mr.Chips's DSO
     
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