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Thread: Adjustable backlight?

  1. #11
    Constant Bitrate
    Join Date
    Mar 2010
    Posts
    160
    For my display there are two circuit boards. The one you see in the pics is easily removed. You don't really need to disassemble the actual display panel.
    There is a thicker ribbon cable that connects to the other circuit board.

    The second board that you can't see is enclosed in the metal that houses the actual glass and backlight.
    The glass that is the display is permanently attached to that board with fragile ribbon cables.
    My backlight was soldered to that board with a fragile ribbom cable. The driver for the backlight is integrated into it.
    I assume that it's a PWM type of supply. I'm sure you could take that power and modify it to dim the led's. I'm not quite sure how you would modify a signal that's already pwm.

    Getting to that second board does require opening the actual display panel but, in mine, the board was right on the back and I didn't have to remove the glass.
    Regardless, it can be nerve racking to do if you've not got a lot of experience opening things up.

  2. #12
    Raw Wave
    Join Date
    Nov 2009
    Posts
    2,118
    "I'm not quite sure how you would modify a signal that's already pwm"...

    It must be PWM for a reason, but that could be to minimise the resistor size as I outlined.

    Regardless, if it's a circuit that generates the PWM duty cycle based on a resistor, that resistor could be potted so to speak (ie, replaced with a pot). Making a voltage-dependent resistor (to respond to electronic signal rather than a pot) can be done, but that adds complexity. (Is that a transconductance amplifier, or should I be embarrassed again?) And a duty-cycle to voltage converter would probably be the input (to the VDR) if required.

    Many PWMs are set with an R-C combination, but others could be fixed in some program (PIC, controller, etc) or have some other voltage input (LDR, external, etc). That becomes a firmware hack exercise and is usually possible (even if it takes extreme work which is never economically justified) but for practical purposes, it probably isn't possible or practical. (How I loved computers that loaded their OS or peripheral call routines into RAM. A hackers dream....)


    But I reckon I'll bow out of this. Yet again I have no detailed familiarity with the hardware concerned (crap!, I have zilch familiarity with it!) - but I intended only so provide some ideas or possibilities.
    In my case, I'd return the display else threaten "misleading advertising" action. Then again, I have been silly enough to attempt workarounds, and they are probably still in my room(s) of unfinished project LOL!

    Best of luck.


    And davekra, thanks for your insights and links. You're the man, ... I mean... Poster.

  3. #13
    Maximum Bitrate
    Join Date
    May 2005
    Posts
    725
    Thanks guys for the responses! This is getting more and more over my head. I have no problem replacing an LCD panel or motherboard in a laptop, but I'm just not willing to experiment on this screen.


    My screen is a Lilliput. There's the main controller board where the VGA is connected, then there's the LCD panel. Embedded into the back of the LCD panel's plastic backing is a thin circuit board where the main board is connected with a 50 pin ribon cable. That "embedded" board in turn drives the LCD and I do now see a smaller ribon cable for the backlight.

    My previous Xenarc with a CCFL had an entirely seperate inverter board for the backlight.


    I was poking around in my parent's Dodge truck - the backlighting was clearly adjustable, the brightness wasn't simply image processing. If my screen worked like that I'd have been happy.

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