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LCD Backlight Upgrade Autodimming control

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  • LCD Backlight Upgrade Autodimming control

    This project is pat of the LCD backlight upgrade designed by JCDillin and Scouse Monkey (Me )

    Threads about the CCFL design can be found here: (main thread) (initial thread)

    There is a sister thread to this one here:

    The CCFL upgrade involves removing the stock CCFL and inverter from the Panasonic and Hitachi panels found in the common LCDs (e.g. Xenarc and Lilliput) and replacing it with two custom designed CCFLs.

    These CCFLs require a much more powerful inverter (around 12W) and due to the brightness this screen will produce and to reduce un-necessary heat from excess light we have opted for an auto-dimming control circuit for the inverters.

    This post will be updated with the status of the project and notification will be sent to those subscribed when it is updated. You can subscribe using the ‘thread tools’ at the top of the page so please do not make pointless posts to subscribe.


    ***************BE PATIENT*******************



    1. Q. How will this work?
    A. We intend to use a microprocessor to take input from a photocell mounted in the screen bezel to adjust the screen according to the light falling on the screen. There will be some sort of adjustment to this auto-dimming, hopefully using push buttons, and also a manual/auto selector switch.

    2. Q. Can I buy this from you?
    A. I doubt it! We will probably release the plans to be built by each member as it is not going to be possible to us to build and test every control module. We may get circuit boards made up and provide them with pre-programmed chips to protect. This will make it easier for people without access to PIC programmers. On-board programming may be built in however to allow upgrades and there may be a serial link.

    3. Q. How much will it cost?
    A. I have no idea at this stage. A simple PIC can be bought for a few pounds and other things like photocells, resistors, 555 ICs will all be very cheap.

    4. Q. Can I help? How can I help?
    A. Yes I hope you can. This is a community and we are looking to it for help and ideas. We already have several offers for help with code (Chis31 and UK_mp3car) and any suggestions of possible hardware we could use will also be a big help however the project will be pretty straight forward.

    5. Q. How will the control circuit be powered?
    A. It is likely that it will either be 5V or 12V so it can be powered off your USB power or from the main screen power. It is likely that we will suggest people build/purchase a separate 12V backlight power supply that is capable of providing at least 1200mA due to the potential for noise from the inverters and also because a lot of people already have highly stressed 12V lines and a screen drawing 2A not 1A will be the straw that breaks the camels back!

    More to follow. Check the main CCFL thread for now.


    Scouse Monkey

  • #2
    The inverters have not yet been finalised and there is basically two ways by which they could be controlled:

    1. Analogue voltage - with an input pin connected to ground the inverters will be at full power. With the input pin at 5V the inverters will be at minimum power. This method can be quite simply hooked up to a pot to allow manual adjustment and an LDR could also be used to provide some auto dimming. These inverters have an in-board PWM circuit.

    2. PWM control – this is when the PWM is performed externally from a simple 555 IC. This gives us the freedom to tune the auto-dimming and also have push button control of the auto/manual mode and manual adjustment of the auto-dimming. Obviously this is our preferred method of control and primarily what this thread is for.

    The inverters may have onboard PWM that can also be bypassed which would enable people to choose the complicated control circuit or simple manual adjustment.


    • #3
      New idea due to this thread:

      Basically we might look into making the backlight stay dim while the PC is booting so you dont have any nasty OSD images or screen flcikers that make your install look less OEM.

      Also it could be linked up so any AV sources (eg reverse cam) can bring the backlight out of the low power state with a small delay to allow the screen to adust to the resolution etc (might have the ability to wire an auto-press for the auto-adjust on the lilliputs too)

      PS No posting yet!