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LCD Backlight 'On' switch

Discussion in 'General Chat' started by Comm, May 15, 2005.

  1. Comm

    Comm
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    I have found an old LCD panel in the local skip, which has no casing, just the panel and controller board.

    I have managed to read some of the PCB writing and found out it needs a 12v input, so am using a normal molex connection. I have worked out which pins goto which vga pins and have fashioned a cable.

    Upon testing the power AND vga connection, the screen comes on, showing the correct display, but then goes dark after a second, but the display is still there, much like a laptop does when you close the lid?

    After this I tested the cables between the main controller board and the inverter, and one pair has a 2.8v running across it for those few seconds the screen is on, then it drops to 0v.

    Does anyone know anymore about controller boards/backlight on-off switching/inverters that can tell me how I can create a constant 2.8v current through those cables to keep the screen alive??

    Thanks in Advance
     
  2. Reiner

    Reiner
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    Does the controller perhaps have some (TTL) input to activate the light?

    Else you could remove the wires from the connection at the controller board and connect them to a resistor network that creates the required voltage.
    I.e. two resistors are connected in series, splitting the 12V supply into 2.8V and 10.2V. The backlight (BL) connects in parallel to the resistor that provides 2.8V:

    0V ----- R1 -------R2-----12V
    .......|............|
    .......|............|
    .......----BL----

    (... just use as spacer)

    To calculate the resistors you would need to measure the current drawn by the backlight.
     
  3. Comm

    Comm
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    Unfortunatly I havent got the kind of electronics knowledge to tell if there's a TimeToLive device, what does one look like?

    I am going to test the current this evening, I can get hold of resistors fairly easily, how would I calculate the resistors I need from this?

    Thanks for your time and help!
     
  4. Chris Muriel

    Chris Muriel
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    TTL = Transistor Transistor Logic.
    This means a logic 1 or high = nominal 5 volts and a logic zero or low = nominal zero volts.

    Chris Muriel, Manchester
     
  5. Comm

    Comm
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    A right, well that shows how much I know about electronics, what does one of those look like? And would this be on the Controller board or the Inverter?

    Thanks again,
     
  6. Reiner

    Reiner
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    Integrated circuits (IC) are usually TTL compatible, so TTL is not a device by it's own but just a signal standard.
    What I meant that the controller IC may have one input (one pin) that switches off the backlight. This input may be TTL compatible, i.e. connecting it to GND (0V, low) or 5V (high), depending on its design, would activate the backlight.
    To see if there is such an input and what signal is required you would need the manufacturer's data sheet of the controller.
    If you provide the name and type maybe I can find it for you (can't promise though) and check it out ....

    Anyhow, this may be a bit too complicated, so perhaps the solution with the resistors is easier. Just measure the current the backlight draws and I can calculate them for you.
     

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