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New hd44780 LCD problem (Contrast)

Discussion in 'Beginner Electronics' started by Chris Fonville, Jul 3, 2005.

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  1. I'm back, I bought another hd44780 LCD and have wired it up. This one
    gives me a good test screen and when I send commands to it from the
    computer I can see the correct thing. The only problem is that it is
    very dark. The screen is filled with all black squares and the letters
    I'm sending are only somewhat visible. If I look at the display at an
    angle on either side I see the characters correctly. I am guessing this
    has to do with the fact that I am just grounding out Pin 3 (contrast).
    What do I need to do to fix this problem? Sorry for all the trouble,
    but thanks for any help,
  2. I assume your using the LM series of LCDs or one of its compatables
    which all have the same pinout (As I havent seen any others that use the
    hd44780, but i admit, its been a while)

    Contrast is very simple, just put a 10k variable resistor between the
    voltage rails, and connect its wiper to the pin 3.
    Contrast gets darker the further it gets to the lower rail.

    I seem to remember that the size of the VR didnt make a great deal of
    difference, although the lower the resistance, the more wasted current.

    Please forgive the quality of my ASCII art :)
    --+---- +5v
    - vr1 (>10k)
    | |
    | |<--- pin 3
    | |
    --+---- 0v
  3. Alexander

    Alexander Guest

    This seems to me like the solution,

    At least one problem is solved ;)
  4. Thank you for the help, I have acouple pots ordered and I believe this
    will fix it. Thanks again,
    Chris Fonville
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