How to dimmable the LCD(Display)

Discussion in 'The Projects Forum' started by vivek20055, Dec 18, 2012.

  1. vivek20055

    Thread Starter Member

    Nov 4, 2012
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    0
    Hi,

    I am using MCCOG21605B6W-SPTLYI LCD(Display) in my project. I need to dimmable the LCD.How I need to do this?



    Best regards,
    Vivek Alaparthi
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,145
    1,791
    Don't know about dimming. Most displays have a contrast adjustment which is controlled by a potentiometer or a voltage source.

    After that you may need to use an explicit command to the display to set one or more discrete brightness levels.
     
  3. absf

    Senior Member

    Dec 29, 2010
    1,493
    372
    Are you trying to dim the back-light of the LCD so it appears not too bright when all the surrounding lights are out?

    Allen
     
  4. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hi Allen,

    I need to dimmable the LCD for long life. The LEDS inside this display must be supplied with typical current 32mA. Then the lifetime of the display will be around 50000 hours. I dont understand why this bjt is used in the circuit???


    Best regards,
    Vivek Alaparthi
     
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    Last edited: Dec 19, 2012
  5. John P

    AAC Fanatic!

    Oct 14, 2008
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    The transistor is functioning as a switch controlled by a voltage (there must be a resistor in series, which isn't shown) coming in on the LCD B/L line.

    If you want the backlight dim all the time, replace the 33 ohm resistor with a larger one. Or, pulse the LCD B/L line. But then what you'd be doing would be to alternate the LEDs between full brightness and off, which might actually be worse than running them at an even current. Is there some way you can run the LEDs under user control, only driving them when you need to look at the display?
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  7. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
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    Hi john,


    Thanks for your reply. I have modified the circuit as shown below. Can you please check whether this will work out or not



    Thanks & regards,
    Vivek Alaparthi
     
  8. John P

    AAC Fanatic!

    Oct 14, 2008
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    Don't run this circuit! You are likely to destroy the LEDs.

    I see what you're trying to do, have a "bright" and a "dim" setting. And maybe you didn't actually remove the 33 ohm resistor, but just left it off the diagram. If so, no problem. You can run the "dim" setting with the 33 ohms in place--compared with 1K, it's almost negligible, but it has to be there for the "bright" setting. I'm slightly surprised that the lights are usable with 1K in series, but if it works for you, then that's fine.

    Incidentally, both transistor bases are running off "LCD-B/L". I assume that's not the real intention.
     
  9. vivek20055

    Thread Starter Member

    Nov 4, 2012
    88
    0
    Hello John,

    Thanks for your reply,
    Ithink this will work.

    Generally what resistance is good to run the LEDS in series.


    Best regards,
    Vivek Alaparthi
     
    Last edited: Dec 19, 2012
  10. John P

    AAC Fanatic!

    Oct 14, 2008
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    If it were just one LED on a 5V supply, I'd say start with 330 ohms and see how it looks. I don't know. Maybe 1K is right, but it would depend on what's actually in the LCD unit and what your lighting conditions are. You're the designer--what does the project need?
     
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