LCD power-up problem - Wiring issue?

Discussion in 'The Projects Forum' started by l46kok, Oct 1, 2016.

  1. l46kok

    Thread Starter New Member

    Apr 7, 2011
    4
    0
    I'm trying to power on a LCD on a breadboard. For some reason, the LCD is not turning on (No backlight). Here's how I wired it and I'd like to know if I messed up on anything:

    Datasheet: http://www.lcd-module.de/fileadmin/eng/pdf/doma/dip203-4e.pdf

    [​IMG]

    [​IMG]

    I've checked the voltages on VDD (Pin 2) and LED Backlight (Pin 17) and they are getting 3.3V. Measuring voltage on VEE (Pin 3) gets about 2V, which I'm assuming is the voltage being dropped from the pot and internal resistor inside VEE.

    I've also measured the current using an ammeter on LED B/L+ (17) and it's at 33mA. The datasheet says the maximum current on LED Backlight pin is 45mA so I think I'm safe here.

    I haven't wired the data lines yet because I can't even get this LCD to power up.

    The LCD was bought 2 days ago, so while not impossible, it's very unlikely this is defective.

    Is there anything I've messed up in my wiring?
     
  2. upand_at_them

    Active Member

    May 15, 2010
    246
    29
    Well, without data you're not going to see anything on the display.

    As far as the backlight. What color is yours? Your 3.3V is likely not enough to overcome the forward voltage drop. Use 5V, your 100 ohm resistor is enough to limit the current.
     
  3. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
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    It seems that pin 16 has the wrong voltage. You seem to need a L (0 V).
     
  4. upand_at_them

    Active Member

    May 15, 2010
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    My interpretation of that is the RESET is active low, so he needs to tie it high?
     
  5. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    You are right on what it is. My bad. The (internal) pullup keeps it already H. I understand you do not even need to input a H.

    I suppose he does not intend to RESET it at any time after power up, but if he plans to RESET then he should input a H until the moment comes to input the L pulse. That should be through an I/O pin from the micro or a pushbutton connected across pin 16 and GND.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,791
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    33mA through 100 Ohm = 3.3V. Therefore voltage across back-light = 0 ! Either your wiring is wrong or the LED is dead.
     
  7. upand_at_them

    Active Member

    May 15, 2010
    246
    29
    Or he needs more voltage!

    He didn't say what color LED he has, but he's clearly operating at the low end with 3.3V. He needs to give it 5V (keeping the resistor) to know for sure.
     
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