Serial LCD problem

Discussion in 'General Electronics Chat' started by Tobias, Sep 5, 2009.

  1. Tobias

    Thread Starter Active Member

    May 19, 2008
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    The LCD works fine except for sometimes when I apply power (ie turn on the device) the screen goes black. I am sure its some power spike problem. I have an APp1117 5v regulator on the board with a 0.1uf and 10uf on the incoming and 5v lines. Any ideas?
     
  2. kkazem

    Active Member

    Jul 23, 2009
    160
    26
    Hi,

    In order to help you, I need to know what the LCD is part of, a TV SET? A computer board, or a calculator? Also, how is the unit powered (batteries, AC line, etc.)?
    It's very unlikely it's a cap on a 5V regulator. But that is easily checked with a DMM or a scope if you have one.

    Feel free to contact me with additional questions. I'm a 30+ year degreed electrical engineer.

    Good Luck,
    Kamran Kazem,
    kkazem
     
  3. Tobias

    Thread Starter Active Member

    May 19, 2008
    158
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    Part number is NHD-0420D3Z-FL-GBW. Here is a link http://www.newhavendisplay.com/inde...ducts_id=922&zenid=25qd5e5a6575meuv4n9ducfgn3

    Its getting power from a 16v battery. It is on a PCB board. Here is a picture of the project, http://dragtraction.com/Octo.JPG

    Thank you
    Toby

     
  4. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    How do you know it's not a firmware issue?
     
  5. Tobias

    Thread Starter Active Member

    May 19, 2008
    158
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    Because the device works correctly. Its not just one LCD either. I have fourty of them in my office right now and it will do it to any of them. It only does it on startup. This part goes on a race car with a 16v battery. There is a master disconnect switch on the car for battery power. This deal gets its power directly from the switch. When this switch is turned on, everything else in the car is powered too. The screen blacks out every time the switch is closed. Yet if I leave the switch closed and just remove then reattach the ground for this deal the LCD works fine. It has to be a power deal its looking like to me.

     
  6. nanovate

    Distinguished Member

    May 7, 2007
    665
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    How long does the screen go black?
     
  7. MikeD_72

    Active Member

    Nov 11, 2008
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    In my experience, the LCD displays I have used are designed to start up with the block character until data is sent to the display.
     
  8. alitex

    Active Member

    Mar 5, 2007
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    try to change ur lcd,if there is the same problem i think you should use PWM to run it
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    There is probably a big glitch on the main rail caused when the motor controller is powered up. Put a big cap on the + pwr input to the LCD unit, like 220uF. Then put a series resistor from the 16v main rail to the + pwr input, choose a resistor that drops a few volts when the LCD is fully powered and operating. I would start with 10 ohms, you may need to go larger after you test it.

    That decouples the LCD micrcontroller from the nasty 16v rail, it should solve your latchup problem.
     
  10. Tobias

    Thread Starter Active Member

    May 19, 2008
    158
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    Thanks for the input guys. I will give the suggestions a try and report back the results.

    When the screen 'blacks' out, it lasts until I repower. Its done it on every one of the LCDs I have tried to far.

    Thanks again
     
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