NHD-0420D3Z-NSW-BBW-V3 back-light flickers

rickford66

• April 03, 2014 09:07

NHD-0420D3Z-NSW-BBW-V3, back-light flickers randomly during normal operation.  The display seems to work fine in every other capacity.  I've left the baud rate at the standard 9600.  I wrote a routine to change the back-light to see if I could dim it and that works fine, so I'm pretty sure the dimmer circuit is working properly.  Is this common and has anyone found a fix for it?  Thanks.

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  Michael_L

  • April 04, 2014 09:07

  This is not a common issue.  What are you using as your power supply for the display?  Is it very steady, or is some noise present?  Also, check if you have any loose connections/cold solder joints, as this could cause what you are referring to.

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  Battman_56

  • April 05, 2014 10:07

  I’m having the identical problem as rickford66. I’m also using the NHD-0420D3Z-BBW-V3 and sending it data via the serial port at 9600 baud. He describes the issue perfectly as a “back-light” flicker. It appears to be random with the flashes occurring a couple of times per second to as long as 15 or so seconds apart. The length of the flash varies as well.
  
  My first suspicion was a poor connection. I ran wires directly from the voltage regulator (SPX2940) to the LCD. No change. Used a battery to feed the regulator. Still no change.
  Upon power up, my circuit displays a company name on the LCD and then goes into a holding pattern until a push button is pressed. No new commands are sent to the LCD until the button is pressed. The LCD does not flicker.
  
  Pressing the button starts the main program which loops once per second. I’m not sending a “Clear Screen” command after each loop. The loop consists of reading several sensors and updating a couple of the values on the display. I've tried inserting a 5mS delay after every LCD command to ensure it had time to keep up. It made no difference.
  
  I hope someone has a suggestion to solve my problem.

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  fraryb

  • May 06, 2014 10:07

  The LED back light requires a series resistor to limit current to 30mA or less as specified in the data sheet. The LEDs are probably overheating if you use a constant voltage rather than a constant current supply.  A 3.3 volt supply will not work.  Try 5.0 volts regulated with an 82 ohm resistor in series.

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