Help with a 4x20 LCD display please

Hi, I am new to all of this and my background is mainly in industrial electrical not electronics but I am learning. I am trying to repair a piece of equipment that uses this display to prompt the operator through the proper steps. The display appeared to be dead except for each block (matrix 5X8) would be extremely dim. Turning the power on and off would allow you to see that something was there but not much. All of the blocks would appear solid with no digits. I removed the display and found that the chrome metal bezel may have been shorting some of the connections at the ribbon terminations. I removed the bezel and connected as accurately as I could to an UNO, that I purchased last year, and ran a couple different sketches. It makes the display come alive but with no readable characters as I know that my wiring scheme and sketch probably isn't correct. But at least I know the display isn't complete trash. The display has 14 conductors instead of the 16 that I have read about and unfortunately I cannot follow but a couple traces leading from the ribbon connectors. The controller is an HD44780A00 with KS0065 segment drivers. The logo on the board is Daewoo with a number of P20006A. thanks, Bill

I removed the bezel ...

This is most likely the source of at least some of your problem. The LCD glass is connected to the PC board by contacts that rely on the pressure of the bezel. By removing the bezel you have opened at least some of these connections.

... and connected as accurately as I could to an UNO ...

This is a run-of-the-mill LCD display that should work properly with the LiquidCrystal library and any of the tutorials that are out there.

The display has 14 conductors instead of the 16 ...

Every HD44780 based LCD uses a 14 pin interface in spite of what you may have read. The other two pins, if they are present, are for an LED backlight which has nothing to do with the control of the LCD.

but if someone could lead me in the right direction I would be grateful ...

Start out by trying to get the bezel reattached.

Next disconnect everything except the connections to pins 1, 2, and 3. You should see blocks on rows 1 and 3. I don't see a potentiometer so I assume that you have connected pin 3 to GND. This isn't ideal but it will produce a usable display.

If that works then you can make the six or ten connections to the Arduino. Don't forget to connect pin 5 (R/W) to GND.


I just took a closer look at your first picture. Your LCD has an electroluminescent backlight, that's what the little power supply at the end of the display is for. I haven't seen one of those in decades although I know I have a bunch of them around here somewhere. As I recall you apply 5V to the supply and it produces the high voltage (>100V) needed for the backlight. I guess that's taken care of by the black wire. Keep your fingers away from those two connections at the end of the display.


Thank you Don, it works well now. I ground away the area of the bezel that was shorting the connections and applied a piece of tape just to be sure. Bill