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Topic: 16x2 lcd with UnoR3 probs (Read 20555 times) previous topic - next topic


Good info -

I went back and looked at the tutorial again - oh yeah no resistor on the LED connection ;)

Seems to be a good idea to use the limiting resister for the backlight on all displays
unless you need the full brightness of the back light.....


Ok. Now I've got a brand new display. Ive solder a header on it, then made the right connections. Anyway the LCD's backlight wont light up.
And yes I have tried from the beginning with resistors. I've started on 680 ohm resistor and then went down to a 560,470,390,330,270,180,150 and now a 100 ohm, still this stupid backlight wont show up.
Here's a pic with little more Christmasfeeling..

Now when I thougt of it.. When I had my old display and the wrong connections the backlight went up at least.
Like here: https://vimeo.com/54704282
Something is very mysterious with this special lcd.
Seems like the LCD from usa on ebay is much more easy than this model.


And here is the code :

#include <LiquidCrystal.h>

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

void setup() {
  lcd.begin(16, 2);
  lcd.print("Hello arduino.cc!");

void loop() {
  lcd.setCursor(0, 1);


The code and pins 1 <--> 14 have absolutely nothing to do with the backlight.  

The backlight is basically an LED or more likely an array of LEDs that you can treat as a single LED.  

You need the positive lead of a 5v DC supply connected through a resistor to the anode (+) side of the backlight and you need the negative lead of the 5v DC supply connected to the cathode (-) side of the backlight.

So, as long as the backlight is still good, and they are relatively hard to destroy, you just have to get the anode and cathode connections identified.  The problem is that your datasheet has conflicting information.  The 'Mechanical Diagram' shows the end pin as (+) but the 'Description of Terminals' on the next page implies that the end pin may be (-).

You have wired your circuit in accordance with the 'Mechanical Diagram' so I would now try it the other way.  Move the blue wire from pin 15 to the (+) line and move the purple wire (attached to the resistor) to the (-) line.  This puts the resistor in the cathode lead instead of the anode but that's ok.



Why don't you just flip the polarity of power to the led and see if it works that way.

It shows you how valuable a datasheet is.


Finally! Thanks for all help! Really appreciate it:D

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