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Hello,

I have a major problem.  When trying to use an LCD screen, it just won't work.  I have been trying the "Hello World" example from the Examples section of the Arduino webpage.  I am not using a potentiometer, because from what I have heard it is not necessary.  My circuits are all fine, but yet the LCD screen remains dark.  Any help?
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Which Lcd screen are you referring to, 16x2, 20x4, 128x64, or a certain TFT screen?

A link or a picture of what you have and if you would also post your code, would be really helpful. Otherwise we will just be guessing and getting nowhere fast, or we would simply ignore your thread until more information is provided.

If you decided to post your code, please use code tags [ code ] ... [/ code ]. Look for the # symbol above the smiley faces.
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Hmm...
Why not follow the example as it was written?
If the pot wasn't needed don't you think it would have been left out to make it simpler/easier?

--- bill
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I am not using a potentiometer,
Well there's your problem!

You heard wrong. You need a pot for contrast adjust.
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the display may be working great.  just that your eyes require the contrast to be set so you can see it.

if you don't have a pot, try different resistors to see if that has any effect.
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Quote
I am not using a potentiometer, because from what I have heard it is not necessary.
It is not always necessary to use a potentiometer but it is always necessary to deal with pin 3 of the LCD.  This means that you cannot merely omit the potentiometer, you must substitute something else.

Most LCDs require about 0.5v or less on pin 3.  You can achieve this with a pair of resistors, 1 K between pin 3 and GND and 10 K between pin 3 and +5v will get you close.

Many LCDs work acceptably with 0v on pin 3.  You can achieve this by connecting pin 3 to GND.


Don
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Please, do you know how to control backlight brightness digitally from code?
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Please, do you know how to control backlight brightness digitally from code?
That's a different topic -- start a new thread.

Don
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I have a couple of serial backpacks from PH Anderson... He supplies a 4K7 resistor and a 330R resistor... place a 330 R resistor from 3 to gnd and a 4K7 resistor from Vcc to pin 3..
The combination works well for me..

Doc
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That voltage divider does essentially the same job as the one I mentioned ... at about twice the current draw. 

The bottom line is that you want to start with about a 1:10 ratio for the resistors where the actual values aren't important as long as they aren't extremely high or extremely low.  Resistors that you have on hand are preferred to those that you have to purchase.


Don
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Hi,

I have (some sort of) the same problem. I have an 20x4 2004A lcd screen and an arduino duemilanove with the hello world loaded. everything is wired correctly (including a pot). I only changed the sort of lcd (16x2 to 20x4) in the code.

The result I'm getting is that the left top corner shows the text (not completely) and the rest of the screen shows randomly filled in pixels.

What am I doing wrong?
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Quote
What am I doing wrong?
Start a new thread.

Post a photograph that shows the 'random' pixels.


Don
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