I have 20x4 blue LCD, when i connect it this way: Arduino Tutorial - connecting a parallel LCD
It's running only a blue screen and there are NOT any chars, only blue screen and nothing more, can you tell me how can I fix it ?
Half way through is this line (Just before the section called 'Bus Wiring') : "This means you've got the logic, backlight and contrast all worked out. Don't keep going unless you've got this figured out!"
What were your results at this stage ?
I use potentiometer for contrast, there is voltage trough it but, its not changing the contrast and I dont have idea how to fix this ?! Can you help me figure that out ?
Is it necessary to use external power like battery or its enough to use the USB cable, Power trough potentiometer is 4.04 V
I cant control the contrast with potentiometer, can you help me ?
You have one leg of the pot on ground, the other on 5V and the wiper on the LCD pin. The voltage on the wiper/pin should vary between 0v and 5v as you turn the pot.
Here I uploaded a few pictures: westony | Flickr
the LCD is QY-12864F
datasheet: https://docs.google.com/leaf?id=0B3hDTknDHqyGYjk4YmI5Y2UtZGE4Yi00YTIwLTljMTgtODYyMWFiMzgxYmZk&hl=bg&authkey=CP7lpOEF
None of the pictures are clear on how the pot is wired, at this stage of the game everything but power,backlight and contrast is irrelevant. It will display the blocks shown in the tutorial without any connections other than power, contrast and back light. As your tutorial says, there's no point in going beyond that point until you get the blocks showing. Your LCD panel is a standard HD47780 compatible, its available in a variety of sizes but they all work the same way.
Errm, fundamental error here. The LCD in your flickr pictures is a 128x64 graphics LCD with a KS0108 controller, not an HD44780 character LCD!
Just what Andy Brown said, that LCD is not a 20 x 4.
This 'could' be the right library for you: GLCD (ks0108) Graphic LCD Arduino Library, on Teensyduino
Here is your PIN out scheme.
y, I fixed it thanks 
But how? Did you get an actual 20*4 display and fixed it or did you manage to run the dot-matrix display?
If you got that dot-matrix display for the price of 20*4 display, this might be a good deal.
Don't trash this thread without posting the solution. I hate when I am trying to find a solution on the search engine and the OP says "I got it, thanks and good bye".
It would be nice to post your solution, pin outs and actually working code.
oh well... another bastard thread.
Just remember not to answer any more questions from him until the solution to this one is disclosed.
Don
OK I'm in. floresta, maybe you can go and punch him in the face since he might be in your area (westony-> west of new york)