U8glib and QC12864B (ST7920 chip) : diplay issues

Other Hardware Displays
1

Hello,

I bought a glcd a few weeks ago but i didn't succeed in making it work (ST7920 chip).
I used that tutorials : Geek 101 : Introduction to Geekiness: Intermediate: QC12864B (128x64 LCD using u8glib.h)
Cheap 128×64 graphic lcd (12864zw) - Bajdi electronics
First, i didn't know i have to de-soldered R9 and R11 so i had nothing on the screen.
Yesterday, i found that i had to do that so i did and tried the second method of the
first tutorial to make the helloWorld sketch work.
The result of that (helloWorld and Graphictest) was a display of chinese symbols...
That appears even before the end of the uploading of the sketch and stayed on the screen;

Any idea to help me?

Thanks,
Kikiz

2

Hi

I it is impossible to help you, because you did not sent any usefull information.
Please post:

  • Datasheet of your display
  • A picture of our display including setup often is also usefull
  • U8glib constructor/Other software setup
  • Wiring table

Oliver

3

Hi,

Here is a link of the datasheet of my screen : http://www.electronicoscaldas.com/datasheet/QC12864B_Qingen.pdf

I used that U8glib constructor : U8GLIB_ST7920_128X64_4X u8g(10);

I'll post some photos of my wiring in a few minutes.

But there's something weird, this morning i had chinese symbols and when i tried an hour
ago i had all pixels on... I didn't change anything since this morning...

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4

thanks for helping me

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5

i'm a little bit lost

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6

.

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7

I tried with a potentiometer wired on Vin/Vout/Ground but that doesn't change the
fact that the hello world doesnt appear...
Kikiz

8

hmmm.... did you connect the Reset input somewhere?

Oliver

9

No, because i saw on a forum that it could cause some upload issues...

10

Well, it might be one of your problems.
Connect the reset input at least to 5V

Oliver

11

Hi,

That's wotking with the reset connected to 5V :-).
Thanks!! But sometimes when put the arduino on, chinese symbols appear.
So i push the reset button on the arduino and the sketch works fine.

Do you know what's the reason?

Kikiz

12

I received a lot of strange behaviour regarding the ST7920 from many users. There are several solutions which might or might not solve the problem:

  • send another software reset (u8g.begin()). Usually this is done automatically at startup, but you could call this function again.
  • use shorter wires
  • delay the reset input to the ST7920 (use a low pass filter for example): Connect Vout from this picture to the reset input of your display.
  • Do not use a breadboard, solder all wires.

Oliver