Arduino Forum

Using Arduino => Displays => Topic started by: satoer on Apr 30, 2015, 02:14 pm

Title: What’s the difference between these two ST7920 lcd’s?
Post by: satoer on Apr 30, 2015, 02:14 pm
I'm trying to recreate I project I've done for a friend. In this project I used an atmega1284p and an ST7920 lcd with SPI. I thought I ordered the same parts, and although the pinout description is the same, the PCB's are different.
(http://forum.arduino.cc/index.php?action=dlattach;topic=319705.0;attach=124329) (http://forum.arduino.cc/index.php?action=dlattach;topic=319705.0;attach=124329)

My project was done with LCD B, and hooked up like the attached schematic.
(http://forum.arduino.cc/index.php?action=dlattach;topic=319705.0;attach=124331)

Using Hardware SPI on a atmega1284p, LCD B and u8glib. This worked fine.

But now I've recreated the project the same way, but now with LCD A. This gave me a short-circuit. After investigating it turned out the resistance between pin PSB (marked CS1 in the schematic) and pin Vdd on LCD A is 0,7 Ohm. In display B te resistance is 10 mega Ohm. With LCD A this gave me the short-circuit.

Anyhow. Can anyone tell me the difference between these display's and why LCD A refuses to work?
Title: Re: What’s the difference between these two ST7920 lcd’s?
Post by: satoer on Apr 30, 2015, 02:41 pm
 :-[  :-[ This is so stupid... Took me the whole day investigating and 15 minutes after posting this topic I have found the answer.
 
Turns out LCD A is hard wired into parallel mode. To enable SPI you have to remove R9 on the PCB. Now it works fine :)

Maybe someone else has the same problem and find's this solution otherwise sorry for the wasted server space. ;)
Title: Re: What’s the difference between these two ST7920 lcd’s?
Post by: mainlin on Apr 30, 2015, 09:46 pm
Someone will eventually have the same problem and hopefully, they find your post.
Title: Re: What’s the difference between these two ST7920 lcd’s?
Post by: mnbv on Jul 11, 2015, 04:34 pm
Dear satoer

Hi!

I have a similar (but not same) problem!

I am using atmega32a + LCD B with parallel mode (psb --> vcc)

My project is running on proteus but not in real circuit!

Can you help?  :|
Title: Re: What’s the difference between these two ST7920 lcd’s?
Post by: raphaelfribeiro on Mar 07, 2017, 07:18 pm
Someone got simulate the ST7920 in Proteus? I'm using Proteus 8.5 version.

I want to buy this: http://www.filipeflop.com/pd-6b7ea-display-lcd-grafico-128x64.html
Title: Re: What’s the difference between these two ST7920 lcd’s?
Post by: gsvincze on Mar 07, 2018, 02:49 pm
I'm trying to recreate I project I've done for a friend. In this project I used an atmega1284p and an ST7920 lcd with SPI. I thought I ordered the same parts, and although the pinout description is the same, the PCB's are different.
(http://forum.arduino.cc/index.php?action=dlattach;topic=319705.0;attach=124329) (http://forum.arduino.cc/index.php?action=dlattach;topic=319705.0;attach=124329)

My project was done with LCD B, and hooked up like the attached schematic.
(http://forum.arduino.cc/index.php?action=dlattach;topic=319705.0;attach=124331)

Using Hardware SPI on a atmega1284p, LCD B and u8glib. This worked fine.

But now I've recreated the project the same way, but now with LCD A. This gave me a short-circuit. After investigating it turned out the resistance between pin PSB (marked CS1 in the schematic) and pin Vdd on LCD A is 0,7 Ohm. In display B te resistance is 10 mega Ohm. With LCD A this gave me the short-circuit.

Anyhow. Can anyone tell me the difference between these display's and why LCD A refuses to work?

If you still looking for a solution I think it's might help.

You need to remove the two 0 Ohm resistor named R9 and R11, read it somewhere a couple years ago when I used this display. I know this because mine is a "version A" and those two are not on the board and I remember removing it. I think it's the selection of SPI or parallel input.