LCD chain troubles

[endernoumea]

I actually have 16 LCD screens connected to the MBNG.

 

Declared as follow in bootloader :

 

lcd_num_x 4

lcd_num_y 4

lcd_width 16

lcd height 2

 

Here the issue:

 

if i plug all the 16 screens, they seems to be initialized correctly but none of them work.

If i remove any of them and reset they all works 15/15.

 

To check them i use the CLCD_16.ngc from the MBNG tool and according the LCDs i've disconected I'm able to say they all (16/16) working correctly and are addressed correctly as well.

 

Any idea where it comes from ?

 

Thank you in advance,

Ender

 

 

 

 

[Duggle]

Hi Ender!

Congratulations, you are the second person in the world to have attempted this. And the good news, is that I'm the first, and I spent many weeks sorting out the issues with plenty of suggestions from TK over the email.

I have 24 16x2LCDs all working perfectly.

The above circuit solves the issue of the array ceasing to work after certain number are connected. For me it was 14!

I wired the 74HC541 on a small peice of matrix board basically in series with the LCD cable, close the core.

The problem basically stems from the 3.3V signals of the core. The circuit shifts them to 5V logic (the same as Vcc of the LCDs).

The 220R series resistors are important for suppressing the edges and reduce crosstalk (was getting corrupt custom characters). Just wire them into the ribbon cable close to the core. The Dout resistors are stuffed into the PCB locations.

Let me know if you have any questions! 

 

 

 

 

[Duggle]

Actually, there is something you can try that is much easier to do, that may help you:

Change Vcc (from the usual 5V), down to 4.5V.

This can have a similar effect to level shifting the signals up.

If you have 15/16 LCDs working this would be much easier to achieve than implementing the circuit above. 

[endernoumea]

I should have 22 LCD at the end so the circuit you attach is is probably my solution too :)

 

Thank you very much for it !!!

 

I will now search an online provider for those components.

 

Regards,

Ender

[endernoumea]

I ordered the components yesrterday. They should be here in a week. I'll keep you in touch :p

 

Ender

[endernoumea]

Hi !

I received the 74HC541 and make the circuit as illustrated before.

I also added a 220r for D0 to D7 and  powered the Dout with 5V from J4A.

 

Actually none of this works but i believe i miss something with : "BL and V0 are replicated for every 4 to 8 LCD units. " because i didnt do anything about that... what does this comments means please ?

Ender

[Duggle]

BL is the backlight driver. IIRC you have other plans for the Backlights (RGB) so don't worry about this for now.
The Vo is the contrast bias. If you look on the Core circuit its just coming from a pot. If the contrast is even between the displays you may drive all of them off the core circuit.

 

 

Actually none of this works

What precisely do you mean? 

It does not work at all?   If so there is a wiring mistake....

[endernoumea]

Hi !

I had 2 crazy months at my job so I did not answer before... sorry about that.

 

All the LCD are now working perfectly without using the above circuit. I just split the LCDs in 2 chains and plug half of them on J15a and the other half on J15b.

It means 8 lcd screens per socket in my actual case (16 in total). In the final configuration i should have 22 LCD screens so I will keep in touch about this workaround.

 

Regards,

Ender