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hd44780 contrast problem

xaif

New member
i have hd44780 2x20 LCD wired up correctly , PIN3 (Vlc) is wired to ground the lcd works fine the upper blocks are displayed but the contrast is so bright (barely seen) is this acceptable ??

the default is that the contrast should be acceptable and clearly seen right ??

ANY help or suggestions
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CF Tech

Administrator
Typically pin 3 is connected to a pot so the contrast can be adjusted. Usually pin 3 should be set to around 1v.
 

xaif

New member
Typically pin 3 is connected to a pot so the contrast can be adjusted. Usually pin 3 should be set to around 1v.
i tried the 10k pot , when it is set to 0 itgives me the same result as the pin connected to ground
any variation will cause the contrast to lower , and finally it fades away

i really dnt know wat to do ????? :(
 
... the lcd works fine the upper blocks are displayed ...
Do you mean that the upper row contains all solid black cells, or do you actually have text displayed? If they are solid black, the display is not initialized. Also, the contrast setting for showing text is usually different than when the solid blocks are displayed.
 

CF Tech

Administrator
It might also be that the display takes mere than 5v for Vlcd, in which case you need to move pin 3 below ground.

Link to the data sheet?
 

CF Tech

Administrator
The range of Vlcd is listed as 3v to 6v. That means pin 3 should be from 2v to -1v (for a 5v supply).

Putting pin 3 at ground (0v) will make Vlcd 5v.

I think that the display should be visible for Vlcd at 5v (pin 3 at ground).

So you probably have trouble with the initialization routine.
 

Kyle_Katarn

New member
Hi all, it's my first post and I'm from Spain, so sorry about bad english.
I have a similar problem, but I'm sure it no a bar contrast.

I'm trying to make work one character LCD CFAH2004D-TMI-ET. It's connected to another board throught this wiring and ping out:



As you can see, the data lines 0 to 3 are cut because the LCD must work in 4-bit's mode.
I have doitmyself this squeme in a little board and wired to the LCD.
All this is connected thought a 10 lines flat cable to a that control all this party, and this control module it's connected to USB port.
The LCD it's power on and contrast and bright controls works fine so I think all lines are ok and I don't make any wrong solderind or missing line.
But, and here is the problem, when I run the software that rules all I only get the 1 and 3 lines full with squares. The software it's form a third party and work because I connect another too much big LCD supplied from them and all work fine.
The software I think recognises the Crystalfontz LCD because it show a little draw similar to LCD and say something about "module found", and at this point I must get a message from the software.

So all looks like its fine but I dont get caracters. But, Do I need sosmething to make the LCD work on 4-bit's mode or with the wiring squeme he must know that must work in 4-bit's?

I hope you could help me, thanks.
 
Your wiring diagram looks OK. I suggest that you connect the D0-D3 inputs to ground, instead of 'no connect', and see if it makes any difference.
... when I run the software that rules all I only get the 1 and 3 lines full with squares.
That means the initialization software is not working.
The software I think recognises the Crystalfontz LCD because it show a little draw similar to LCD and say something about "module found", and at this point I must get a message from the software.
It seems that the software is finding the USB module, but there is no way that the software can know if a display is connected to the USB module. Do you have any links for more info on the software, and also the USB module?
 

Kyle_Katarn

New member
Thanks for the reply.
I was soldered the D0 to D3 lines in this moment but the LCD do the same thing.

The USB module (a Plasmalite V2) and the sofware (RSIM) are from BetaInnovations. I get a LCD 20x4, 97x77 sized from BetaInnovations and work perfect, but it's too much big to fit in the place it must be, so I get the 77x47 from Crystanfontz and now I must domyself the wiring between LCD<==>Brightness/Contrast module<==>Plasmalite.

The squeme I show in my previous post it's from the Plasmalite user manual.
From BetaInnovation say to me that any LCD based en hd44780 must work.

A question from my other post is stiil on the air, I think I know the answer but, I must do anythong to make work LCD on a 4-bit's mode? No, isn't?

What is the squeme to test the LCD with the Test & Demo Software thought serial port?

Thanks for all.
 
You are right, there is nothing to do for 4-bit mode, it is only a function of the software. The CFA 20*4 display should work just the same as your larger one.

Check the Vcc to be sure it is 5 volts. I can not think of anything else to try. Do you have an oscilloscope or a way to observe the signals to the LCD?

I have done a USB to LCD test using 4-bit, but using a much simpler USB product, you can see a photo here: https://forum.crystalfontz.com/showpost.php?p=23145&postcount=25
but I don't think that will be any help to you.
 

Kyle_Katarn

New member
No, I don't any oscilloscope near to use, only have a polymeter to check Vcc, amp's and resistor values.

I'm going to redo all wiring in a new board because maybe I'm wrong in something and I can found it :confused::confused:

I'll post the results, stay tunned :D
 
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