Strange behavior of a Sharp LM32019T 320x240 LCD display

[Alexander Avtanski]

Hello,

I recently found an old Sharp LM32019T 320x240 LCD display and started
experimenting with it. I'm currently trying to get it to show a very
basic test pattern using a PIC16F690 microcontroller. So far the
results are mixed - it does show the test pattern sometimes, but most
often the display either remains blank, or shows a while rectangle on
the top 1/3 of the screen, or shows the pattern only in the top 1/3.

One very strange thing that I noticed is that if I detach the DISP_OFF
pin and hold the wire in my hand it mostly shows the whole test
pattern, but if I set it to logical 1, or logical 0, it most often
remains blank.

This made me think that I got the pin numbers wrong - I started to
think that what I thought is the DISP_OFF pin is in fact some the data
pulse or row latch signal. But this doesn't explain how sometimes the
pattern is shown correctly with DISP_OFF set to 1...

Another thing is that it seems what the display shows depends on the
LCD drive voltage - when the voltage is higher the display pattern is
more likely to show properly; when the drive voltage is lower, the
pattern may completely disappear. My limited understanding is that
what the LCD drive voltage should mostly affect the display contrast,
but not the pattern itself - is this correct?

I'm trying now to rule out power supply problems - nose, things like
that. Of course, the display itself might be faulty... Anything else
I should check or try? What would you do in my place?

Thanks,

- Alex

 

[Alexander Avtanski]

Hello again,

I tried several different things in order to get the LCD running (see
my original message below) - better filtered power supply, running the
PIC controller on different frequencies, what not. So far I can't get
a reliable image out of it and I'm still looking for ideas what might
be wrong.

Maybe a few pictures will help to explain my problem.

Here is what is supposed to happen:

http://avtanski.net/projects/lcd_320x240/LCD01.JPG

What most often happens is either a completely blank screen (no need
of a picture), or this:

http://avtanski.net/projects/lcd_320x240/LCD02.JPG

Sometimes, especially if I touch the wiring and specifically the
DISP_OFF wire, I get this:

http://avtanski.net/projects/lcd_320x240/LCD03.JPG

On these pictures the display is actually upside-down (it was easier
to take the picture this way).

Note that even on the first picture (the "correct" test pattern) the
top 1/3 of the display height is slightly brighter than the rest, so I
suspect even there the display is not working properly.

Any clue what might be causing this? Any ideas what to try before
giving up or blaming the LCD?

Regards,

- Alex

P.S. Below is my original post for reference: