New hd44780 LCD problem (Contrast)
 

I'm back, I bought another hd44780 LCD and have wired it up. This one
gives me a good test screen and when I send commands to it from the
computer I can see the correct thing. The only problem is that it is
very dark. The screen is filled with all black squares and the letters
I'm sending are only somewhat visible. If I look at the display at an
angle on either side I see the characters correctly. I am guessing this
has to do with the fact that I am just grounding out Pin 3 (contrast).
What do I need to do to fix this problem? Sorry for all the trouble,
but thanks for any help,
Chris

I assume your using the LM series of LCDs or one of its compatables
which all have the same pinout (As I havent seen any others that use the
hd44780, but i admit, its been a while)

Contrast is very simple, just put a 10k variable resistor between the
voltage rails, and connect its wiper to the pin 3.
Contrast gets darker the further it gets to the lower rail.

I seem to remember that the size of the VR didnt make a great deal of
difference, although the lower the resistance, the more wasted current.

Please forgive the quality of my ASCII art :-)
--+---- +5v
|
- vr1 (10k)
| |
| |--- pin 3
| |
-
|
--+---- 0v


Chris Fonville wrote:
I'm back, I bought another hd44780 LCD and have wired it up. This one
gives me a good test screen and when I send commands to it from the
computer I can see the correct thing. The only problem is that it is
very dark. The screen is filled with all black squares and the letters
I'm sending are only somewhat visible. If I look at the display at an
angle on either side I see the characters correctly. I am guessing this
has to do with the fact that I am just grounding out Pin 3 (contrast).
What do I need to do to fix this problem? Sorry for all the trouble,
but thanks for any help,
Chris

"graham salkin" schreef in bericht
...
I assume your using the LM series of LCDs or one of its compatables which
all have the same pinout (As I havent seen any others that use the hd44780,
but i admit, its been a while)

Contrast is very simple, just put a 10k variable resistor between the
voltage rails, and connect its wiper to the pin 3.
Contrast gets darker the further it gets to the lower rail.

I seem to remember that the size of the VR didnt make a great deal of
difference, although the lower the resistance, the more wasted current.

Please forgive the quality of my ASCII art :-)
--+---- +5v
|
- vr1 (10k)
| |
| |--- pin 3
| |
-
|
--+---- 0v


Chris Fonville wrote:
I'm back, I bought another hd44780 LCD and have wired it up. This one
gives me a good test screen and when I send commands to it from the
computer I can see the correct thing. The only problem is that it is
very dark. The screen is filled with all black squares and the letters
I'm sending are only somewhat visible. If I look at the display at an
angle on either side I see the characters correctly. I am guessing this
has to do with the fact that I am just grounding out Pin 3 (contrast).
What do I need to do to fix this problem? Sorry for all the trouble, but
thanks for any help,
Chris

This seems to me like the solution,

At least one problem is solved ;)

graham salkin wrote:
I assume your using the LM series of LCDs or one of its compatables
which all have the same pinout (As I havent seen any others that use the
hd44780, but i admit, its been a while)

Contrast is very simple, just put a 10k variable resistor between the
voltage rails, and connect its wiper to the pin 3.
Contrast gets darker the further it gets to the lower rail.

I seem to remember that the size of the VR didnt make a great deal of
difference, although the lower the resistance, the more wasted current.

Please forgive the quality of my ASCII art :-)
--+---- +5v
|
- vr1 (10k)
| |
| |--- pin 3
| |
-
|
--+---- 0v


Chris Fonville wrote:

I'm back, I bought another hd44780 LCD and have wired it up. This one
gives me a good test screen and when I send commands to it from the
computer I can see the correct thing. The only problem is that it is
very dark. The screen is filled with all black squares and the
letters I'm sending are only somewhat visible. If I look at the
display at an angle on either side I see the characters correctly. I
am guessing this has to do with the fact that I am just grounding out
Pin 3 (contrast). What do I need to do to fix this problem? Sorry for
all the trouble, but thanks for any help,
Chris

Thank you for the help, I have acouple pots ordered and I believe this
will fix it. Thanks again,
Chris Fonville