Another LCD contrast (different) question

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello all,

I have been reading the forum posts about LCD contrast in attempt to get sorted what is going on in here but still no clue.

It´s a 16x2 LCD. Im sorry, my LCD dont have a datasheet it says only: "Made in China" and "HA-1602", but cant find any datasheet. It have two big chips in it´s back: "5M2 8 / HD44780A00" and "5L3 7R / HD44100FS". It dont have a backlight.

I have a 20k pot correctly wired to the contrast control, tested alredy with a 10k pot also but getting the same: If i change the pot value contrast this will increase or decrease contrast but I get an usable contrast just if pot is set to the max possible.

Point is that in the best contrast pot position, visualization is still very weak.

But testing things i realized that if i set LCD as if it was 16x1 on the sketch, contrast is all good and i can do fine adjustment using the pot. If i set LCD as 16x2 contrast goes weak.
So the first logic point i think it´s: "The LCD is running at some clock, some refresh rate, if i set it to double lines it divides the same refresh rate but across two lines... making it weak" I know this maybe have nothing to do but it´s the only logical explanation i can find.

In this sense I was looking in the LCD library to see if I can find any clock value set, to change it and maybe try to tweak that but cant find anything, someone knows how to do it? Or if it´s even possible?

Or may I consider my LCD is just a bad one and go for another one ?

Thanks,

Rodrigo

2

Thinking of it what i said seems to not make sense because characters are stored on display RAM, if i disconnect the data pins but left Vcc and ground for it, it keeps the last contrast aspect.

So still a mistery why in 16X1 mode contrast is good and not in 16x2 mode.

Would be my LCD draining too much current from the 7805? o.O

cheers,

Rodrigo

3

Rodrigo:

The overall potentiometer value doesn't matter too much since it is running as a very lightly loaded voltage divider.

My ancient 16x2 displays behave much like yours. The best contrast setting occurs when the voltage on pin 3 is at or near 0v. If you change the viewing angle the contrast changes from poor to worse.

Mine also behaves as yours does when you program it as a 1-line display. I believe that your refresh rate analysis is correct. There is a reference to this on page 2 of the Hitachi datasheet.

·  Programmable duty cycles
-- 1/8 for one line of 5 x 8 dots with cursor
-- 1/11 for one line of 5 x 10 dots with cursor
-- 1/16 for two lines of 5 x 8 dots with cursor

There are no programming options that I know of, so another display might be your best choice.

Don

4

Hey hello floresta,

Very thanks for the considerations and pointing that info from datasheet, for me it confirms it´s hardware aspect, so i feel better now in not keep trying to fix I mean: "everything is fine" :wink: Will just buy something better for the final setup. In fact looking at the display 90 degrees straight you can see the data but it´s uncomfortably, looking at it in 45 degrees so things get better.

Best regards,

Rodrigo