Another LCD contrast (different) question

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 ?



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




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.


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,