Slow based HD44780 LCD

[kgavionics]

Hi
I bought a couple of 20x4 based hd44780 from China. The displays are working fine, except they are too slow, at least compared to my old 16x4 LCD. I made a video showing both displays (the first one is the old and the second one is the new).


Does someone have an idea why?
Thanks in advance

 

[danadakk]

There are clone chips that may not be clocked as fast. They all have an onboard
clock to run their internal state machines, and its variation is > 2:1 spec wise.

One thing that helps is to create a display buffer of your display data. When you
try to write to these parts at high speed you can get artifacts that make display
quality and clarity poor. Your display routines examine the date you want against
the data in the buffer, and any differences, char for char, are written out to the display.
If data is not changing then display is not continuously over written which creates the
artifacts.

You using the ones with the I2C interface adapter or writing nibble/byte wide to the
display ?

As an aside the blue mode displays, white chars on blue background, much better looking in
daylight than the pea green ones.

Lastly what is the concern about displays changing digits so fast you cannot read them ?
Is that considered an attribute for the user interface or an undesired result ?


Regards, Dana.

 

[kgavionics]

Thanks, Dana, for your input!
I'm using 4 bit mode (no I2C) and the LCD is hooked to an Stm32 board which I use with the older LCD as well.
So, my code is not the culprit. It's the display itself.

 

[danadakk]

My suggestion about code is not to be interpreted as the specific problem.

The display buffer suggestion is more oriented if you are in a tight loop writing to
display the same value over and over, you will see artifacts in the display. Try it. The
buffer solves that issue.

I think the main problem you are seeing is of 2 possible explanations, the variation
in onchip osc driving the onchip LCDS controller, or the use of a "44780" clone chip.


Regards, Dana.

 

[pjmelect]

The contrast setting is very critical in how fast the display will change, more contrast will make the disply change slower while not enough contrast will make the display faster but look washed out, the setting between the two is dificult to get just right.

 

[danadakk]

The contrast setting is very critical in how fast the display will change, more contrast will make the disply change slower while not enough contrast will make the display faster but look washed out, the setting between the two is dificult to get just right.

What is the physical phenomenon going on with contrast, just the rotation latency of the molecules
in the fluid ? Smaller angle faster display ? Just curious.

Regards, Dana.

 

[kgavionics]

The contrast setting is very critical in how fast the display will change, more contrast will make the disply change slower while not enough contrast will make the display faster but look washed out, the setting between the two is dificult to get just right.

The problem has nothing to do with contrast, it's rather a refresh rate issue due to a crappy Chinese hd44780 clone.

 

[pjmelect]

What is the physical phenomenon going on with contrast, just the rotation latency of the molecules
in the fluid ? Smaller angle faster display ? Just curious.

Regards, Dana.

I am not sure, but I have always thought that with lower contrast the degree of twist of the molecules is less so that the amount of movement of the molecules is less and so faster.

--- Updated Apr 18, 2022 ---

The problem has nothing to do with contrast, it's rather a refresh rate issue due to a crappy Chinese hd44780 clone.

The contrast and refresh rate are related to one another particularly on cheap displays.