[SOLVED] LCD 4ax20 display - weird behaviour

[D'Crex]

Dear Community!

I replaced my 16x2 LCD display with 20x4 display (4 lines).

Everything seems to work fine. Both display text "Savio" on the first line. However, after taking a closer look I saw, what appears to be a reflection of the first line on the second line (when using 20x4 lcd).

I'm attaching an image of the problem.



Now, could it be that it is because the LED+ and LED- pins are not connected? Right now, I can not test this.

Thank you all.

 

[betwixt]

The LED+ and LED- pins are connections to the backlight LEDs, they will not change the effect you are seeing although the presence of exta light may allow you to adjust the contrast and make the effect less pronounced. The underlying problem is the poor quality of the LCD and/or it's driver ICs, the ones on the back of the module. They are not turning the segment and backplane voltages on and off quickly enough and the effect is some of the voltage 'overlows' into the time slot for the adjacent character. Other than use a better quality module there isn't much you can do about it but check your supply voltage is correct as a low voltage will make the problem worse.

Brian.

 

[Gorgon]

The only thing you may try is to adjust the contrast voltage of the display.

Depending on the scan matrix of the display it looks like the display is scanned vertically, and what you see is a bleeding on the driver output, or a fault internally in the displays driver circuit, causing the ghosting.

 

[D'Crex]

Thank you, for you responses. I think I 'fixed' it. I had my contrast all the way up to the fullest (I just grounded the contrast pin). Now hooked up the pin to ground but through 2x 330Ω resistors and it appears to be ok now.

Thanks again! :wink:

 

[betwixt]

Well done, but note that the contrast connection to the module expects a voltage on it, not just a resistance. You might find the contrast setting varies unexpectedly, a better solution is to wire it to a small potentiometer sitting between ground and supply voltage.

Brian.

 

[FvM]

Well done, but note that the contrast connection to the module expects a voltage on it, not just a resistance.

With most alphanumeric LCD displays, the contrast setting pin V0 is the footpoint of a voltage divider and can be well biased by a resistor against ground (or a negative voltage for 3.3V supplied displays). But driving it with a voltage or potentiometer works well, too. It has the advantage that you don't need to change the resistor range if you chose a display brand with different voltage divider resistance.

For best constrast over a wide temperature range, V0 should be made temperature dependend.

 

[D'Crex]

I am sorry for a late reply. I want to thank both of you, for all your help and advices. I will follow what you two have said.

I was very busy for the last two days. After work, I was trying to figure out, why I was only able to access two lines of my LCD. I feel somewhat silly now, it was a really basic error that was not a part of my LCD controller, but the one that was telling this controller what to do. I'm glad I got that solved now.

Thanks again! :thumbsup: