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CFAL12864C Uneven brightness problem

ananda

New member
Hello,

I am using CFAL12864C display and running into this issue where it almost seems like turning some pixels on or off affects the contrast level of other pixels. Has anyone run into this?

On my display I see these horizontal lines which are less brighter than the rest of the display. I also have a block of size 24 pixels by 3 pixels that is blinking( On for 700msec and off for 300 msec). When it is off it seems to dim the whole line (128 pixels by 3 pixels).

Anybody has any idea why would something like this happen? I have played around different values of pre-charge periods, clock divider and the oscillator frequency but nothing seem to make a difference.

Thanks in advance,
Ananda
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CF Tech

Administrator
(Edit: this response was for an LCD. My apologies.)
Generally, if Vo (the contrast) is set correctly, this kind of ghosting is minimized.

Some minimal ghosting is normal in any passive STN display, but it should not be noticeable from straight on if the Vo is set optimally.

If you adjust Vo and there is still ghosting, it might be that the controller or display is damaged.
 

CF Support2

Administrator
Vpanel for the OLED displays needs to be, in simple terms "rock solid". It can be changed for brightness levels, but any ripples in the voltage level can cause the display to act as described.

Also, double check your connections to ensure they are good. Sometimes something as simple as a cold solder joint can cause erratic behavior in the OLED display.
 

ananda

New member
We checked with an external power supply so that we could have a "rock solid" vpanel voltage and we still see the problem.

And the problem is not erratic. For a specific display image, same pixels are dimmer. Also, another thing to note is that the problem is more visible when I put the display in the inverted mode because more pixels are turned on and less pixels are turned off. However, in regular mode also I can see that horizontal lines are dimmer than vertical lines.

Thanks all for your help..

-Ananda
 

ananda

New member
Is it true on the passive matrix OLEDs it is common for rows with a large number of pixels on to have slightly lower brightness levels than surrounding rows with fewer pixels activated?
 

CF Tech

Administrator
There is a transparent, conductive coating (ITO) on the glass that carries the current to the individual LED elements. ITO has some resistance, which may be part of the dimming.

Are you running the display at the correct voltages and current? Is the effect worse or better if the brightness is reduced?
 
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