Uneven row brightness on 1.5" greyscale OLED display

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clementprdhomme
 
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Uneven row brightness on 1.5" greyscale OLED display

Post by clementprdhomme »

Hello,

I recently purchased the 1.5" greyscale OLED display (4741). I noticed that the more white pixels are on on a row, the dimmer they get.

For example, here is a basic Arduino sketch that I run on a Feather ESP32 V2 (5400):

Code: Select all

#include <Adafruit_SSD1327.h>

#define OLED_CS A5
#define OLED_DC 27
#define OLED_RESET -1

Adafruit_SSD1327 display(128, 128, &SPI, OLED_DC, OLED_RESET, OLED_CS);

void setup()   {                
  display.begin();
  display.clearDisplay();
  display.fillRect(0, 0, 20, 20, 15);
  display.fillRect(0, 20, 100, 20, 15);
  display.fillRect(0, 40, 128, 20, 15);
  display.display();
}

void loop() {
}
The display is connected via SPI. VIN to the Feather's 3V pin.

As you can see on the attached photo, there is a very noticeable difference between the rectangles. When only displaying text, it's alright but for anything else, it doesn't look good at all.

Is this expected from this display? Is there any other display that doesn't produce this artifact? Anything to be done software-wise?

Thank you.
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adafruit_support_bill
 
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Re: Uneven row brightness on 1.5" greyscale OLED display

Post by adafruit_support_bill »

Try powering the display via the Feather's USB pin instead of the 3V pin.

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clementprdhomme
 
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Re: Uneven row brightness on 1.5" greyscale OLED display

Post by clementprdhomme »

Hello adafruit_support_bill, thanks for your reply.

I tested connecting VIN to the Feather's USB pin but I don't see any noticeable difference.

My lighting condition is not the same as yesterday but you can clearly still see the contrast difference between the 3 bars. Any other suggestion?

Note that the 3rd bar exhibits 2 colours due to the camera.
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adafruit_support_bill
 
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Re: Uneven row brightness on 1.5" greyscale OLED display

Post by adafruit_support_bill »

Looks like a voltage sag issue. With OLEDs, the current draw is proportional to the number of illuminated pixels. And since it is multiplexed by rows, the rows with more pixels showing will pull more current. The dimming pixels suggests that the drive voltage is sagging under the current demand for those rows.

That said, I'd expect that the USB pin would be capable of supplying more than enough current to drive that display. I will check to see if this is typical behavior with these displays.
Is there any other display that doesn't produce this artifact?
An LCD display would not be prone to that issue. With an LCD, the backlight illumination is constant, and the liquid crystal pixels draw minimal current.

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clementprdhomme
 
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Re: Uneven row brightness on 1.5" greyscale OLED display

Post by clementprdhomme »

Hey Bill,

Just checking in if you've got the opportunity to test yourself or if you've been able to gather more information about this specific screen.

There's very little information online about people experiencing this issue so I'm wondering if that's a screen defect.

This is the only recent case I found online (not an Adafruit screen): https://www.reddit.com/r/arduino/commen ... _242_oled/

Thanks.

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adafruit_support_bill
 
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Re: Uneven row brightness on 1.5" greyscale OLED display

Post by adafruit_support_bill »

I've reproduced similar results with one of the smaller OLEDs that I have on hand. It seems to be a common phenomenon with this type of display & driver. One of the major display manufacturers says it is "normal" (see post #6 in this thread): https://forum.arduino.cc/t/why-is-my-ol ... ncy/957396

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