NHD-1.5-128128G brightness control through Iref

ncardoso

Hi,

Could you explain if and how brightness can be adjusted by changing Iref (or the resistor connected to pin IREF) in display NHD-1.5-128128G?
In NHD-1.5-128128G datasheet there is the equation R1 = (voltage at IREF - VSS)/IREF, but it is not clear to me if IREF is a constant and the input voltage of pin IREF would be the parameter to control the brightness.

The motivation that made arise this question is the noticeable difference between the brightness of some parts we are using in our product.

Best wishes,

Newton

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Comments

5 comments

Date Votes
  • Ted M.
    NHD Staff

    Hi Newton,

    The resistor value calculation for IREF can be found in more detail on page 25 of the SSD1351 datasheet and I also attached it to this post for your reference. 

    https://support.newhavendisplay.com/hc/en-us/articles/4414478016663-SSD1351 

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  • ncardoso

    Hi Ted,

    Thank you for the answer.
    I am not sure if we are facing problems with the brightness or the contrast. I attached a photo of two displays side by side, it is noticeable the difference between them, and they are connected to similar boards, if we exchange them the appearance of the displays is still the same, independent of what board they are connected to. Please could you give us a hint to solve this issue?
    We changed the contents of register 0xC1 from 0xC8 to 0xFF, and kept the contents of register 0xC7 as 0x0F, and we also changed the value of resistor connected to pin IREF, but nothing changed.
    Should we have changed the resistor attached to Vsl pin?

    Best wishes,

    Newton

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  • Ted M.
    NHD Staff

    The resistor at at VSL would typically be 50 Ohms. Please review the schematic for the NHD-1.5-128128ASC3 display as a reference.
    https://newhavendisplay.com/content/specs/NHD-1.5-128128ASC3.pdf 

    If changing the contrast register values in software does not make a difference, there may be an issue with the OLED display.
    Have you found any others that show a similar issue? 




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  • ncardoso

    Hi Ted,

    It seems that the contrast changes suitably, but we suspect that the last displays we bought may have any non-standard feature.
    The brightness seems to be different.
    Should we try to change contents of commands B1h, B6h, B8h and B9h to improve the brightness?


    Best regards,

    Newton 

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  • Ted M.
    NHD Staff

    Hi Newton,

    Try increasing the contrast current using C1

    Here are some values from our example code on Github https://github.com/NewhavenDisplay/NHD-1.5-128128ASC3_Example/blob/master/examples/test/test.ino

    OLED_Command_128128RGB(0xC1); // Set contrast current for A,B,C
        OLED_Data_128128RGB(0x8A);  // Color A
        OLED_Data_128128RGB(0x70);  // Color B
        OLED_Data_128128RGB(0x8A);  // Color C
        OLED_Command_128128RGB(0xC7); // Set master contrast
        OLED_Data_128128RGB(0x0F);  // 
        OLED_Command_128128RGB(0xB9); // use linear grayscale LUT
        OLED_Command_128128RGB(0xB1); // Set pre & dis-charge
        OLED_Data_128128RGB(0x32);  // pre=1h, dis=1h 
        OLED_Command_128128RGB(0xBB); // Set precharge voltage of color A,B,C
        OLED_Data_128128RGB(0x07);  //
        OLED_Command_128128RGB(0xB2);       // display enhancement
        OLED_Data_128128RGB(0xa4);  
        OLED_Data_128128RGB(0x00);
        OLED_Data_128128RGB(0x00);
        OLED_Command_128128RGB(0xB6); // precharge period
        OLED_Data_128128RGB(0x01);  
        OLED_Command_128128RGB(0xBE); // Set VcomH
        OLED_Data_128128RGB(0x07);
        OLED_Command_128128RGB(0xA6); // Normal display
        OLED_Command_128128RGB(0xAF); // Display on
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