I have a NHD-C12864WO-B1TFH#-M screen, the version driven with an ST7565P.
While trying to display shapes on it, I realized that the contrast of a column tends to fade with the number of pixels displayed. The more pixels a column has, the lower the contrast.
I've tried a number of settings, but to no avail: the overall contrast changes, but it's never uniform.
Finally, I went back to the default settings given in the example code in the documentation.
Here are the commands I send during the initialization sequence.
0xA2 // LCD bias 1/9
0xA0 // ADC Select normal
0xC0 // Common Output Mode normal
0x40 // Display Start Line set to 0
0x25 // Internal resistor ratio set to 5 (seems to have no effect)
0x81 // Electronic volume mode set
0x25 // Electronic volume reg set
0x2F // Power control set to 7 (any other value set the display OFF)
0xA6 // Display normal
0xAF // Display ON
I've attached an image of the screen (Electronic Volume at value 0x20) to try and highlight the differences in contrast. But I don't know if it shows up well on the picture). I've also provided the electronic diagram of the screen connector. We experimented with several things, including a potentiometer to adjust the contrast, but here again, we only manage to modify the overall contrast, and that doesn't make the whole thing uniform.
What could be wrong?
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