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OLEDs / Re: OLED dark horizontal bands
« on: May 08, 2015, 07:29:04 PM »
Thanks for your reply Paul_B. I have identified the problem with the “dark bands” and I’m posting my findings here for documentation purposes; should anyone run into this problem in the future.
I narrowed down the issue to the values set in the SEPS525’s 0Bh, 0Ch, and 0Dh pre-charge current registers. I was using the values given in the Arduino example code from NHD. I played around until I found the values that worked for me (the SEPS525 datasheet is very vague about describing these registers). After tampering with these values, I found better color accuracy by using lower values that the ones given in the Arduino example. Lowering pre-charge current created better-contrasted images; however lowering them too much start making the colors in a photo look a bit off, for example “cyans” to start to look “greenish”. Bottom line: one has to play with these registers until one finds the right color temperature that works for the application.
The picture below describes the problem and solution for the “dark bands”, or better termed, contrast issues:
The following values did the trick for me:
Best Regards,
-Edwin
UPDATE:
After much tinkering; the "dark bands" are still appearing around bright objects moving over medium-to-dark colored backgrounds; adjusting the the pre-charge currents help reducing the "dark band" effect but the artifact is still visible.
Here is a video showing the problem - vector balls animation over a medium-dark blue background; observe the ghostly dark bands dancing over the solid background color (this is not a flicker/interlace artifact between the screen refresh rate and the camcorder - you can see these bands clearly with the naked eye)
http://www.lopezworks.info/darkbands-oled.wmv
I'm frustrated. Any comments are welcome.
-Edwin
I narrowed down the issue to the values set in the SEPS525’s 0Bh, 0Ch, and 0Dh pre-charge current registers. I was using the values given in the Arduino example code from NHD. I played around until I found the values that worked for me (the SEPS525 datasheet is very vague about describing these registers). After tampering with these values, I found better color accuracy by using lower values that the ones given in the Arduino example. Lowering pre-charge current created better-contrasted images; however lowering them too much start making the colors in a photo look a bit off, for example “cyans” to start to look “greenish”. Bottom line: one has to play with these registers until one finds the right color temperature that works for the application.
The picture below describes the problem and solution for the “dark bands”, or better termed, contrast issues:
The following values did the trick for me:
Code: [Select]
oledWriteCommand( 0x0B ); // Set Pre-Charge Current of Red
oledWriteData( 0x0A );
oledWriteCommand( 0x07 ); // Set Pre-Charge Current of Green
oledWriteData( 0x17 );
oledWriteCommand( 0x0D ); // Set Pre-Charge Current of Blue
oledWriteData( 0x02 );
Best Regards,
-Edwin
UPDATE:
After much tinkering; the "dark bands" are still appearing around bright objects moving over medium-to-dark colored backgrounds; adjusting the the pre-charge currents help reducing the "dark band" effect but the artifact is still visible.
Here is a video showing the problem - vector balls animation over a medium-dark blue background; observe the ghostly dark bands dancing over the solid background color (this is not a flicker/interlace artifact between the screen refresh rate and the camcorder - you can see these bands clearly with the naked eye)
http://www.lopezworks.info/darkbands-oled.wmv
I'm frustrated. Any comments are welcome.
-Edwin
