Has anyone else had a row of "opposite" pixels?

Question

2 nights ago I started noticing that one row of pixels is always the opposite direction than the others.  Has anyone seen this? 

Here is a screenshot of "mid change" and then black on white. https://i.imgur.com/IrlMTdW.png

Answer 1

Hi mudmin

While I haven't seen this exact behavior before I have a couple of ideas what could cause this. But be warned, they lead you deep into the parts under the hood and I'm not sure how risky they are. 

1. Try out ZinggMJ's e-paper library instead of Minigrafx: https://github.com/ZinggJM/GxEPD2 Maybe his settings don't show this behavior...
2. The flexible connector between the PCB and the e-ink display might be badly connected or dirty. Open the enclosure, remove the acrylic walls on the side where the flex connector is. Carefully open the latch mechanism, pull out the flex ribbon straight by helping on both sides. Clean the connectors, push the ribbon back in and close the latch. Be careful to not damage the ribbon while doing this. I usually use some tweezers for this.
3. It seems that the manufacturer of the e-ink displays has some variability in the production process and can't control all parameters very precisely. To compensate this the use variables in the software. Locate the minigrafx library and look for a file called EPD_WaveShare_42.cpp. There around line 78 you can find some settings: https://github.com/ThingPulse/minigrafx/blob/master/src/EPD_WaveShare_42.cpp#L78. You can read more about these settings in the data sheet: https://www.waveshare.com/w/upload/6/6a/4.2inch-e-paper-specification.pdf page 14/45, Booster Soft Start. 

I would try out the suggestions in this order, the last is the most risky one while the first can't do much harm.

Kind regards,

Daniel

Comments

Wow! Thank you for the detailed response! I will go through the steps!

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It looks like a failed column driver, a common fault. Send a picture to the supplier and see if they will replace it, Waveshare are very good with their warranties.