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Test Waveforms

A project log for Understanding ACeP Tecnology

A journey towards driving full-color e-Paper displays

Manuel TosoneManuel Tosone 05/12/2021 at 17:563 Comments

Time has come to poke at the display and see what color comes out. The simplest test that we can do, is to apply a constant voltage for an x amount of frames.
The controller can apply 9 different voltages (-30V -25V -15V -5V 0V +5V +15V +25V +30V). We already know that 0V doesn't do anything, so we can focus on the other values. I made two sets of waveforms one positive and one negative.

Starting with the positive one. The picture below shows the waveform. It is made up of 3 phases. The first one is to prevent any DC buildup in the panel. The second serves to drive the particles ard towards the top and bottom layers, leaving the display in the extreme optical state. The last phase applies the target voltage for the desired number of frames.

Below are the results of the experiments. For each experiment, starting from the top left and ending at the bottom right, the voltage is applied for 2, 4, 8, 16, 32, 64, 128, 255 frames.

Testing is done at 21°C, framerate is 50Hz.

Positive 5V Step
Positive 5V step
Positive 15V step
Positive 15V step
Positive 25V step
Positive 25V step
Positive 30V step
Positive 30V step

The negative waveform is the same as above, with all the polarities reversed. It is made up of the same 3 phases. The first one is to prevent any DC buildup in the panel. The second serves to drive the particles ard towards the top and bottom layers, leaving the display in the extreme optical state. The last phase applies the target voltage for the desired number of frames.

Below are the results of the experiments. For each experiment, starting from the top left and ending at the bottom right, the voltage is applied for 2, 4, 8, 16, 32, 64, 128, 255 frames.

Testing is done at 21°C, framerate is 50Hz.

Negative 5V step
Negative 5V step
Negative 15V step
Negative 15V step
Negative 25V step
Negative 25V step
Negative 30V step
Negative 30V step

Conclusions

What can we derive from the positive step?

What can we derive from the positive step?

What do you see? leave a comment below.

Discussions

jlarnal wrote 12/06/2021 at 22:35 point

This is indeed some splendid in-depth research ! Especially the FPC-mounted flash dump ! 🤩👍👍👍

I had no idea color pigments were actually translucent 😵. This explains why my custom WKR luts were displaying darker reds than I hoped for ( I was whacking the white pigments down when trying to depolarize the cups on white-black-red EPDs, assuming I was manipulating B&R pigments in a white non-polar medium. 😅 )

I'd love to see more waveform experiment, especially around the green region. It seems the green tints are finicky to obtain ? 

Anyway, I've finally frankenstein'ed a Lilygo EPD_T_Display (as the board's silkscreen says), also known as Lilygo EPD-Watch ( [url]https://github.com/Xinyuan-LilyGO/E-Paper-watch[/url] ), swapping the 32MB flash for a 128BM one, and deadbug-mounting an ESP-PSRAM64H on top of it (to manipulate an actual framebuffer). The 5.65" ACep display is directly connected  to it. Finally the perfect board to torture EPDs with !

Time to experiment on my side too.

Thousands thanks for this article ! *bows in awe*

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Martin Fasani wrote 09/27/2021 at 21:12 point

Nice research. Would like to see code examples!

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GooDisplayEpaper wrote 08/02/2021 at 06:40 point

Marvellous work!

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