Although e-paper displays are famous for being low-power and lasting essentially forever if not damaged physically, the recent push to drive even cheaper e-paper displays at a framerate like 30 FPS for a decent monochrome gaming experience does raise a few questions. The first being what this does to the power usage of these displays, and the second whether this will wear out the display in short order. To investigate this, [Bo Made It] set up a few experiments.

Subject of this test was a Waveshare ESP32-S3-ePaper board, which had previously been demonstrated running a Game Boy emulator at 30 FPS. With this software running, the board consumed on average about 115 mA, which would run down the device’s 400 mAh battery in about 3.5 hours. From here key was to isolate the power consumption of the display itself, with the system minus the display updates consuming about 90 mA.

Running the frame calculations for the greyscale mode without rendering to the screen pushed that up to 107.6 mA, with even in the 30 FPS greyscale mode the display thus only consuming about 7.4 mA, which is vanishingly small. Clearly the low-power claims of e-paper remain intact even at higher framerates.

As for lifespan, one datasheet gives the typical lifespan as one million updates. This would translate to about 9.3 hours at 30 FPS, though that assumes a full display refresh. Since a smart driver only updates changed pixels, obviously this will be longer, but the question is how much longer, and what will degradation look like?

After running 2.16 million frames of a custom endurance test featuring repeating patterns, some ghosting was apparent, but repeated refreshing made this go away again. This means that so far no permanent damage has been detected within the no doubt conservative limit provided by e-paper manufacturers.

It should be noted that Waveshare itself also recommends against running such high-FPS applications on their device, meaning that this is definitely one big longevity experiment. If actual damage occurs, this means that obviously this won’t be covered under any warranty.

Slow refresh, ghosting and low-contrast — wait, are we talking about passive matrix LCDs, or e-paper displays? That might be why e-paper Game Boy emulators are a thing: the limitations of the black-on-grey e-paper screens remind us of the grey-on-green LCDs Nintendo used in the 80s. In this case [Bo Made It] made it out of a Waveshare ESP32-S3-ePaper-1.54, and got 30 FPS from it. 

Now, regular readers might be thinking, “So, we’ve seen the 60 FPS e-paper monitor, how is this special?” It’s a fair question. The answer is that [Bo] is doing this on a randomly chosen dev board with a built in wavetable e-paper controller, rather than the bare inputs that allowed the [Wenting Zhang]’s project to work. On the other hand, [Bo] does credit [Wenting], particularly his e-ink PaperBoy project, with directly inspiring both the project and his implementation.

Again, the big difference is going through the blob of the controller, but it turns out you can still address individual pixels through it. [Bo] gave each pixel a ‘budget’ for up to 8 pulses it depending on how much it needs to change, speeding things up immensely. Our favorite part is how he achieves the Game Boy’s 4-bit greyscale by, in effect, deliberately ghosting the display. Pixels aren’t driven long enough to fully flip them if they’re going only one shade lighter or darker. This complicated matters, since going from black to ‘white’ now takes longer than ‘white’ to the next darker grey, and the exact timing needs to be worked out for each color transition. Getting that timing right took a lot of calibration, and we like how he used video to help automate the process.

That process is still ongoing, so there’s no GitHub link yet. [Bo] will open source everything when it’s ready, and we look forward to it. We also look forward to the PDA-like device he’s going to be using this display driver for. If this all sounds similar to a recent 20 FPS e-paper hack, that’s because it’s the same underlying technology.