Tiny E-Ink Picture Display

After being surprised by the capabilities of a three-color e-ink display (and struggling to get it to work!), I thought I'd put together a little guide.

Hardware

The hardware I used:

• Adafruit 2.13 E-Ink Tricolor Display (ThinkInk)
• Adafruit ESP32 Feather (ESP32-WROOM-32E)
• A micro SD card

In this case, I messed up a little. I already had an ESP32 feather board from Adafruit, so I should have grabbed an e-ink "feather wing" which would have plugged straight into the ESP32 board.

But since I did not do that... here's how I wired up the display:

• 3V3 (power) to 3V
• GND (ground) to GND
• SCK (clock) to SCK
• MISO to MISO
• MOSI to MOSI
• ECS to 27
• D/C to 33
• SRCS to 15
• SDCS to 32

The rest I didn't connect.

Note: Don't be tempted to use pins 12 and 13!! Pin 13 is actually shared with the onboard LED, and documentation for pin 12 says "this pin has a pull-down resistor built into it, we recommend using it as an output only".

The names on the board don't quite match the names in the code, so here's a cheatsheet:

#define EPD_DC 33     // D/C
#define EPD_CS 27     // ECS
#define SRAM_CS 15    // SRCS
#define EPD_BUSY -1   // can set to -1 to not use a pin
#define EPD_RESET -1  // can set to -1 and share with chip Reset (can't deep sleep)
#define SD_CS 32      // SDCS

The libraries use defaults for the rest of the pins automatically.

Setting Up Pictures

To fit the display exactly, pictures should be 250 pixels x 122 pixels. However, the display will crop as needed.

I used Gimp and ImageMagick to make the pictures, but the main thing is the images need to be 24-bit bitmaps. I couldn't get Gimp to save images directly to a working format.

Here are the steps I took:

• In Gimp, crop and resize to 250x122 pixels (I prefer to crop, resize to 250 pixels wide, crop again to 122 pixels high.)
• Set palette:
  • Go to Image → Mode → Indexed...
  • Select "black and white 1 bit palette"
  • OR create a new black/red/white palette and use that
  • Choose a dithering option that looks good

As far as the color to use for "red", I believe as long as it has the r value of 255, it will work.

Then...

• File → Export As...
• Rename to end in .bmp and save

Then...

From the command line, run

• convert your_image.bmp -type truecolor your_image_24.bmp

Upload

Save the pictures to the root directory of a micro SD card, then put the card in the display (for me, it's text "down"). The slot is spring-loaded, so just push on the end to eject.

Arduino

I used the Arduino IDE (2.3.2).

For the board type, use "Adafruit ESP32 Feather". (This may seem obvious, but it took me a while to figure out which to use!)

These are the libraries I used (via the IDE's Library Manager):

• Adafruit ImageReader library (v2.9.2)
• Adafruit EPD (v4.5.4)

Code

Full code is available here!

Other good examples to start from:

• Tricolor test
• Image reader

You'll want to adjust the pin definitions like I did above if you are following along.

ThinkInk_213_Tricolor_RW is the right type to use for the display above.

In my code, I stripped out anything not related to loading and displaying images from the SD card. If you are doing something different, try looking at the other examples.

Update these lines with the names of your images!

  int num_images = 4; // Update with number of images

  // List image paths
  char *images[num_images] = {
    "/image1.bmp",
    "/image2.bmp",
    "/image3.bmp",
    "/image4.bmp",
  };

The program will cycle through the images and update every 5 minutes (or whatever you change the delay to - recommended minimum is 3 minutes).

Results

Here are some examples. Images look best from a little distance.

No Power?!

Yep, the main cool thing about an e-ink display is that they don't need power to maintain the image.

However, I found just removing power from the ESP32 would cause the red pixels to "bloom" and make everything a bit pink.

To prevent this, just disconnect power from the display first. It's possible there is a way to fix this in the code - let me know if you figure it out!

Have Fun!