E Ink Corporation (founded 1997, spin-off from MIT Media Lab, now headquartered in Hsinchu, Taiwan) invented and manufactures electrophoretic display panels. “E Ink” is their trademark. E-paper (electronic paper) is the generic term for the technology category. Nearly every e-paper display you can buy uses E Ink Corporation’s electrophoretic film under license — Waveshare, Good Display, and others make the driver boards and connectors, but the display film inside comes from E Ink. The relationship is analogous to “Band-Aid” (brand) vs “adhesive bandage” (category).
How Electrophoretic Displays Work
An electrophoretic display panel contains millions of microcapsules (~40µm diameter), each filled with a clear fluid and tiny charged pigment particles. In the simplest black-and-white version: white particles (titanium dioxide, positively charged) and black particles (carbon, negatively charged). Applying a positive electric field to a pixel pushes white particles to the viewing surface and black ones to the back; reversing the field swaps them.
Electrophoretic
The word comes from Greek: electro (electric) + phoresis (carrying). Electrophoresis is the movement of charged particles through a medium under the influence of an electric field. In an e-paper display, the “medium” is the clear fluid inside each microcapsule, and the “charged particles” are the pigment particles (black carbon, white titanium dioxide, or colored pigments in ACeP displays). Applying a voltage across a pixel creates an electric field that carries the desired pigment color to the viewing surface. The same physical principle — electrophoresis — is used in biology to separate DNA fragments by size in a gel, and in chemistry to separate proteins. E Ink’s innovation was turning it into a display technology by trapping the particles in millions of tiny capsules and addressing them individually as pixels.
The key property is bistability: once positioned, the particles stay put with zero power applied. The display consumes energy only during a refresh. This is why an e-paper device can show a static image for months on a coin cell battery — the display itself draws nothing between updates.
The display does not emit light. It reflects ambient light exactly like printed paper, which gives it excellent readability in daylight and at wide viewing angles. The tradeoff is that it requires a front-light (like a book light) for dark environments, and refresh times are measured in seconds rather than milliseconds.
Color Variants
Three-color (Spectra)
E Ink Spectra uses three pigment types per microcapsule: black, white, and one accent color — red or yellow. Each pixel can be black, white, or the accent color. This is the technology in electronic shelf labels at grocery stores. Refresh time is ~15 seconds (the colored pigment is slower to settle). Visually, a motivational sentence in black with red emphasis words looks striking.
Color filter array (Kaleido)
E Ink Kaleido (used in some Kindles and Kobo e-readers) overlays an RGB color filter on a standard black-and-white electrophoretic panel. Each pixel is subdivided into RGB subpixels. Color is muted (newspaper-print quality, not LCD vivid), and effective color resolution is ~1/3 of the panel’s native resolution. Black-and-white content remains sharp at full resolution. These panels are not readily available as hobbyist modules.
Full-color (ACeP / Gallery)
Advanced Color ePaper (ACeP), marketed as E Ink Gallery, uses four or more differently-colored pigment particles per microcapsule — cyan, magenta, yellow, and white. No color filter is needed; each pixel independently produces a full color by controlling the layering of pigments. The result is ~32,000 colors with richness far beyond Spectra. Refresh time is 25–35 seconds for a full-color update. E Ink Gallery 3 (2023) improved refresh speed and color gamut.
Hobbyist Modules
Waveshare is the dominant supplier of e-paper modules for prototyping. All connect via SPI with the same signal set (SCK, MOSI, CS, DC, RST, BUSY — see Serial Communication Protocols). The SPI wiring to any MCU is identical regardless of display model.
| Type | Model | Resolution | Refresh Time | Approx. Price |
|---|---|---|---|---|
| Black/white | Waveshare 2.9” BW | 296×128 | ~2s full, ~0.3s partial | ~$12 |
| Black/white/red | Waveshare 4.2” BWR | 400×300 | ~15s | ~$22 |
| 7-color ACeP | Waveshare 4.01” ACeP | 640×400 | ~30s | ~$35 |
| 7-color ACeP | Waveshare 5.65” ACeP | 600×448 | ~30s | ~$47 |
| 7-color ACeP | Waveshare 7.3” ACeP | 800×480 | ~35s | ~$55–80 |
Tip
For a desk sentence display that updates a few times per day, the 30-second refresh of a 7-color ACeP display is irrelevant — you won’t be watching it refresh. The result is a vivid, paper-like color image that persists with zero power.
Framebuffer Math
The MCU composes the image in a RAM buffer before sending it to the display in a single SPI transaction. Buffer size depends on color depth:
Black/white displays use 1 bit per pixel. A 296×128 display needs 296 × 128 / 8 = 4,736 bytes.
Three-color displays use 2 bits per pixel (or two separate 1-bpp buffers: one for black/white, one for the accent color). A 400×300 BWR display needs roughly 30,000 bytes.
Seven-color ACeP displays use 4 bits per pixel (to encode 7 colors). A 7.3” 800×480 display needs 800 × 480 × 4 / 8 = 192,000 bytes. The STM32H743’s 1MB of SRAM handles this easily. An ESP32-S3 with 8MB of PSRAM handles it even more easily.