Template: Pico e-Paper 7.5-B Spec

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Overview

7.5inch EPD (Electronic Paper Display) Module For Raspberry Pi Pico, 800 × 480 Pixels, Black / White /Red, SPI Interface.

Features

  • No backlight keeps displaying last content for a long time even when power down.
  • Ultra-low power consumption, basically power is only required for refreshing.
  • SPI interface requires minimal IO pins.
  • 2 x user buttons and 1 x reset button for easy interaction.

Specification

  • Dimension: 7.5inch
  • Outline dimensions(raw panel): 170.2mm x 111.2mm x 1.18mm
  • Outline dimensions(driver board): 65mm x 31mm
  • Display Size: 163.2mm x 97.92mm
  • Operating voltage: 3.3V
  • Interface: SPI
  • Dot pitch: 0.205x 0.204
  • Display color: Black, White
  • Resolution: 800 x 480
  • Greyscale: 2
  • Full refresh time: 16s
  • Refresh power: 48mW (typ.)
  • Standby current: <0.01uA (almost none)

【Note】: Refresh time: The refresh time is the experimental test data, the actual refresh time will have errors, and the actual effect shall prevail. There will be a flickering effect during the global refresh process, this is a normal phenomenon.
Power consumption: The power consumption data is the experimental test data. The actual power consumption will have a certain error due to the existence of the driver board and the actual use situation. The actual effect shall prevail.

SPI Timing

1.54inch-e-paper-manual-1.png
Note: Different from the traditional SPI protocol, the data line from the slave to the master is hidden since the device only has a display requirement.

  • CS is slave chip select, when CS is low, the chip is enabled.
  • DC is data/command control pin, when DC = 0, write command, when DC = 1, write data.
  • SCLK is the SPI communication clock.
  • SDIN is the data line from the master to the slave in SPI communication.
  • Timing: CPHL=0, CPOL=0 (SPI0)

[Remarks] For specific information about SPI, you can search for information online.

Working principle

This product is an E-paper device adopting the image display technology of Microencapsulated Electrophoretic Display, MED. The initial approach is to create tiny spheres, in which the charged color pigments are suspended in the transparent oil and would move depending on the electronic charge. The E-paper screen displays patterns by reflecting the ambient light, so it has no background light requirement. Under ambient light, the E-paper screen still has high visibility with a wide viewing angle of 180 degrees. It is the ideal choice for E-reading.

Pixel & Byte

We define the pixels in a monochrome picture, 0 is black and 1 is white.
White:□, Bit 1
Black:■, Bit 0

  • The dot in the figure is called a pixel. As we know, 1 and 0 are used to define the color, therefore we can use one bit to define the color of one pixel, and 1 byte = 8pixels.
  • For example, If we set the first 8 pixels to black and the last 8 pixels to white, we show it by codes, they will be 16 bit as below:

E-paper hardware work 1.png
For computer, the data is saved in MSB format:
E-paper hardware work 2.png
So we can use two bytes for 16 pixels.

For e-paper B, the display colors are red, black, and white. We need to split the picture into 2 pictures, one is the black and white picture, another is the red and white picture. When transmitting, because one register controls a black or white pixel, one controls a Red or white display. The black and white part of the display uses 1 byte to control 8 pixels, and the red and white part uses 1 byte to control 8 pixels.
For example, suppose there are 8 pixels, the first 4 are red, and the back 4 are black:
They need to be disassembled into a black and white picture and a red and white picture. Both pictures have 8 pixels, but the first four pixels of the black and white picture are white, the last 4 pixels are black, and the first 4 pixels of the red and white picture One pixel is red, and the last four pixels are white.

2.13inch-epPaer-B-pixels.png

If you define that the data of the white pixel is 1 and the black is 0, then we can get:

2.13inch-epPaer-B-pixels-2.png

So that we can use 1 byte to control every eight pixels.

2.13inch-epPaer-B-pixels-3.png