Template: Pico e-Paper 4.2 B Spec
Overview
This is a 4.2inch e-Paper display module for Raspberry Pi Pico, 400 x 300 pixels, supports red, black, white colors. 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.
- Onboard voltage translator, compatible with 3.3V / 5V MCUs.
- 2 x user buttons for easy interaction.
Specification
- Size: 4.2 inch
- Outline dimensions (bare screen): 90.1mm × 77.0mm × 1.18mm
- Outline dimensions (driver board): 93.5mm × 78.5mm
- Display size: 84.8mm x 63.6mm
- Operating voltage: 3.3V/5V
- Communication interface: SPI
- Pitch: 0.212 x 0.212
- Resolution: 400 x 300
- Display color: Red, Black, white
- Greyscale: 2
- Full refresh: 15s
- Refreshing power: 38.4mW(typ.)
- Sleep current: <0.01uA (almost 0)
Note: Refresh time: refresh time for the experimental test data, the actual refresh time will be inaccurate, subject to the actual effect. The global refresh process will have a flickering effect, this is a normal phenomenon.
Power consumption: power consumption data for the experimental test data, the actual power consumption due to the existence of the driver board, and the actual use of different circumstances, there will be a certain error, subject to the actual effect.
SPI Timing
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 a 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)
【Note】: for more details about SPI communication, you can search on the Internet.
Working Protocol
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 suspending 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. (Note that the e-Paper cannot support updating directly under sunlight).
How to define pixels
In a monochrome picture we define the pixels, 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:
For computer, the data is saved in MSB format:
So we can use two bytes for 16 pixels.
For 2.13inch 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 Red or white display. The black and white part of 2.13 use 1 byte to control 8 pixels, and the red and white part use 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.
If you define that the data of white pixel is 1 and the black is 0, then we can get:
So that we can use 1 byte to control every eight pixels.
Pinout
