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Note: The raw panel requires a driver board, If you are the first time use this e-Paper, we recommend you to buy the HAT version or buy more one driver hat for easy use, otherwise you need to make the driver board yourself. And this instruction is based on the HAT version.
480x280, 3.7inch E-Ink display HAT for Raspberry Pi, SPI interface
VCC | 3.3V |
GND | GND |
DIN | SPI MOSI |
CLK | SPI SCK |
CS | SPI chip select (Low active) |
DC | Data/Command control pin (High for data, and low for command) |
RST | External reset pin (Low for reset) |
BUSY | Busy state output pin (Low for busy) |
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 display 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. (Note that the e-Paper cannot support updating directly under sunlight)
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.
SPI communication has data transfer timing, which is combined with CPHA and CPOL.
As you can see from the figure above, data transmission starts at the first falling edge of SCLK, and 8 bits of data are transferred in one clock cycle. Here, SPI0 is in used, and data is transferred by bits, MSB first.
We define the pixels in a monochrome picture, 0 is black and 1 is white.
White:□,Bit 1
Black:■:Bit 0
For computer, the data is saved in MSB format:
So we can use two bytes for 16 pixels.
Pixel | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | ||||||||
Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
Data | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 |
Color | Black | Black | Dark Grey | Dark Grey | Light Grey | Light Grey | White | White | ||||||||
Byte | 0x0A | 0x5F |
The display divides a four-grayscale picture into two pictures. The pixels in the same position of pictures are combined into one pixel.
Register | White | Light Grey | Dark Grey | Black |
0x24 | 0x01 | 0x00 | 0x01 | 0x00 |
0x26 | 0x01 | 0x01 | 0x00 | 0x00 |
With the tables above, you can define the data which can be used to display grayscale pixels in the 3.7inch e-Paper
Pixel | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | ||||||||
Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
Data | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 |
Color | Black | Black | Dark Grey | Dark Grey | Light Grey | Light Grey | White | White | ||||||||
Byte | 0x0A | 0x5F | ||||||||||||||
Bit in 0x24 register | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | ||||||||
Bit in 0x26 register | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | ||||||||
Data sent to 0x24 register | 0x33 | |||||||||||||||
Data sent to 0x26 register | 0x0F |