Template: 7.5inch e-Paper Spec

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Introduction

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.

800x480, 7.5inch EPD(Electronic Paper Display) HAT for Raspberry Pi, SPI interface

【Version update instructions】:

  • This product has been updated to V2 version with higher resolution, supporting 800x480 resolution (V1 version has 640x384 resolution)
  • The hardware structure and interface of the V2 version of this product are compatible with the V1 version, but the software needs to be updated. Please use the V2 Demo Codes.


Interfaces

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 a command)
RST External reset pin (Low for reset)
BUSY Busy state output pin (Low for busy)

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 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)

Communication protocol

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 display requirements.

  • 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.

SPI communication has data transfer timing, which is combined by CPHA and CPOL.

  1. CPOL determines the level of the serial synchronous clock at an idle state. When CPOL = 0, the level is Low. However, CPOL has little effect to the transmission.
  2. CPHA determines data is collected at the first clock edge or at the second clock edge of the serial synchronous clock; when CPHL = 0, data is collected at the first clock edge.
  • There are 4 SPI communication modes. SPI0 is commonly used, in which CPHL = 0, CPOL = 0.

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 use, and data is transferred by bits, MSB first.

Precautions

  1. For the screen that supports partial update, please note that you cannot refresh the screen with the partial mode all the time. After several partial updating, you need to fully refresh the screen once. Otherwise, the screen display effect will be abnormal, which cannot be repaired!
  2. Because of the different batches, some of them have aberrations. Store the e-Paper right side up will reduce it. And if the e-Paper didn't be refreshed for a long time, it will become more and more reddish/yellowish. Please use the demo code to refresh the e-paper several times in this case.
  3. Note that the screen cannot be powered on for a long time. When the screen is not refreshed, please set the screen to sleep mode, or power off the e-Paper. Otherwise, the screen will remain in a high voltage state for a long time, which will damage the e-Paper and cannot be repaired!
  4. When using the e-Paper, it is recommended that the refresh interval be at least 180s, and refresh at least once every 24 hours. If the e-Paper is not used for a long time, the ink screen should be brushed and stored. (Refer to the datasheet for specific storage environment requirements)
  5. After the screen enters sleep mode, the sent image data will be ignored, and it can be refreshed normally only after initializing again.
  6. Control the 0x3C or 0x50 (refer to the datasheet for details) register to adjust the border color. In the routine, you can adjust the Border Waveform Control register or VCOM AND DATA INTERVAL SETTING to set the border.
  7. If you find that the created image data is displayed incorrectly on the screen, it is recommended to check whether the image size setting is correct, change the width and height settings of the image and try again.
  8. The working voltage of the e-Paper is 3.3V. If you buy the raw panel and you need to add a level convert circuit for compatibility with 5V voltage. The new version of the driver board (V2.1 and subsequent versions) has added a level processing circuit, which can support both 3.3V and 5V working environments. The old version can only support a 3.3V working environment. You can confirm the version before using it. (The one with the 20-pin chip on the PCB is generally the new version)
  9. The FPC cable of the screen is relatively fragile, pay attention to bending the cable along the horizontal direction of the screen when using it, and do not bend the cable along the vertical direction of the screen
  10. The screen of e-Paper is relatively fragile, please try to avoid dropping, bumping, and pressing hard.
  11. We recommend that customers use the sample program provided by us to test with the corresponding development board after they get the screen.