After completing the Teams status light, for my next project, I’m moving on to something useful for the other half. This project requires very low power draw while driving an external display. E-ink displays are great for this task and once displayed, the device can go to sleep while still displaying the summary data with no power. As the e-ink display will be using SPI, and my sensors will be using I2C to keep the number of pins down. In the small microprocessors, not all can supply both I2C and SPI, however the Seeeduino Xiao met all my needs. I came across a few challenges on this project, so this post covers how to connect a Seeeduino Xiao with a Waveshare 1.02 e-ink display.

Parts

For this project, I used the following parts:

• Waveshare 1.02″ e-ink SPI display
• Seeeduino Xiao

Both Seeed Studio and Waveshare provide guides on how to install the Arduino IDE and get it working with their hardware. This guide covers specifically the wiring and changes made to the code to get the 1.02″ display working with the Seeeduino Xiao

Seeeduino Xiao Pinout selection

The Seeeduino Xiao has 16 pins as below:

For this project, I am using:

Pins	Purpose
3V3, GND	Powering the display and sensors
D8, D10	Display SPI pins
D4, D5	I2C sensors
D0-D3	Display pins

Waveshare 1.02″ e-ink pins

The Waveshare display has the following pins:

Connecting the Seeeduino Xiao with a Waveshare 1.02 inch display

The pins are connected as follows:

Waveshare e-ink display	Seeeduino Xiao
VCC	3V3
GND	GND
DIN	D10/MOSI
CLK	D8/SCK
CS	D0
DC	D1
RST	D2
BUSY	D3

Configuring the example code

Waveshare have example code for their screens running with various hardware platforms on their GitHub page. I downloaded the “epd1in02d” directory and opened it up in the Arduino IDE.

Before compiling the sample code, I first needed to update it to reflect the Seeeduino Xiao pin numbers.

The GPIO pins are defined in DEV_Config.h. I updated the pin numbers to reflect the Xiao’s configuration:

/**
 * GPIO config
**/
#define EPD_RST_PIN         2
#define EPD_DC_PIN          1
#define EPD_CS_PIN          0
#define EPD_BUSY_PIN        3

My test compile still failed, due to the following error:

invalid conversion from 'const unsigned char*' to 'uint8_t* {aka unsigned char*}' [-fpermissive]

This occurred in a couple of places. If I updated the IDE to compile for an Arduino UNO, there were no problems with the compile. This error was specific to the Xiao code compile.

Investigating the errors, I found them to occur with the following files:

• font24cn.cpp
• imagedata.cpp

As I’m not using chinese fonts or loading images, I commented out the fonts from the file fonts.h:

// extern cFONT Font12CN;
// extern cFONT Font24CN;

and I commented out the the image processing code from the sample file:

#include "GUI_Paint.h"
#include "DEV_Config.h"
#include "EPD_1in02d.h"
#include "fonts.h"

//#include "imagedata.h"

and removed the image display:

//  EPD_Display_Image(IMAGE_DATA);
//  DEV_Delay_ms(500);
//  EPD_Clear();

At this point, the code successfully compiled and was able to display the first sample page on the display:

And there you have it, a Seeeduino Xiao with a Waveshare 1.02Now on the rest of the project.