ESP32

We will use the DFRobot Firebeetle 2 ESP32 S3 development board as the controller MCU:

It might be a bit overkill, but this ESP32 board at least has the charging circuit and good documentation. As we don’t have that much room for the boards, we opt to solder all connections directly to the board. This means that we have to be sure which connections we are making!

The Waveshare HAT uses a 3 or 4 line SPI, we opt for the (regular) 4 line SPI. Next to the SPI interface, some other pins are needed:

Waveshare HAT	ESP32	Pin	Description
PWR	D13	11	Power signal to e-Paper
BUSY	D12	12	Busy signal from e-Paper
RST	D11	13	Reset pin of e-Paper
DC	D10	14	Data / Command selection
CS	D5	7	SPI Chip Select
CLK	SCK	17	SPI Clock
DIN	MOSI	15	SPI Master Output Slave Input
	MISO	16	SPI Master Input Slave Output (not used)
GND	GND	GND	Ground
VCC	3V3	3V3	Power source
	A0	4	Analog input pin for voltage measurement

The second screen should also have some pins:

Waveshare HAT	ESP32	Pin	Description
PWR	A1	11	Power signal to e-Paper
BUSY	A2	10	Busy signal from e-Paper
RST	A3	8	Reset pin of e-Paper
DC	A4	6	Data / Command selection
CS	A5	5	SPI Chip Select

This Firebeetle doesn’t seem to have a way to measure battery status :-(. We could make a small circuit that does just that, as described in this reddit post.

To test the software, I will first use a different WROOM-32 ESP board, with this pin configuration:

Color	Waveshare HAT	ESP32	Pin	Description
Brown	PWR		GPIO13	Power signal to e-Paper
Purple	BUSY		GPIO12	Busy signal from e-Paper
White	RST		GPIO14	Reset pin of e-Paper
Green	DC	D10	GPIO27	Data / Command selection
Orange	CS	CS0	GPIO5	SPI Chip Select
Yellow	CLK	CLK	GPIO18	SPI Clock
Blue	DIN	MOSI	GPIO23	SPI Master Output Slave Input
		MISO	GPIO19	SPI Master Input Slave Output (not used)
Black	GND	GND	GND	Ground
Red	VCC	3V3	3V3	Power source