ESP32

MCU - ESP32 S3

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!

HAT connection

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	D12	12	Power signal to e-Paper
BUSY	A1	5	Busy signal from e-Paper
RST	D11	13	Reset pin of e-Paper
DC	D10	14	Data / Command selection
CS	A3	8	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
	T10	10	Touch pin

The second screen should also have some pins:

Waveshare HAT	ESP32	Pin	Description
PWR	D7	9	Power signal to e-Paper
BUSY	A2	6	Busy signal from e-Paper
RST	D6	18	Reset pin of e-Paper
DC	D5	7	Data / Command selection
CS	D3	38	SPI Chip Select

Pins to avoid:

ESP32	Pin	Description
D9	0	Boot
D2	3	JTAG boot
D14	47	User key (button on board)
D13	21	LED on board

This means that 4 pins are shared (3V3, GND, SCK, MOSI).

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. According to this blog the resistor should be between 10k and 242k. We choose 220k resistors.

Connection via the breakout board

The breakout board is directly connected to the MCU, with combined connections for GND, 3V3, SPI SCK and SPI MOSI. Via the breakout board it is easy to connect both displays, using the 9 pins cable (colors correspond to the colors of the cable).

Pinout testing board

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