W800_Smart_Watch

Why this project :

I was interested in working on a bigger project with more challenges and which could be useful.
I am also quite unhappy with the smartwatches that are on the market (expensive, no access to the firmware, data collection and privacy issues), that's why I decided to try doing my own that I can fully customize. This is going to be a long adventure with a lot of discoveries along the way :).
I also wanted to test this W800 SOC more deeply and see what it could do and I think it is a perfect fit for the project.
So let's go !

A Smart Watch project using the Chinese W800 SOC.

The W800 is a pretty interesting chip with impressive characteristics for its price (around 1$) :

Core :

• 32bit XT804 CPU
• 240 Mhz frequency

Memory :

• 2 MB on chip flash
• 288 KB RAM

Wireless connectivity :

• Bluetooth EDR(Classic) and BLE 4.2
• WiFi 2.4Ghz 802.11 b/g/n

Sensors :

The goal is to embed the following sensors in the watch :

• An accelerometer (for wrist tilt detection, single and double tap detection , foot step counting and more) Possible choices :
  • ADXL345
  • MPU6050
  • BMI160
  • LSM6DS3
  • BMA456 <-- SELECTED i2c addr : 0x18 or 0x19 7 bit address, has the wrist tilt detection feature.
• A magnetometer (possible choices):
  • HMC5883L <-- After reading some comparison articles between the HMC5883L and QMC5883L and the datasheets, the later seems better in term of perfomances.
  • QMC5883L <-- SELECTED i2c addr : 0x0D 7 bit address, better soldering footprint
  • LSM303DLHC
  • BMM150 <-- Package with balls, hard to solder
• An air pressure/temperature sensor (to display the altitude for example)
  • BMP280 <-- SELECTED i2c addr : 0x76 or 0x77

Actuators :

• A vibration motor to notify events to the user.
• A piezo buzzer : dropped, maybe in next version.

Power source :

• 1 cell lipo 450 mAh battery.
• A charge/discharge controller.

Screen + touch element :

• Screen with touch : GC9A01 with touch panel. It uses the required 4 line Serial Interface.
• Touch element i2c addr : 0x15, CST816D I2C touch driver.

Programming and charging :

• The smart watch programming and charging is done through the same USB port
  using a magnetic 4 pin plug.

MCU Pin assignement table :

Pin Number	Pin Name	Type	Function	Pull UP/DOWN	Connected to	Comment
	PB_20	I/O	UART0_RX/PWM1/UART1_CTS/I²C_SCL	U/D	USB/Serial TX flash pin
	PB_19	I/O	UART0_TX/PWM0/UART1_RTS/I²C_SDA	U/D	USB/Serial RX flash pin and BMA456, Touch Panel, HMC5883L and BMP280 SDA pins
	WAKEUP	I	External Wake Up Pin	D	BMA456 IRQ line and Touch Panel IRQ line through NAND Gate	The chip is waken up when the pin is HIGH
	RESET	I	Reset Pin	D	Micro switch and USB/Serial RTS pin
	XTAL_OUT	O	External crystal output
	XTAL_IN	I	External crystal input
	AVDD3V3	P	Chip power supply, 3.3V
	ANT	I/O	RF Antenna
	AVDD3V3	P	Chip power supply, 3.3V
	AVDD3V3	P	Chip power supply, 3.3V
	AVDD3V3_AUX	P	Chip power supply, 3.3V
	TEST	I	Test function configuration pin
	BOOTMODE	I/O	BOOTMODE and I²S_MCLK/LSPI_CS/PWM2/I²S_DO	U/D	Touch Panel Reset line
	PA_1	I/O	JTAG_CK/I²C_SCL/PWM3/I²S_LRCK/ADC0	U/D	BMA456, Touch Panel, HMC5883L and BMP280 SCL pins
	PA_4	I/O	JTAG_SWO/I²C_SDA/PWM4/I²S_BCK/ADC1	U/D	Battery resistor voltage divider output
	PA_7	I/O	PWM4/LSPI_MOSI/I²S_MCK/I²S_DI/Touch0	U/D	LCD backlight N-MOSFET driver
	VDD3V3IO	P	IO power supply, 3.3V
	PB_0	I/O	PWM0/LSPI_MISO/UART3_TX/PSRAM_CK/Touch3	U/D	Vibration motor control pin
	PB_1	I/O	PWM1/LSPI_CK/UART3_RX/PSRAM_CS/Touch4	U/D	Touch Panel IRQ line
	PB_2	I/O	PWM2/LSPI_CK/UART2_TX/PSRAM_D0/Touch5	U/D	Debug UART serial output
	PB_3	I/O	PWM3/LSPI_MISO/UART2_RX/PSRAM_D1/Touch6	U/D	TP4056A Charging Signal
	PB_4	I/O	LSPI_CS/UART2_RTS/UART4_TX/PSRAM_D2/Touch7	U/D	TP4056A Charged Signal
	PB_5	I/O	LSPI_MOSI/UART2_CTS/UART4_RX/PSRAM_D3/Touch8	U/D	Battery resistor voltage divider enable
	VDD3V3IO	P	IO power supply, 3.3V
	CAP	I	External capacitor, 4.7µF
	PB_6	I/O	UART1_TX/MMC_CLK/HSPI_CK/SDIO_CK/Touch9	U/D	LCD Serial Clock Pin
	PB_7	I/O	UART1_RX/MMC_CMD/HSPI_INT/SDIO_CMD/Touch10	U/D	LCD Serial Data Pin
	PB_8	I/O	I²S_BCK/MMC_D0/PWM_BREAK/SDIO_D0/Touch11	U/D	LCD Data or Command Selection Pin
	PB_9	I/O	I²S_LRCK/MMC_D1/HSPI_CS/SDIO_D1/Touch12	U/D	LCD Reset Pin
	PB_10	I/O	I²S_DI/MMC_D2/HSPI_DI/SDIO_D2	U/D	LCD Chip Select Pin
	VDD3V3IO	P	IO power supply, 3.3V
	PB_11	I/O	I²S_DO/MMC_D3/HSPI_DO/SDIO_D3	U/D	BMA456 IRQ 2 line
	GND	P	Ground (Central Pad)

What is done/working so far :

• LVGL 8.3.3 running on the SOC using DMA.
  • Supported LCD drivers :
    • ILI9341 in 4-line serial mode (8 bits) with D/C pin
    • ST7789 in 4-line serial mode (8 bits) with D/C pin
    • GC9A01 in 4-line serial mode (8 bits) with D/C pin
  • Supported LCD touch screen :
    • CST816D capacitive touch ic.
  • Three screens designed and working with LVGL :
    • 1 watch face based on a casio watch.
    • 1 menu list screen with icons.
    • 1 setting screen with basic settings (date and time + display brightness) (work in progress).
• Debug UART on PB_2 (output only)
• Wake up interrupts handling :
  • Wrist tilt MCU wake up working
  • LCD touch wake up
• Sensors/Actuators :
  • QMC5883L driver working
  • BMA456 driver working
  • BMP280 driver working (temperature + pressure)
  • Battery voltage sense using ADC is working
  • Vibration motor controlled by PWM working

To do :

• Write I2C drivers for the :
  • BMA456
    • Wrist tilt detection
  • BMP280
    • Temperature
    • Pressure
  • QMC5883L
• Write the init sequence for the GC9A01 LCD driver.
• Make LCD display + touch work.
• Design and test battery voltage sensing circuit -> voltage divider bridge because ADC input can sense 2.5V Max.
• Finish to design the settings page.
• Implement a good algorithm to handle adaptiv MCU clock to save power
• Test the charge circuit.
• Handle watch auto sleep feature with wake up on screen touch + wrist tilt (POC could be improved).
• Design and test the :
  • vibration motor circuit
• Draw the schematic, the first revision of the schematic is available here.
• Design the PCB (routing, placement etc..) on a 2 layer PCB (might need 4 though) - In progress.

Achieved power consumption recap:

(Need to work on sleep current :-( )

Mode	Current draw	Estimated battery life (450 mAh lipo)
Active (40Mhz clk) (No BLE / No WiFi)	~52 mA	~8 hour
Active (240Mhz clk) (No BLE / No WiFi)	~72 mA	~6 hour
Sleep	~4.5 mA	~4 days and 4 hours
Standby	~1.8 mA	~10 days and 15 hours

Here is a preview of what the PCB should look like :

The front :

The back :