Hacktor Watch 2.0 - Fitness Watchface

A full-featured analog watchface and fitness tracker app for the Hacktor Watch 2.0, built with Zephyr OS 4.3 on the ESP32-S3 platform.

Built during the Hacktor Watch hackathon (April 2026).

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Features

Analog Watchface

• Beautiful analog clock with hour, minute, and second hands (red) on a round 240x240 GC9A01 display
• All 12 hour numbers displayed (12/3/6/9 in large font, others in small font)
• 60 minute tick dots (gray) and 8 hour tick dots (white) around the dial
• Date display (e.g. "Sat 4 Apr") above center
• Battery indicator with graphical icon (green fill, turns yellow below 20%) and percentage text
• Step counter in large light-blue font below center

Fitness Tracking

• Hardware pedometer using the LSM6DSL's built-in step counter (PEDO_EN register)
• Steps read directly from hardware registers STEP_COUNTER_L/H (0x4B/0x4C) — zero CPU overhead
• Daily step goal ring — an arc around the watchface edge that fills green as you walk toward 6000 steps, turns gold when the goal is reached
• Automatic daily reset at midnight (writes PEDO_RST_STEP to CTRL10_C)

Sleep & Wake

• Display enters sleep mode after 30 seconds of inactivity (backlight off + display blanking)
• Three wake methods:
  • Double-tap on the touchscreen (CST816S capacitive touch)
  • Wrist-raise gesture via LSM6DSL hardware tilt detection (WRIST_TILT_EN + TILT_EN in CTRL10_C)
  • Boot button press (GPIO 0)
• Haptic buzz (DRV2605) on every wake event for tactile feedback
• CPU continues running in sleep (software clock keeps time, pedometer keeps counting)

BLE Connectivity

• Advertises as "Hacktor Watch" via BLE peripheral
• Custom GATT service (12345678-1234-5678-1234-56789abcdef0) with two characteristics:
  • Weather characteristic (...def1): write UTF-8 string "TEMP,CONDITION" (e.g. "22,1") to display weather on the watchface
    • Conditions: 0=Clear, 1=Sunny, 2=Cloudy, 3=Rain, 4=Snow, 5=Storm
  • WiFi characteristic (...def2): write "SSID,PASSWORD,CITY" for future WiFi weather fetch
• Compatible with nRF Connect app on iOS/Android

Shell Interface

Access via USB serial for debugging and configuration:

• battery — show battery percentage and voltage
• imu — show accelerometer/gyroscope data + tilt status registers
• steps — show current step count
• buzz [1-123] — play a DRV2605 haptic effect from the ROM library
• settime HH:MM:SS — set the software clock
• setdate DD/MM/YYYY W — set date (W: 0=Sun..6=Sat)
• i2c scan i2c@60027000 — scan I2C bus for connected devices

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Hardware

Hacktor Watch 2.0 — open-source wearable by Dan Tudose & Radu Pascale

Component	Chip	Interface	I2C Address
MCU	ESP32-S3 (dual-core 240MHz, 512KB SRAM)	—	—
Display	GC9A01 1.28" 240x240 round LCD	SPI3 (GPIO 11/12/13, CS=GPIO4, DC=GPIO5, RST=GPIO3)	—
Touch	CST816S capacitive	I2C1 (GPIO8/GPIO9)	0x15
IMU	LSM6DSLTR (6-axis accel+gyro)	I2C1	0x6A
Fuel Gauge	MAX17048	I2C1	0x36
Haptic	DRV2605 (ERM motor)	I2C1	0x5A
Backlight	GPIO-controlled LED	GPIO7	—
LCD Power	PMIC enable	GPIO18 (always on via gpio-hog)	—
Buttons	BOOT=GPIO0, RESET=EN	—	—
Battery	200mAh LiPo + BQ24040 charger	USB-C	—
Flash	W25Q256 32MB external SPI	—	—
PSRAM	ESP-PSRAM64H 8MB	—	—
Microphone	LMD2718T261-OA1	—	—
Speaker	MAX98357 I2S amplifier	—	—

All I2C peripherals share a single bus (I2C1) at 400kHz on GPIO8 (SDA) / GPIO9 (SCL).

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Project Structure

hacktor_hello/
├── CMakeLists.txt          # Build configuration
├── prj.conf                # Zephyr Kconfig (drivers, LVGL, BLE, etc.)
├── app.overlay             # Devicetree overlay (display, touch, IMU, fuel gauge, haptic)
├── build.sh                # Build & flash script
├── README.md               # This file
└── src/
    ├── main.c              # App entry, main loop, time tracking, sleep/wake logic
    ├── display.c / .h      # Display + LVGL init, sleep/wake (backlight + blanking)
    ├── watchface.c / .h    # Analog watchface UI (dial, hands, labels, goal arc)
    ├── battery.c / .h      # MAX17048 fuel gauge (SOC%, voltage)
    ├── imu.c / .h          # LSM6DSL (accel/gyro, hardware pedometer, wrist-tilt)
    ├── haptic.c / .h       # DRV2605 haptic motor (ROM effects library)
    ├── ble.c / .h          # BLE peripheral (weather + WiFi GATT characteristics)
    └── weather.c / .h      # Weather data storage (WiFi fetch stub)

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Building & Flashing

Prerequisites

• Zephyr OS 4.3.0
• Zephyr SDK 0.16.8
• ESP32-S3 toolchain
• BLE blobs: west blobs fetch hal_espressif

Build

./build.sh --pristine       # full clean build
./build.sh                  # incremental build

Flash

./build.sh --flash --port /dev/ttyACM0

Binary size

~623KB flash — well under the 4MB limit.

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Usage

1. Flash the firmware to the Hacktor Watch
2. The watchface appears with default time 10:10:00
3. Set time via USB shell: settime 14:30:00
4. Set date via USB shell: setdate 04/04/2026 6
5. Walk and watch the step counter and goal ring update
6. Wait 30s or let the display sleep, then double-tap, raise wrist, or press BOOT to wake
7. Send weather via nRF Connect: connect to "Hacktor Watch", write 22,1 (UTF-8) to characteristic ...def1

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Roadmap / Future Work

Deep Sleep Mode

• Implement true ESP32 light sleep with RTC wake sources
• Investigate GC9A01 hardware sleep commands (SLPIN/SLPOUT 0x10/0x11) instead of power cycling GPIO18 (power cycling was tested and breaks re-init)
• Wake via GPIO interrupt from IMU INT1 pin (pin mapping TBD from schematic)
• Target: extend battery life from hours to days on the 200mAh cell

App Launcher & Multiple Screens

• Swipe-based navigation between screens (left/right to switch, up/down for quick settings)
• Home screen — the analog watchface (current)
• Fitness screen — detailed step history, distance estimate (steps x stride), calories estimate, daily/weekly graph
• Weather screen — current temperature, condition icon, hourly/daily forecast (once WiFi is working)
• Notifications screen — display BLE notifications (ANCS for iPhone, or custom via nRF Connect)
• Settings screen — brightness control, sleep timeout, step goal, watchface style
• Stopwatch / Timer screen — with haptic alerts at completion
• Alarm screen — set alarms that vibrate via DRV2605

WiFi Weather (Auto-Fetch)

• Connect to WiFi using credentials sent via BLE (SSID, password, city)
• Fetch weather from wttr.in (free, no API key) over HTTP
• Auto-refresh every 30 minutes, then disable WiFi radio to save power
• Display temperature, condition, and forecast on a dedicated weather screen
• Show weather icon (sun/cloud/rain/snow) on watchface complication

Text Input on Watch

• Implement an on-screen keyboard using the touchscreen for short text input
• T9-style circular keyboard optimized for the round display
• Use cases: enter WiFi password, set alarm label, quick reply to notifications
• Handwriting recognition using the IMU (draw letters in the air)

Enhanced Fitness Tracking

• Distance estimation — step count x configurable stride length
• Calorie estimation — based on steps, weight, and activity intensity
• Activity detection — walking vs running vs idle using IMU data patterns
• Inactivity reminders — vibrate every hour if no steps detected
• Sleep tracking — detect sleep onset/wake using overnight IMU movement patterns
• Heart rate (if hardware supports external sensor via I2C sensorhub)
• Workout mode — dedicated tracking screen with lap timer, pace, HR zones

Watchface Customization

• Multiple watchface styles (analog, digital, minimal, data-heavy)
• Configurable complications (weather, steps, battery, date, next alarm)
• Color theme selection (red, blue, green, custom)
• Animated second hand with smooth 60fps sweep (currently 1fps tick)

Phone Companion (BLE)

• ANCS integration — receive iPhone notifications (calls, messages, app alerts)
• Apple Media Service — music play/pause/skip controls from the watch
• Find my phone — trigger an alert on the phone from the watch
• Phone battery sync — show phone battery level on the watchface
• Time sync — auto-set watch time from phone's current time via BLE
• Quick replies — predefined responses to messages sent via BLE

Audio

• Voice memos — record short clips using the onboard LMD2718 microphone
• Audio playback — play alerts/sounds via MAX98357 I2S amplifier + speaker
• Keyword detection — on-device TinyML model for "Hey Watch" wake word

Power Optimization

• Clock down CPU from 240MHz to 80MHz during idle/sleep
• Disable gyroscope when not needed (accel-only mode for pedometer)
• BLE advertising interval optimization (slower when not actively connecting)
• Display frame rate reduction when showing static content
• Target: 2+ days battery life with normal usage

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Known Issues

• GC9A01 R/B color swap: the display panel swaps red and blue channels. Use 0x0000FF for red, 0xFF0000 for blue, green is unchanged. White/gray are unaffected.
• LCD power cycling: cutting GPIO18 (LCD power) during sleep permanently breaks display re-initialization. Use backlight-only sleep instead.
• LSM6DSL wrist-tilt: hardware tilt detection is enabled via direct register writes (CTRL10_C + TAP_CFG INTERRUPTS_ENABLE). Reliability depends on wearing position.
• Software clock: time is tracked via k_uptime_get() with no RTC — drifts slightly over days. Set time via shell or future BLE time sync.

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License

Built on the open-source Hacktor Watch 2.0 hardware platform.