Bike Computer MVP — ESP32-S3 MicroPython

Hardware target: LilyGo T-Display S3 (or any ESP32-S3 with SPI display) + ATGM336H GPS + BLE CSC sensor

MVP Scope

• GPS track recording (ATGM336H @ 115200 baud, NMEA)
• Real-time speed display
• Clock (synced from GPS UTC)
• BLE Cycling Speed & Cadence (CSC) client
• Track save to LittleFS/flash
• Basic UI: speed, time, distance, cadence

Pinout (LilyGo T-Display S3 1.9")

Function	GPIO
Display SPI CS	14
Display SPI SCK	12
Display SPI MOSI	11
Display DC	13
Display RST	15
Display BL	10 (PWM)
GPS UART TX	43 (to GPS RX)
GPS UART RX	44 (from GPS TX)
GPS PPS (optional)	42
Button 1 (Boot)	0
Button 2	14 (shared with CS - check schematic)
Battery ADC	4

Adjust for your specific board — check schematic.

Project Structure

bike-computer-mvp/
├── main.py                 # Entry point
├── config.py               # Hardware config, constants
├── lib/
│   ├── gps/
│   │   ├── __init__.py
│   │   ├── nmea.py         # NMEA parser
│   │   └── driver.py       # Async GPS driver with smoothing
│   ├── display/
│   │   ├── __init__.py
│   │   ├── st7789.py       # Display driver
│   │   └── ui.py           # UI rendering
│   ├── ble/
│   │   ├── __init__.py
│   │   └── csc.py          # BLE CSC client
│   ├── storage/
│   │   ├── __init__.py
│   │   └── tracks.py       # Track logging (LittleFS)
│   └── utils/
│       ├── __init__.py
│       └── time.py         # GPS time sync
├── assets/
│   └── fonts/              # .fnt files for display
└── tests/
    └── test_gps.py

Quick Start

# Flash MicroPython to ESP32-S3
esptool.py --chip esp32s3 --port /dev/ttyACM0 erase_flash
esptool.py --chip esp32s3 --port /dev/ttyACM0 write_flash -z 0x0 micropython-esp32s3-<version>.bin

# Copy files
ampy --port /dev/ttyACM0 put main.py
ampy --port /dev/ttyACM0 put config.py
ampy --port /dev/ttyACM0 mkdir lib
ampy --port /dev/ttyACM0 put lib/gps /lib/gps
# ... etc

# Or use mpremote (recommended)
mpremote connect /dev/ttyACM0 fs cp -r . :
mpremote connect /dev/ttyACM0 repl

Dependencies

• MicroPython 1.23+ (ESP32-S3 build with _thread, bluetooth, framebuf)
• micropython-bluez for BLE (included in recent builds)

GPS Notes

• ATGM336H default: 115200 baud, NMEA (GGA, RMC, GSA, GSV, VTG)
• Enable PPS on GPIO for precise time sync if needed
• Cold start ~30s, hot start ~1s

BLE CSC Service (UUIDs)

• Service: 0x1816 (Cycling Speed and Cadence)
• Measurement: 0x2A5B (notify)
• Feature: 0x2A5C (read)
• Sensor Location: 0x2A5D (read)

Track Format (JSON Lines)

{"t": "2026-07-11T05:13:19Z", "lat": 48.486057, "lon": -1.715130, "ele": 89.6, "speed": 5.2, "cad": 82}
{"t": "2026-07-11T05:13:20Z", "lat": 48.486084, "lon": -1.715156, "ele": 88.6, "speed": 5.3, "cad": 83}

One line per GPS fix. Append-only, rotate daily.

License

MIT