An embedded GNSS navigation device built around the ESP32-S3 microcontroller and the Quectel LC29H(AA) dual-band receiver. The device operates as a self-contained Wi-Fi access point, serving a full web application to any connected phone - no internet, no cell towers, no infrastructure required.
Developed during the STMP26 SENSATE-X 2.0 Short Term Mobility Programme at TU Dublin, Tallaght Campus.
Assembled prototype: TenStar ESP32-S3 with TFT dashboard, Quectel LC29H(AA) GNSS module, and external patch antenna housed in a custom 3D-printed enclosure. The TFT screen displays live PVT (Position, Velocity, Time) telemetry and a directional navigation arrow.
- Overview
- System Architecture
- Hardware
- Communication Approach Evolution
- Firmware - AP Program
- Web Application
- Map Generator
- 3D-Printed Enclosure
- Technical Highlights
- Project Structure
- Getting Started
- Wiring Diagram
- License
Sensatex is designed for scenarios where conventional navigation infrastructure is unavailable: natural disasters, remote wilderness areas, conflict zones, or any situation where a user needs directional guidance without relying on cellular networks or cloud services.
The system provides:
- Real-time GNSS positioning via the LC29H(AA) multi-constellation receiver (GPS, Galileo, GLONASS, BeiDou)
- On-device TFT dashboard showing position, velocity, time, satellite count, HDOP, and a directional arrow pointing toward the target
- Self-hosted web interface served over a local Wi-Fi access point - any phone with a browser can connect and interact with the device
- Off-grid compass navigation with live bearing, distance, and heading indicators rendered as an SVG compass on the phone
- Coordinate system support for Decimal Degrees, DMS (Degrees/Minutes/Seconds), and UTM with full bidirectional conversion
- Persistent location storage using the browser's localStorage, surviving page reloads and reconnections
┌─────────────────────────────────────────────────────────────┐
│ SENSATEX DEVICE │
│ │
│ ┌──────────────┐ UART 115200 ┌──────────────────┐ │
│ │ LC29H(AA) │ ──────────────── │ ESP32-S3 │ │
│ │ GNSS Module │ TX→GPIO17 │ TenStar Board │ │
│ │ │ RX→GPIO18 │ │ │
│ │ External │ │ ┌────────────┐ │ │
│ │ Patch │ │ │ ST7789 │ │ │
│ │ Antenna │ │ │ TFT 240× │ │ │
│ └──────────────┘ │ │ 135 LCD │ │ │
│ │ └────────────┘ │ │
│ │ │ │
│ │ Wi-Fi Soft AP │ │
│ │ 192.168.4.1 │ │
│ └──────────────────┘ │
│ │ │
└─────────────────────────────────────────────│──────────────┘
│ HTTP
│
┌─────────▼──────────┐
│ Phone / Tablet │
│ │
│ Browser connects │
│ to 192.168.4.1 │
│ │
│ Full web app: │
│ - SVG Compass │
│ - Location mgmt │
│ - Live GPS data │
└────────────────────┘
| Component | Model | Role |
|---|---|---|
| Microcontroller | TenStar TS-ESP32-S3 | Main processing unit, Wi-Fi AP, TFT host, web server |
| GNSS Receiver | Waveshare LC29H(AA) (Quectel) | Dual-band multi-constellation GNSS receiver |
| Antenna | External active patch antenna | Required for satellite acquisition (SMA connector) |
| Display | Built-in ST7789 TFT (240 x 135) | On-device PVT dashboard and navigation arrow |
| Status LED | Onboard WS2812 NeoPixel | Visual fix/navigation status indicator |
| Enclosure | Custom 3D-printed (PLA) | Two-piece box housing both modules and antenna |
The LC29H(AA) is powered independently via its own USB cable, not from the ESP32, ensuring stable power delivery to both modules. Communication between them is through a 3-wire UART connection (TX, RX, GND).
The final architecture was reached through an iterative design process, evaluating three different communication strategies between the microcontroller and the user's phone:
The initial approach hardcoded a fixed target latitude and longitude directly in the firmware. While simple and useful for verifying that GNSS parsing and TFT rendering worked correctly, it offered zero flexibility - changing the destination required reflashing the entire board.
The second iteration introduced BLE communication. The ESP32 advertised a GATT service, and a companion app could write a destination index to a characteristic. This worked but had significant drawbacks:
- Required a dedicated BLE app (not just a browser)
- Limited to predefined destination indices rather than arbitrary coordinates
- BLE pairing and reconnection added complexity and fragility in the field
The final and adopted solution uses the ESP32 as a Wi-Fi Soft Access Point. The device creates its own network (Sensatex_Emergency, open for immediate access) and runs a full HTTP web server. Any phone connects to the network and navigates to 192.168.4.1 in a standard browser - no app installation required.
This approach eliminates all external dependencies. The entire web application (HTML, CSS, JavaScript) is embedded in the firmware using PROGMEM raw string literals and served directly from flash memory.
The production firmware (NMEA_Reader/AP_Program/AP_Program.ino) is a single-file Arduino sketch (~2300 lines) that integrates:
- Reads raw NMEA 0183 sentences from the LC29H(AA) over UART1 at 115200 baud (8N1)
- Parses
$GN-prefixed multi-system sentences using the TinyGPS++ library - Extracts position, velocity, time, satellite count, and HDOP in a non-blocking loop
- Computes great-circle distance (Haversine) and initial bearing to the target using
TinyGPSPlus::distanceBetween()andTinyGPSPlus::courseTo()
- Renders to the built-in ST7789 display in landscape mode (rotation 3)
- Displays a directional arrow using trigonometric vector math and the Bresenham-based
drawLineprimitive - Shows a PVT telemetry bar at the bottom: lat/lon, speed (km/h), UTC time, satellite count, HDOP
- Uses non-blocking 1-second refresh intervals to prevent flicker while continuously reading GPS bytes
- Computes relative bearing (target bearing minus current heading) for a turn-indicator arrow
- Heading is derived from GPS Course Over Ground, only updated when speed exceeds 0.8 km/h to suppress stationary noise
- Last known heading is held indefinitely to maintain arrow direction even when stopped
- Arrival detection triggers a full-screen green confirmation when within 20 m of the target
- Dim blue: Booting / waiting for fix
- Orange: Navigating (fix acquired, en route)
- Green: Arrived at destination
- Soft AP created with
WiFi.softAP()on the default192.168.4.1address - HTTP routes serve the embedded web application:
GET /- HTML pageGET /style.css- CSS stylesheetGET /app.js- JavaScript applicationGET /gps- JSON endpoint returning live{ valid, lat, lon, heading, speed }GET /set?lat=...&lon=...&name=...- Sets a new navigation target dynamically
server.handleClient()is called every loop iteration alongside GPS parsing
The web application (website/) is a self-contained mobile-first interface with no external dependencies other than Google Fonts. It is embedded in the firmware but also available as standalone files for development.
- SVG Compass: A dynamically rendered compass with smooth heading interpolation, cardinal indicators, degree tick marks, and an animated directional arrow pointing toward the active target
- Location Management: Add, save, delete, and navigate to locations. Locations persist in
localStorage - Multi-format Coordinate Input: Supports Decimal Degrees (lat/lon), DMS, and UTM. The UTM-to-lat/lon conversion implements the inverse transverse Mercator projection based on Karney (2011) with WGS84 ellipsoid constants
- Real-time ESP32 Communication: Polls the
/gpsendpoint every second to override the phone's GPS with the high-precision GNSS data from the LC29H(AA). Falls back to the phone's ownnavigator.geolocationwhen disconnected - Device Orientation: Uses the
DeviceOrientationEventAPI (with iOS 13+ permission handling) for magnetometer-based heading. When unavailable (HTTP context), falls back to GPS Course Over Ground from the ESP32 - Haversine Calculations: Distance and bearing computed client-side using the Haversine formula (
R = 6,371,000 m) - Glassmorphism Design: Dark theme with backdrop blur, gradient accents, and micro-animations
| Layer | Technology |
|---|---|
| Markup | HTML5 semantic elements |
| Styling | Vanilla CSS with CSS custom properties, glassmorphism, keyframe animations |
| Logic | Vanilla JavaScript (no frameworks, no build step) |
| Fonts | Inter (UI), JetBrains Mono (data/coordinates) |
| Storage | localStorage for persistent location data |
map_generator.py is a Python utility for downloading and stitching OpenStreetMap tiles into high-resolution JPEG images for offline use. It supports configurable zoom levels, bounding boxes, and aspect ratio correction.
pip install pillow requests
python map_generator.pyThe script outputs tile boundary coordinates in a format ready to be pasted into code, and applies rate limiting to respect OSM's tile usage policy.
The 3D Models/ directory contains STL files for the custom enclosure:
| File | Description |
|---|---|
Box.STL |
Main body housing the ESP32-S3 and GNSS module |
TOP1.STL |
Top lid with cutouts for the TFT display and antenna placement |
The enclosure was designed to securely hold both modules side by side, with the TFT screen and USB ports accessible through the front panel and the antenna mounted on the adjacent compartment.
The entire web application (~30 KB HTML + CSS + JS) is stored in flash memory using C++ raw string literals (R"rawliteral(...)rawliteral") and served using server.send_P(), which reads directly from program memory without copying to RAM - critical on a microcontroller with limited SRAM.
The main loop() runs three concurrent tasks without threads or RTOS:
- GPS byte ingestion (
GPSSerial.available()+gps.encode()) - HTTP client handling (
server.handleClient()) - Timer-based TFT refresh (every 1000 ms)
No task blocks the others. GPS data is stored in global state variables immediately upon reception and consumed by the display on its own schedule.
GPS Course Over Ground is only valid when the receiver is moving. At rest, it produces random values. The firmware applies a speed gate (0.8 km/h threshold) and holds the last valid heading indefinitely, ensuring the directional arrow remains stable when the user stops walking.
The web application implements a full inverse transverse Mercator projection with fourth-order Fourier series coefficients, using the WGS84 ellipsoid parameters (a = 6,378,137 m, f = 1/298.257223563). This allows field personnel to input coordinates from military or topographic maps directly.
When connected to the ESP32's Wi-Fi network, the web app polls the /gps endpoint and uses the LC29H(AA)'s position data, which is more precise than a phone's built-in GPS. When disconnected from the device (e.g., for standalone use), it transparently falls back to the phone's navigator.geolocation API.
Sensatex/
├── NMEA_Reader/
│ ├── AP_Program/ # Production firmware (Wi-Fi AP + Web Server)
│ │ └── AP_Program.ino
│ ├── BLE_Program/ # Iteration 2: Bluetooth Low Energy approach
│ │ └── BLE_Program/
│ │ └── BLE_Program.ino
│ └── Hardcoded_Program/ # Iteration 1: Fixed coordinates approach
│ └── Hardcoded_Program.ino
├── website/ # Standalone web application (also embedded in AP_Program)
│ ├── index.html
│ ├── style.css
│ └── app.js
├── 3D Models/
│ ├── Box.STL # Enclosure body
│ └── TOP1.STL # Enclosure lid
├── resources/
│ ├── Assembled_Device.png # Physical prototype photo
│ └── Dublin.jpg # Map reference image
├── map_generator.py # Offline map tile downloader
├── INSTRUCTIONS.txt # Lab hardware/wiring reference
└── README.md
- Arduino IDE 2.x with the Espressif ESP32 board package installed
- USB-C cable for the TenStar ESP32-S3
- Micro-USB cable for the LC29H(AA) GNSS module (separate power)
| Setting | Value |
|---|---|
| Board | ESP32S3 Dev Module |
| USB CDC On Boot | Enabled |
| Board Package | Espressif ESP32 (not the Arduino fork) |
Install via the Arduino Library Manager:
| Library | Purpose |
|---|---|
| TinyGPSPlus | NMEA sentence parsing |
| Adafruit GFX | Core graphics primitives |
| Adafruit ST7789 | TFT display driver |
| Adafruit NeoPixel | Onboard LED control |
- Connect the ESP32-S3 via USB-C
- Open
NMEA_Reader/AP_Program/AP_Program.inoin Arduino IDE - Select the correct COM port under Tools > Port
- Click Upload
- Connect the LC29H(AA) via its own USB cable
- Press the RST button on the board if the sketch does not start automatically
- On your phone, connect to the Wi-Fi network
Sensatex_Emergency(no password) - Open a browser and navigate to
192.168.4.1 - The web application will load with a compass, location management, and live GPS data
LC29H(AA) GNSS Module ESP32-S3 TenStar Board
┌─────────────────┐ ┌─────────────────────┐
│ │ │ │
│ GND ───────────│── Black ──│── GND │
│ TX ───────────│── Yellow ─│── GPIO 17 (RX) │
│ RX ───────────│── Blue ──│── GPIO 18 (TX) │
│ │ │ │
│ USB (power) │ │ USB-C (power+prog) │
└─────────────────┘ └─────────────────────┘
#define GPS_RX 17 // UART1 receive from LC29H TX
#define GPS_TX 18 // UART1 transmit to LC29H RX
#define TFT_CS 7 // SPI chip select
#define TFT_DC 39 // Data/Command
#define TFT_RST 40 // Hardware reset
#define TFT_BACKLIGHT 45 // Must be HIGH before tft.init()
#define SPI_SCK 36 // SPI clock
#define SPI_MISO 37 // SPI data in
#define SPI_MOSI 35 // SPI data out
#define LED_PIN 33 // NeoPixel dataThis project was developed as part of an academic mobility programme. See the repository for licensing details.