Speed Limit Display v2

Speed Limit Display

A real-time speed limit display built with an ESP32, GPS module, and OLED screen. Shows the current road's speed limit with color-coded overspeed warnings (green/yellow/red).

Uses the TomTom Snap-to-Roads API for accurate road matching — sends your heading and speed so it picks the correct road, even near highway ramps and parallel roads.

Hardware

Wiring

Pin assignments can be changed in config.h.

Features

• Snap-to-Roads API — sends GPS heading + speed for accurate road matching
• GPS point buffering — 5-point trajectory for better map matching
• Speed limit smoothing — rejects false readings from nearby roads
• Overspeed alerts — green (ok), yellow (close to limit), red (over limit) with hysteresis
• Dual-core HTTP — API calls on Core 0, GPS/display on Core 1 (no display freezes)
• Non-blocking WiFi — GPS keeps working during WiFi reconnects
• API rate limiting — exponential backoff on HTTP 429, daily quota tracking
• Watchdog timer — auto-reboots if the device freezes
• One-button menu — adjust brightness, alert thresholds, API timing, GPS reset
• Persistent settings — brightness and thresholds saved across reboots

Setup

1. Install Arduino Libraries

Open Arduino IDE, go to Sketch > Include Library > Manage Libraries and install:

• TinyGPSPlus (by Mikal Hart)
• ArduinoJson (by Benoit Blanchon, version 6.x)
• Adafruit GFX Library
• Adafruit SSD1351 Library

2. Get a TomTom API Key (free)

1. Go to developer.tomtom.com
2. Create a free account
3. Go to Dashboard > My Apps > Add New App
4. Copy your API key (free tier = 2,500 requests/day)

3. Configure Credentials

1. In the SpeedLimitDisplay/ folder, copy config_secrets_example.h to config_secrets.h
2. Edit config_secrets.h with your WiFi name, password, and TomTom API key
3. config_secrets.h is in .gitignore — it will never be uploaded to GitHub

4. Upload to ESP32

1. Open SpeedLimitDisplay/SpeedLimitDisplay.ino in Arduino IDE
2. Select your ESP32 board in Tools > Board
3. Click Upload

5. Serial Monitor (optional, for debugging)

Open Tools > Serial Monitor at 115200 baud. Type:

• d — full debug status dump
• r — reboot the device

Button Controls

Configuration

All tunable settings (pins, timing, thresholds) are in config.h. Secrets (WiFi, API key) are in config_secrets.h.

Custom PCB (v2)

A custom 2-layer PCB designed in KiCad 10.0 with everything on one board:

Gerber files are in PCB Design/.../Gerber/ ready to upload to PCBWay or JLCPCB.

See docs/hardware/PCB_DESIGN.md for full design details, ordering instructions, and assembly guide.

Project Structure

Speed-Limit-Display/
├── SpeedLimitDisplay/              # Arduino sketch folder
│   ├── SpeedLimitDisplay.ino       # Main code
│   ├── config.h                    # All tunable settings
│   ├── config_secrets.h            # Your credentials (git-ignored)
│   └── config_secrets_example.h    # Template for credentials
├── PCB Design/                     # KiCad PCB project
│   └── .../Speed-Limit-Display-v2/
│       ├── *.kicad_sch             # Schematic
│       ├── *.kicad_pcb             # PCB layout
│       ├── *.kicad_dru             # Custom DRC rules
│       └── Gerber/                 # Manufacturing files (.zip)
├── docs/
│   ├── hardware/
│   │   ├── PCB_DESIGN.md           # PCB specs, ordering, assembly guide
│   │   └── DRC_FIXES_CHECKLIST.md  # DRC fixes applied
│   └── PRODUCT_PLAN.md             # Product roadmap
├── .gitignore
├── CONTRIBUTING.md                 # How to contribute
├── LICENSE
└── README.md                       # This file

Contributing

See CONTRIBUTING.md for how to set up your environment, create branches, and submit changes.

License

See LICENSE for details.