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ESP32 GPS Digital Speedometer

A high-precision digital speedometer built with ESP32, featuring a color OLED display and GPS functionality. This project provides accurate speed readings, trip tracking, and a demo mode for testing along with a custom boot screen. My 1971 BMW 2002 has a mechanically driven speedometer and it's not always accurate. I needed something I can use on a per-need basis. I also wanted to try out working with a NEO-6M module which is just a few bucks online.

Features

• Customizable boot screen
• Real-time GPS speed tracking
• Configurable "High Speed" warning to alert driver when exceeding specified speed
• Bright OLED color display (96x64 pixels)
• Trip meter with reset functionality
• Satellite acquisition indicator
• Demo mode for testing
• Average speed calculation
• Total distance tracking
• Battery powered operation (~3-4 hours on 450mAh LiPo)

Hardware Requirements

• LILYGO T2 V1.6 ESP32 Development Board with OLED Display (SSD1331)
• NEO-6M GPS Module
• 3-Position SPDT Slide Switch (for trip/odometer toggle)
• 3-Position SPDT Slide Switch (for battery power)
• 10kΩ Resistors
• 3.7V LiPo battery (450mAh tested)
• Jumper wires
• USB-C cable for programming

Software Requirements

Arduino IDE Dependencies

• ESP32 board support TTGO T2
• Adafruit_GFX library
• Adafruit_SSD1331 library
• TinyGPS++ library

Boot Screen Conversion Script Dependencies

• Python 3.x
• PIL (Python Imaging Library)
• NumPy

Wiring Diagram

Display Connection (Built into LILYGO T2)

ESP32 Pin | Display Pin
----------|------------
GPIO14    | SCLK
GPIO13    | MOSI
GPIO15    | CS
GPIO16    | DC
GPIO4     | RST

GPS Module Connection

ESP32 Pin | GPS Module
----------|------------
GPIO12    | TX
GPIO2     | RX
3.3V      | VCC
GND       | GND

Trip Switch Connection

ESP32 Pin     | Switch
--------------|------------
GPIO34        | Outside Pin
GND           | Middle Pin
3.3V --- 10kΩ | Outside Pin (GPIO34)

Installation

1. Install the necessary ESP32 board support into your Arduino IDE
2. Install required libraries through Arduino Library Manager:
   • Adafruit_GFX
   • Adafruit_SSD1331
   • TinyGPS++
3. Clone this repository
4. Open esp32-gps-speedometer.ino in Arduino IDE
5. [Optional] Use image_to_bitmap.py to convert an image to bitmap - See Custom Boot Screen
6. Select "ESP32 Dev Module" as your board
7. Upload the code to your ESP32

Custom Boot Screen

To create your own boot screen:

1. Install Python dependencies:

pip install pillow numpy

2. Prepare your image:

   • Size: Will be resized to 96x64 pixels
   • Format: Any format supported by PIL (PNG, JPG, etc.)

3. Convert the image:

python image_to_bitmap.py input_image.png output.h

4. Replace the contents of image_data[] array in the main code with the generated bitmap data

Usage

1. Power up the device via USB or battery power
   • Battery operation: Use the power rocker switch to turn on/off
   • USB operation: Device powers on automatically
2. Wait for the custom logo splash screen
3. Device will show satellite acquisition screen
4. Once satellites are acquired (usually 4+ satellites), speed will display
5. Use the slide switch to toggle between total and trip distance
6. Press the IO36 button on TTGO to enter/exit demo mode

Operating Modes

• Normal Mode: Displays actual GPS speed and distance
• Trip Mode: Shows resettable trip distance
• Demo Mode: Simulates speed for testing (useful for development)

Power Management

The device supports two power modes:

• USB-C powered: Automatic power-on when connected
• Battery powered: 3.7V LiPo with ~3-4 hours runtime on 450mAh battery
  • Built-in charging when USB is connected
  • Power rocker switch for battery operation

Technical Details

• Speed Range: 0-120 MPH (configurable in code)
• GPS Update Rate: 1Hz
• Display Resolution: 96x64 pixels
• Power Supply: 5V USB or 3.7V Li-Po battery
• Current Consumption: ~100mA typical
• Battery Life: ~3-4 hours on 450mAh LiPo

Future Development

• Design 52mm gauge pod enclosure
• Improve power efficiency
• Add configuration options for display preferences
• Create simple webapp for managing system settings
• Implement speed logging capability

License

MIT

Acknowledgments

• TTGO for the T2 ESP32 board design
• Adafruit for the display libraries
• Mikal Hart for TinyGPS++