Arduino OBD2 Interface: Displaying Car Data with ELM327, I2C LCD, and HC-05 Bluetooth

This guide provides a comprehensive walkthrough for building an Arduino-based OBD2 interface to display vehicle data on an I2C LCD screen using an ELM327 Bluetooth adapter and an HC-05 Bluetooth module. This project demystifies the process of extracting and displaying real-time information like coolant temperature from your car’s ECU.

Decoding the OBD2 Maze with ELM327

The OBD2 standard, while seemingly universal, presents challenges due to the variety of internal protocols used by car manufacturers. The ELM327 integrated circuit acts as a crucial translator, converting these diverse protocols into a single, understandable language. Affordable ELM327 Bluetooth adapters readily available online make this project accessible to everyone. This project leverages the ELM327’s capabilities to access and interpret the vehicle’s data.

Building the Hardware Bridge

This project utilizes readily available and inexpensive components:

ELM327 Bluetooth OBD2 Adapter: The bridge between your car and the project.
Arduino Uno: The microcontroller brain of the operation.
HC-05 Bluetooth Module: Enables wireless communication with the ELM327.
I2C LCD Display: Visually presents the retrieved data.

Wiring the Components

The connections are straightforward:

Arduino Uno & HC-05: Connect the HC-05’s TX pin to the Arduino’s RX pin, and the HC-05’s RX pin to the Arduino’s TX pin. Power the HC-05 with 5V and ground.
Arduino Uno & I2C LCD: Connect the LCD’s SDA pin to the Arduino’s A4 pin and the LCD’s SCL pin to the Arduino’s A5 pin. These pins are mirrored to the dedicated SCL and SDA pins on the Arduino Uno.

Configuring the HC-05 for Master Mode

The HC-05 needs to be configured as the master device to initiate communication with the ELM327 (slave).

AT Command Mode: Enter AT command mode by holding the HC-05’s button down while powering it up. The LED should blink slowly (every 2 seconds).
Connect to HC-05: Use a serial monitor or terminal to connect to the HC-05 via its COM port.
Execute AT Commands: Use the following AT commands, substituting placeholders with your ELM327’s Bluetooth address (e.g., 12:34:56:78:9A:BC):
```
AT+RESET
AT+ORGL
AT+ROLE=1
AT+CMODE=0
AT+BIND=1234,56,789ABC 
AT+INIT
AT+PAIR=1234,56,789ABC,20
AT+LINK=1234,56,789ABC
```

Programming the Arduino & Displaying Data

Disconnect HC-05: Detach the HC-05’s TX/RX from the Arduino before uploading the code.
Include Libraries: Add the necessary libraries to your Arduino sketch:
```
#include <Wire.h>
#include <LiquidCrystal_I2C.h> 
```
Ensure the Wire.h library is in your Arduino libraries folder.
Initialize LCD: Initialize the I2C LCD with its address (commonly 0x27 or 0x3F). You may need to adjust this value based on your specific LCD model.
```
LiquidCrystal_I2C lcd(0x3F, 16, 2); // Adjust address if needed
lcd.init();
lcd.backlight();
```
Arduino Code: Write the Arduino code to receive data from the HC-05 (and subsequently the ELM327), parse it, and display relevant information (e.g., coolant temperature) on the LCD. This will involve serial communication and data processing based on the specific OBD2 PIDs (Parameter IDs) you wish to read.

Conclusion

This comprehensive guide provides a solid foundation for building your own Arduino OBD2 interface. By combining the power of the ELM327, Arduino, HC-05, and an I2C LCD, you can unlock a wealth of real-time vehicle data and customize its display. This project empowers you to understand and interact with your car on a deeper level. Remember to consult your vehicle’s documentation for specific OBD2 PIDs and data interpretation.