For automotive enthusiasts and makers, the ability to access vehicle diagnostic data opens up a world of possibilities. Creating your own OBD scanner, customized for specific projects, is more accessible than you might think. This guide will walk you through the process of modifying a readily available ELM327 OBD2 scanner for use in your DIY automotive electronics projects, focusing on connecting it with microcontrollers like Arduino.
Disassembling the ELM327 Scanner
The first step in modifying your ELM327 scanner is to carefully disassemble it to access the internal circuit board. This process is straightforward and requires minimal tools.
Step 1: Removing the Enclosure
Begin by peeling off any stickers or labels that are on the plastic enclosure of your ELM327 cable. Beneath these, you will typically find four small screws.
Step 2: Accessing the Circuit Board
Using a small star screwdriver, carefully remove these four screws. Once the screws are removed, you can gently separate the two halves of the enclosure to reveal the circuit board inside.
Alt text: Disassembled ELM327 OBD2 scanner showing the internal circuit board after removing the enclosure screws, preparing for modification.
Tip for Connector Orientation: Before you proceed further, especially if you intend to fully remove the board, take a moment to mark the orientation of the connector that leads to the OBD2 port. A simple mark on one side with a marker or nail polish will help you correctly reassemble it later. While not strictly necessary for this modification, it’s a good practice for general electronics work.
Soldering Wires for Arduino Communication
To enable communication with a microcontroller like an Arduino, we need to establish a serial connection to the ELM327’s main chip. This involves soldering wires to the Transmit (TX) and Receive (RX) pins on the circuit board.
Step 3: Identifying TX and RX Pins
Locate the USB bridge chip on the ELM327 board. This chip is responsible for converting USB communication to serial. Refer to the datasheet of your specific USB bridge chip (often CH340 or FT232 variants) or the pin-out diagram readily available online for ELM327 boards. Identify the TX and RX pins on this chip. These are the points where we will solder our wires.
Step 4: Soldering the Connection Wires
Carefully solder two wires to the identified TX and RX pins on the USB bridge chip. Use a soldering iron with a fine tip and work in a well-lit area to avoid damaging the small components on the board. Take extra caution to prevent solder bridges between pins.
Alt text: Close-up of soldering wires to the TX and RX pins on the ELM327 circuit board’s USB bridge chip for Arduino serial communication in a DIY OBD scanner project.
Pro Tip for Pin Identification: A helpful trick to quickly locate the TX pin is to use your Arduino. Program your Arduino to continuously send serial data to the serial monitor with short delays. Connect a jumper wire to the Arduino’s TX pin and gently probe around the pins of the USB bridge chip on the ELM327 board with the other end of the jumper. Observe the surface-mounted LEDs on the ELM327 board. When you touch the TX pin, the LEDs should flicker, indicating serial communication activity. While this method is less reliable for identifying the RX pin, the included images often clearly show the RX pin location.
Modifying the USB Power Connection (Optional)
To prevent potential conflicts and ensure that the ELM327 scanner only communicates with your Arduino and not your PC simultaneously, you can modify the USB connection to provide power only.
Step 5: Isolating USB Data Lines
The USB cable connects to the ELM327 board via a 4-pin connector (VCC, Data-, Data+, GND). If desired, you can carefully cut or remove the middle two pins (Data- and Data+) from this connector. This modification ensures that the ELM327 receives power from the USB port but the data lines are disconnected, preventing the scanner from attempting to establish a USB data connection with your computer and freeing up the serial communication for your Arduino.
Reassembling and Testing Your DIY OBD Scanner
With the necessary modifications complete, it’s time to reassemble the scanner and test your new DIY OBD setup.
Step 6: Reassembling the Enclosure
Carefully place the modified circuit board back into the enclosure halves, ensuring the OBD2 connector and any other external connectors align correctly. Fasten the enclosure back together using the screws you removed earlier. If the enclosure becomes cumbersome for your project, you can opt to leave it open or use tape for a temporary closure, especially if space is a constraint in your vehicle.
Step 7: Testing with Arduino
Connect the wires you soldered to the TX and RX pins of the ELM327 to the RX and TX pins of your Arduino, respectively (remember to cross-connect TX to RX and RX to TX). Power the ELM327 through the USB connection, and power your Arduino. Upload Arduino code designed to communicate with an OBD2 interface using libraries like OBD-II UART. You should now be able to send OBD-II requests through your Arduino and receive vehicle diagnostic data from your modified ELM327 scanner.
Conclusion
By following these steps, you’ve successfully transformed a standard ELM327 OBD2 scanner into a customizable tool for your DIY automotive projects. This modification allows you to leverage the capabilities of microcontrollers like Arduino to create custom dashboards, data loggers, or automated vehicle control systems, all powered by readily accessible OBD-II data. This opens up a wide range of possibilities for automotive innovation and experimentation.
