For automotive enthusiasts and DIYers, the OBD2 (On-Board Diagnostics II) port is a goldmine of vehicle data. While off-the-shelf OBD2 scanners offer valuable insights into your car’s health, sometimes you need a more customized approach for specific projects. This guide will walk you through modifying a readily available and affordable ELM327 OBD2 scanner, transforming it into a versatile tool for your DIY automotive electronics endeavors.
To begin, carefully disassemble your ELM327 scanner. Most enclosures are held together by screws hidden beneath a sticker. Start by peeling off the sticker on the ELM327 cable enclosure to reveal the screws. Using a small star screwdriver, typically a Torx screwdriver, remove the four screws.
Once the screws are removed, gently separate the top and bottom halves of the enclosure to access the internal circuit board. Carefully take out the board.
Pro Tip: Before fully disconnecting any internal connectors, especially if you intend to remove the OBD2 connector, use a marker to indicate the orientation. Mark one side of the connector that runs to the OBD2 port. This will help you ensure correct reconnection later, although for this modification, removing this connector is usually not necessary.
The key to modifying your ELM327 for DIY projects lies in accessing the serial communication pins. Locate the TX (Transmit) and RX (Receive) pins on the ELM327 circuit board. These pins are typically connected to the USB bridge chip on the board. Refer to the pin-out information for your specific USB bridge chip model (often available online or on the chip datasheet) to accurately identify the TX and RX pins. Solder two wires to these TX and RX pins. Exercise caution during soldering to avoid accidentally desoldering or damaging nearby small surface mount components. Delicate soldering skills are beneficial here.
Troubleshooting Tip: To confirm you’ve correctly identified the TX pin, you can use an Arduino and a simple test. Program your Arduino to send serial data to the serial monitor with short delays. Connect a jumper wire to the Arduino’s TX pin and carefully probe around the pins on the ELM327 board with the other end of the jumper. Look for serial activity. Surface-mounted LEDs on the ELM327 board might flicker when communication occurs, indicating you’ve found the TX pin. Unfortunately, this method is less effective for identifying the RX side, but the provided images usually offer clear visual guidance for RX pin location.
Important Note: The USB cable connects to the ELM327 board via a 4-pin connector. For dedicated DIY use, consider modifying the USB connection to prevent conflicts when connected to a PC simultaneously with your microcontroller project. One method is to carefully cut the middle two pins of the 4-pin USB connector. This modification allows the ELM327 to draw power from the PC’s USB port but prevents data communication via USB, ensuring the serial interface is exclusively available for your Arduino or other microcontroller to communicate with the ELM327 chip.
Once the modifications are complete and tested, carefully reassemble the ELM327 by placing the board back into its enclosure. If the original screws are inconvenient or if you’ve altered the enclosure, you can use tape or another suitable method to securely close the housing. In some vehicle installations, the standard ELM327 enclosure might be bulky or obstruct access. In such cases, you might consider forgoing the enclosure entirely or repurposing it for a different project.
