Car Scanner Cables, essential tools for modern vehicle diagnostics, can be further enhanced for advanced users and specific projects. This guide will walk you through a modification process for your car scanner cable, originally designed for basic OBD2 diagnostics, to unlock its potential for more intricate applications, such as interfacing with microcontrollers like Arduino for custom automotive projects. This modification focuses on accessing the raw serial communication of the ELM327 chip, the heart of many affordable car scanner cables.
First, begin by disassembling your ELM327-based car scanner cable. Carefully peel off any sticker or label on the enclosure of your car scanner cable. Underneath, you’ll find screws, typically four, that secure the casing. Use a small star screwdriver, ensuring it’s the correct size to avoid stripping the screw heads, to remove these screws.
Once the screws are removed, gently separate the two halves of the enclosure to reveal the internal circuit board of your car scanner cable.
At this stage, you’ll need to identify the TX (Transmit) and RX (Receive) pins on the ELM327 board. These pins are crucial for serial communication. Refer to the datasheet of the USB bridge chip on your board for the exact pinout. The image below illustrates a common pinout configuration which should be similar for many car scanner cables using a USB bridge.
Carefully solder two wires to the TX and RX pins you’ve identified. Precision is key here. Use a soldering iron with a fine tip and work in a well-lit area. Be extremely cautious to avoid accidentally desoldering any surface mount components near the pins. If you’re new to soldering, practice on some scrap electronics first to get comfortable with the process. Accidental shorts or detached components can render your car scanner cable unusable.
Tip for Identifying TX/RX: If you’re unsure which pins are TX and RX, and don’t have the exact datasheet handy, you can use an Arduino as a signal sniffer. Program your Arduino to send serial data continuously. Connect a jumper wire to the Arduino’s TX pin and carefully probe the pins on the car scanner cable’s board while observing for serial activity. An LED connected to the serial line, if present on the board, might flicker when communication occurs, indicating you’ve found the TX pin (or RX if probing from the other side). However, visually verifying the pinout from the chip datasheet is the most reliable method.
Important Note on USB Connection: To prevent conflicts and ensure your Arduino or other microcontroller has exclusive control over the serial communication, it’s recommended to disable the direct USB communication of the ELM327 chip with your PC while modified. The USB cable typically connects to the board via a 4-pin connector. You can carefully cut or remove the middle two pins on this connector. This modification ensures that the ELM327 chip only receives power from the USB port, and the serial communication is solely handled through the wires you soldered to the TX and RX pins, allowing your external microcontroller to communicate effectively with the car’s OBD2 system via the modified car scanner cable.
After soldering and modifying the USB connector, carefully reassemble the car scanner cable by placing the board back into its enclosure and securing it with the screws. If the original enclosure is no longer suitable or convenient for your project, you can use electrical tape or another suitable method to protect the modified board, especially if it will be used in an environment where the original casing might be cumbersome, such as inside a vehicle for permanent monitoring or custom installations.
This modification transforms your standard car scanner cable into a versatile tool for advanced car diagnostics and custom automotive electronics projects. By accessing the raw serial data, you can now interface your car’s OBD2 system with microcontrollers, opening up possibilities for personalized dashboards, data logging, and automated vehicle monitoring systems. Remember to always exercise caution when working with electronics and ensure proper connections to avoid damaging your car’s electronic systems or the car scanner cable itself.
