The ELM327 chip, developed by Elm Electronics, serves as an industry-standard decoder for accessing your car’s Engine Control Unit (ECU) data. This firmware, typically running on a PIC18 microcontroller, can communicate with various OBD-II protocols and translate them into a universal ASCII format. While OBD-II provides a standardized connector, the specific communication protocols and pins used can differ across car manufacturers and models. Historically, software vendors capitalized on the ELM327, offering expensive “specialized” diagnostic packages. However, Asian manufacturers began producing affordable clones of the ELM327, often using PIC18 or alternative microcontrollers, and offering diverse interface options like USB, Bluetooth, Serial, and WiFi. These clones are readily available online at very competitive prices, with varying degrees of quality. Even a budget-friendly USB unit can function effectively with any computer capable of virtualizing a USB connection as a COM port. Many software programs offer limited free access to encourage upgrades to their full, paid versions, but basic terminal programs can also be used to extract data.
Stanley provides an ELM327-compatible Arduino Obd2 Interface that simplifies connecting to Arduino boards. This interface comes with a cable delivering TTL-compatible serial data, enabling direct connection to Arduino I/O pins. This serial connection allows Arduino users, even those with basic experience, to easily query, store, and display vehicle parameters. Stanley also offers example code to help users get started.
To begin working with an arduino obd2 interface, understanding the fundamental AT commands for controlling the ELM327 is crucial. Next, delve into the OBD “PID” (Parameter IDs) which are used to request specific data points from your vehicle’s engine. OBD-II is primarily designed as a read-only system for monitoring, but it does offer some limited control functions. Wikipedia offers a comprehensive list of PIDs for further exploration.
Using a terminal program is a helpful first step to familiarize yourself with the system. For example, sending the command “ATI” (followed by a Carriage Return) should elicit a response like “ELM327 v1.5”, despite the fact that ELM never officially released a version 1.5. Once the interface is connected to your car’s OBD-II port, the command “ATRV” will return the vehicle’s battery voltage. Interestingly, a simple command exists to clear the Check Engine Light and erase all associated diagnostic trouble codes and data, although this command will not be disclosed here.
While reading data using an arduino obd2 interface is relatively straightforward thanks to the ELM327’s protocol translation, attempting to emulate an ECU and transmit commands back to the car is significantly more complex. This would require a deep understanding of the specific OBD-II protocols used by the vehicle, including modulation schemes, handshaking procedures, and error handling. Many of these protocols employ security measures like non-disclosure agreements and obfuscation, adding considerable difficulty to reverse engineering efforts.
