How to Use OBD-II UART Adapter: Examples, Pinouts, and Specs

The OBD-II UART Adapter by Freematics is a versatile device designed to interface with a vehicle's On-Board Diagnostics (OBD-II) system. It connects to the OBD-II port of a vehicle and communicates with the onboard diagnostics system via a UART (Universal Asynchronous Receiver-Transmitter) interface. This adapter enables users to retrieve real-time vehicle data, perform diagnostics, and monitor performance metrics.

• Vehicle diagnostics and troubleshooting
• Real-time data logging for performance analysis
• Integration with microcontrollers (e.g., Arduino) for custom automotive projects
• Fleet management and telematics systems
• Educational purposes for learning about vehicle communication protocols

The following table outlines the key technical details of the Freematics OBD-II UART Adapter:

The adapter features a UART interface for communication. Below is the pinout for the UART connector:

1. Connect the Adapter to the Vehicle:
   • Plug the OBD-II UART Adapter into the vehicle's OBD-II port, typically located under the dashboard.
2. Connect to a Microcontroller:
   • Use the UART interface to connect the adapter to a microcontroller (e.g., Arduino UNO). Ensure proper voltage levels (3.3V or 5V) for the UART pins.
3. Power the Adapter:
   • The adapter is powered directly from the vehicle's OBD-II port. No external power supply is required.
4. Configure Communication:
   • Set the UART baud rate on the microcontroller to match the adapter's default (9600 bps) or a custom baud rate if configured.

• Ensure the vehicle's ignition is turned on to allow the OBD-II system to communicate.
• Use a level shifter if your microcontroller operates at 5V logic levels, as the adapter uses 3.3V logic.
• Avoid prolonged connections to prevent draining the vehicle's battery.
• Verify the supported OBD-II protocol of your vehicle to ensure compatibility.

Below is an example Arduino sketch to retrieve and display vehicle speed using the OBD-II UART Adapter:

#include <SoftwareSerial.h>

// Define RX and TX pins for SoftwareSerial
SoftwareSerial obdSerial(10, 11); // RX = pin 10, TX = pin 11

void setup() {
  Serial.begin(9600); // Initialize Serial Monitor
  obdSerial.begin(9600); // Initialize OBD-II UART communication

  // Send initialization command to the OBD-II adapter
  obdSerial.println("ATZ"); // Reset the adapter
  delay(1000); // Wait for the adapter to reset

  // Set the protocol to automatic
  obdSerial.println("ATSP0");
  delay(1000);

  Serial.println("OBD-II Adapter Initialized");
}

void loop() {
  // Request vehicle speed (PID 0D)
  obdSerial.println("010D");
  delay(100); // Wait for the response

  // Read the response from the adapter
  while (obdSerial.available()) {
    char c = obdSerial.read();
    Serial.print(c); // Print the response to the Serial Monitor
  }
  delay(1000); // Wait before sending the next request
}

• Replace 10 and 11 with the appropriate pins if using different connections.
• Ensure the vehicle supports the requested PID (e.g., 0D for speed).

1. No Response from the Adapter:

   • Ensure the vehicle's ignition is turned on.
   • Verify the UART connections (TX, RX, VCC, GND) are correct.
   • Check the baud rate configuration on the microcontroller.

2. Incorrect or Garbled Data:

   • Confirm the UART voltage levels match between the adapter and the microcontroller.
   • Ensure the OBD-II protocol is supported by the vehicle.

3. Adapter Not Powering On:

   • Check the OBD-II port for proper power output (typically 12V).
   • Inspect the adapter for physical damage or loose connections.

Q: Can this adapter work with all vehicles?
A: The adapter supports most vehicles manufactured after 1996 that comply with OBD-II standards. However, compatibility depends on the specific protocol used by the vehicle.

Q: How do I change the baud rate of the adapter?
A: Use the ATBRx command, where x specifies the desired baud rate. Refer to the Freematics user manual for details.

Q: Can I use this adapter with a Raspberry Pi?
A: Yes, the adapter can be connected to a Raspberry Pi via its UART interface. Ensure proper voltage level conversion if needed.

Q: Is it safe to leave the adapter connected to the vehicle?
A: While the adapter has low power consumption, it is recommended to disconnect it when the vehicle is not in use to prevent battery drain.