Please do not try to test your application while in motion! Testing OpenXC apps while driving is absolutely a two person job.

Your iOS device likely doesn’t have any vehicle data flowing through it yet. The next step is to use a pre-recorded vehicle trace file to simulate a real vehicle interface on your desk. The library ships with a method for playing back previously recorded vehicle measurement trace files for testing. The Measurement objects received by your application are identical to those received from a live vehicle.

The trace file format is simply a plain text file of OpenXC JSON messages with an additional timestamp field, separated by newlines:

{"timestamp": 1351176963.426318, "name": "door_status", "value": "passenger", "event": true}
{"timestamp": 1351176963.438087, "name": "fine_odometer_since_restart", "value": 0.0}
{"timestamp": 1351176963.438211, "name": "brake_pedal_status", "value": false}
{"timestamp": 1351176963.438318, "name": "transmission_gear_position", "value": "second"}

Install the Demo App app if you haven’t already. That application helps control the source of vehicle data, e.g. a vehicle interface or a trace file.

Download the driving trace and copy it to your iOS device using iTunes.


  • Connect the iOS device to your laptop/desktop.
  • Open iTunes
  • Drag and drop the trace file and Sync

Finally, the last steps:

  1. Run the OpenXC Demo app on the device
  2. In the Demo app, Go to Settings -> Data Sources and change the vehicle interface to a Pre-recorded Trace File.
  3. At the bottom of the screen under Trace File Playback, select a trace file for playback.
  4. Return to the front view of the Demo app - the message count should be increasing, indicating the trace is playing.