Knowledge Note KN1047
CPJexr
How CPJexr works at Android

You can control Android device with steering wheel controls by CPJexr.
Android 3.1 or later version is required to use CPJexr in Android.
Use USB OTG cable to connect CPJexr to Android device.

Drag and drop a button to Remote controller to connect the button to the function. 

https://www.exinterface.com/d/an/1047/KN1047-(CPJexr)How_CPJexr_works_in_Android.pdf