I need your help 
I've successfully tested AndroidBlinkLed sample on a Arduino Adk with a mobile phone Android 5.1 + OTG cable. Its working fine. I'm able to set Arduino's led ON and OFF from Android app 
Now I can't make it work (same Arduino and same Android app) on my car Android head unit 5.1. This unit is USB host, so detects a keyboard, flash drive or even a mouse, but does not detects the Arduino ADK!
On the head unit it's not possible to connect the OTG cable because the USB port it's Type A.
What's wrong? Head unit drivers for Arduino ADK?