Looking at building a custom HID keyboard for an Android device

[malaki86]

The Android radio that I just installed in my car has no "soft buttons" for Home, Back, etc. So, I started looking into building my own with an Arduino Pro Micro, 4 buttons and a rotary encoder. The newly built device will plug directly into the Android radio's USB.

The buttons I'm creating are Home, Back, Play/Pause & Skip. The rotary encoder will be volume up/down with the button being a mute. I've found the media codes in the Consumer API:

• Skip - MEDIA_NEXT
• Play/Pause - MEDIA_PLAY_PAUSE
• Mute - MEDIA_VOLUME_MUTE
• Vol up - MEDIA_VOLUME_UP
• Vol down - MEDIA_VOLUME_DOWN

What I'm not seeing is how to send the 'command' modifier & specifier key:

• Home screen - COMMAND && KEY_RETURN
• Back screen - COMMAND && KEY_BACKSPACE

Can someone help me with that last part before I finish forcefully removing the hair from my skull?