The attached file demonstrates USB Host Communication directly between an Android machine and an Arduino. It uses a service application called Arduino Uno Communicator created by Mat Jeppsson. This is currently available free from Google Play. (Java source is also available - see ReadMe file in attached .zip for details.)
The B4A app I have written, uses the BroadCastReceiver, Phone and ByteConverter libraries so you will need to download these also, if you don't have them already. My thanks to those who contributed these.
The app "Android-Arduino_Blink" allows you to turn ON/OFF a flashing LED on pin 13 of the Arduino from your Android system. An Arduino program file is included in the .zip.
Unfortunately the Communicator app does not work with every Uno and Mega that is out there! I suggest that you download Arduino Uno Communicator first and if it works with your kit, the b4A code should work too!
The files are here:View attachment AA_Blink.zip
I hope this helps some of the people interested in this topic.