Unable to connect to Creality CR-7

Has anyone succesfully connected Astrobox to a Creality CR-7 printer?
I am new to both astrobox and 3D printing. The printer runs ok from an SD card using gcode files.
The Raspberry pi boots up and is accessible from my android tablet but am unable to make it connect to the printer. USB cable is connected. I have tried several baud rates but no success. I would welcome any suggestions.

John