Question: What do you get when you connect your Android Phone or Tablet with a USB-OTG cable and connect that into another USB cable connected to an Arduino?
Answer: A easy way to program and/or control your Arduino. This is a handy way to control (and/or re-program) your Arduinos in the field where it might be too inconvenient to use a laptop PC. The USB OTG cable tells the Android device to be the host and so the Arduino will be powered by the phone or tablet. Make sure your Android device is fully charged because this can drain the battery quickly. Also, make sure your Android device supports a USB OTG cable, not all do.
There are a number of Android apps that were created for both Electronics and MicroControllers such as the PICs and Arduinos.
Here is a list of my favorite apps:
Electronics: ElectroDroid EveryCircuit Electronics Toolkit
AVR: AVR Atmega Database
PIC: PICmicro Database
Arduino: ArduinoDroid Arduino Examples Arduino Companion Arduino Commander Arduino Libraries Arduino Cheat Sheet
These apps are quite handy when you are ‘in the field’ and working on a project. Note: the Arduino DUE has a USB host port, so you can plug your android phone or tablet directly into it, however the above mentioned apps only support the older IDE, they do not support the DUE.