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USB OTG (On-The-Go) , often abbreviated USB OTG or just OTG, is a specification that allows USB devices such as digital audio players or mobile phones to act as a host, allowing other USB devices like a USB flash drive, mouse, or keyboard to be attached to them. Unlike conventional USB systems, USB OTG systems can drop the hosting role and act as normal USB devices when attached to another host. This can be used to allow a mobile phone to act as host for a flash drive and read its contents, downloading music for instance, but then act as a flash drive when plugged into a host computer and allow the host to read off the new content. Read more: Wikipedia Official USB.org - USB On-The-Go

In order to connect Arduino Due with Android device to achieve ADK function , a Micro USB OTG Cable is needed, connected to Native USB Port of Arduino Due. Another normal USB cable is used to connect the USB OTG Cable and Android device. In such connection, the Arduino Due act as host, the Android act as accessory. Connect Arduino Due and Android device with OTG USB Cable