Since Bluetooth is a peer-to-peer communication protocol,
Amarino only communicates with one Bluetooth device (one
Arduino) at a time. From now on we will refer to the Arduino
that is currently paired with the phone as the active Arduino.
Amarino also remembers which device it was most recently
connected to, and clicking the connect/disconnect button on the
main screen (Figure 3) will cause the application to connect to or
disconnect from this device.