ProjectProto

int ledPin = 13;
void setup(){ 
 Serial.begin(9600);
 Serial.setTimeout(200);
 pinMode(ledPin, OUTPUT); 
} 
void loop(){
 if (Serial.available()){
 String c = Serial.readString();
 if (c.equals("TONLED")) digitalWrite(ledPin, HIGH); 
 else if (c.equals("TOFFLED")) digitalWrite(ledPin, LOW);
 else Serial.print(c);
 }
}

allprojects {
 repositories {
 jcenter()
 maven { url "https://jitpack.io" }
 }
}

compile 'com.github.felHR85:UsbSerial:4.3'

private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
UsbDevice device;
UsbDeviceConnection connection;
UsbManager usbManager;
UsbSerialDevice serialPort;
PendingIntent pendingIntent;

private final BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
 @Override
 public void onReceive(Context context, Intent intent) {
 if (intent.getAction().equals(ACTION_USB_PERMISSION)) {
 boolean granted = intent.getExtras().getBoolean(UsbManager.EXTRA_PERMISSION_GRANTED);
 if (granted) {
 connection = usbManager.openDevice(device);
 serialPort = UsbSerialDevice.createUsbSerialDevice(device, connection);
 if (serialPort != null) {
 if (serialPort.open()) {
 serialPort.setBaudRate(9600);
 serialPort.setDataBits(UsbSerialInterface.DATA_BITS_8);
 serialPort.setStopBits(UsbSerialInterface.STOP_BITS_1);
 serialPort.setParity(UsbSerialInterface.PARITY_NONE);
 serialPort.setFlowControl(UsbSerialInterface.FLOW_CONTROL_OFF);
 serialPort.read(mCallback); 
 } else {
 Log.d("SERIAL", "PORT NOT OPEN");
 }
 } else {
 Log.d("SERIAL", "PORT IS NULL");
 }
 } else {
 Log.d("SERIAL", "PERMISSION NOT GRANTED");
 }
 } else if (intent.getAction().equals(UsbManager.ACTION_USB_DEVICE_ATTACHED)) {
 onClickStart(startButton);
 } else if (intent.getAction().equals(UsbManager.ACTION_USB_DEVICE_DETACHED)) {
 //can add something to close the connection
 }
 };
};

pendingIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
registerReceiver(broadcastReceiver, filter);

public void onClickStart(View view) {
 if (!isSerialStarted) {
 usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
 HashMap<String, UsbDevice> usbDevices = usbManager.getDeviceList();
 if (!usbDevices.isEmpty()) {
 boolean keep = true;
 for (Map.Entry<String, UsbDevice> entry : usbDevices.entrySet()) {
 device = entry.getValue();
 int deviceVID = device.getVendorId();
 if (deviceVID == 1027 || deviceVID == 9025) { //Arduino Vendor ID
 usbManager.requestPermission(device, pendingIntent); 
 keep = false;
 } else {
 connection = null;
 device = null;
 }
 if (!keep)
 break;
 }
 }
 }
}

private UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() {
 //Defining a Callback which triggers whenever data is read.
 @Override
 public void onReceivedData(byte[] arg0) {
 String data = null;
 try {
 data = new String(arg0, "UTF-8");
 data.concat("/n");
 tvAppend(displayView, data);
 } catch (UnsupportedEncodingException e) {
 e.printStackTrace();
 }
 }
};
private void tvAppend(final TextView tv, final CharSequence text) {
 runOnUiThread(new Runnable() {
 @Override public void run() {
 if (text != null) {
 tv.append(text); 
 }
 }
 });
}

public void onClickSend(View view) {
 String textInput = inputView.getText().toString();
 serialPort.write(textInput.getBytes());
}

public void onClickToggle(View view) {
 if (isLedON == false) {
 isLedON = true;
 tvAppend(displayView, "\nLED TURNED ON\n");
 serialPort.write("TONLED".getBytes());
 } else {
 isLedON = false;
 serialPort.write("TOFFLED".getBytes());
 tvAppend(displayView, "\nLED TURNED OFF\n");
 }
}

serialPort.close();

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 package="yourpackage.com.name">
 <uses-feature android:name="android.hardware.usb.host" />
 <application
 android:allowBackup="true"
 android:icon="@mipmap/ic_launcher"
 android:label="@string/app_name"
 android:supportsRtl="true"
 android:theme="@style/AppTheme">
 <activity
 android:name=".MainActivity"
 android:label="@string/app_name"
 android:theme="@style/AppTheme.NoActionBar">
 <intent-filter>
 <action android:name="android.intent.action.MAIN" />
 <category android:name="android.intent.category.LAUNCHER" />
 </intent-filter>
 <intent-filter>
 <action android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED" />
 </intent-filter>
 <meta-data
 android:name="android.hardware.usb.action.USB_DEVICE_ATTACHED"
 android:resource="@xml/device_filter" />
 <intent-filter>
 <action android:name="android.hardware.usb.action.USB_DEVICE_DETACHED" />
 </intent-filter>
 </activity>
 </application>
</manifest>

<?xml version="1.0" encoding="utf-8"?>
<resources>
 <usb-device
 vendor-id="9025"/>
</resources>

mScrollView.smoothScrollTo(0, displayView.getBottom());