Bi-directional communication between Android and Arduino in USB Host Mode, example 2

It's another example to implement Bi-directional communication between Android and Arduino in USB Host Mode. A button on Andndroid is used to turn ON/OFF the on-board LED of Arduino Uno, and EditText to send string to Arduino Uno. it will be displayed on connected LCD, and sent back to Android.


Notice:
- Sync word of '0xFF' is used to mark the beginning of data, to sync the communication. Extra in-correct '0x00' received in Android side (I don't know why), so have to ignore it. Make sure the data will not be '0xFF' and '0x00'.
- Command 0x01, 0x02, and 0x03 are used to define LED ON, LED OFF, and string of text.
- Data will lost if sent too fast, so I break the message and insert dummy delay between bytes. (inside method sendArduinoText())
- A USB OTG cable is need to connect to Android side, and a normal USB is used to connect USB OTG cable and Arduino Uno.

---

Android side:

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.androidusbhostarduino"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-feature android:name="android.hardware.usb.host" />
    <uses-sdk
        android:minSdkVersion="12"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <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" />
        </activity>
    </application>

</manifest>

/res/xml/device_filter.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <!-- idVendor=2341, idProduct=0043 for Arduino Uno R3 -->
    <usb-device 
        vendor-id="9025" 
        product-id="0067" />
</resources>

/res/layout/activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.androidusbhostarduino.MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />

    <ToggleButton 
        android:id="@+id/arduinoled"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textOn="ON"
        android:textOff="OFF" />
    
    <EditText
        android:id="@+id/textout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
    <Button
        android:id="@+id/send"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Send"/>
    <TextView
        android:id="@+id/textin"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

MainActivity.java

package com.example.androidusbhostarduino;

import java.nio.ByteBuffer;

import android.support.v7.app.ActionBarActivity;
import android.content.Context;
import android.content.Intent;
import android.hardware.usb.UsbConstants;
import android.hardware.usb.UsbDevice;
import android.hardware.usb.UsbDeviceConnection;
import android.hardware.usb.UsbEndpoint;
import android.hardware.usb.UsbInterface;
import android.hardware.usb.UsbManager;
import android.hardware.usb.UsbRequest;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.ToggleButton;
import android.widget.CompoundButton.OnCheckedChangeListener;

public class MainActivity extends ActionBarActivity implements Runnable{
 
 private static final String TAG = "AndroidUsbHostArduino";

 private static final byte IGNORE_00 = (byte) 0x00;
 private static final byte SYNC_WORD = (byte) 0xFF;
 
 private static final int CMD_LED_OFF = 2;
 private static final int CMD_LED_ON = 1;
 private static final int CMD_TEXT = 3;
 private static final int MAX_TEXT_LENGTH = 16;

 ToggleButton buttonLed;
 EditText textOut;
 Button buttonSend;
 TextView textIn;
 
 String stringToRx;
 
 private UsbManager usbManager;
    private UsbDevice deviceFound;
    private UsbDeviceConnection usbDeviceConnection;
    private UsbInterface usbInterfaceFound = null;
 private UsbEndpoint endpointOut = null;
 private UsbEndpoint endpointIn = null;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  buttonLed = (ToggleButton)findViewById(R.id.arduinoled);
  buttonLed.setOnCheckedChangeListener(new OnCheckedChangeListener(){

   @Override
   public void onCheckedChanged(CompoundButton buttonView,
     boolean isChecked) {
    if(isChecked){
     sendArduinoCommand(CMD_LED_ON);
    }else{
     sendArduinoCommand(CMD_LED_OFF);
    }
   }});
  
  textOut = (EditText)findViewById(R.id.textout);
  textIn = (TextView)findViewById(R.id.textin);
  buttonSend = (Button)findViewById(R.id.send);
  buttonSend.setOnClickListener(new OnClickListener(){

   @Override
   public void onClick(View v) {
    final String textToSend = textOut.getText().toString();
    if(textToSend!=""){
     stringToRx = "";
     textIn.setText("");
     Thread threadsendArduinoText = 
      new Thread(new Runnable(){

       @Override
       public void run() {
        sendArduinoText(textToSend);
       }});
     threadsendArduinoText.start();
    }
    
   }});
  
  usbManager = (UsbManager)getSystemService(Context.USB_SERVICE);
 }

 @Override
    public void onResume() {
        super.onResume();

        Intent intent = getIntent();
        String action = intent.getAction();

        UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
        if (UsbManager.ACTION_USB_DEVICE_ATTACHED.equals(action)) {
            setDevice(device);
        } else if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
            if (deviceFound != null && deviceFound.equals(device)) {
                setDevice(null);
            }
        }
    }
 
 private void setDevice(UsbDevice device) {
        usbInterfaceFound = null;
     endpointOut = null;
     endpointIn = null;

        for (int i = 0; i < device.getInterfaceCount(); i++) {         
   UsbInterface usbif = device.getInterface(i);

   UsbEndpoint tOut = null;
   UsbEndpoint tIn = null;

   int tEndpointCnt = usbif.getEndpointCount();
   if (tEndpointCnt >= 2) {
    for (int j = 0; j < tEndpointCnt; j++) {
     if (usbif.getEndpoint(j).getType() 
      == UsbConstants.USB_ENDPOINT_XFER_BULK) {
      if (usbif.getEndpoint(j).getDirection() 
       == UsbConstants.USB_DIR_OUT) {
       tOut = usbif.getEndpoint(j);
      } else if (usbif.getEndpoint(j).getDirection() 
       == UsbConstants.USB_DIR_IN) {
       tIn = usbif.getEndpoint(j);
      }
     }
    }

    if (tOut != null && tIn != null) {
     // This interface have both USB_DIR_OUT
     // and USB_DIR_IN of USB_ENDPOINT_XFER_BULK
     usbInterfaceFound = usbif;
     endpointOut = tOut;
     endpointIn = tIn;
    }
   }
  }
        
        if (usbInterfaceFound == null) {
            return;
        }

        deviceFound = device;
        
        if (device != null) {
            UsbDeviceConnection connection = 
             usbManager.openDevice(device);
            if (connection != null && 
             connection.claimInterface(usbInterfaceFound, true)) {
             
             connection.controlTransfer(0x21, 34, 0, 0, null, 0, 0);
             connection.controlTransfer(0x21, 32, 0, 0, 
               new byte[] { (byte) 0x80, 0x25, 0x00, 
                0x00, 0x00, 0x00, 0x08 }, 
               7, 0);
             
                usbDeviceConnection = connection;
                Thread thread = new Thread(this);
                thread.start();

            } else {
                usbDeviceConnection = null;
            }
         }
    }
 
 private void sendArduinoCommand(int control) {
        synchronized (this) {

            if (usbDeviceConnection != null) {
                byte[] message = new byte[2];
                message[0] = SYNC_WORD;
                message[1] = (byte)control;

                usbDeviceConnection.bulkTransfer(endpointOut,
                  message, message.length, 0);
                
                Log.d(TAG, "sendArduinoCommand: " + String.valueOf(control));
            }
        }
    }
 
 private void sendArduinoText(String s) {
        synchronized (this) {

            if (usbDeviceConnection != null) {
             
             Log.d(TAG, "sendArduinoText: " + s);
             
             int length = s.length();
             if(length>MAX_TEXT_LENGTH){
              length = MAX_TEXT_LENGTH;
             }
                byte[] message = new byte[length + 3];
                message[0] = SYNC_WORD;
                message[1] = (byte)CMD_TEXT;
                message[2] = (byte)length;
                s.getBytes(0, length, message, 3);
                
                /*
                usbDeviceConnection.bulkTransfer(endpointOut,
                  message, message.length, 0);
                */
                
                byte[] b = new byte[1];
                for(int i=0; i< length+3; i++){
                 b[0] = message[i];
                 Log.d(TAG, "sendArduinoTextb[0]: " + b[0]);
                 usbDeviceConnection.bulkTransfer(endpointOut,
                      b, 1, 0);
                 try {
      Thread.sleep(100);
     } catch (InterruptedException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
                }
            }
        }
    }

 @Override
 public void run() {
  ByteBuffer buffer = ByteBuffer.allocate(1);
        UsbRequest request = new UsbRequest();
        request.initialize(usbDeviceConnection, endpointIn);
        while (true) {
            request.queue(buffer, 1);
            if (usbDeviceConnection.requestWait() == request) {
                byte dataRx = buffer.get(0);
                Log.d(TAG, "dataRx: " + dataRx);
                if(dataRx!=IGNORE_00){
                 
                 stringToRx += (char)dataRx;
                 runOnUiThread(new Runnable(){

      @Override
      public void run() {
       textIn.setText(stringToRx);
      }});
                }
            } else {
                break;
            }
        }
  
 }

}

Download the files.

---

Arduino side:

UsbSlave.ino

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
int pinLED = 13;

const int ST_0 = 0;      //waiting Sync word
const int ST_1_CMD = 1;  //Waiting CMD
const int ST_2_LENGTH= 2;//Receiving Length for CMD_03_TEXT
const int ST_3_DATA= 3;  //Receiving Data for CMD_03_TEXT
const byte IGNORE_00 = 0x00;
const byte SYNC_WORD = 0xFF;
const byte CMD_01_LEDON = 0x01;
const byte CMD_02_LEDOFF= 0x02;
const byte CMD_03_TEXT  = 0x03;
int cmdState;
int dataIndex;

const int MAX_LENGTH = 16;
byte data[MAX_LENGTH];
int dataLength;

void setup() {
  Serial.begin(9600);
  pinMode(pinLED, OUTPUT);
  digitalWrite(pinLED, LOW);
  
  lcd.begin(16, 2);
  lcd.print("USB Host Mode:");
}

void loop() {
  
  if(Serial.available()){
    //lcd.setCursor(0, 1);
    //lcd.print("                ");
    //delay(100);
    //lcd.setCursor(0, 1);
    while(Serial.available() > 0){
      int byteIn = Serial.read();
      //Serial.write(byteIn);
      //lcd.write(byteIn);
      cmdHandle(byteIn);
    }
  }
}

void cmdHandle(int incomingByte){
  
  //prevent from lost-sync
  if(incomingByte == SYNC_WORD){
    cmdState = ST_1_CMD;
    return;
  }
  if(incomingByte == IGNORE_00){
    return;
  }
  
  switch(cmdState){
    case ST_1_CMD:{
          switch(incomingByte){
            case CMD_01_LEDON:
                digitalWrite(pinLED, HIGH);
                break;
            case CMD_02_LEDOFF:
                digitalWrite(pinLED, LOW);
                break;
            case CMD_03_TEXT:
                for(int i=0; i < MAX_LENGTH; i++){
                  data[i] = 0;
                }
                lcd.setCursor(0, 1);
                lcd.print("                ");
                lcd.setCursor(0, 1);
            
                cmdState = ST_2_LENGTH;
                dataIndex = 0;
                break;
            default:
                cmdState = ST_0;
          }
        }
        break;
    case ST_2_LENGTH:{
        dataLength = incomingByte;
        if(dataLength > MAX_LENGTH){
          dataLength = MAX_LENGTH;
        }
        cmdState = ST_3_DATA;
        }
        break;
    case ST_3_DATA:{
          data[dataIndex] = incomingByte;
          dataIndex++;
          
          Serial.write(incomingByte);
          lcd.write(incomingByte);
          
          if(dataIndex==dataLength){
            cmdState = ST_0;
          }
        }
        break;
  }
  
}

Download HERE.

Connection of LCD in Arduino Uno:

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- Bi-directional communication between Android and Arduino in USB Host Mode, example 1
- Bi-directional communication between Android and Arduino in USB Host Mode, example 3 - work with 8x8 LED Matrix

Related:
- More example of communication between Android to Arduino Uno, in USB Host Mode