Send Hello to Arduino from Android in USB Host Mode

This example send bytes of "Hello..." to Arduino Esplora board from Android in USB Host Mode. Please notice that it's just a middle stage in my exercise in USB Host Mode, not a final and mature example.


In Android Side:

MainActivity.java

package com.example.androidusbhost;

import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Iterator;

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.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;
import android.app.Activity;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;

public class MainActivity extends Activity {

 TextView textInfo;
 TextView textSearchedEndpoint;
 
 TextView textDeviceName;
 TextView textStatus;
 
 private static final int targetVendorID= 9025;
 private static final int targetProductID = 32828;
 UsbDevice deviceFound = null;
 UsbInterface usbInterfaceFound = null;
 UsbEndpoint endpointIn = null;
 UsbEndpoint endpointOut = null;

 private static final String ACTION_USB_PERMISSION = 
   "com.android.example.USB_PERMISSION";
 PendingIntent mPermissionIntent;
 
 UsbInterface usbInterface;
 UsbDeviceConnection usbDeviceConnection;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  
  textStatus = (TextView)findViewById(R.id.textstatus);
  
  textDeviceName = (TextView)findViewById(R.id.textdevicename);
  textInfo = (TextView) findViewById(R.id.info);
  textSearchedEndpoint = (TextView)findViewById(R.id.searchedendpoint);
  
  //register the broadcast receiver
  mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
  IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
  registerReceiver(mUsbReceiver, filter);
  
  registerReceiver(mUsbDeviceReceiver, new IntentFilter(UsbManager.ACTION_USB_DEVICE_ATTACHED));
  registerReceiver(mUsbDeviceReceiver, new IntentFilter(UsbManager.ACTION_USB_DEVICE_DETACHED));
  
  connectUsb();
 }

 @Override
 protected void onDestroy() {
  releaseUsb();
  unregisterReceiver(mUsbReceiver);
  unregisterReceiver(mUsbDeviceReceiver);
  super.onDestroy();
 }
 
 private void connectUsb(){
  
  Toast.makeText(MainActivity.this, 
    "connectUsb()", 
    Toast.LENGTH_LONG).show();
  textStatus.setText("connectUsb()");

  searchEndPoint();

  if(usbInterfaceFound != null){
   setupUsbComm();
  }
  
 }

 private void releaseUsb(){
  
  Toast.makeText(MainActivity.this, 
    "releaseUsb()", 
    Toast.LENGTH_LONG).show();
  textStatus.setText("releaseUsb()");
  
  if(usbDeviceConnection != null){
   if(usbInterface != null){
    usbDeviceConnection.releaseInterface(usbInterface);
    usbInterface = null;
   }
   usbDeviceConnection.close();
   usbDeviceConnection = null;
  }
  
  deviceFound = null;
  usbInterfaceFound = null;
  endpointIn = null;
  endpointOut = null;
 }
 
 private void searchEndPoint(){
  
  textInfo.setText("");
  textSearchedEndpoint.setText("");
  
  usbInterfaceFound = null;
  endpointOut = null;
  endpointIn = null;
  
  //Search device for targetVendorID and targetProductID
  if(deviceFound == null){
   UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
   HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
   Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();

   while (deviceIterator.hasNext()) {
    UsbDevice device = deviceIterator.next();

    if(device.getVendorId()==targetVendorID){
     if(device.getProductId()==targetProductID){
      deviceFound = device;
     }
    }
   }
  }

  if(deviceFound==null){
   Toast.makeText(MainActivity.this, 
     "device not found", 
     Toast.LENGTH_LONG).show();
   textStatus.setText("device not found");
  }else{
   String s = deviceFound.toString() + "\n" + 
     "DeviceID: " + deviceFound.getDeviceId() + "\n" +
     "DeviceName: " + deviceFound.getDeviceName() + "\n" +
     "DeviceClass: " + deviceFound.getDeviceClass() + "\n" +
     "DeviceSubClass: " + deviceFound.getDeviceSubclass() + "\n" +
     "VendorID: " + deviceFound.getVendorId() + "\n" +
     "ProductID: " + deviceFound.getProductId() + "\n" +
     "InterfaceCount: " + deviceFound.getInterfaceCount();
   textInfo.setText(s);
      
   //Search for UsbInterface with Endpoint of USB_ENDPOINT_XFER_BULK,
   //and direction USB_DIR_OUT and USB_DIR_IN
   
   for(int i=0; i<deviceFound.getInterfaceCount(); i++){
    UsbInterface usbif = deviceFound.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){
    textSearchedEndpoint.setText("No suitable interface found!");
   }else{
    textSearchedEndpoint.setText(
     "UsbInterface found: " + usbInterfaceFound.toString() + "\n\n" +
     "Endpoint OUT: " + endpointOut.toString() + "\n\n" +
     "Endpoint IN: " + endpointIn.toString());
   }
  }
 }
 
 private boolean setupUsbComm(){
  
  //for more info, search SET_LINE_CODING and 
  //SET_CONTROL_LINE_STATE in the document:
  //"Universal Serial Bus Class Definitions for Communication Devices"
  //at http://adf.ly/dppFt
  final int RQSID_SET_LINE_CODING = 0x20;
  final int RQSID_SET_CONTROL_LINE_STATE = 0x22;
  
  boolean success = false;

  UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
  Boolean permitToRead = manager.hasPermission(deviceFound);
  
  if(permitToRead){
   usbDeviceConnection = manager.openDevice(deviceFound);
   if(usbDeviceConnection != null){
    usbDeviceConnection.claimInterface(usbInterfaceFound, true);
    
    showRawDescriptors(); //skip it if you no need show RawDescriptors
    
    int usbResult;
    usbResult = usbDeviceConnection.controlTransfer(
      0x21,        //requestType
      RQSID_SET_CONTROL_LINE_STATE, //SET_CONTROL_LINE_STATE 
      0,     //value
      0,     //index
      null,    //buffer
      0,     //length
      0);    //timeout
    
    Toast.makeText(MainActivity.this, 
      "controlTransfer(SET_CONTROL_LINE_STATE): " + usbResult, 
      Toast.LENGTH_LONG).show();
    
    //baud rate = 9600
    //8 data bit
    //1 stop bit
    byte[] encodingSetting = 
      new byte[] {(byte)0x80, 0x25, 0x00, 0x00, 0x00, 0x00, 0x08 };
    usbResult = usbDeviceConnection.controlTransfer(
      0x21,       //requestType
      RQSID_SET_LINE_CODING,   //SET_LINE_CODING
      0,      //value
      0,      //index
      encodingSetting,  //buffer
      7,      //length
      0);     //timeout
    Toast.makeText(MainActivity.this, 
      "controlTransfer(RQSID_SET_LINE_CODING): " + usbResult, 
      Toast.LENGTH_LONG).show();
    
    byte[] bytesHello = 
      new byte[] {(byte)'H', 'e', 'l', 'l', 'o', ' ', 
      'f', 'r', 'o', 'm', ' ', 
      'A', 'n', 'd', 'r', 'o', 'i', 'd'};
    usbResult = usbDeviceConnection.bulkTransfer(
      endpointOut, 
      bytesHello, 
      bytesHello.length, 
      0);
    Toast.makeText(MainActivity.this, 
      "bulkTransfer: " + usbResult, 
      Toast.LENGTH_LONG).show();
   }

  }else{
   manager.requestPermission(deviceFound, mPermissionIntent);
   Toast.makeText(MainActivity.this, 
     "Permission: " + permitToRead, 
     Toast.LENGTH_LONG).show();
   textStatus.setText("Permission: " + permitToRead);
  }
  
  
  
  return success;
 }
 
 private void showRawDescriptors(){
  final int STD_USB_REQUEST_GET_DESCRIPTOR = 0x06;
  final int LIBUSB_DT_STRING = 0x03;
  
  byte[] buffer = new byte[255];
        int indexManufacturer = 14;
        int indexProduct = 15;
        String stringManufacturer = "";
        String stringProduct = "";
  
        byte[] rawDescriptors = usbDeviceConnection.getRawDescriptors();
   
        int lengthManufacturer = usbDeviceConnection.controlTransfer(
          UsbConstants.USB_DIR_IN|UsbConstants.USB_TYPE_STANDARD,   //requestType
          STD_USB_REQUEST_GET_DESCRIPTOR,         //request ID for this transaction
          (LIBUSB_DT_STRING << 8) | rawDescriptors[indexManufacturer], //value
          0,   //index
          buffer,  //buffer
          0xFF,  //length
          0);   //timeout
        try {
         stringManufacturer = new String(buffer, 2, lengthManufacturer-2, "UTF-16LE");
        } catch (UnsupportedEncodingException e) {
         Toast.makeText(MainActivity.this, e.toString(), Toast.LENGTH_LONG).show();
         textStatus.setText(e.toString()); 
        }
   
        int lengthProduct = usbDeviceConnection.controlTransfer(
          UsbConstants.USB_DIR_IN|UsbConstants.USB_TYPE_STANDARD,
          STD_USB_REQUEST_GET_DESCRIPTOR,
          (LIBUSB_DT_STRING << 8) | rawDescriptors[indexProduct],
          0,
          buffer,
          0xFF,
          0);
        try {
         stringProduct = new String(buffer, 2, lengthProduct-2, "UTF-16LE"); 
        } catch (UnsupportedEncodingException e) {
         // TODO Auto-generated catch block
         e.printStackTrace(); 
        }
   
        textStatus.setText("Manufacturer: " + stringManufacturer + "\n" +
          "Product: " + stringProduct);
 }

 private final BroadcastReceiver mUsbReceiver = 
   new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
     String action = intent.getAction();
     if (ACTION_USB_PERMISSION.equals(action)) {
      
      Toast.makeText(MainActivity.this, 
        "ACTION_USB_PERMISSION", 
        Toast.LENGTH_LONG).show();
      textStatus.setText("ACTION_USB_PERMISSION");
      
                  synchronized (this) {
                      UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                      if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                          if(device != null){
                           connectUsb();
                         }
                      } 
                      else {
                          Toast.makeText(MainActivity.this, 
                            "permission denied for device " + device, 
                            Toast.LENGTH_LONG).show();
                          textStatus.setText("permission denied for device " + device);
                      }
                  }
              }
    }
 };
 
 private final BroadcastReceiver mUsbDeviceReceiver = 
   new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
     String action = intent.getAction();
     if (UsbManager.ACTION_USB_DEVICE_ATTACHED.equals(action)) {
      
      deviceFound = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
      Toast.makeText(MainActivity.this, 
        "ACTION_USB_DEVICE_ATTACHED: \n" +
        deviceFound.toString(), 
        Toast.LENGTH_LONG).show();
      textStatus.setText("ACTION_USB_DEVICE_ATTACHED: \n" +
        deviceFound.toString());
      
      connectUsb();

     }else if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
      
      UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
      
      Toast.makeText(MainActivity.this, 
        "ACTION_USB_DEVICE_DETACHED: \n" +
        device.toString(), 
        Toast.LENGTH_LONG).show();
      textStatus.setText("ACTION_USB_DEVICE_DETACHED: \n" +
        device.toString());
      
      if(device!=null){
       if(device == deviceFound){
        releaseUsb();
       }
      }
      
      textInfo.setText("");
     }
    }
  
 };

}

The setting of usbDeviceConnection.controlTransfer() inside setupUsbComm() is copied from the post: Android USB Host + Arduino: How to communicate without rooting your Android Tablet or Phone

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=".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" />
    
    <TextView
        android:id="@+id/textstatus"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/textdevicename"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textStyle="bold|italic" />

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical" >

            <TextView
                android:id="@+id/info"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" />
            
            <TextView
                android:id="@+id/searchedendpoint"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:textStyle="bold" />
            
        </LinearLayout>
    </ScrollView>

</LinearLayout>

AndroidManifest.xml

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

    <uses-feature android:name="android.hardware.usb.host" />
    <uses-sdk
        android:minSdkVersion="13"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.androidusbhost.MainActivity"
            android:label="@string/app_name"
            android:configChanges="keyboard|orientation" >
            <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>

Download the files.

In Arduino Side:

testSerial.ino

#include <Esplora.h>
#include <TFT.h>
#include <SPI.h>

int prevSw1 = HIGH;
int incomingByte = 0;
String charsIn = "";
char printout[20];  //max char to print: 20
 
void setup() {
  
    EsploraTFT.begin();  
    EsploraTFT.background(0,0,0);
    EsploraTFT.stroke(255,255,255);  //preset stroke color
     
    //Setup Serial Port with baud rate of 9600
    Serial.begin(9600);
    
    //indicate start
    Esplora.writeRGB(255, 255, 255);
    delay(250);
    Esplora.writeRGB(0, 0, 0);
    
}
 
void loop() {
    int sw1 = Esplora.readButton(SWITCH_1);
    if(sw1 != prevSw1){
      if(sw1 == LOW){
        Serial.println("Hello from Arduino Esplora");
      }
      prevSw1 = sw1;
    }
    
    while (Serial.available()) {
      char charRead = Serial.read();
      charsIn.concat(charRead);
    }
    if(charsIn != ""){
      Serial.println("How are you, " + charsIn);
      charsIn.toCharArray(printout, 21);
      EsploraTFT.background(0,0,0);
      EsploraTFT.text(printout, 0, 10);
      charsIn = "";
    }
}

It's same as the code in my another blog: Serial communication between Arduino Esplora and PC

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Step-by-step: Android USB Host Mode programming