How to receive serial data using android bluetooth

Question

I am new to android. I am designing an android application that receives serial data from a hardware device through bluetooth. I am working on Htc desire S. I used the sample Bluetooth chat code to receive data. But the data received is incorrect. It misses some values. Can anyone please provide me any other sample code to receive large amount of data through bluetooth and save it in a file.

Kanaka

Answer 1

try this code :

Activity:

package Android.Arduino.Bluetooth;
import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.TextView;
import android.widget.EditText;  
import android.widget.Button;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Set;
import java.util.UUID;

public class MainActivity extends Activity
{
TextView myLabel;
EditText myTextbox;
BluetoothAdapter mBluetoothAdapter;
BluetoothSocket mmSocket;
BluetoothDevice mmDevice;
OutputStream mmOutputStream;
InputStream mmInputStream;
Thread workerThread;
byte[] readBuffer;
int readBufferPosition;
int counter;
volatile boolean stopWorker;

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button openButton = (Button)findViewById(R.id.open);
    Button sendButton = (Button)findViewById(R.id.send);
    Button closeButton = (Button)findViewById(R.id.close);
    myLabel = (TextView)findViewById(R.id.label);
    myTextbox = (EditText)findViewById(R.id.entry);

    //Open Button
    openButton.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v)
        {
            try 
            {
                findBT();
                openBT();
            }
            catch (IOException ex) { }
        }
    });

    //Send Button
    sendButton.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v)
        {
            try 
            {
                sendData();
            }
            catch (IOException ex) { }
        }
    });

    //Close button
    closeButton.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v)
        {
            try 
            {
                closeBT();
            }
            catch (IOException ex) { }
        }
    });
}

void findBT()
{
    mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    if(mBluetoothAdapter == null)
    {
        myLabel.setText("No bluetooth adapter available");
    }

    if(!mBluetoothAdapter.isEnabled())
    {
        Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBluetooth, 0);
    }

    Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();
    if(pairedDevices.size() > 0)
    {
        for(BluetoothDevice device : pairedDevices)
        {
            if(device.getName().equals("MattsBlueTooth")) 
            {
                mmDevice = device;
                break;
            }
        }
    }
    myLabel.setText("Bluetooth Device Found");
}

void openBT() throws IOException
{
    UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"); //Standard SerialPortService ID
    mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid);        
    mmSocket.connect();
    mmOutputStream = mmSocket.getOutputStream();
    mmInputStream = mmSocket.getInputStream();

    beginListenForData();

    myLabel.setText("Bluetooth Opened");
}

void beginListenForData()
{
    final Handler handler = new Handler(); 
    final byte delimiter = 10; //This is the ASCII code for a newline character

    stopWorker = false;
    readBufferPosition = 0;
    readBuffer = new byte[1024];
    workerThread = new Thread(new Runnable()
    {
        public void run()
        {                
           while(!Thread.currentThread().isInterrupted() && !stopWorker)
           {
                try 
                {
                    int bytesAvailable = mmInputStream.available();                        
                    if(bytesAvailable > 0)
                    {
                        byte[] packetBytes = new byte[bytesAvailable];
                        mmInputStream.read(packetBytes);
                        for(int i=0;i<bytesAvailable;i++)
                        {
                            byte b = packetBytes[i];
                            if(b == delimiter)
                            {
     byte[] encodedBytes = new byte[readBufferPosition];
     System.arraycopy(readBuffer, 0, encodedBytes, 0, encodedBytes.length);
     final String data = new String(encodedBytes, "US-ASCII");
     readBufferPosition = 0;

                                handler.post(new Runnable()
                                {
                                    public void run()
                                    {
                                        myLabel.setText(data);
                                    }
                                });
                            }
                            else
                            {
                                readBuffer[readBufferPosition++] = b;
                            }
                        }
                    }
                } 
                catch (IOException ex) 
                {
                    stopWorker = true;
                }
           }
        }
    });

    workerThread.start();
}

void sendData() throws IOException
{
    String msg = myTextbox.getText().toString();
    msg += "\n";
    mmOutputStream.write(msg.getBytes());
    myLabel.setText("Data Sent");
}

void closeBT() throws IOException
{
    stopWorker = true;
    mmOutputStream.close();
    mmInputStream.close();
    mmSocket.close();
    myLabel.setText("Bluetooth Closed");
}
}

AND Here the layout:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
tools:ignore="TextFields,HardcodedText" >

<TextView
    android:id="@+id/label"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="Type here:" />

<EditText
    android:id="@+id/entry"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_below="@id/label"
    android:background="@android:drawable/editbox_background" />

<Button
    android:id="@+id/open"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:layout_below="@id/entry"
    android:layout_marginLeft="10dip"
    android:text="Open" />

<Button
    android:id="@+id/send"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@id/open"
    android:layout_toLeftOf="@id/open"
    android:text="Send" />

<Button
    android:id="@+id/close"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignTop="@id/send"
    android:layout_toLeftOf="@id/send"
    android:text="Close" />

</RelativeLayout>

Here for Manifest: add to Application

// permission must be enabled complete
<manifest ....>

    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <application>


    </application>
</manifest>

Metastasis

I get a NullPointerException on the line mmSocket = mmDevice.createRfcommSocketToServiceRecord(uuid); any help, please? – Falconer

Tomas I think you might have an incorrect UUID for the device? What value are you using? – Coelom

I am also getting a NullPointerException . Had u found any solution?? @Tomáš'GunsBlazing'Frček – Sarnen

I am not able to work this out. getting below error. getBluetoothService() called with no BluetoothManagerCallback W/System.err: java.io.IOException: read failed, socket might closed or timeout, read ret: -1 W/System.err: at android.bluetooth.BluetoothSocket.readAll(BluetoothSocket.java:684) – Entomologize

Replace MattsBlueTooth with your device name. – Cleaning

I suppose the <uses-permission...> would be outside the <application> tag. – Jacobite

Got this working -- translated the code to Kotlin. Thanks so much. This helps me get started with sending and receiving data to/from my HC-05 device. Fantastic help! – Kantor

This answer was very helpful & I want to help others. I converted the code to Kotlin (and a current Android Studio project) & have stored it in my public Github (github.com/raddevus/SoBtEx) This new version adds a couple of things: 1) drop list will display all paired devices on the android device where you run the app 2) multi-line textview so that if your HC-05 returns multiple lines after sending it a command you will be able to see all lines (data) returned. I've included a snapshot in the readme.md at the github repo. I hope the code helps as much as this post helped me. 🤓 👍🏽 – Kantor

Answer 2

I tried this out for transmitting continuous data (float values converted to string) from my PC (MATLAB) to my phone. But, still my App misreads the delimiter '\n' and still data gets garbled. So, I took the character 'N' as the delimiter rather than '\n' (it could be any character that doesn't occur as part of your data) and I've achieved better transmission speed - I gave just 0.1 seconds delay between transmitting successive samples - with more than 99% data integrity at the receiver i.e. out of 2000 samples (float values) that I transmitted, only 10 were not decoded properly in my application.

My answer in short is: Choose a delimiter other than '\r' or '\n' as these create more problems for real-time data transmission when compared to other characters like the one I've used. If we work more, may be we can increase the transmission rate even more. I hope my answer helps someone!

Peshawar

Answer 3

The issue with the null connection is related to the findBT() function. you must change the device name from "MattsBlueTooth" to your device name as well as confirm the UUID for your service/device. Use something like BLEScanner app to confrim both on Android.

Affiance

how to confirm the UUID for any device/service? – Comfortable

Answer 4

Take a look at incredible Bluetooth Serial class that has onResume() ability that helped me so much. I hope this helps ;)

Hetti

Answer 5

You can use android-bluetooth-serial library to send/receive messages.

Add this package as dependency in app build.gradle.

dependencies {
    implementation 'com.github.harry1453:android-bluetooth-serial:v1.1'

    // RxJava is also required.
    implementation 'io.reactivex.rxjava2:rxjava:2.1.12'
    implementation 'io.reactivex.rxjava2:rxandroid:2.0.2'
}

In your app, add a class to interact with device.

private void connectDevice(String mac) {
    bluetoothManager.openSerialDevice(mac)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(this::onConnected, this::onError);
}

private void onConnected(BluetoothSerialDevice connectedDevice) {
    // You are now connected to this device!
    // Here you may want to retain an instance to your device:
    deviceInterface = connectedDevice.toSimpleDeviceInterface();
    
    // Listen to bluetooth events
    deviceInterface.setListeners(this::onMessageReceived, this::onMessageSent, this::onError);
    
    // Let's send a message:
    deviceInterface.sendMessage("Hello world!");
}

private void onMessageSent(String message) {
    // We sent a message! Handle it here.
    Toast.makeText(context, "Sent a message! Message was: " + message, Toast.LENGTH_LONG).show(); // Replace context with your context instance.
}

private void onMessageReceived(String message) {
    // We received a message! Handle it here.
    Toast.makeText(context, "Received a message! Message was: " + message, Toast.LENGTH_LONG).show(); // Replace context with your context instance.
}

You can see the readme page for more details on using this package.

Noted