Using BluetoothChat to communicate with ELM327

Question

I am currently trying to communicate with the ELM327 OBDII Bluetooth dongle through the BluetoothChat application. I can connect as I changed the UUID, however I can only get the launch commands and the ">" prompt to send a command, whenever I try to send a command, I get the following

• CAN OBDII: ELM327 v1.2a>
• Me: ATRV
• CAN OBDII: ATRV
• CAN OBDII:>
• CAN OBDII :?

Now I am reading here to add the "\ r" commands, but when I do this, I get the same answer. I am using the bluetoothchat sample application

The main class ...

public class BluetoothChat extends Activity { // Debugging private static final String TAG = "BluetoothChat"; private static final boolean D = true; // Message types sent from the BluetoothChatService Handler public static final int MESSAGE_STATE_CHANGE = 1; public static final int MESSAGE_READ = 2; public static final int MESSAGE_WRITE = 3; public static final int MESSAGE_DEVICE_NAME = 4; public static final int MESSAGE_TOAST = 5; // Key names received from the BluetoothChatService Handler public static final String DEVICE_NAME = "device_name"; public static final String TOAST = "toast"; // Intent request codes private static final int REQUEST_CONNECT_DEVICE_SECURE = 1; private static final int REQUEST_CONNECT_DEVICE_INSECURE = 2; private static final int REQUEST_ENABLE_BT = 3; // Layout Views private TextView mTitle; private ListView mConversationView; private EditText mOutEditText; private Button mSendButton; // Name of the connected device private String mConnectedDeviceName = null; // Array adapter for the conversation thread private ArrayAdapter<String> mConversationArrayAdapter; // String buffer for outgoing messages private StringBuffer mOutStringBuffer; // Local Bluetooth adapter private BluetoothAdapter mBluetoothAdapter = null; // Member object for the chat services private BluetoothChatService mChatService = null; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); if(D) Log.e(TAG, "+++ ON CREATE +++"); // Set up the window layout requestWindowFeature(Window.FEATURE_CUSTOM_TITLE); setContentView(R.layout.main); getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.custom_title); // Set up the custom title mTitle = (TextView) findViewById(R.id.title_left_text); mTitle.setText(R.string.app_name); mTitle = (TextView) findViewById(R.id.title_right_text); // Get local Bluetooth adapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter(); // If the adapter is null, then Bluetooth is not supported if (mBluetoothAdapter == null) { Toast.makeText(this, "Bluetooth is not available", Toast.LENGTH_LONG).show(); finish(); return; } } @Override public void onStart() { super.onStart(); if(D) Log.e(TAG, "++ ON START ++"); // If BT is not on, request that it be enabled. // setupChat() will then be called during onActivityResult if (!mBluetoothAdapter.isEnabled()) { Intent enableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); startActivityForResult(enableIntent, REQUEST_ENABLE_BT); // Otherwise, setup the chat session } else { if (mChatService == null) setupChat(); } } @Override public synchronized void onResume() { super.onResume(); if(D) Log.e(TAG, "+ ON RESUME +"); // Performing this check in onResume() covers the case in which BT was // not enabled during onStart(), so we were paused to enable it... // onResume() will be called when ACTION_REQUEST_ENABLE activity returns. if (mChatService != null) { // Only if the state is STATE_NONE, do we know that we haven't started already if (mChatService.getState() == BluetoothChatService.STATE_NONE) { // Start the Bluetooth chat services mChatService.start(); } } } private void setupChat() { Log.d(TAG, "setupChat()"); // Initialize the array adapter for the conversation thread mConversationArrayAdapter = new ArrayAdapter<String>(this, R.layout.message); mConversationView = (ListView) findViewById(R.id.in); mConversationView.setAdapter(mConversationArrayAdapter); // Initialize the compose field with a listener for the return key mOutEditText = (EditText) findViewById(R.id.edit_text_out); mOutEditText.setOnEditorActionListener(mWriteListener); // Initialize the send button with a listener that for click events mSendButton = (Button) findViewById(R.id.button_send); mSendButton.setOnClickListener(new OnClickListener() { public void onClick(View v) { // Send a message using content of the edit text widget TextView view = (TextView) findViewById(R.id.edit_text_out); String message = view.getText().toString(); sendMessage(message); } }); // Initialize the BluetoothChatService to perform bluetooth connections mChatService = new BluetoothChatService(this, mHandler); // Initialize the buffer for outgoing messages mOutStringBuffer = new StringBuffer(""); } @Override public synchronized void onPause() { super.onPause(); if(D) Log.e(TAG, "- ON PAUSE -"); } @Override public void onStop() { super.onStop(); if(D) Log.e(TAG, "-- ON STOP --"); } @Override public void onDestroy() { super.onDestroy(); // Stop the Bluetooth chat services if (mChatService != null) mChatService.stop(); if(D) Log.e(TAG, "--- ON DESTROY ---"); } private void ensureDiscoverable() { if(D) Log.d(TAG, "ensure discoverable"); if (mBluetoothAdapter.getScanMode() != BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE) { Intent discoverableIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE); discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300); startActivity(discoverableIntent); } } /** * Sends a message. * @param message A string of text to send. */ private void sendMessage(String message) { // Check that we're actually connected before trying anything if (mChatService.getState() != BluetoothChatService.STATE_CONNECTED) { Toast.makeText(this, R.string.not_connected, Toast.LENGTH_SHORT).show(); return; } // Check that there actually something to send if (message.length() > 0) { // Get the message bytes and tell the BluetoothChatService to write byte[] send = message.getBytes(); mChatService.write(send); // Reset out string buffer to zero and clear the edit text field mOutStringBuffer.setLength(0); mOutEditText.setText(mOutStringBuffer); } } // The action listener for the EditText widget, to listen for the return key private TextView.OnEditorActionListener mWriteListener = new TextView.OnEditorActionListener() { public boolean onEditorAction(TextView view, int actionId, KeyEvent event) { // If the action is a key-up event on the return key, send the message if (actionId == EditorInfo.IME_NULL && event.getAction() == KeyEvent.ACTION_UP) { String message = view.getText().toString(); sendMessage(message); } if(D) Log.i(TAG, "END onEditorAction"); return true; } }; // The Handler that gets information back from the BluetoothChatService private final Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { case MESSAGE_STATE_CHANGE: if(D) Log.i(TAG, "MESSAGE_STATE_CHANGE: " + msg.arg1); switch (msg.arg1) { case BluetoothChatService.STATE_CONNECTED: mTitle.setText(R.string.title_connected_to); mTitle.append(mConnectedDeviceName); mConversationArrayAdapter.clear(); break; case BluetoothChatService.STATE_CONNECTING: mTitle.setText(R.string.title_connecting); break; case BluetoothChatService.STATE_LISTEN: case BluetoothChatService.STATE_NONE: mTitle.setText(R.string.title_not_connected); break; } break; case MESSAGE_WRITE: Log.i(TAG, "WRITING!"); byte[] writeBuf = (byte[]) msg.obj; // construct a string from the buffer String writeMessage = new String(writeBuf); mConversationArrayAdapter.add("Me: " + writeMessage); break; case MESSAGE_READ: Log.i(TAG, "READING"); String readMessage = (String) msg.obj; // construct a string from the valid bytes in the buffer mConversationArrayAdapter.add(mConnectedDeviceName+": " + readMessage); break; case MESSAGE_DEVICE_NAME: // save the connected device name mConnectedDeviceName = msg.getData().getString(DEVICE_NAME); Toast.makeText(getApplicationContext(), "Connected to " + mConnectedDeviceName, Toast.LENGTH_SHORT).show(); break; case MESSAGE_TOAST: Toast.makeText(getApplicationContext(), msg.getData().getString(TOAST), Toast.LENGTH_SHORT).show(); break; } } }; public void onActivityResult(int requestCode, int resultCode, Intent data) { if(D) Log.d(TAG, "onActivityResult " + resultCode); switch (requestCode) { case REQUEST_CONNECT_DEVICE_SECURE: // When DeviceListActivity returns with a device to connect if (resultCode == Activity.RESULT_OK) { connectDevice(data, true); } break; case REQUEST_CONNECT_DEVICE_INSECURE: // When DeviceListActivity returns with a device to connect if (resultCode == Activity.RESULT_OK) { connectDevice(data, false); } break; case REQUEST_ENABLE_BT: // When the request to enable Bluetooth returns if (resultCode == Activity.RESULT_OK) { // Bluetooth is now enabled, so set up a chat session setupChat(); } else { // User did not enable Bluetooth or an error occured Log.d(TAG, "BT not enabled"); Toast.makeText(this, R.string.bt_not_enabled_leaving, Toast.LENGTH_SHORT).show(); finish(); } } } private void connectDevice(Intent data, boolean secure) { // Get the device MAC address String address = data.getExtras() .getString(DeviceListActivity.EXTRA_DEVICE_ADDRESS); // Get the BLuetoothDevice object BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address); // Attempt to connect to the device mChatService.connect(device, secure); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.option_menu, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { Intent serverIntent = null; switch (item.getItemId()) { case R.id.secure_connect_scan: // Launch the DeviceListActivity to see devices and do scan serverIntent = new Intent(this, DeviceListActivity.class); startActivityForResult(serverIntent, REQUEST_CONNECT_DEVICE_SECURE); return true; case R.id.insecure_connect_scan: // Launch the DeviceListActivity to see devices and do scan serverIntent = new Intent(this, DeviceListActivity.class); startActivityForResult(serverIntent, REQUEST_CONNECT_DEVICE_INSECURE); return true; case R.id.discoverable: // Ensure this device is discoverable by others ensureDiscoverable(); return true; } return false; } } package com.example.android.BluetoothChat; import java.io.IOException; /** * This class does all the work for setting up and managing Bluetooth * connections with other devices. It has a thread that listens for * incoming connections, a thread for connecting with a device, and a * thread for performing data transmissions when connected. */ public class BluetoothChatService { // Debugging private static final String TAG = "BluetoothChatService"; private static final boolean D = true; // Name for the SDP record when creating server socket private static final String NAME_SECURE = "BluetoothChatSecure"; private static final String NAME_INSECURE = "BluetoothChatInsecure"; // Unique UUID for this application private static final UUID MY_UUID_SECURE = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"); private static final UUID MY_UUID_INSECURE = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"); // Member fields private final BluetoothAdapter mAdapter; private final Handler mHandler; private AcceptThread mSecureAcceptThread; private AcceptThread mInsecureAcceptThread; private ConnectThread mConnectThread; private ConnectedThread mConnectedThread; private int mState; // Constants that indicate the current connection state public static final int STATE_NONE = 0; // we're doing nothing public static final int STATE_LISTEN = 1; // now listening for incoming connections public static final int STATE_CONNECTING = 2; // now initiating an outgoing connection public static final int STATE_CONNECTED = 3; // now connected to a remote device /** * Constructor. Prepares a new BluetoothChat session. * @param context The UI Activity Context * @param handler A Handler to send messages back to the UI Activity */ public BluetoothChatService(Context context, Handler handler) { mAdapter = BluetoothAdapter.getDefaultAdapter(); mState = STATE_NONE; mHandler = handler; } /** * Set the current state of the chat connection * @param state An integer defining the current connection state */ private synchronized void setState(int state) { if (D) Log.d(TAG, "setState() " + mState + " -> " + state); mState = state; // Give the new state to the Handler so the UI Activity can update mHandler.obtainMessage(BluetoothChat.MESSAGE_STATE_CHANGE, state, -1).sendToTarget(); } /** * Return the current connection state. */ public synchronized int getState() { return mState; } /** * Start the chat service. Specifically start AcceptThread to begin a * session in listening (server) mode. Called by the Activity onResume() */ public synchronized void start() { if (D) Log.d(TAG, "start"); // Cancel any thread attempting to make a connection if (mConnectThread != null) {mConnectThread.cancel(); mConnectThread = null;} // Cancel any thread currently running a connection if (mConnectedThread != null) {mConnectedThread.cancel(); mConnectedThread = null;} setState(STATE_LISTEN); // Start the thread to listen on a BluetoothServerSocket if (mSecureAcceptThread == null) { mSecureAcceptThread = new AcceptThread(true); mSecureAcceptThread.start(); } if (mInsecureAcceptThread == null) { mInsecureAcceptThread = new AcceptThread(false); mInsecureAcceptThread.start(); } } /** * Start the ConnectThread to initiate a connection to a remote device. * @param device The BluetoothDevice to connect * @param secure Socket Security type - Secure (true) , Insecure (false) */ public synchronized void connect(BluetoothDevice device, boolean secure) { if (D) Log.d(TAG, "connect to: " + device); // Cancel any thread attempting to make a connection if (mState == STATE_CONNECTING) { if (mConnectThread != null) {mConnectThread.cancel(); mConnectThread = null;} } // Cancel any thread currently running a connection if (mConnectedThread != null) {mConnectedThread.cancel(); mConnectedThread = null;} // Start the thread to connect with the given device mConnectThread = new ConnectThread(device, secure); mConnectThread.start(); setState(STATE_CONNECTING); } /** * Start the ConnectedThread to begin managing a Bluetooth connection * @param socket The BluetoothSocket on which the connection was made * @param device The BluetoothDevice that has been connected */ public synchronized void connected(BluetoothSocket socket, BluetoothDevice device, final String socketType) { if (D) Log.d(TAG, "connected, Socket Type:" + socketType); // Cancel the thread that completed the connection if (mConnectThread != null) {mConnectThread.cancel(); mConnectThread = null;} // Cancel any thread currently running a connection if (mConnectedThread != null) {mConnectedThread.cancel(); mConnectedThread = null;} // Cancel the accept thread because we only want to connect to one device if (mSecureAcceptThread != null) { mSecureAcceptThread.cancel(); mSecureAcceptThread = null; } if (mInsecureAcceptThread != null) { mInsecureAcceptThread.cancel(); mInsecureAcceptThread = null; } // Start the thread to manage the connection and perform transmissions mConnectedThread = new ConnectedThread(socket, socketType); mConnectedThread.start(); // Send the name of the connected device back to the UI Activity Message msg = mHandler.obtainMessage(BluetoothChat.MESSAGE_DEVICE_NAME); Bundle bundle = new Bundle(); bundle.putString(BluetoothChat.DEVICE_NAME, device.getName()); msg.setData(bundle); mHandler.sendMessage(msg); setState(STATE_CONNECTED); } /** * Stop all threads */ public synchronized void stop() { if (D) Log.d(TAG, "stop"); if (mConnectThread != null) { mConnectThread.cancel(); mConnectThread = null; } if (mConnectedThread != null) { mConnectedThread.cancel(); mConnectedThread = null; } if (mSecureAcceptThread != null) { mSecureAcceptThread.cancel(); mSecureAcceptThread = null; } if (mInsecureAcceptThread != null) { mInsecureAcceptThread.cancel(); mInsecureAcceptThread = null; } setState(STATE_NONE); } /** * Write to the ConnectedThread in an unsynchronized manner * @param out The bytes to write * @see ConnectedThread#write(byte[]) */ public void write(byte[] out) { // Create temporary object ConnectedThread r; // Synchronize a copy of the ConnectedThread synchronized (this) { if (mState != STATE_CONNECTED) return; r = mConnectedThread; } // Perform the write unsynchronized r.write(out); } /** * Indicate that the connection attempt failed and notify the UI Activity. */ private void connectionFailed() { // Send a failure message back to the Activity Message msg = mHandler.obtainMessage(BluetoothChat.MESSAGE_TOAST); Bundle bundle = new Bundle(); bundle.putString(BluetoothChat.TOAST, "Unable to connect device"); msg.setData(bundle); mHandler.sendMessage(msg); // Start the service over to restart listening mode BluetoothChatService.this.start(); } /** * Indicate that the connection was lost and notify the UI Activity. */ private void connectionLost() { // Send a failure message back to the Activity Message msg = mHandler.obtainMessage(BluetoothChat.MESSAGE_TOAST); Bundle bundle = new Bundle(); bundle.putString(BluetoothChat.TOAST, "Device connection was lost"); msg.setData(bundle); mHandler.sendMessage(msg); // Start the service over to restart listening mode BluetoothChatService.this.start(); } /** * This thread runs while listening for incoming connections. It behaves * like a server-side client. It runs until a connection is accepted * (or until cancelled). */ private class AcceptThread extends Thread { // The local server socket private final BluetoothServerSocket mmServerSocket; private String mSocketType; public AcceptThread(boolean secure) { BluetoothServerSocket tmp = null; mSocketType = secure ? "Secure":"Insecure"; // Create a new listening server socket try { if (secure) { tmp = mAdapter.listenUsingRfcommWithServiceRecord(NAME_SECURE, MY_UUID_SECURE); } else { tmp = mAdapter.listenUsingInsecureRfcommWithServiceRecord( NAME_INSECURE, MY_UUID_INSECURE); } } catch (IOException e) { Log.e(TAG, "Socket Type: " + mSocketType + "listen() failed", e); } mmServerSocket = tmp; } public void run() { if (D) Log.d(TAG, "Socket Type: " + mSocketType + "BEGIN mAcceptThread" + this); setName("AcceptThread" + mSocketType); BluetoothSocket socket = null; // Listen to the server socket if we're not connected while (mState != STATE_CONNECTED) { try { // This is a blocking call and will only return on a // successful connection or an exception socket = mmServerSocket.accept(); } catch (IOException e) { Log.e(TAG, "Socket Type: " + mSocketType + "accept() failed", e); break; } // If a connection was accepted if (socket != null) { synchronized (BluetoothChatService.this) { switch (mState) { case STATE_LISTEN: case STATE_CONNECTING: // Situation normal. Start the connected thread. connected(socket, socket.getRemoteDevice(), mSocketType); break; case STATE_NONE: case STATE_CONNECTED: // Either not ready or already connected. Terminate new socket. try { socket.close(); } catch (IOException e) { Log.e(TAG, "Could not close unwanted socket", e); } break; } } } } if (D) Log.i(TAG, "END mAcceptThread, socket Type: " + mSocketType); } public void cancel() { if (D) Log.d(TAG, "Socket Type" + mSocketType + "cancel " + this); try { mmServerSocket.close(); } catch (IOException e) { Log.e(TAG, "Socket Type" + mSocketType + "close() of server failed", e); } } } /** * This thread runs while attempting to make an outgoing connection * with a device. It runs straight through; the connection either * succeeds or fails. */ private class ConnectThread extends Thread { private final BluetoothSocket mmSocket; private final BluetoothDevice mmDevice; private String mSocketType; public ConnectThread(BluetoothDevice device, boolean secure) { mmDevice = device; BluetoothSocket tmp = null; mSocketType = secure ? "Secure" : "Insecure"; // Get a BluetoothSocket for a connection with the // given BluetoothDevice try { if (secure) { tmp = device.createRfcommSocketToServiceRecord( MY_UUID_SECURE); } else { tmp = device.createInsecureRfcommSocketToServiceRecord( MY_UUID_INSECURE); } } catch (IOException e) { Log.e(TAG, "Socket Type: " + mSocketType + "create() failed", e); } mmSocket = tmp; } public void run() { Log.i(TAG, "BEGIN mConnectThread SocketType:" + mSocketType); setName("ConnectThread" + mSocketType); // Always cancel discovery because it will slow down a connection mAdapter.cancelDiscovery(); // Make a connection to the BluetoothSocket try { // This is a blocking call and will only return on a // successful connection or an exception mmSocket.connect(); } catch (IOException e) { // Close the socket try { mmSocket 

Answer 1

The fact that the characters returned correctly probably indicates that the data rate is set correctly and the device sees the characters you need. It sounds, however, that the device still does not see the correctly completed query string (which ends with a carriage return).

I mention this because you noted the addition of "/ r", which is not the same as "\ r" (CR character). For example, in Java:

 OutputStream out; String correct = "ATRV\r"; //This line will correctly write 5 bytes (in hex): 41 54 52 56 0D out.write(correct.getBytes()); String incorrect = "ATRV/r"; //This line will incorrectly write 6 bytes (in hex): 41 54 52 56 2F 72 out.write(incorrect.getBytes()); 

The 0x0D symbol is what the ELM327 is looking to complete the AT command and parse it.

Edit:

If you manually enter the characters "atrv \ r" using your keyboard in the sample application, the same problem exists. The text is interpreted as 6 unique letters (ie "A", "T", "R", "V", "\" and "r" or hex 41 54 52 56 5C 72 ), and "\ r" is not interpreted as a single CR character.

You probably won’t be able to do this from your sample code unless you add special code to analyze combinations with "\" and replace them with special character values. A better solution would be to change the code sample so that you always add the character "\ r" (remember ... different from just adding "\" followed by "r") to everything you type when you press the submit button, so all you need to do is enter "ATRV" in the text box. Something like this in your OnEditorActionListener code (again, pay attention to the direction of the slash or just add two characters):

 public boolean onEditorAction(TextView view, int actionId, KeyEvent event) { // If the action is a key-up event on the return key, send the message if (actionId == EditorInfo.IME_NULL && event.getAction() == KeyEvent.ACTION_UP) { //This gets the raw text from the box String message = view.getText().toString(); //Append a CR to every message sent. The added string is defined as a literal, // so Java parses is as a single CR character. sendMessage(message + "\r"); } if(D) Log.i(TAG, "END onEditorAction"); return true; } 

You can also change your example by hard-coding a string command, as it was in the above example. Java interprets the string literal value "ATRV \ r" correctly by putting this CR character at the end (making it a 5-character string).