Data transfer between HC-05 and Android

HC-05 bluetooth module is the most common BT module for Andruino. Chances are that if you’re working on sending or receiving data via bluetooth with Arduino you’ll be using the HC-05 module.

Now, there are loads of articles and tutorials directing how to make an app which will connect to the module and send/ receive data hence I won’t be rewriting that. What this post is about how I overcame a problem with respect to data transfer between HC-05 and Android app with a simple fix.

Problem - Data being accepted getting jumbled up to the point where the data made no sense. Example, the module emits data like this - 0,501,486,995; But the android device receives the data like this - ,496,482,995;0,503,488,995;0,501,486,995;0,496,480,996;0,502,486,995;0, or 996;,474,.

The code to accept data is usually similar to this -

private void getDataFromDevice() {

	byte[] buffer = new byte[256];  // buffer store for the stream
	int bytes; // bytes returned from read()
	int length;
		try {

    		InputStream tmpIn = null;
    		OutputStream tmpOut = null;

    		// Get the BluetoothSocket input and output streams
    		tmpIn = bTSocket.getInputStream();
    		tmpOut = bTSocket.getOutputStream();

    		DataInputStream mmInStream = new DataInputStream(tmpIn);
    		DataOutputStream mmOutStream = new DataOutputStream(tmpOut);

    		// Read from the InputStream
    		while(true) {

        		bytes = mmInStream.read(buffer);
        		length = mmInStream.read(buffer);

        		String readMessage = new String(buffer, 0, bytes);
        		// Send the obtained bytes to the UI Activity

        		Log.i("DATA---", readMessage);
    		}

		} catch (IOException ex) {
    		ex.printStackTrace();
    		cancel();
	}
}

The variable buffer instructs how many bytes to read from the stream at a time. This is what the source of problem was in my case; reducing it to a single byte did the trick for me. Hence, byte[] buffer = new byte[1]; fixed the sequence of the input stream.