Netduino and Bluetooth

Best Answer enough, 07 July 2013 - 09:54 AM

For anyone else interested in the Seeedstudio Bluetooth Shield:

You need to configure the shield first to make it discoverable to other Bluetooth devices. This shield is also very chatty, it confirms every configuration and let's you know when a connection is made, lost, etc. Sounds good in theory but it means that you need to parse received data to strip out the chatter from the shield.

Here's the relevant bit of the configuration code:

// initialize the serial port for COM2 (using D2 & D3)_serial = new SerialPort(SerialPorts.COM2, 38400, Parity.None, 8, StopBits.One);// open the serial-port, so we can send & receive data_serial.Open();// add an event-handler for handling incoming data_serial.DataReceived += new SerialDataReceivedEventHandler(serial_DataReceived);// configure seeedstudio:write("rn+STWMOD=0rn", _serial); //set the bluetooth work in slave modewrite("rn+STNA=SeeedBTSlavern", _serial); //set the bluetooth name as "SeeedBTSlave"write("rn+STOAUT=1rn", _serial); // Permit Paired device to connect mewrite("rn+STAUTO=0rn", _serial); // Auto-connection should be forbidden hereThread.Sleep(2000); // This delay is required.write("rn+INQ=1rn", _serial); //make the slave bluetooth inquirable

Here's the write method:

private static void write(string command, SerialPort serial){    byte[] buffer = System.Text.Encoding.UTF8.GetBytes(command);    serial.Write(buffer, 0, buffer.Length);}

To strip out the data send by the shield (like "+BTSTATE:4", "CONNECT:OK", etc) I first try to load the data completely - I am not sure, if this works in all circumstances, though. I just read the data until nothing more is available. Then I'm discarding all lines but the last one (this assumes that no line breaks are send) and do a sanity check on that line. You might want to add some magic value or so in the data send to the shield to make this one easier.

static void serial_DataReceived(object sender, SerialDataReceivedEventArgs e){    byte[] bytes = null;    int destinationIndex = 0;    int read = 0;    while (_serial.BytesToRead > 0)    {        int expected = _serial.BytesToRead;        byte[] data = new byte[expected];        int currentRead = _serial.Read(data, 0, expected);        read += currentRead;        if (bytes == null)        {            bytes = data;            destinationIndex = read;        }        else        {            byte[] intermediate = new byte[read];            System.Array.Copy(bytes, intermediate, read - currentRead);            System.Array.Copy(data, 0, intermediate, destinationIndex, currentRead);            bytes = intermediate;            destinationIndex += currentRead;        }    }    if (!_isInitialized)    {        // just chatter from the shield        return;    }    char[] chars = new char[read];    for (int i = 0; i < read; i++)    {        char c = (char)bytes[i];        chars[i] = c;    }    string result = new string(chars);    string[] lines = result.Split('r', 'n');    string receivedData = lines[lines.Length - 1];    if (receivedData.Length > 1)    {        if ((receivedData[0] == '+') || "CONNECT:OK".Equals(receivedData))        {            // that's just chatter from the shield like +BTSTATE:4            return;        }        processReceivedData(receivedData);    }}

The shield is documented quite poorly in my opinion, I haven't found a list of configuration options, for example.

Here's the complete Program.cs - have fun hacking!

Robert

using System;using System.Net;using System.Net.Sockets;using System.Threading;using Microsoft.SPOT;using Microsoft.SPOT.Hardware;using SecretLabs.NETMF.Hardware;using SecretLabs.NETMF.Hardware.Netduino;using System.IO.Ports;using System.Text;namespace robert_netduino_seeedstudio_bluetooth{    public class Program    {        private static SerialPort _serial;        private static bool _isInitialized;        public static void Main()        {            Thread.Sleep(2000); // not sure if this delay is required.            // initialize the serial port for COM2 (using D2 & D3)            _serial = new SerialPort(SerialPorts.COM2, 38400, Parity.None, 8, StopBits.One);            // open the serial-port, so we can send & receive data            _serial.Open();            // add an event-handler for handling incoming data            _serial.DataReceived += new SerialDataReceivedEventHandler(serial_DataReceived);            // configure seeedstudio:            write("rn+STWMOD=0rn", _serial); //set the bluetooth work in slave mode            write("rn+STNA=SeeedBTSlavern", _serial); //set the bluetooth name as "SeeedBTSlave"            write("rn+STOAUT=1rn", _serial); // Permit Paired device to connect me            write("rn+STAUTO=0rn", _serial); // Auto-connection should be forbidden here            Thread.Sleep(2000); // This delay is required.            write("rn+INQ=1rn", _serial); //make the slave bluetooth inquirable            Thread.Sleep(2000); // not sure if this delay is required.            _isInitialized = true;            // wait forever...            Thread.Sleep(Timeout.Infinite);        }        private static void write(string command, SerialPort serial, bool addLength = false)        {            byte[] buffer = System.Text.Encoding.UTF8.GetBytes(command);            if (addLength)            {                int length = buffer.Length;                serial.WriteByte((byte)(length >> 24));                serial.WriteByte((byte)((length >> 16) & 0x00ff));                serial.WriteByte((byte)((length >> 8) & 0x0000ff));                serial.WriteByte((byte)((length & 0x000000ff)));            }            serial.Write(buffer, 0, buffer.Length);        }        static void serial_DataReceived(object sender, SerialDataReceivedEventArgs e)        {            byte[] bytes = null;            int destinationIndex = 0;            int read = 0;            while (_serial.BytesToRead > 0)            {                int expected = _serial.BytesToRead;                byte[] data = new byte[expected];                int currentRead = _serial.Read(data, 0, expected);                read += currentRead;                if (bytes == null)                {                    bytes = data;                    destinationIndex = read;                }                else                {                    byte[] intermediate = new byte[read];                    System.Array.Copy(bytes, intermediate, read - currentRead);                    System.Array.Copy(data, 0, intermediate, destinationIndex, currentRead);                    bytes = intermediate;                    destinationIndex += currentRead;                }            }            if (!_isInitialized)            {                // just chatter from the shield                return;            }            char[] chars = new char[read];            for (int i = 0; i < read; i++)            {                char c = (char)bytes[i];                chars[i] = c;            }            string result = new string(chars);            string[] lines = result.Split('r', 'n');            string receivedData = lines[lines.Length - 1];            if (receivedData.Length > 1)            {                if ((receivedData[0] == '+') || "CONNECT:OK".Equals(receivedData))                {                    // that's just chatter from the shield like +BTSTATE:4                    return;                }                processReceivedData(receivedData);            }        }        private static void processReceivedData(string receivedData)        {            // okay, we have real data. Just send a confirmation back:             // an int32 that describes the length of our feedback and then the received data plus something            string responseStr = receivedData + " from netduino";            write(responseStr, _serial, addLength: true);        }    }}

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