Use Bluetooth between Win 10 UWP and Arduino

This is part 3 of a series of blogs about device communication between Arduino, RaspberryPi etc:

• Part 1: Using I2C to connect two Arduino Nano’s
• Part 2: Using I2C between Rpi Master and Arduino Slave
• Part 3: Use Bluetooth between Win 10 UWP and Arduino
• Part 4: Add virtual Arduino ports to your UWP app
• Part 5: Custom Firmata function called by Windows 10 IoT Core
• Part 6: Better long running custom Firmata functions
• Part 7: Custom servo usage in Firmata
• Part 8: Using NRF24L01+ modules between Arduino’s
• Part 9: Cheap Arduino mesh using RF24 radio modules

In previous blogs, I have written about combining one or more Arduino Nano’s with a RaspberryPi using the I2C protocol. Although this is very useful, the communication is limited to the length of the cables. This is not very practical for a local gateway.

So I looked at communication using Bluetooth. So I bought some Bluetooth modules. These little components are relatively cheap and reliable. They come with four and six pins (for now, it has just two extra pins not needed, the inner four are the same with the four pins version) but the four pin variant is used in this example.

 

Note: Ignore the ‘module base plates’ for only 30 cents. These do not contain the actual Bluetooth logic. In fact: it’s just the base plate, hence the price difference 🙂

Wiring the Bluetooth module is very simple. In this diagram is shown how I wired power, ground, RX and TX.

Do you see how RX and TX are crossed?

In some examples, the Bluetooth RX and TW are attached to port 0 and 1. I use port 4 and 3 because 0 and 1 are traditionally used for uploading the code to the Arduino using the USB cable. Now the upload is not interfered.

So upload the code:

#include <SoftwareSerial.h>
int ledPin = 13;

/* This sample code demonstrates the normal use of reading Bluetooth serial port.
It requires the use of SoftwareSerial, and assumes that you have the 9600-baud Bluetooth serial device hooked up on pins 4(rx) and 3(tx).
This way, port 0 and 1 stay clear for uploading and serial monitor.
*/

SoftwareSerial ss(4, 3);

void setup() {
  // Force the Bluetooth module to communicate 9600 baud on Serial
  ss.begin(9600);
  ss.print("$");
  ss.print("$");
  ss.print("$");
  delay(100);
  ss.println("SU,96");
  delay(100);
  ss.println("---");
  ss.begin(9600);

  // 9600 is the default baud rate for the screen module
  Serial.begin( 9600 );
  Serial.print("Start... ");
}

void loop() {
  // listen for serial data
  if ( ss.available() > 0 ) {
    // read a numbers from serial port
    int count = ss.parseInt();// print out the received number
    if (count > 0) {
      Serial.print("You have input: ");
      Serial.println(String(count));

      // blink the LED
      blinkLED(count);
    }
    else {
      Serial.print("nope");
    }
  }
}

void blinkLED(int count) {
  for (int i=0; i < count; i++) {
    digitalWrite(ledPin, HIGH);
    delay(500);
    digitalWrite(ledPin, LOW);
    delay(500);
  }
}

So I use the SoftwareSerial library to communicate over port 4 and 3. And during the setup phase, I send some information to the Bluetooth module so it will communicate at 9600 baud.

And every time a character is received by the Bluetooth module, it is turned into an integer. This is shown on the serial monitor of the Arduino IDE but, more important, Led13 will blink so many times.

Here I attach the Bluetooth to a power bank (once the code is uploaded), just to proof that it works: without wires!?!

The Arduino Nano is now ready for use.

Let’s go to the RaspberryPi. Attach a Bluetooth dongle to it. Although it seems still a limited amount of types are supported, just try the ones you have already. I had some luck, a cheap dongle I already had is supported.

And use the newest version of the Windows 10 IoT Core because it makes your life very easy when you want to pair to a Bluetooth module. How do you get the new image? Use the new Windows 10 IoT Core Dashboard.  You can find it here.

After you have flashed the newest image and rebooted your pi, find it in the My Devices list. Select it and open the web interface (a tiny web server is running on your Rpi). Log into your Rpi (do you know the default username-password?) and go to the Bluetooth page.

Observation: Woo hoo, now we have a Windows Update feature!

When your Bluetooth dongle is recognised and your Bluetooth module is powered up, try to find it in the list of available devices. Do you see something like HC-5 or HC-6?

Try to pair with them. I have two modules and paired to both of them. I found out that ‘1234’ is the pass key for both of them.

So now your Pi can talk over Bluetooth! But wait, we have to connect first.

Note: because we are going to work with a UWP app, try to avoid as long as possible to debug on the Rpi. Why? Simply, speed up your development. It’s just too slow to debug your code in progress!  If you pair the module also to a Windows Phone 10 or just to your own development desktop or laptop or Surface (lucky ****** 😉 ) use those devices. It works just the same!

Start a new empty UWP template. First of all, add Bluetooth to the list of capabilities your app needs to run on.

Go to the XAML page and add these controls to the grid (in a vertical stack panel):

<StackPanel>
  <Button Name="btnConnect" 
          Content="Connect" 
          Click="btnConnect_Click" 
          FontSize="40" />
  <Button Name="btnDisconnect" 
          Content="Disconnect" 
          Click="btnDisconnect_Click" 
          FontSize="40" />
  <TextBox Name="tbInput" 
           Text="2" 
           FontSize="40" />
  <Button Name="btnSend" 
          Content="Send" 
          Click="btnSend_Click" 
          FontSize="40" />
  <TextBlock Name="tbError" 
             FontSize="40" />
</StackPanel>

Now we have buttons to connect and disconnect and we can send an integer.

The code behind is:

public sealed partial class MainPage : Page
{
  private StreamSocket _socket;

  private RfcommDeviceService _service;
  public MainPage()
  {
    this.InitializeComponent();
  }

  private async void btnSend_Click(object sender,
                                   RoutedEventArgs e)
  {
    int dummy;

    if (!int.TryParse(tbInput.Text, out dummy))
    {
      tbError.Text = "Invalid input";
    }

    var noOfCharsSent = await Send(tbInput.Text);

    if (noOfCharsSent != 0)
    {
      tbError.Text = noOfCharsSent.ToString();
    }
  }
  private async Task<uint> Send(string msg)
  {
    tbError.Text = string.Empty;

    try
    {
      var writer = new DataWriter(_socket.OutputStream);

      writer.WriteString(msg);

      // Launch an async task to 
      //complete the write operation
      var store = writer.StoreAsync().AsTask();

      return await store;
    }
    catch (Exception ex)
    {
      tbError.Text = ex.Message;

      return 0;
    }
  }

  private async void btnConnect_Click(object sender, 
                                      RoutedEventArgs e)
  {
    tbError.Text = string.Empty;

    try
    {
      var devices = 
            await DeviceInformation.FindAllAsync(
              RfcommDeviceService.GetDeviceSelector(
                RfcommServiceId.SerialPort));

      var device = devices.Single(x => x.Name == "HC-05");

      _service = await RfcommDeviceService.FromIdAsync(
                                              device.Id);

      _socket = new StreamSocket();

      await _socket.ConnectAsync(
            _service.ConnectionHostName, 
            _service.ConnectionServiceName, 
            SocketProtectionLevel.
            BluetoothEncryptionAllowNullAuthentication);
    }
    catch (Exception ex)
    {
      tbError.Text = ex.Message;
    }
  }

  private async void btnDisconnect_Click(object sender, 
                                       RoutedEventArgs e)
  {
    tbError.Text = string.Empty;

    try
    {
      await _socket.CancelIOAsync();
      _socket.Dispose();
      _socket = null;
      _service.Dispose();
      _service = null;
    }
    catch (Exception ex)
    {
      tbError.Text = ex.Message;
    }
  }
}

Look at the code. Maybe you will have to make a simple adjustment: I have hard coded “HC-5” because that is the name of the module that I just used. Check the name of your module. An exception will be thrown when the name does not exist.

Run the code. Try to connect.

Note: if you use the UWP app on your PC and connect for the first time, you will get this consent screen. You have to say Yes:

If the connection is established, you will observe that the rhythm of the blinking led on the Bluetooth module (not led 13!) will change in modulation (it will slow down).

Now try to send the character 2 (and later on 3, 4 and 5):

Tadaah, is Led 13 blinking twice? And is the serial monitor showing:

Then you have succeeded!

Now it’s time to deploy your app to your Rpi. I worked on my machine. I also deployed the same app to my Windows Phone. It just works:

Every time I deploy to both laptop, RaspberryPi and a Windows Phone I am surprised again that the same code is working on these different devices. It’s great to develop UWP apps!

This code is the most simple example to show you how to communicate using Bluetooth. After this, try to receive a value from the module or make the pairing/connection process more robust.