CODEWITHSUNDEEP
androidarduinobluetooth-lowenergy
NextGenHen
NextGenHen

Reputation: 141

Problems when sending a continuous stream of data over BLE

I'm wondering if anybody can help me figure out what is causing the data I am sending to become corrupt.

My setup is currently an Arduino pro mini with a HM-10 bluetooth module connected (I have also tried HM-11 Module too) and an Android application to receive the bluetooth data.

Module setup: http://letsmakerobots.com/node/38009

If I send data with big enough intervals then the data is fine, but if I send the data continuously I see messages getting mixed up and lost. To test this I send "$0.1,0.2,0.3,0.4,0.5" to the Android application from the Arduino, sometimes the stream of data appears to send fine but other times it is really quite scrambled. Please see the below graphs that demonstrate this:

Good case:

enter image description here

Bad case:

enter image description here

Arduino code:

String inputString = ""; //Hold the incoming data.
boolean stringComplete = false; //Determines if the string is complete.
boolean realtime = false;

void setup()
{
  Serial.begin(9600);
  delay(500);
  Serial.print("AT+START");
  delay(500);
}

void loop()
{
  if(stringComplete)
  {
    if(inputString.equals("rStart"))
    {
      Serial.println("$startACK");
      realtime = true;
   }
    else if(inputString.equals("stop"))
    {
      Serial.println("$stopACK");
      realtime = false;
    }
    else{
      Serial.print(inputString);
    }

    inputString = "";
    stringComplete = false;
  }


  if(realtime)
  {
    Serial.println("$0.1,0.2,0.3,0.4,0.5,0.6");
   delay(10); 
  }
}

void serialEvent() {
  while (Serial.available())
  {
    // get the new byte:
    char inChar = (char)Serial.read(); 

    if (inChar == '\n')
    {
      stringComplete = true;
    }
    else
    {
      inputString += inChar;
    }
  }
}

The Android side just receives the data and then parses it in an IntentService:

@Override
protected void onHandleIntent(Intent intent) {
    //Incoming command.
    String rawData =  intent.getStringExtra(DataProcessingIntentService.REQUEST);

    //Append our new data to our data helper.
    Log.i(this.getClass().getName(), "Previous Raw: (" + DataProcessingHelper.getInstance().getData() + ")");
    DataProcessingHelper.getInstance().appendData(rawData);
    Log.i(this.getClass().getName(), "New Raw: (" + DataProcessingHelper.getInstance().getData() + ")");

    commandStartIndex = DataProcessingHelper.getInstance().getData().indexOf("$");
    commandEndIndex = DataProcessingHelper.getInstance().getData().indexOf("\n");

    //Set this as the data starting point.
    if(commandStartIndex != -1){
        DataProcessingHelper.getInstance().offsetData(commandStartIndex);
    }

    //Ensure that a command has been found and that the end index is after the starting index.
    if(commandStartIndex != -1 && commandEndIndex > commandStartIndex){
        //Remove the command structure from the command.
        command = DataProcessingHelper.getInstance().getData().substring(commandStartIndex+1, commandEndIndex-1); //Remove the \r\n end command.
        DataProcessingHelper.getInstance().offsetData(commandEndIndex+1);

        if(command.length() > 1){
            //Split the data out of the comand.
            splitData = command.split(","); 

            Log.i(this.getClass().getName(), "Broadcasting the processed data. (" + command + ")");
            //Broadcast data.
            Intent broadcastIntent = new Intent();
            broadcastIntent.setAction(DataProcessingIntentService.RESPONSE);
            broadcastIntent.addCategory(Intent.CATEGORY_DEFAULT);
            broadcastIntent.putExtra(DataProcessingIntentService.RESPONSE, splitData);
            sendBroadcast(broadcastIntent);
        }else{
            Log.e(this.getClass().getName(), "Command is less than 1 character long!");
        }
    }           
}

Thank you for any help!

Upvotes: 1

Views: 4654

Answers (1)

NextGenHen
NextGenHen

Reputation: 141

I have now figured out what was causing this problem. It appears that BLE only supports a maximum of 20 bytes per a transaction. The time between these transactions is different depending on what you are using. I'm currently using notifications which means that I can send 20 bytes every 7.5 milliseconds maximum. I have opted for 10 milliseconds to be safe. I will now need to look into breaking up packets into 20 bytes maximum to ensure no data corruption.

Upvotes: 5

Related Questions