Android BLE Characteristic setValue Unable To Write Correct Data

Question

I am trying to develop an Android App that connects to my NRF51822 based system using BLE. The aim is to write a 3 byte value (RGB) to a my custom characteristic.

Android is the GATT client and NRF51 based device is GATT server.

I am able to establish the ble connection and discover my characteristic successfully.

However the data sending part (setValue) is giving me troubles. No matter what 3 bytes I write, I get the same constant data on the NRF51 side

Below is my rellevant code (Android)

 @Override
 public void onServicesDiscovered(BluetoothGatt gatt, int status) {
       Log.d("BLENotifier", "BLE GAT : SERVICES DISCOVERED");
       for(BluetoothGattService gs: gatt.getServices()) {
           Log.d("BLENotifier", "SERVICE = " + gs.getUuid().toString());
       }
       //SELECT MY CHARACTERSTIC
       ble_my_characterstic = gatt.getService(ble_service_uuid).getCharacteristic(ble_characterstic_uuid);
       Log.d("BLENotifier", "BLE SELECTED CHARACTERSTIC " + ble_my_characterstic.getUuid().toString());
       ble_connected = true;
    }

public void writedata(String data){
    //WRITE DATA TO MY CHARACTERSTIC
    if(ble_my_characterstic != null && ble_connected == true){

        my_gatt_handle.executeReliableWrite();
        //ble_my_characterstic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE);
        ble_my_characterstic.setValue(hexStringToByteArray(data));
        my_gatt_handle.writeCharacteristic(ble_my_characterstic);

        Log.d("BLENotifier", "BLE WRITE DATA " + data);
    }

public static byte[] hexStringToByteArray(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                + Character.digit(s.charAt(i+1), 16));
    }
    Log.d("BLENotifier", "hexStringToByteArray " + Integer.toString((int)data[0]) + " " + Integer.toString((int)data[1]) + " " + Integer.toString((int)data[2]));
    return data;
}

I am invoking the writeData method as ble_handle.writedata("0000FF")

This is what I get on the NRF51 side

R = 4 | G = 239 | B= 1

Thanks

Answer 1

I did like this.Not exact answer but may help you.

    @Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) 
    {
        List<BluetoothGattService> services = gatt.getServices();
        Log.i("onServicesDiscovered", services.toString());
        keepConnect=services.get(3).getCharacteristics().get(0);
        if(keepConnect!=null){
            writeCharacteristic(gatt,keepConnect);
        }
    }

    private void writeCharacteristic(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic)
    {

        byte[] byteData = hexToBytes("6fd362e40ebcd0945bf58dc4");
        byte[] writeData = new byte[byteData.length];
        for (int i = 0; i < byteData.length; i++) {
            writeData[i] = byteData[i];
        }
        characteristic.setValue(writeData);
        gatt.writeCharacteristic(characteristic);       

    }

public static byte[] hexToBytes(String hexRepresentation) {
    int len = hexRepresentation.length();
    byte[] data = new byte[len / 2];

    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(hexRepresentation.charAt(i), 16) << 4)
                + Character.digit(hexRepresentation.charAt(i + 1), 16));
    }

    return data;
}