CODEWITHSUNDEEP
androidbluetoothbluetooth-lowenergy
justin018
justin018

Reputation: 117

Understanding Characteristics in Bluetooth Low Energy for Android

I am trying to simply read and Write Hello World from an galaxy S3 to a blueradio dongle which is connected to a virtual serial port. but I am getting 

Unhandled exception: java.lang.NullPointerException

when ever i call 

gatt.readCharacteristic(characteristic);

I use this to define the characteristic

private static final UUID MY_UUID = UUID.fromString("00001801-0000-1000-8000-00805f9b34fb");
private static final UUID charUUID = UUID.fromString("00002a01-0000-1000-8000-00805f9b34fb");
characteristic = gatt.getService(MY_UUID).getCharacteristic(charUUID);

The UUID I took from the LogCat when i called discoverServices() as so

D/BluetoothGatt(7083): discoverServices() - device: EC:FE:7E:11:12:A4
D/BluetoothGatt(7083): onGetService() - Device=EC:FE:7E:11:12:A4 UUID=00001800-0000-1000-8000-00805f9b34fb
D/BluetoothGatt(7083): onGetService() - Device=EC:FE:7E:11:12:A4 UUID=00001801-0000-1000-8000-00805f9b34fb
D/BluetoothGatt(7083): onGetService() - Device=EC:FE:7E:11:12:A4 UUID=0000180f-0000-1000-8000-00805f9b34fb
D/BluetoothGatt(7083): onGetService() - Device=EC:FE:7E:11:12:A4 UUID=da2b84f1-6279-48de-bdc0-afbea0226079
D/BluetoothGatt(7083): onGetCharacteristic() - Device=EC:FE:7E:11:12:A4 UUID=00002a00-0000-1000-8000-00805f9b34fb
D/BluetoothGatt(7083): onGetCharacteristic() - Device=EC:FE:7E:11:12:A4 UUID=00002a01-0000-1000-8000-00805f9b34fb
D/BluetoothGatt(7083): onGetCharacteristic() - Device=EC:FE:7E:11:12:A4 UUID=00002a02-0000-1000-8000-00805f9b34fb
D/BluetoothGatt(7083): onGetCharacteristic() - Device=EC:FE:7E:11:12:A4 UUID=00002a03-0000-1000-8000-00805f9b34fb

This is where Im not sure if I am doing i correctly I dont know how to get the proper UUID for a characteristic and service

Beloiw is my full Callback function

private BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {

    public void testFunction(BluetoothGatt gatt){
        Log.d(TAG, "In Test Function");
        gatt.readRemoteRssi();
        BluetoothGattCharacteristic characteristic;
        characteristic = gatt.getService(MY_UUID).getCharacteristic(charUUID);
        characteristic.setValue("Hello World");
        gatt.readCharacteristic(characteristic);
    }
     @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status,
            int newState) {


            gatt.discoverServices();


    }


@Override
public void onServicesDiscovered(BluetoothGatt gatt, int status) {
    Log.d(TAG, "Services Discovered: "+ status);
    //mHandler.sendMessage(Message.obtain(null, MSG_PROGRESS, "Enabling Sensors..."));
    /*
     * With services discovered, we are going to reset our state machine and start
     * working through the sensors we need to enable
     */
            testFunction(gatt);
}


public void     onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic){
    Log.d(TAG, "Characteristic Changed: "+ characteristic.getValue());
}

public void     onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status){
    Log.d(TAG, "Characteristic Read: "+ status);
}

public void     onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status){
    Log.d(TAG, "Characteristic Write: "+ status);
}



public void     onDescriptorRead(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status){
    Log.d(TAG, "Descriptor Read: "+ status);
}

public void     onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status){
    Log.d(TAG, "Descriptor Write: "+ status);
}

public void     onReadRemoteRssi(BluetoothGatt gatt, int rssi, int status){
    Log.d(TAG, "Read Rssi: "+ status);
}

public void     onReliableWriteCompleted(BluetoothGatt gatt, int status){
    Log.d(TAG, "Reliable Write: "+ status);
}


};

Upvotes: 3

Views: 20340

Answers (2)

jp_eagle
jp_eagle

Reputation: 148

UUID is predefined by bluetooth.org, it defines the prefix, e.g. 00001800, the last part "0000-1000-8000-00805f9b34fb" are same for all.

see the list of predefined UUID here.

Upvotes: 5

John Samathanam
John Samathanam

Reputation: 1

I'm trying to to the same thing with the Blueradio USB dongle. I found the following info on BlueRadio Android example project. May be this info might be useful to you

UUID for BRSP SERVICE

DA2B84F1627948DEBDC0AFBEA0226079

Characteristic UUID for BRSP

99564A02DC014D3CB04E3BB1EF0571B2  --> Info

A87988B9694C479C900E95DFA6C00A24  --> Mode

BF03260C72054C25AF4393B1C299D159  --> RX

18CDA7844BD3437085BBBFED91EC86AF  --> TX(Data sent to Client PC/ANDROID from BLE)

0A1934F524B84F13984237BB167C6AFF  --> CTS

FDD6B4D3046D4330BDEC1FD0C90CB43B --> RTS

If you find out more info please share.

Thanks John

Upvotes: 0

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