Vfrdtyky

I want to create android app, which can connect with bluetooth low energy module and can receive data. In my system microcontroller stm32f1 send data of measurements over UART to the BT LE module.

My question is how to start? I read a lot about GATT and UART Service, but still don't know how to start. Give me some information please.

You need:

• UUIDs of your Service, Characteristic and Descriptor;




• Permissions' Bluetooth Low Energy

The program must:

1. Scan BLE devices


2. Connect a device


3. Set callbacks' BLE

AndroidManifest.xml

<uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>

<uses-permission android:name="android.permission.BLUETOOTH"/>

<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>

<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

Activity.java

// Bluetooth's variables

    BluetoothAdapter bluetoothAdapter;

    BluetoothLeScanner bluetoothLeScanner;

    BluetoothManager bluetoothManager;

    BluetoothScanCallback bluetoothScanCallback;

    BluetoothGatt gattClient;



    BluetoothGattCharacteristic characteristicID; // To get Value



// UUID's (set yours)

final UUID SERVICE_UUID = UUID.fromString("ab0828b1-198e-4351-b779-901fa0e0371e");

final UUID CHARACTERISTIC_UUID_ID = UUID.fromString("1a220d0a-6b06-4767-8692-243153d94d85");

final UUID DESCRIPTOR_UUID_ID = UUID.fromString("ec6e1003-884b-4a1c-850f-1cfce9cf6567");



@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);



    // Bluetooth

    bluetoothManager = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE);

    bluetoothAdapter = bluetoothManager.getAdapter();

    startScan();

}



 // BLUETOOTH SCAN



private void startScan(){

    Log.i(TAG,"startScan()");

    bluetoothScanCallback = new BluetoothScanCallback();

    bluetoothLeScanner = bluetoothAdapter.getBluetoothLeScanner();

    bluetoothLeScanner.startScan(bluetoothScanCallback);

}



// BLUETOOTH CONNECTION

private void connectDevice(BluetoothDevice device) {

    if (device == null) Log.i(TAG,"Device is null");

    GattClientCallback gattClientCallback = new GattClientCallback();

    gattClient = device.connectGatt(this,false,gattClientCallback);

}



// BLE Scan Callbacks

private class BluetoothScanCallback extends ScanCallback {



    @Override

    public void onScanResult(int callbackType, ScanResult result) {

        Log.i(TAG, "onScanResult");

        if (result.getDevice().getName() != null){

            if (result.getDevice().getName().equals(YOUR_DEVICE_NAME)) {

                // When find your device, connect.

                connectDevice(result.getDevice());

                bluetoothLeScanner.stopScan(bluetoothScanCallback); // stop scan

            }

        }

    }



    @Override

    public void onBatchScanResults(List<ScanResult> results) {

        Log.i(TAG, "onBathScanResults");

    }



    @Override

    public void onScanFailed(int errorCode) {

        Log.i(TAG, "ErrorCode: " + errorCode);

    }            

}



// Bluetooth GATT Client Callback

private class GattClientCallback extends BluetoothGattCallback {

    @Override

    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {

        super.onConnectionStateChange(gatt, status, newState);

        Log.i(TAG,"onConnectionStateChange");



        if (status == BluetoothGatt.GATT_FAILURE) {

            Log.i(TAG, "onConnectionStateChange GATT FAILURE");

            return;

        } else if (status != BluetoothGatt.GATT_SUCCESS) {

            Log.i(TAG, "onConnectionStateChange != GATT_SUCCESS");

            return;

        }



        if (newState == BluetoothProfile.STATE_CONNECTED) {

            Log.i(TAG, "onConnectionStateChange CONNECTED");

            gatt.discoverServices();

        } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {

            Log.i(TAG, "onConnectionStateChange DISCONNECTED");

        }

    }



    @Override

    public void onServicesDiscovered(BluetoothGatt gatt, int status) {

        super.onServicesDiscovered(gatt, status);

        Log.i(TAG,"onServicesDiscovered");

        if (status != BluetoothGatt.GATT_SUCCESS) return;



        // Reference your UUIDs

        characteristicID = gatt.getService(SERVICE_UUID).getCharacteristic(CHARACTERISTIC_UUID_ID);

        gatt.setCharacteristicNotification(characteristicID,true);



        BluetoothGattDescriptor descriptor = characteristicID.getDescriptor(DESCRIPTOR_UUID_ID);

        descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);

        gatt.writeDescriptor(descriptor);

    }



    @Override

    public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {

        super.onCharacteristicRead(gatt, characteristic, status);

        Log.i(TAG,"onCharacteristicRead");

    }



    @Override

    public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {

        super.onCharacteristicWrite(gatt, characteristic, status);

        Log.i(TAG,"onCharacteristicWrite");

    }



    @Override

    public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {

        super.onCharacteristicChanged(gatt, characteristic);

        Log.i(TAG,"onCharacteristicChanged");

        // Here you can read the characteristc's value

        // new String(characteristic.getValue();

    }



    @Override

    public void onDescriptorRead(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {

        super.onDescriptorRead(gatt, descriptor, status);

        Log.i(TAG,"onDescriptorRead");

    }



    @Override

    public void onDescriptorWrite(BluetoothGatt gatt, BluetoothGattDescriptor descriptor, int status) {

        super.onDescriptorWrite(gatt, descriptor, status);

        Log.i(TAG,"onDescriptorWrite");

    }

}

Libs:

import android.bluetooth.BluetoothAdapter;

import android.bluetooth.BluetoothDevice;

import android.bluetooth.BluetoothGatt;

import android.bluetooth.BluetoothGattCallback;

import android.bluetooth.BluetoothGattCharacteristic;

import android.bluetooth.BluetoothGattDescriptor;

import android.bluetooth.BluetoothManager;

import android.bluetooth.BluetoothProfile;

import android.bluetooth.le.BluetoothLeScanner;

import android.bluetooth.le.ScanCallback;

import android.bluetooth.le.ScanResult;

Notes:

• The UUIDs must be same seted on the module.


• In your program you must have two callbacks: ScanCallback and GattCallback. Scan callback is to manage the scan results and the GattCallback you can manage the data input/output.


• This code the basic to show how use BLE on Android, works fine for me.


• You can generate UUID here: https://www.uuidgenerator.net/