Develop Reference

How to detect when a BLE device is not in range anymore?

I use a LeScanCallback (can not use the newer scan methods because I'm developing for api 18. Not that it matters, since the android 5.0+ apis don't offer this functionality either) to detect when a nearby BLE device is detected:
private BluetoothAdapter.LeScanCallback bleCallback = new BluetoothAdapter.LeScanCallback() {
#Override
public void onLeScan(BluetoothDevice bluetoothDevice, int i, byte[] bytes) {
discoveredDevices.add(bluetoothDevice);
}
};
I am not pairing or connecting with the devices because that's not required, I simply want to see which devices are nearby.
I'm trying to make a service that, every 5 mins or so, calls a webserver to update which devices are nearby at that moment.
Tricky part is that the android device will be moving, so a bluetooth device that is nearby right now, might not be in 5 mins. In that case I need to remove it from discoveredDevices.
Ideally, I would like to receive a callback when a bluetooth device was in range before, but is not anymore. This callback doesn't exist though.
(I'm aware of the android.bluetooth.device.action.ACL_CONNECTED and android.bluetooth.device.action.ACL_DISCONNECTED broadcasts, but those are for when you connect to a bluetooth device, which I don't want.)
An option is to do a fresh scan every 5 mins, but you can't tell when all nearby devices have been discovered, so you would have to do a timed scan, e.g. scan for 5 seconds and then send the collected data to the webservice.
This sounds dirty and risky because you can never know for sure all nearby devices were discovered within the allotted time, so I would very much like to avoid doing it like that.
Is there another way to do this?
Edit
Some devices continuously report discovery of nearby bluetooth devices, even if they were already discovered before. If that functionality was universal I could solve my problem, however this is device specific.
My phone's bluetooth adapter for example only discovers nearby devices once. Some other devices I have tested with do continuously report the same nearby devices, but not all devices do, so I can't rely on that unfortunately.

This sounds dirty and risky because you can never know for sure all nearby devices were discovered within the allotted time, so I would very much like to avoid doing it like that.
That sounds like a reasonable assumption, but it's wrong.
Bluetooth low energy works in a particular way and BLE devices have some limits. For instance, they have a fixed range of possible advertising frequencies, ranging from 20 milliseconds to 10.24 seconds, in steps of 0.625 milliseconds. See here and here for more detailed information.
This means that it can take at most 10.24 seconds before a device will broadcast a new advertisement package. BLE devices generally, if not always, provide a way for their owner to adjust their advertising frequency, so the frequency can of course vary.
In cases where you are periodically collecting data about nearby devices, like yours, it is fine to use a scan with a fixed time limit, save that data somewhere, restart the scan, collect new data, compare with old data --> get results.
For example, if a device was found in scan 1 but not in scan 2, you can conclude that the device was in range, but is not anymore.
Same goes for the other way around: if a device was found in scan 4 but not in scan 3, it is a newly discovered device.
Finally, if a device was found in scan 5, was not found in scan 6, but was again found in scan 7, it is rediscovered and can be handled as such if need be.
Because I'm answering my own question here, I'll add the code that I used to implement this.
I have the scanning done in a background service, and communicate to other parts of the app using BroadcastReceivers. Asset is a custom class of mine that holds some data. DataManager is a custom class of mine that - how did you guess it - manages data.
public class BLEDiscoveryService extends Service {
// Broadcast identifiers.
public static final String EVENT_NEW_ASSET = "EVENT_NEW_ASSET ";
public static final String EVENT_LOST_ASSET = "EVENT_LOST_ASSET ";
private static Handler handler;
private static final int BLE_SCAN_TIMEOUT = 11000; // 11 seconds
// Lists to keep track of current and previous detected devices.
// Used to determine which are in range and which are not anymore.
private List<Asset> previouslyDiscoveredAssets;
private List<Asset> currentlyDiscoveredAssets;
private BluetoothAdapter bluetoothAdapter;
private BluetoothAdapter.LeScanCallback BLECallback = new BluetoothAdapter.LeScanCallback() {
#Override
public void onLeScan(BluetoothDevice bluetoothDevice, int i, byte[] bytes) {
Asset asset = DataManager.getAssetForMACAddress(bluetoothDevice.getAddress());
handleDiscoveredAsset(asset);
}
};
#Override
public void onCreate() {
super.onCreate();
BluetoothManager manager = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE);
bluetoothAdapter = manager.getAdapter();
previouslyDiscoveredAssets = new ArrayList<>();
currentlyDiscoveredAssets = new ArrayList<>();
handler = new Handler();
}
#Override
public int onStartCommand(Intent intent, int flags, int startId) {
// Start scanning.
startBLEScan();
// After a period of time, stop the current scan and start a new one.
// This is used to detect when assets are not in range anymore.
handler.postDelayed(new Runnable() {
#Override
public void run() {
performRepeatingTask();
// Repeat.
handler.postDelayed(this, BLE_SCAN_TIMEOUT);
}
}, BLE_SCAN_TIMEOUT);
// Service is not restarted if it gets terminated.
return Service.START_NOT_STICKY;
}
#Override
public IBinder onBind(Intent intent) {
return null;
}
#Override
public void onDestroy() {
handler.removeCallbacksAndMessages(null);
stopBLEScan();
super.onDestroy();
}
private void startBLEScan() {
bluetoothAdapter.startLeScan(BLECallback);
}
private void stopBLEScan() {
bluetoothAdapter.stopLeScan(BLECallback);
}
private void handleDiscoveredAsset(Asset asset) {
currentlyDiscoveredAssets.add(asset);
// Notify observers that we have a new asset discovered, but only if it was not
// discovered previously.
if (currentlyDiscoveredAssets.contains(asset) &&
!previouslyDiscoveredAssets.contains(asset)) {
notifyObserversOfNewAsset(asset);
}
}
private void performRepeatingTask() {
// Check if a previously discovered asset is not discovered this scan round,
// meaning it's not in range anymore.
for (Asset asset : previouslyDiscoveredAssets) {
if (!currentlyDiscoveredAssets.contains(asset)) {
notifyObserversOfLostAsset(asset);
}
}
// Update lists for a new round of scanning.
previouslyDiscoveredAssets.clear();
previouslyDiscoveredAssets.addAll(currentlyDiscoveredAssets);
currentlyDiscoveredAssets.clear();
// Reset the scan.
stopBLEScan();
startBLEScan();
}
private void notifyObserversOfNewAsset(Asset asset) {
Intent intent = new Intent();
intent.putExtra("macAddress", asset.MAC_address);
intent.setAction(EVENT_NEW_ASSET);
sendBroadcast(intent);
}
private void notifyObserversOfLostAsset(Asset asset) {
Intent intent = new Intent();
intent.putExtra("macAddress", asset.MAC_address);
intent.setAction(EVENT_LOST_ASSET);
sendBroadcast(intent);
}
}
This code is not perfect and might even be buggy, but it will at least give you an idea or example of how this can be implemented.

I can recommend this approach:
Use Map<BluetoothDevice, Long> structure to store the discovered devices, where Long is the time of detection of the device (can be System.currentTimeMillis() for example).
Then in your service (as far as I understand from the question there will be implemented some kind of repeated task) just extract actual devices based on the time of their detection.
And you are absolutely right, there are no guarantee that all nearby devices were discovered within the allotted time. Especially this is actual for the Android devices.
iOS devices in it's turn have another issue - they can change their BluetoothDevice's adress in runtime without apparent external cause.
Hope this will help you to save the time during debugging.
Edit
As a result of research of this topic found this discussion on code.google.com
Issue is still open and seems that it is related to the hardware features and can't be fixed programmatically. Moreover, it seems that bug will remains on problem devices even after a system updates.
So restarting the scan periodically might be acceptable workaround for this case.

BLE Device Name irretrievable

I have a project that is scanning for beacons that run on BLE.
I can scan for the beacon and list them in a nice custom ListView just fine. However retrieving their names seems to not work.
In my OnLeScan callback I use device.getName() which appears to always be returning null?
Furthermore, when I attempt to parse the ScanRecord byte[] array for the data in concordance with this post - I still am not having much luck. Any ideas/tips?
Should I be retrieving the local name from the BluetoothDevice class? Should I retrieve it from parsing the ScanRecord/ScanResult class?
Here is what my onLeScan looks like:
public void onLeScan(final BluetoothDevice device, int rssi, final byte[] scanRecord) {
runOnUiThread(new Runnable() {
#Override
public void run() {
Log.v(device.getName(),device.getName());
mLeDeviceListAdapter.addDevice(device);
mLeDeviceListAdapter.notifyDataSetChanged();
}
}
});
}
Edit:
I attempted some modification of the code from the linked post. Adding a case 0x08: as suggested in the comments. However my ListView still lists all found devices as "unknown device" by default and will not retrieve the friendly name.

See this answer for a breakdown of an iBeacon advertisement packet. There is no name.
The official spec is only available via Apple's MFi program.

Android KitKat Bluetooth connect

Am i the only one having problems connecting to the bluetooth with startBluetoothSco? This works fine in all versions of Android except 4.4.2 (kitkat). Any suggestions? And yes, I have verified that I am connected to Bluetooth before I call this. Did something changed in 4.4.2?
Here is my code:
am = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
am.setMode(AudioManager.MODE_IN_CALL);
am.setBluetoothScoOn(true);
am.startBluetoothSco();
Following your suggestion i did the following, but this is driving me nuts! What am I doing wrong. I have the listener in my MainActivity as follows...
private final BluetoothHandler.Listener mBluetoothListener = new BluetoothHandler.Listener() {
#Override
public void onConnectionComplete() {
final BluetoothHandler bluetoothHandler = mBluetoothHandler;
if (bluetoothHandler != null) {
am.setMode(AudioManager.MODE_IN_COMMUNICATION);
}
}
};
Then in my OnCreate I initialize the BluetoothHandler
if(mBluetoothHandler == null){
mBluetoothHandler = new BluetoothHandler(5000, mBluetoothListener);
} else {
mBluetoothHandler.stopSco();
mBluetoothHandler.stop();
mBluetoothHandler = null;
}
if (!mBluetoothHandler.isAudioConnected()) {
mBluetoothHandler.start(mContext);
}
The problem I'm having is that the listener doesn't detect when a BT device connects or even says that one is connected. Any suggestions? I appreciate your help...

The functionality of startBluetoothSco() changed between API 17 and API 18. In API 17, this function initiates a virtual call via SCO. In API 18, the function opens a raw SCO link. Some Bluetooth units will only respond to a virtual call.
Unfortunately it doesn't seem that Google have given us an option of choosing whether to open a virtual call or raw link so if you require a virtual call, you will need to ensure your app is built with API 17.
From the Android Developer reference:
"NOTE: up to and including API version JELLY_BEAN_MR1, this method
initiates a virtual voice call to the bluetooth headset. After API
version JELLY_BEAN_MR2 only a raw SCO audio connection is
established."
http://developer.android.com/reference/android/media/AudioManager.html#startBluetoothSco()

Which device do you use? I know that there is sometimes a Bluetooth problem with nexus devices (nexus 5 with kit at also) as described here:
http://www.androidpolice.com/2013/12/28/bug-watch-many-nexus-devices-still-suffer-from-assorted-bluetooth-issues/

Had the same problem with an app I was developming. Upong updating my phone to KitKat, the SCO connection to my car stopped working.
I finally come up with a solultion using a somehow private api in the bluetooth headset profile, while keeping my code compatible with API 19.
Fist I'm checking if current version is API 17, in that case, I use the standard startBluetoothSco from AudioManager, if not the case, I get the current BluetoothHeadset profile and use the following method to create the virtual call sco link (I can't take credit for this, I found it in the Google TalkBack application):
class BluetoothHeadsetCompatWrapper {
private static final Class<?> CLASS_BluetoothHeadset = BluetoothHeadset.class;
private static final Method METHOD_startScoUsingVirtualVoiceCall = CompatUtils.getMethod(
CLASS_BluetoothHeadset, "startScoUsingVirtualVoiceCall", BluetoothDevice.class);
private static final Method METHOD_stopScoUsingVirtualVoiceCall = CompatUtils.getMethod(
CLASS_BluetoothHeadset, "stopScoUsingVirtualVoiceCall", BluetoothDevice.class);
private final BluetoothHeadset mHeadset;
public BluetoothHeadsetCompatWrapper(BluetoothHeadset headset) {
mHeadset = headset;
}
public boolean startScoUsingVirtualVoiceCall(BluetoothDevice device) {
return (Boolean) CompatUtils.invoke(mHeadset, false, METHOD_startScoUsingVirtualVoiceCall,
device);
}
public boolean stopScoUsingVirtualVoiceCall(BluetoothDevice device) {
return (Boolean) CompatUtils.invoke(mHeadset, false, METHOD_stopScoUsingVirtualVoiceCall,
device);
}
}
I found this solution when I was looking into the BluetoothHeadset code and found out the method actually exists, but it's hidden to the compiler https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/bluetooth/BluetoothHeadset.java
I know my anwser may be late, but I posted anyway to help others.

Android 4.3: How to connect to multiple Bluetooth Low Energy devices

My Question is: Can Android 4.3 (client) have active connections with multiple BLE devices (servers)? If so, how can I achieve it?
What I did so far
I try to evaluate what throughput you can achieve using BLE and Android 4.3 BLE API. In addition I also try to find out how many devices can be connected and active at the same time. I use a Nexus 7 (2013), Android 4.4 as master and TI CC2540 Keyfob as slaves.
I wrote a simple server software for the slaves, which transmits 10000 20Byte packets through BLE notifications. I based my Android App on the Application Accelerator from the Bluetooth SIG.
It works well for one device and I can achieve around 56 kBits payload throughput at a Connection Interval of 7.5 ms. To connect to multiple slaves I followed the advice of a Nordic Employee who wrote in the Nordic Developer Zone:
Yes it's possible to handle multiple slaves with a single app. You would need to handle each slave with one BluetoothGatt instance. You would also need specific BluetoothGattCallback for each slave you connect to.
So I tried that and it partly works. I can connect to multiple slaves. I can also register for notifications on multiple slaves. The problem begins when I start the test. I receive at first notifications from all slaves, but after a couple Connection Intervals just the notifications from one device come trough. After about 10 seconds the other slaves disconnect, because they seem to reach the connection time-out. Sometimes I receive right from the start of the test just notifications from one slave.
I also tried accessing the attribute over a read operation with the same result. After a couple of reads just the answers from one device came trough.
I am aware that there are a few similar questions on this forum: Does Android 4.3 support multiple BLE device connections?, Has native Android BLE GATT implementation synchronous nature? or Ble multiple connection. But none of this answers made it clear for me, if it is possible and how to do it.
I would be very grateful for advice.

I suspect everyone adding delays is just allowing the BLE system to complete the action you have asked before you submit another one. Android's BLE system has no form of queueing. If you do
BluetoothGatt g;
g.writeDescriptor(a);
g.writeDescriptor(b);
then the first write operation will immediately be overwritten with the second one. Yes it's really stupid and the documentation should probably actually mention this.
If you insert a wait, it allows the first operation to complete before doing the second. That is a huge ugly hack though. A better solution is to implement your own queue (like Google should have). Fortunately Nordic have released one for us.
https://github.com/NordicSemiconductor/puck-central-android/tree/master/PuckCentral/app/src/main/java/no/nordicsemi/puckcentral/bluetooth/gatt
Edit: By the way this is the universal behaviour for BLE APIs. WebBluetooth behaves the same way (but Javascript does make it easier to use), and I believe iOS's BLE API also behaves the same.

Re visting the bluetooth-lowenergy problem on android: I am still using delays.
The concept: after every major action that provokes the BluetoothGattCallback (e.g. conenction, service discovery, write, read) a dealy is needed. P.S. have a look at Google example on BLE API level 19 sample for connectivity to understand how Broadcasts should be sent and get some general understanding etc...
Firstly, scan (or scan) for BluetoothDevices, populate the connectionQueue with desired devices and call initConnection().
Have a look on the following example.
private Queue<BluetoothDevice> connectionQueue = new LinkedList<BluetoothDevice>();
public void initConnection(){
if(connectionThread == null){
connectionThread = new Thread(new Runnable() {
#Override
public void run() {
connectionLoop();
connectionThread.interrupt();
connectionThread = null;
}
});
connectionThread.start();
}
}
private void connectionLoop(){
while(!connectionQueue.isEmpty()){
connectionQueue.poll().connectGatt(context, false, bleInterface.mGattCallback);
try {
Thread.sleep(250);
} catch (InterruptedException e) {}
}
}
Now if all is good, you have made connections and BluetoothGattCallback.onConnectionStateChange(BluetoothGatt gatt, int status, int newState) has been called.
public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
switch(status){
case BluetoothGatt.GATT_SUCCESS:
if (newState == BluetoothProfile.STATE_CONNECTED) {
broadcastUpdate(BluetoothConstants.ACTION_GATT_CONNECTED, gatt);
}else if(newState == BluetoothProfile.STATE_DISCONNECTED){
broadcastUpdate(BluetoothConstants.ACTION_GATT_DISCONNECTED, gatt);
}
break;
}
}
protected void broadcastUpdate(String action, BluetoothGatt gatt) {
final Intent intent = new Intent(action);
intent.putExtra(BluetoothConstants.EXTRA_MAC, gatt.getDevice().getAddress());
sendBroadcast(intent);
}
P.S. sendBroadcast(intent) might need to be done like this:
Context context = activity.getBaseContext();
context.sendBroadcast(intent);
Then the broadcast is received by BroadcastReceiver.onReceive(...)
public BroadcastReceiver myUpdateReceiver = new BroadcastReceiver(){
#Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if(BluetoothConstants.ACTION_GATT_CONNECTED.equals(action)){
//Connection made, here you can make a decision: do you want to initiate service discovery.
// P.S. If you are working with multiple devices,
// make sure that you start the service discovery
// after all desired connections are made
}
....
}
}
After doing whatever you want in the broadcast receiver, here is how I continue:
private Queue<BluetoothGatt> serviceDiscoveryQueue = new LinkedList<BluetoothGatt>();
private void initServiceDiscovery(){
if(serviceDiscoveryThread == null){
serviceDiscoveryThread = new Thread(new Runnable() {
#Override
public void run() {
serviceDiscovery();
serviceDiscoveryThread.interrupt();
serviceDiscoveryThread = null;
}
});
serviceDiscoveryThread.start();
}
}
private void serviceDiscovery(){
while(!serviceDiscoveryQueue.isEmpty()){
serviceDiscoveryQueue.poll().discoverServices();
try {
Thread.sleep(250);
} catch (InterruptedException e){}
}
}
Again, after a successful service discovery, BluetoothGattCallback.onServicesDiscovered(...) is called. Again, I send an intent to the BroadcastReceiver (this time with different action String) and it is now that you can start reading, writing and enabling notifications/indications...
P.S. If you are working with multiple devices, make sure that you start the reading, writing etc... stuff after all devices have reported that their services have been discovered.
private Queue<BluetoothGattCharacteristic> characteristicReadQueue = new LinkedList<BluetoothGattCharacteristic>();
private void startThread(){
if(initialisationThread == null){
initialisationThread = new Thread(new Runnable() {
#Override
public void run() {
loopQueues();
initialisationThread.interrupt();
initialisationThread = null;
}
});
initialisationThread.start();
}
}
private void loopQueues() {
while(!characteristicReadQueue.isEmpty()){
readCharacteristic(characteristicReadQueue.poll());
try {
Thread.sleep(BluetoothConstants.DELAY);
} catch (InterruptedException e) {}
}
// A loop for starting indications and all other stuff goes here!
}
BluetoothGattCallback will have all your incoming data from the BLE sensor. A good practice is to send a broadcast with the data to your BroadcastReceiver and handle it over there.

I am developing an app with BLE features myself. The way I managed to connect to multiple devices and turn on notifications was to implement delays.
So I make a new thread (in order not to block UI thread) and in the new thread connect and turn on notifications.
For example, after BluetoothDevice.connectGatt(); call Thread.sleep();
And add the same delay for read/write and enable/dissable notifications.
EDIT
Use wait like this so that Android dindn't reaise ANR
public static boolean waitIdle() {
int i = 300;
i /= 10;
while (--i > 0) {
if (true)
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return i > 0;
}

Unfortunately notifications in the current Android BLE stack are a bit buggy. There are some hardcoded limits and I've found some stability issues even with a single device. (I read at one point that you could only have 4 notifications... not sure if that's across all devices or per device. Trying to find the source for that info now.)
I would try switching to a polling loop (say, poll the items in question 1/sec) and seeing if you find your stability increases. I would also consider switching to a different slave device (say a HRM or the TI SensorTag) to see if there is perhaps an issue with the slave-side code (unless you can test that against iOS or another platform and confirm it isn't part of the issue).
Edit: Reference for notification limitation

Rain is right in his answer, you need delays for pretty much everything when you work with BLE in Android. I developed several apps with it and it is really necessary. By using them you avoid a lot of crashes.
In my case, I use delays after every read/write command. Doing so, you ensure you receive the response from the BLE device almost always. I do something like this: (of course everything is done in a separate thread to avoid to much work on the main thread)
readCharacteristic(myChar);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
myChar.getValue();
or:
myChar.setValue(myByte);
writeCharacteristic(myChar);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
This is really useful when you read/write several characteristics in a row... As Android is enough fast to execute the commands almost instantly, if you don't use a delay between them you may get errors or incoherent values...
Hope it helps even if it is not exactly the answer to your question.

BluetoothHeadset - Can't access public method

On the following page I am browsing the android source code for the BluetoothHeadset object:
http://androidxref.com/4.2.2_r1/xref/frameworks/base/core/java/android/bluetooth/BluetoothHeadset.java
Now in my code after getting the BluetoothHeadset object, I cannot access the method:
public void phoneStateChanged(args...)
Does anyone knows why it's not accessible? I tried using reflection but without effect...
My code:
protected BluetoothProfile.ServiceListener headsetProfileListener = new BluetoothProfile.ServiceListener()
{
#Override
public void onServiceConnected(int profile, BluetoothProfile proxy)
{
// mBluetoothHeadset is just a head set profile,
// it does not represent a head set device.
bluetoothHeadset = (BluetoothHeadset) proxy;
bluetoothHeadset.phoneStateChanged(...); //this method doesnt get autocompleted or recognised
}
};
EDIT: I know the method isn't mentioned in the android docs, but it probably is in the source code and maybe is made private, also I run a Cyanogen rom where the function is declared...
It's an app to experiment around with bluetooth and sending notifications...
Also I'm new to using reflection, so maybe the issue lies here:
bluetoothHeadset.getClass().getDeclaredMethod("phoneStateChanged", null);

That function isn't part of the API here: http://developer.android.com/reference/android/bluetooth/BluetoothHeadset.html
If its not part of the published API, you can't count on it. It may not actually be in the version of the framework you're using.