Develop Reference

Android App receives 2 connections from the same device (nRF Module)

I have an android app which scans and connects to a predefined device name. My peripheral is an nRF module which is sending an incrementing data at 1Hz.
However, when I launch the app, it scans and logs multiple connections to the same device and consequently the values received duplicated values. So if there is a log for 3 connections then I get 3 duplicate values and 2 duplicates if there are 2 connections.
D/BluetoothGatt: onClientConnectionState() - status=0 clientIf=14 device=FD:72:38:AA:1A:E7
I/BLE log: Connected to device FD:72:38:AA:1A:E7
D/BluetoothGatt: onClientConnectionState() - status=0 clientIf=15 device=FD:72:38:AA:1A:E7
I/BLE log: Connected to device FD:72:38:AA:1A:E7
Here is my code:
Scanning:
private fun bleScan() {
val scanFilter = ScanFilter.Builder()
.setDeviceName("VEGA-TEST")
.build()
val scanSettings = ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.build()
bleScanner.startScan(mutableListOf(scanFilter), scanSettings, object : ScanCallback() {
override fun onScanResult(callbackType: Int, result: ScanResult) {
super.onScanResult(callbackType, result)
with(result.device) {
Log.i("BLE log", "Found device $address")
connectGatt(this#BluetoothService, false ,gattCallback)
}
}
})
}
GATT Connections
private val gattCallback = object : BluetoothGattCallback() {
override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
super.onConnectionStateChange(gatt, status, newState)
val deviceAddr = gatt.device.address
if(status == BluetoothGatt.GATT_SUCCESS) {
when(newState) {
BluetoothProfile.STATE_CONNECTED -> {
Log.i("BLE log", "Connected to device $deviceAddr")
bleStopScan()
Handler(Looper.getMainLooper()).post {
gatt.discoverServices()
}
}
BluetoothProfile.STATE_DISCONNECTED -> {
Log.i("BLE log", "Disconnected from device $deviceAddr")
}
else -> {
Log.i("BLE log", "Hit event $newState")
}
}
} else {
Log.e("BLE log", "BLE error $status for $deviceAddr")
}
}
override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
super.onServicesDiscovered(gatt, status)
with(gatt) {
Log.i("BLE log","Discovered ${services.size} services for ${device.address}")
printGattTable()
enableNotification(gatt)
}
}
}
On the NRF Side i am sending data using a timer
static void txTimer_hander(void *p_context){
//TODO: Handle timeout
// SEND data to Device
//NRF_LOG_INFO("Timer : %d", tx_Data);
memset(val, 0, 7);
if(tx_Data < 50){
// SEND this Data
uint16_t now_data = tx_Data;
val[0] = 0xFF;
val[5] = now_data;
//memcpy(&val[0], (uint16_t*)0xFF, 1);
//memcpy(&val[6], &now_data, 2);
//val[0] = now_data;
//
tx_Data++;
}else{
tx_Data = 0;
// SEND this Data
uint16_t now_data = tx_Data;
//memcpy(&val[0], (uint16_t*)0xFF, 1);
val[0] = 0xFF;
val[5] = now_data;
//memcpy(&val[6], &now_data, 2);
//
tx_Data++;
}
NRF_LOG_INFO("Sending %d", tx_Data);
send_nus_data(val, 7);
}
NOTE I am using Android 12 and testing using Android Studio
I would appreciate any help!
Thanks

If your phone catches two advertisement packets, it will create two logical connections. You should check before you call connectGatt if you have already called connectGatt, and if so don't connect again. You should also stop the scan if you don't need the scan to continue when you have already found a device.

How to receive data from BLE device using greenbot EventBus in my code?

I have an application that sends and receives data using BLE. Originally it was classical bluetooth but I was tasked with changing the project to BLE.
So far I have succeeded in sending data but not receiving it. The main activity contains multiple fragments. On of those is responsible for sending data where as the other sends a request and then receives a response with the data from the BLE device.
one fragment is called Parameter and the other Memory. Each fragment has a viewmodel and repository as the architecture is based on MVVM. the flow is as follows:
Parameter fragment -> View model -> repository -> DataStore class -> DataStore uses instance from BLEConnectionManager class to send the data of the corresponding parameter. Example of a function in DataStore:
fun sendToolAddressParam(data: Int){
toolAddress = data
var value = Integer.toHexString(data)
if (value.length == 1) value = "0$value"
val message = WriteCommandCodes.TOOL_ADDRESS.value + " " + value + " " + WriteCommandCodes.EXTRA2.value
BleConnectionManager.sendMessage(message)
Timber.i("Payload: $message")
}
There are also functions that request data:
fun requestToolAddress(){
BleConnectionManager.requestReadValues(ReadRequestCodes.TOOL_ADDRESS.value)
}
in the BLE class the functions are written as the following:
fun write(message:String){
val bytes = BigInteger(message.replace("\\s".toRegex(), ""), 16).toByteArray()
Timber.i("Bytes value ---> ${bytes.toHexString()}")
val device = getBleDevice()
// val characteristicRX = getBleCharacteristic()
val characteristicRX = bluetoothGattRef.getService(XpressStreamingServiceUUID).getCharacteristic(
peripheralRX)
writeCharacteristic(device, characteristicRX, bytes)
}
fun requestReadValues(requestCode:String){
if(isConnected.value!!){
write(requestCode)
}else{
Timber.e("Make sure that you connected and paired with the desired device.")
}
}
fun sendMessage(message:String){
Timber.i("Check if isConnected = true --> ${isConnected.value}")
if(isConnected.value == true){
write(message)
}else{
Timber.e("Make sure that you connected and paired with the desired device.")
}
}
Now here is my issue I want to receive data from the BLE device after I send the request, the device's documentation when it comes to BLE data exchange is here: https://docs.silabs.com/gecko-os/1/bgx/latest/ble-services
Now I have a function that supposedly receives the incoming messages but this was when classical bluetooth was used.
fun readIncomingMessages(message: String){
when{
message.startsWith(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.KEY_ADDRESS.value) ->{
EventBus.getDefault().post(
ReadKeyAddressEvent(message.substring(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.KEY_ADDRESS.value.length+1, com.brainsocket.milink.data.bluetooth.ReadResponseCodes.KEY_ADDRESS.value.length+3))
)
Timber.i("Message received: $message")
}
message.startsWith(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.TOOL_ADDRESS.value) ->{
EventBus.getDefault().post(
ReadToolAddressEvent(message.substring(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.TOOL_ADDRESS.value.length+1, com.brainsocket.milink.data.bluetooth.ReadResponseCodes.TOOL_ADDRESS.value.length+3))
)
Timber.i("Message received: $message")}
message.startsWith(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.RPM_THRESHOLD.value) ->{
EventBus.getDefault().post(
ReadRPMThresholdEvent(message.substring(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.RPM_THRESHOLD.value.length+1, com.brainsocket.milink.data.bluetooth.ReadResponseCodes.RPM_THRESHOLD.value.length+3))
)
Timber.i("Message received: $message")}
message.startsWith(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.BACKLASH.value) ->{
EventBus.getDefault().post(
ReadBacklashEvent(message.substring(com.brainsocket.milink.data.bluetooth.ReadResponseCodes.BACKLASH.value.length+1, com.brainsocket.milink.data.bluetooth.ReadResponseCodes.BACKLASH.value.length+6))
)
Timber.i("Message received: $message")}
As you can see the Event Bus is used here, it is also used here in the DataStore:
#Subscribe(threadMode = ThreadMode.MAIN)
fun onKeyAddressEvent(event: ReadKeyAddressEvent) {
Timber.i("onKeyAddressEvent: data:${event.data}")
keyAddress = Integer.parseInt(event.data , 16)
EventBus.getDefault().post(ReadMemoryItemsEvent())
}
#Subscribe(threadMode = ThreadMode.MAIN)
fun onToolAddressEvent(event: ReadToolAddressEvent) {
Log.d(LOG_TAG, "onToolAddressEvent: data:${event.data}")
when(Integer.parseInt(event.data , 16)){
0 -> toolAddress = 1
1 -> toolAddress = 2
}
EventBus.getDefault().post(ReadMemoryItemsEvent())
}
#Subscribe(threadMode = ThreadMode.MAIN)
fun onRPMThresholdEvent(event: ReadRPMThresholdEvent) {
Log.d(LOG_TAG, "onRPMThresholdEvent: data:${event.data}")
rpmThreshold = Integer.parseInt(event.data , 16)
EventBus.getDefault().post(ReadMemoryItemsEvent())
}
#Subscribe(threadMode = ThreadMode.MAIN)
fun onReadBacklashEvent(event: ReadBacklashEvent) {
Log.d(LOG_TAG, "onReadBacklashEvent: data:${event.data}")
val data = event.data
backlash = parseGotoPos(data)
EventBus.getDefault().post(ReadMemoryItemsEvent())
}
This is in the repository:
fun getMemoryItems() : List<ModesPosItem> = listOf(
ModesPosItem(value = btDataStore.keyAddress, title = context.getString(R.string.key_address_string)),
ModesPosItem(value = btDataStore.toolAddress, title = context.getString(R.string.tool_address_string)),
ModesPosItem(value = btDataStore.rpmThreshold, title = context.getString(R.string.rpm_threshold_string)),
ModesPosItem(value = btDataStore.backlash, title = context.getString(R.string.backlash_string))
)
This is in the viewmodel:
#Subscribe(threadMode = ThreadMode.MAIN)
fun onReadMemoryItemsEvent(event: ReadMemoryItemsEvent) {
memoryItems.value = repository.getMemoryItems()
Timber.i("Memory Items [tool address, keyAddress, RPM threshold, backlash]: ${memoryItems.value.toString()}")
}
This is in the fragment:
override fun onStart() {
super.onStart()
EventBus.getDefault().register(this)
}
override fun onStop() {
EventBus.getDefault().unregister(this)
super.onStop()
}
What exactly am I supposed to do to acquire the data from the BLE device?

I made an app that write and read continous stream data throw BLE connection from a bluetooth device.
The Flow i follow is the following:
Connect Gatt;
Discover Services;
Write To Characteristic;
Subscribe to Notification;
Read Characteristic from notification --> Here the EventBus post() with your data package;
Going deeper into the connection and using some code:
After you connect to the GATT you call onConnectionStateChange to listen for changes in the gatt connection:
private val gattCallback = object : BluetoothGattCallback() {
override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
val deviceAddress = gatt.device.address
if (status == BluetoothGatt.GATT_SUCCESS) {
if (newState == BluetoothProfile.STATE_CONNECTED) {
Log.w("BluetoothGattCallback", "Successfully connected to $deviceAddress")
// NOW DISCOVER SERVICES
gatt.discoverServices()
} else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
Log.w("BluetoothGattCallback", "Successfully disconnected from $deviceAddress")
}
} else {
Log.w(
"BluetoothGattCallback",
"Error $status encountered for $deviceAddress! Disconnecting..."
)
}
If the GATT is connected succesfully it will discover services.
At this step you can write to the characteristic as follow:
override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
with(gatt) {
Log.w(
"BluetoothGattCallback",
"Discovered ${services.size} services for ${device.address}"
)
val msg = byteArrayOf(0x00.toByte())
val newcharacteristic = gatt!!.getService(dataUUID_service).getCharacteristic(
dataUUID_characteristic
)
newcharacteristic!!.value = msg
gatt!!.writeCharacteristic(newcharacteristic)
}
}
This will let you go on the next step, the onCharacteristicWrite listener:
override fun onCharacteristicWrite(
gatt: BluetoothGatt,
characteristic: BluetoothGattCharacteristic,
status: Int
) {
val characteristic = gatt.getService(dataUUID_service).getCharacteristic(
dataUUID_characteristic
)
gatt.setCharacteristicNotification(characteristic, true)
val descriptor = characteristic!!.getDescriptor(descriptor_UUID)
descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE;
if (descriptor != null) {
descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
gatt.writeDescriptor(descriptor)
}
}
Writing the characteristic will let you go into the onCharacteristicChanged listener that will give you back the data from the ble device and in which you can use the event bus to use your data.
override fun onCharacteristicChanged(
gatt: BluetoothGatt,
charac: BluetoothGattCharacteristic
) {
super.onCharacteristicChanged(gatt, charac)
// Log.d("CHARAC", "Characteristic Changed")
onCharacteristicRead(gatt, charac, BluetoothGatt.GATT_SUCCESS)
}
Where onCharacteristicRead should look like:
override fun onCharacteristicRead(
gatt: BluetoothGatt,
characteristic: BluetoothGattCharacteristic,
status: Int
) {
with(characteristic) {
when (status) {
BluetoothGatt.GATT_SUCCESS -> {
Log.i("BluetoothGattCallback","Read characteristic $uuid:\n${value.toHexString()}" )
// value is the read value from ble device
// HERE YOU HANDE YOUR EVENT BUS, example:
val eventData: deviceListener = deviceListener(value)
EventBus.getDefault().post(eventData)
}
BluetoothGatt.GATT_READ_NOT_PERMITTED -> {
Log.e("BluetoothGattCallback", "Read not permitted for $uuid!")
}
else -> {
Log.e(
"BluetoothGattCallback",
"Characteristic read failed for $uuid, error: $status"
)
}
}
}
}
Maybe it is not the most efficent way and not the clearest code but it works like a charm.

Android, BLE continuously writing a characteristic value disconnects the gatt server

I notice that if i write fast and continuously a characteristic value the gatt server disconnect.
I know that I have to wait until onCharacteristicWrite callback, so that's not the problem I think.
This my queue implementation, I'm using a kotlin Channel to syncronize write and read.
private var continuation: CancellableContinuation<BluetoothGattCharacteristic>? = null
private val channel = Channel<WriteOp>(1)
private suspend fun processBluetoothWrite() {
do {
val writeOp = channel.receiveOrNull()
writeOp?.apply {
try {
suspendCancellableCoroutine<BluetoothGattCharacteristic> { cont ->
continuation = cont
characteristic.value = writeOp?.value
Log.d(TAG, "Write to ${characteristic?.uuid} value ${writeOp?.value?.toHexString()}...")
if (gatt?.writeCharacteristic(characteristic) == false) {
cont.resumeWithException(Exception("Write to ${characteristic?.uuid} fails."))
}
}
} catch (ex: Exception) {
Log.e(TAG, ex.message, ex)
}
}
} while (writeOp != null)
}
override fun onCharacteristicWrite(
gatt: BluetoothGatt?,
characteristic: BluetoothGattCharacteristic?,
status: Int
) {
Log.d(TAG, "Write to ${characteristic?.uuid} value ${characteristic?.value?.toHexString()} | ${status}")
characteristic?.apply {
if (status == BluetoothGatt.GATT_SUCCESS) {
continuation?.resume(this)
} else {
continuation?.resumeWithException(Exception("Write to ${characteristic?.uuid} value ${characteristic?.value?.toHexString()} | ${status}"))
}
}
}
I need to add a delay of about 100ms in the queue processing to avoid disconnection.
UPDATE
After setting writeType as default, it seems that onCharacteristicWrite is more realistic (I used to get GATT_SUCCESS even when the device stopped communicating, so I guess it was a "virtual" state), now when the device stopped communicating it didn't get the onCharacteristicWrite callback, though after a while it is fired with status = 133.
characteristic.writeType = BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT
What does it mean?

Android ble: Unable to send large data

I'm trying to implement an app for transfer some strings between ble devices (for now one device act as central and the other one as pheripheral) but without success.
This is how my peripheral (server) is set up.
Characteristic build
fun buildCharacteristic(
characteristicUUID: UUID,
): BluetoothGattCharacteristic {
var properties = BluetoothGattCharacteristic.PROPERTY_READ or
BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE or
BluetoothGattCharacteristic.PROPERTY_NOTIFY
var permission = BluetoothGattCharacteristic.PERMISSION_READ or
BluetoothGattCharacteristic.PERMISSION_WRITE
var characteristic = BluetoothGattCharacteristic(
characteristicUUID,
properties,
permission
)
return characteristic
}
service build
fun buildService(
serviceUUID: UUID,
serviceType: Int,
characteristics: List<BluetoothGattCharacteristic>
) {
bluetoothGattService = BluetoothGattService(
serviceUUID,
BluetoothGattService.SERVICE_TYPE_PRIMARY
)
for (characteristic in characteristics) {
bluetoothGattService.addCharacteristic(characteristic)
}
}
and this is how i start ble server (i omit implementation of callbacks)
fun startServer(
bleAdapter: BluetoothAdapter,
btManager: BluetoothManager,
context: Context
) {
bleAdvertiser = bleAdapter.bluetoothLeAdvertiser
bleGattServer = btManager.openGattServer(context, gattServerCallback)
bleGattServer.addService(bluetoothGattService)
var settings = AdvertiseSettings.Builder().apply {
setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_LOW_LATENCY)
setConnectable(true)
setTimeout(0)
setTxPowerLevel(AdvertiseSettings.ADVERTISE_TX_POWER_HIGH)
}
var data = AdvertiseData.Builder().apply {
setIncludeDeviceName(true)
}
bleAdvertiser.startAdvertising(settings.build(), data.build(), advertiseCallback)
}
On central (client) side, when onScanResult is triggered, i try to connect with device:
fun connectToDevice(device: BluetoothDevice) {
device.connectGatt(
context,
false,
createGattCallback()
)
}
where createGattCallback() is a function return a BluetoothGattCallback object. Inside this callback, when onConnectionStateChange is called, i call service discover, and when service is discovered i try do write data to peripheral
override fun onServicesDiscovered(gatt: BluetoothGatt?, status: Int) {
super.onServicesDiscovered(gatt, status)
if (gatt?.services != null) {
var serviceFound = false
for (service in gatt.services) {
if (service.uuid == Consts.SERVICE_UUID) {
serviceFound = true
var bluetoothGattCharacteristic = service.getCharacteristic(Consts.CHARACTERISTIC_UUID)
writeCharacteristic(
gatt,
bluetoothGattCharacteristic
)
}
}
if (!serviceFound) {
gatt.disconnect()
}
}
}
fun writeCharacteristic(
gatt: BluetoothGatt,
characteristic: BluetoothGattCharacteristic
) {
var toSendString = "A random string for testing purpose only"
var toSendByteArray = toSendString.toByteArray(Charsets.UTF_8)
val chunkSize = 18
val numberOfPackets = ceil(
(toSendByteArray.size).toDouble() / chunkSize.toDouble()
)
for (i in 0 until numberOfPackets.toInt()) {
var startIndex = i * chunkSize
var endIndex = if (startIndex + chunkSize <= toSendByteArray.size) {
startIndex + chunkSize
} else {
toSendByteArray.size
}
var packet = toSendByteArray.copyOfRange(startIndex, endIndex)
characteristic.value = packet
gatt.writeCharacteristic(characteristic)
Thread.sleep(250)
}
}
My code seems not workin, on peripheral i don't receive entire string, but only the first 18 bytes. Where i'm wrong?

You need to wait for onCharacteristicWrite before you can send the next value. See Android BLE BluetoothGatt.writeDescriptor() return sometimes false.
And your sleep won't solve anything.

Unable to read characteristic using Bluetooth LE, readCharacteristic returns false on Android

I want to read blood pressure from Medisana device via bluetooth on my Android device.
Here is my code
override fun onServicesDiscovered(gatt: BluetoothGatt?, status: Int) {
super.onServicesDiscovered(gatt, status)
if (status != BluetoothGatt.GATT_SUCCESS) {
Log.e(TAG, "onServicesDiscovered failed")
return
}
val characteristic = gatt?.getService(BLOOD_PRESSURE_SERVICE_UUID)?.
getCharacteristic(BLOOD_PRESSURE_CHARACTERISTICS_UUID)
if (characteristic == null) {
Log.e(TAG, "blood pressure measurement characteristics is not supported by the device")
} else {
gatt.setCharacteristicNotification(characteristic, true)
val descriptor = characteristic.getDescriptor(CLIENT_CHARACTERISTIC_CONFIG_UUID)
descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE;
gatt.writeDescriptor(descriptor)
if (!gatt.readCharacteristic(characteristic)) {
Log.e(TAG, "Unable to read characteristic")
}
}
}
Here are the constants I copied them from an official Bluetooth website
private val BLOOD_PRESSURE_SERVICE_UUID = UUIDUtils.convertFromInteger(0x1810)
private val BLOOD_PRESSURE_CHARACTERISTICS_UUID = UUIDUtils.convertFromInteger(0x2A35)
object UUIDUtils {
fun convertFromInteger(i: Int): UUID {
val MSB = 0x0000000000001000L
val LSB = -0x7fffff7fa064cb05L
val value = (i and -0x1).toLong()
return UUID(MSB or (value shl 32), LSB)
}
}
When the code is executed I see "Unable to read characteristic" in the logs. When I debug readCharacteristic it returns in the line
public boolean readCharacteristic(BluetoothGattCharacteristic characteristic) {
if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_READ) == 0) {
return false;
}
So the characteristic is not readable, but how to make it readable. I am new in Bluetooth and all this stuff makes me confusing.

Try this
According to the document, blood pressure need to add indication enable to get the data.
So you need to:
First, add "ENABLE_INDICATION_VALUE" to the CLIENT_CHARACTERISTIC_CONFIG descriptor.
This descriptor come from:
descriptor = characteristic.getDescriptor(
UUID.fromString(CLIENT_CHARACTERISTIC_CONFIG)); //CLIENT_CHARACTERISTIC_CONFIG equal to 00002902-0000-1000-8000-00805f9b34fb
Then:
descriptor.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
And last step, write the descriptor to remote device (pressure master)
like this
mBluetoothGatt.writeDescriptor(descriptor);
This work for me, I get the blood pressure data from the devices.
I'm not a native English speaker, sorry for my poor English