How do I get notifications from a BLE device using pygatt in python?
I am developing a Linux application using python which will connect to my BLE device and receive the data notifying the characteristic. I am using pygatt for BLE communication. I can successfully connect and connect to the device and read from / write from specifications. Even I can subscribe to the feature notification, but the problem is that my BLE device is a custom machine and has 4 counters inside it, every time one of the counter data changes, it sets the corresponding flag for notification, thus using onDataChanged - Similar methods I can read the counter data from the read characteristic. In Python using pygatt, I can subscribe to a notification with:
class_name.device.subscribe(uuid.UUID(notify_characteristic),callback=notifyBle)
and notifyBle:
def notifyBle(self,handle,data):
read_data = class_name.device.char_read(uuid.UUID(read_characteristic))
print(read_data)
When I run the program, I first scan the devices and connect to my device and communicate with it, then discover the features and list them. Everything is successful. After listing the characteristics, I write to write the characteristic to clear the notification flags and it succeeds too. The last thing I sign up is to let you know it's successful.
After all these processes I physically increment the device counters (on the device the counters are incremented). When I click the button, the program goes to the notifyBle method and it gives an error that:
Exception in thread Thread-3:
Traceback (most recent call last):
File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
self.run()
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/gatttool.py", line 137, in run
event["callback"](event)
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/gatttool.py", line 479, in _handle_notification_string
self._connected_device.receive_notification(handle, values)
File "/usr/local/lib/python3.5/dist-packages/pygatt/device.py", line 226, in receive_notification
callback(handle, value)
File "/home/acd/Masaüstü/python_workspace/ble.py", line 54, in notifyBle
read_data = bleFunctions.dev.char_read(uuid.UUID(bleFunctions.read_characteristic))
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/device.py", line 17, in wrapper
return func(self, *args, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/device.py", line 40, in char_read
return self._backend.char_read(self, uuid, *args, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/gatttool.py", line 53, in wrapper
return func(self, *args, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/gatttool.py", line 519, in char_read
self.sendline('char-read-uuid %s' % uuid)
File "/usr/lib/python3.5/contextlib.py", line 66, in __exit__
next(self.gen)
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/gatttool.py", line 180, in event
self.wait(event, timeout)
File "/usr/local/lib/python3.5/dist-packages/pygatt/backends/gatttool/gatttool.py", line 154, in wait
raise NotificationTimeout()
pygatt.exceptions.NotificationTimeout
Any help would be appreciated.
PS: I wrote the same program in Android and Windows UWP. With python, I'm going to run this on a raspberry pi 3.
PSS: I am using raspberry pi 3 with Ubuntu Mate installed to develop this program in python.
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First, create an event class as shown below,
class Event:
def __init__(self):
self.handlers = set()
def handle(self, handler):
self.handlers.add(handler)
return self
def unhandle(self, handler):
try:
self.handlers.remove(handler)
except:
raise ValueError("Handler is not handling this event, so cannot unhandle it.")
return self
def fire(self, *args, **kargs):
for handler in self.handlers:
handler(*args, **kargs)
def getHandlerCount(self):
return len(self.handlers)
__iadd__ = handle
__isub__ = unhandle
__call__ = fire
__len__ = getHandlerCount
then, create a class class
import pygatt
from eventclass import Event
class myBle:
ADDRESS_TYPE = pygatt.BLEAddressType.random
read_characteristic = "0000xxxx-0000-1000-8000-00805f9b34fb"
write_characteristic = "0000xxxx-0000-1000-8000-00805f9b34fb"
notify_characteristic = "0000xxxxx-0000-1000-8000-00805f9b34fb"
def __init__(self,device):
self.device = device
self.valueChanged = Event()
self.checkdata = False
def alert(self):
self.valueChanged(self.checkdata)
def write(self,data):
self.device.write_char(self.write_characteristic,binascii.unhexlify(data))
def notify(self,handle,data):
self.checkdata = True
def read(self):
if(self.checkdata):
self.read_data = self.device.char_read(uuid.UUID(self.read_characteristic))
self.write(bytearray(b'\x10\x00'))
self.checkdata = False
return self.read_data
def discover(self):
return self.device.discover_characteristics().keys()
when you receive a notification, you set the boolean value to true, and the alert method will notify you when the boolean value has changed. You will listen to the warning method with
def triggerEvent(checkdata):
print(str(checkdata))
ble = myBle(device)
ble.valueChanged += triggerEvent
ble.alert()
you can call the read method to get the value of the characteristics using the triggerEvent method.
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