Reading from a Polar H7 Bluetooth Heartrate sensor

[arneme]

I have tried to connect to and read the pulse data from a Polar H7 sensor but is not managing to get it to work. Any ideas?
The error I get is:
Got services...
Reading from service 180d
Print chars found
char 2a37
Reading pulse data every second...
Exception caught...
the requested operation failed

Here is the code:

from network import Bluetooth
import time
bt = Bluetooth()
bt.start_scan(-1)

# Code to connect to Polar H7 Bluetooth heartrate sensor
# The detected Heartrate is "published" over the LoRaWAN network

while True:
    adv = bt.get_adv()
    if adv:
        name = bt.resolve_adv_data(adv.data, Bluetooth.ADV_NAME_CMPL)
        if name is not None:
            if name.startswith("Polar H7"):
                print ("Found: " + name)
                bt.stop_scan()
                try:
                    conn = bt.connect(adv.mac)
                    print("Connected...")
                    services = conn.services()
                    print("Got services...")
                    for service in services:
                        time.sleep(0.05)
                        # According to specification from Polar, service.uuid = 0x180D is Heart Rate and char.uuid = 2a37 is value in beats per minutes
                        if service.uuid() == 0x180D:
                            print('Reading from service %x' % service.uuid())
                            chars = service.characteristics()
                            print("Print chars found")
                            for char in chars:
                                print('char %x' % char.uuid())
                                # Charactersistic 2a37 is a notification char and we need to enable notification to receive the ValueError
                                if char.uuid() == 0x2a37:
                                    # Notify sensor that we want to receive pulse data.
                                    byte = bytes([1])
                                    char.write(byte)
                                    while True:
                                        print("Reading pulse data every second...")
                                        print('char {} value = {}'.format(char.uuid(), char.read()))
                except Exception as ex:
                    print("Exception caught...")
                    print(ex)

[arneme]

I was afraid that the notification part was missing in the firmware but great if it appears soon :-). Thanks for the speedy reply.

[jmarcelino]

@arneme
The Heart Rate Measurement profile requires BLE notifications, it doesn't work with simple reads.

However there isn't yet a system to receive BLE notifications on the LoPy so unfortunately you'll have to wait a bit more.

EDIT: Was catching up on the other threads and apparently this functionality could come next week. I also have a Polar H7 and can look into it at some point.