bluetooth - Can't Send Command to BLE Device Philips Hue Bulb (Connection Drops)

Question

I am trying to turn my bluetooth Hue bulb on/off and change brightness using my Raspberry Pi 4B. The bulb is on, and I have successfully connected to it using bluez. When I try to run 'char-write-req 0x0027 01' to turn it on, I get this message:

GLib-WARNING **: 22:53:34.807: Invalid file descriptor

I can see that the connection is successful, but whenever I try to write a value to it, I just get this message and it disconnects. Running bluetoothctl 5.50. I have seen the patch conversation here: https://www.spinics.net/lists/linux-bluetooth/msg67617.html. But I am not sure it applies and I also wouldn't even know how to apply it. Can someone please help me!

EDIT I ditched the gatttool and am using bluetoothctl to connect to the bulb and menu gatt to send commands to it.

I figured out that the characteristic for toggling the light on and off is 932c32bd-0002-47a2-835a-a8d455b859dd (For my Philips Hue A19). After connecting to the bulb, I was able to select this attribute and use 'write 01' to turn it on and 'write 00' to turn it off. The brightness characteristic is 932c32bd-0002-47a2-835a-a8d455b859dd. When I read, it outputs 'fe', which is HEX for 254. This is the highest brightness setting, which it was already set to. I can use 'write ' where value ranges from 1-254 to change the brightness.

question from:https://stackoverflow.com/questions/65948825/cant-send-command-to-ble-device-philips-hue-bulb-connection-drops

Answer 1

Using acquire-write in bluetoothctl is typically not the correct command. read and write are what you want.

After starting starting bluetoothctl I would expect the series of commands to be:

connect <Address of bulb>
menu gatt
select-attribute 932c32bd-0002-47a2-835a-a8d455b859dd
write 1
write 0

If you wanted to script this, then below is a Python3 script that I would expect to turn the bulb on then off.

from time import sleep
from pydbus import SystemBus

BLUEZ_SERVICE = 'org.bluez'
BLUEZ_DEV_IFACE = 'org.bluez.Device1'
BLUEZ_CHR_IFACE = 'org.bluez.GattCharacteristic1'


class Central:

    def __init__(self, address):
        self.bus = SystemBus()
        self.mngr = self.bus.get(BLUEZ_SERVICE, '/')
        self.dev_path = self._from_device_address(address)
        self.device = self.bus.get(BLUEZ_SERVICE, self.dev_path)
        self.chars = {}

    def _from_device_address(self, addr):
        """Look up D-Bus object path from device address"""
        mng_objs = self.mngr.GetManagedObjects()
        for path in mng_objs:
            dev_addr = mng_objs[path].get(BLUEZ_DEV_IFACE, {}).get('Address', '')
            if addr.casefold() == dev_addr.casefold():
                return path

    def _get_device_chars(self):
        mng_objs = self.mngr.GetManagedObjects()
        for path in mng_objs:
            chr_uuid = mng_objs[path].get(BLUEZ_CHR_IFACE, {}).get('UUID')
            if path.startswith(self.dev_path) and chr_uuid:
                self.chars[chr_uuid] = self.bus.get(BLUEZ_SERVICE, path)


    def connect(self):
        """
        Connect to device.
        Wait for GATT services to be resolved before returning
        """
        self.device.Connect()
        while not self.device.ServicesResolved:
            sleep(0.5)
        self._get_device_chars()

    def disconnect(self):
        """Disconnect from device"""
        self.device.Disconnect()

    def char_write(self, uuid, value):
        """Write value to given GATT characteristic UUID"""
        if uuid.casefold() in self.chars:
            self.chars[uuid.casefold()].WriteValue(value, {})
        else:
            raise KeyError(f'UUID {uuid} not found')

    def char_read(self, uuid):
        """Read value of given GATT characteristic UUID"""
        if uuid.casefold() in self.chars:
            return self.chars[uuid.casefold()].ReadValue({})
        else:
            raise KeyError(f'UUID {uuid} not found')


device_address = '11:22:33:44:55:66'
light_state = '932c32bd-0002-47a2-835a-a8d455b859dd'


dev = Central(device_address )
dev.connect()
dev.char_write(light_state , [1])
sleep(5)
dev.char_write(light_state , [0])
print(dev.char_read(light_state ))
dev.disconnect()

As I don't have a bulb the above is untested. But should be a good outline of what is required.