Running the Raspberry Pi as a Bluetooth Peripheral

In this activity, we will set up the Raspberry pi to run a Bluetooth service as a peripheral device.

Update your Raspberry Pi with:

sudo apt update

And then

sudo apt upgrade

We will now install the requirements for pybluez

sudo apt install python3-pip libbluetooth-dev git

We will then install the python packages:

sudo pip3 install pybluez gpiozero

We are now going to modify the Bluetooth Service in the Raspberry Pi to turn on the Bluetooth service.

sudo nano /lib/systemd/system/bluetooth.service

Thet change the following line:

ExecStart=/usr/lib/bluetooth/bluetoothd

To

ExecStart=/usr/lib/bluetooth/bluetoothd -E

The -E flag enables experimental features. After adding the experimental flag to the raspberry pi we need to reboot the pi to enable this feature.

sudo reboot

After you have rebooted, log back into your Pi and return to the terminal.

Now we will use Git to download a package that has been written and use a modified version of one of the files to enable and disable a LED over Bluetooth.

git clone https://github.com/douglas6/cputemp.git

cd into the folder we just downloaded on git

cd cputemp

Then create a script

nano LEDscript.py

Then paste in the code below. Ensure you change the green highlighted text to a service name that is unique (otherwise you might connect to someone else’s pi by accident).

#!/usr/bin/env python3
import dbus

from advertisement import Advertisement
from service import Application, Service, Characteristic, Descriptor
from gpiozero import CPUTemperature

GATT_CHRC_IFACE = "org.bluez.GattCharacteristic1"
NOTIFY_TIMEOUT = 5000

class LEDControlAdvertisement(Advertisement):
    def __init__(self, index):
        Advertisement.__init__(self, index, "peripheral")
        self.add_local_name("IoT Murdoch")
        self.include_tx_power = True

class BLEService(Service):
    MAIN_SVC_UUID = "00000001-710e-4a5b-8d75-3e5b444bc3cf"

    def __init__(self, index):

        Service.__init__(self, index, self.MAIN_SVC_UUID, True)
        self.add_characteristic(LEDControl(self))


class LEDControl(Characteristic):
    UNIT_CHARACTERISTIC_UUID = "00000002-710e-4a5b-8d75-3e5b444bc3cf"

    def __init__(self, service):
        Characteristic.__init__(
                self, self.UNIT_CHARACTERISTIC_UUID,
                ["write"], service)
        #self.add_descriptor(UnitDescriptor(self))

    def WriteValue(self, value, options):
        output = bytes(value).decode()
        if output == "0":
            print('turning LED off')
        elif output == "1":
            print('turning LED on')
        else:
            print('try again')
            print(output)

app = Application()
app.add_service(BLEService(0))
app.register()

adv = LEDControlAdvertisement(0)
adv.register()

try:
    app.run()
except KeyboardInterrupt:
    app.quit()

The yellow UUID is a random identifier that you can generate here https://www.uuidgenerator.net/ general practice is for each characteristic under it to change the service UUID up by one.

128 bit identifiers are able to be used by anyone, you may see shorter ones on other devices these are locked to a specific vendor or a specific service e.g battery levels are 0x180F Read more here https://www.bluetooth.com/specifications/gatt/services/

Now run the script

sudo python3 LEDscript.py

To connect we will use our mobile phone, download the app nRF Connect

Once open search for the name you selected with in the green text below its called IoT Murdoch it will ask you to pair, swipe across to services in the app, then click the up arrow under your service

Then write into the service ensuring you select UTF-8 at the top, 1 means LED on, 0 means led off

you should then see the command line tell you that the LED is enabled, and it switch on