BLE Communication

For BLE communication between IoT Gateway and IoT Device (Feather nRF52840 Sense), we are using the Adafruit Blinka bleio library ().

Create a folder for EE5127 lab work and within this folder create a new Virtual Environment.

Change the current working directory to the newly created folder using the following command. This command will need to be executed every time Raspberry Pi is started for Python work

cd /home/Documents/ee5127

Use the following command to create the new Virtual Environment within the above folder.

python3 -m venv env

Activate the following by running the following command in the same Terminal. This command will need to be executed every time Raspberry Pi is started for Python work.

source env/bin/activate

Install the BLE library by running the following commands:

pip install wheel

pip install --upgrade adafruit-blinka-bleio adafruit-circuitpython-ble

sudo reboot

Open VS Code, select a Python 3 interpreter by opening the Command Palette (Ctrl+Shift+P), start typing the Python: Select Interpreter command to search, then select the command. Select the interpreter that has the prefix of env so that VS Code uses the Python version where we have installed BLE libraries.

BLE Peripheral Device

Run the following code on Feather Sense to transmit data using BLE

# Provide a remote sensing service over Bluetooth Low-Energy (BLE).

# ----------------------------------------------------------------
# Import the standard Python time functions.
import time
import digitalio
import board

# Import the Adafruit Bluetooth library.  Technical reference:
# https://circuitpython.readthedocs.io/projects/ble/en/latest/api.html
from adafruit_ble import BLERadio
from adafruit_ble.advertising.standard import ProvideServicesAdvertisement
from adafruit_ble.services.nordic import UARTService

# ----------------------------------------------------------------
# Initialize global variables for the main loop.
ledpin= digitalio.DigitalInOut(board.BLUE_LED)
ledpin.direction = digitalio.Direction.OUTPUT

ble = BLERadio()
uart = UARTService()
advertisement = ProvideServicesAdvertisement(uart)

# Flags for detecting state changes.
advertised = False
connected  = False

# The sensor sampling rate is precisely regulated using the following timer variables.
sampling_timer    = 0.0
last_time         = time.monotonic()
sampling_interval = 0.10

# ----------------------------------------------------------------
# Begin the main processing loop.

while True:

    # Read the accelerometer at regular intervals.  Measure elapsed time and
    # wait until the update timer has elapsed.
    now = time.monotonic()
    interval = now - last_time
    last_time = now
    sampling_timer -= interval
    if sampling_timer < 0.0:
        sampling_timer += sampling_interval
        x, y, z = (10,20,30)
    else:
        x = None

    if not advertised:
        ble.start_advertising(advertisement)
        print("Waiting for connection.")
        advertised = True

    if not connected and ble.connected:
        print("Connection received.")
        connected = True
        ledpin.value = True
        
    if connected:
        if not ble.connected:
            print("Connection lost.")
            connected = False
            advertised = False
            ledpin.value = False            
        else:
            if x is not None:
                uart.write(b"%.3f,%.3f,%.3f\n" % (x, y, z))

BLE Central Device

Run the following code on Raspberry Pi to read data using BLE.

 ----------------------------------------------------------------
# Import the Adafruit Bluetooth library, part of Blinka.  Technical reference:
# https://circuitpython.readthedocs.io/projects/ble/en/latest/api.html

from adafruit_ble import BLERadio
from adafruit_ble.advertising.standard import ProvideServicesAdvertisement
from adafruit_ble.services.nordic import UARTService

# ----------------------------------------------------------------
# Initialize global variables for the main loop.
ble = BLERadio()
uart_connection = None

# ----------------------------------------------------------------
# Begin the main processing loop.

while True:
    if not uart_connection:
        print("Trying to connect...")
        # Check for any device advertising services
        for adv in ble.start_scan(ProvideServicesAdvertisement):
            # Print name of the device
            name = adv.complete_name
            if name:
                print(name)
            # Print what services that are being advertised
            for svc in adv.services:
                print(str(svc))
            # Look for UART service and establish connection
            if UARTService in adv.services:
                uart_connection = ble.connect(adv)
                print("Connected")
                break
        ble.stop_scan()
    # Once connected start receiving data
    if uart_connection and uart_connection.connected:
        uart_service = uart_connection[UARTService]
        while uart_connection.connected:
            print(uart_service.readline().decode("utf-8").rstrip())