'TypeError: can't convert NoneType to int' using aioble on Pico W

[cchanthompalit]

Hi all,

I am trying to get two Raspberry Pi Pico W's to communicate. The Pico that transmits the data is hooked up to an accelerometer (MPU6050). As it takes the x, y, and z values from the accelerometer, it then attempts to send the data to the receiving Pico. The example code, temp_client.py and temp_sensor.py, was used as a baseline for my code. As for setup, I am using the IDE, Thonny, which is currently running MicroPython v1.22.2.

When I run the program, the two devices connect successfully, and the transmitter appears to successfully retrieve and send the data to the receiver. The problem I'm having is at the receiver end -- when I attempt to read the data using data = accel_char.read() , I get an error that says "TypeError: can't convert NoneType to int". I am unsure why this error is appearing, since it is written the exact way the examples have it (and I tested the example numerous times, along with using a MAX31855 breakout board to receive temperature data.) Here is the code for my receiver which I am having issues for.

import sys

# ruff: noqa: E402
sys.path.append("")

from micropython import const
from machine import RTC

import uasyncio as asyncio
import aioble
import bluetooth

import random
import struct

# org.bluetooth.service.environmental_sensing
_ENV_SENSE_UUID = bluetooth.UUID(0x181A)
# org.bluetooth.characteristic.temperature
_ENV_SENSE_TEMP_UUID = bluetooth.UUID(0x2A6E)

# Experiment ID (arbitrary for now), for file name
Exp_ID = "Acc" + str(24)

# Row ID for file
global rowID
rowID = 1

# Initialize RTC
rtc = machine.RTC()

# Write CSV header
def start_csv(timestamp):
    global accelFile
    accelFile = Exp_ID + '-' + timestamp + '.csv'

    with open(accelFile, 'a') as f:
        f.write("Row ID" + ",")
        f.write("X Accel")
        f.write(",")
        f.write("Y Accel")
        f.write(",")
        f.write("Z Accel")
        f.write("\r\n")

# Get current time to attach to file name
def get_current_time():
    current_time = rtc.datetime()

    curr_year = current_time[0]     # '2024' in 5/20/2024
    curr_month = current_time[1]    # '5' in 5/20/2024
    curr_day = current_time[2]      # '20' in 5/20/2024

    curr_hour = current_time[4]     # '10' in '10:25:56'
    curr_min = current_time[5]      # '25' in '10:25:56'
    curr_sec = current_time[6]      # '56' in '10:25:56'

    # Convert to string to maintain double-digit format during transfer
    year = '{:02d}'.format(curr_year)
    month = '{:02d}'.format(curr_month)
    day = '{:02d}'.format(curr_day)
    hour = '{:02d}'.format(curr_hour)
    minute = '{:02d}'.format(curr_min)
    sec = '{:02d}'.format(curr_sec)

    return year, month, day, hour, minute, sec

# Write to CSV file
def write2file(rowID:int, x_accel:int, y_accel:int, z_accel:int):

    with open(accelFile, 'a') as f:
        f.write(str(rowID))
        f.write(",")
        f.write(str(x_accel))
        f.write(",")
        f.write(str(y_accel))
        f.write(",")
        f.write(str(z_accel))
        f.write("\r\n")

    rowID += 1

# Scan for devices to connect to   
async def find_temp_sensor():
    # Scan for 5 seconds, in active mode, with very low interval/window (to
    # maximise detection rate).
    async with aioble.scan(5000, interval_us=30000, window_us=30000, active=True) as scanner:
        async for result in scanner:
            # See if it matches our name and the environmental sensing service.
            if result.name() == "mpy-accel" and _ENV_SENSE_UUID in result.services():
                # print(result.services())
                return result.device
    return None

# Helper to decode the temperature characteristic encoding (sint16, hundredths of a degree).
def decode_data(data):

    return struct.unpack("8s8s8s", data)

# Reconstruct packets, receive data and append current time to CSV entry
async def receive_data(data):

    recv_data = b''
    unpacked_data = False
    recv_data += data

    if len(recv_data) >= 24:
        unpacked_data = True

        data = decode_data(recv_data[:24])
        x, y, z = data[0], data[1], data[2]

        decoded_x = x.decode('utf-8')
        decoded_y = y.decode('utf-8')
        decoded_z = z.decode('utf-8')

        write2file(rowID, decoded_x, decoded_y, decoded_z)

        print(f"rowID: {rowID}, X Accel: {decoded_x}, Y Accel: {decoded_y}, Z Accel: {decoded_z}") # Print received data to central output

        recv_data = b''      # Reset the received data buffer

async def main():
    connected = False

    device = await find_temp_sensor()
    if not device:
        print("Temperature sensor not found")
        return

    try:
        connection = await device.connect()
        print("Connecting to", device)
        connected = True

    except asyncio.TimeoutError:
        print("Timeout during connection")
        return

    async with connection:
        try:
            accel_service = await connection.service(_ENV_SENSE_UUID)
            print("Accel service: ", accel_service)
            if accel_service is None:
                print("Environmental sensing service not found")
                return

            accel_char = await accel_service.characteristic(_ENV_SENSE_TEMP_UUID)
            print("Accel characteristic: ", accel_char)
            if accel_char is None:
                print("Characteristic not found")
                return

            # await asyncio.sleep(1)

        except asyncio.TimeoutError as e:
            print("Error registering services/characteristics: ", e)

            # Start CSV file
            global accelFile
            year, month, day, hour, minute, sec = get_current_time()

            timestamp = f"{year:04}_{month:02}_{day:02}_{hour:02}-{minute:02}-{sec:02}"
            start_csv(timestamp)

        while connected:
            data = b''
            while data is b'':
                data = await accel_char.read()
                print(type(data))
                print("Waiting until data is not None")

            if data is None:
                print("No more data to receive.")
                break

            print("Received data type: ", type(data))
            print(data)
            await receive_data(data)

            '''
            except Exception as e:
                print("Error receiving data: ", e)
            '''

            await asyncio.sleep_ms(1000)

        print("Disconnected")

asyncio.run(main())

Receiver Output: MPY: soft reboot Connecting to Device(ADDR_PUBLIC, 28:cd:c1:0b:30:b9, CONNECTED) Accel service: Service: 7 9 UUID(0x181a) Accel characteristic: Characteristic: 11 9 10 UUID(0x2a6e) <class 'bytes'> Waiting until data is not None Received data type: <class 'bytes'> b'' Traceback (most recent call last): File "", line 195, in File "asyncio/core.py", line 1, in run File "asyncio/core.py", line 1, in run_until_complete File "asyncio/core.py", line 1, in run_until_complete File "", line 173, in main File "aioble/client.py", line 251, in read TypeError: can't convert NoneType to int

The receiver initially does not receive any data (as marked by b''), but I figure this is due to a timing issue. To my understanding, this error should still not be happening despite this since the datatype of the received data is 'bytes.'

Any help would be greatly appreciated! I've been stuck on this problem for a couple weeks now and have not found a solution despite scrounging through numerous discussion posts and comparing my code to the original example code multiple times. I originally thought it was because the service and characteristic was not being registered properly, but I added a short delay to ensure that it is and the problem is still occurring. I've also added my transmitter code below just in case.

# BLE Transmitter: attached to accelerometer (MPU6050) and an external power supply

import sys

# ruff: noqa: E402
sys.path.append("")

import machine
import micropython
from micropython import const
from machine import Pin
# For MPU6050
import time
import MPU6050
# For BLE
import uasyncio as asyncio
import aioble
import bluetooth
import struct

# org.bluetooth.service.environmental_sensing
_ENV_SENSE_UUID = bluetooth.UUID(0x181A)
# org.bluetooth.characteristic.temperature
_ENV_SENSE_TEMP_UUID = bluetooth.UUID(0x2A6E)
# org.bluetooth.characteristic.gap.appearance.xml
_ADV_APPEARANCE_CYCLING_SPEED_SENSOR = const(1154)

# How frequently to send advertising beacons.
_ADV_INTERVAL_MS = 250_000

# Register GATT server.
accel_service = aioble.Service(_ENV_SENSE_UUID)
accel_char = aioble.Characteristic(accel_service, _ENV_SENSE_TEMP_UUID, read=True, write=True)
aioble.register_services(accel_service)

# Set GPIO pins
start_pin = machine.Pin(5, Pin.IN)
sda = machine.Pin(2)
scl = machine.Pin(3)

# Initialize I2C ([group I2C0 or I2C1], [sda pin], [scl pin], [frequency])
i2c = machine.I2C(1, sda=sda, scl=scl, freq=400000)

# Setup readings (note: transmitter only needs to know duration, receiver will handle
# time and writing/naming file
def setup_readings():

    # Set duration (how long are we measuring? (ms))
    duration = 1000

    return duration

# Measure data from accelerometer
async def get_measuring():

    setup = setup_readings()
    duration = setup
    #print(f"Duration: {duration}")

    # Set up read period (how often accelerometer reads (sec))
    read_period = 1

    # Set up measurement duration
    end_time = time.ticks_add(time.ticks_ms(), duration)
    #print(f"End time: {end_time}")

    # Loop continuously to print data
    while time.ticks_diff(end_time, time.ticks_ms()) > 0:
        # 'Accel' is tuple of 3 that contains x, y, andz data
        accel = mpu.read_accel_data()
        x_accel = accel[0]
        y_accel = accel[1]
        z_accel = accel[2]

        print("Accel data type: ", type(x_accel))

        print("Accel X: " + str(x_accel))
        print("Accel Y: " + str(y_accel))
        print("Accel Z: " + str(z_accel))

        encoded_data = encode_data(x_accel, y_accel, z_accel)
        await send_data(encoded_data)

        time.sleep(read_period)

        if time.ticks_diff(end_time, time.ticks_ms()) <= 0:
            break

    print("Completed measuring for given duration")
    return

# Helper to encode the temperature characteristic encoding (sint16, hundredths of a degree).
def encode_data(x_accel, y_accel, z_accel):

    # Convert 'float' data to strings
    str_x = str(x_accel)
    str_y = str(y_accel)
    str_z = str(z_accel)

    # Encode to bytes for transfer / data consistency
    encode_x = str_x.encode('utf-8')
    encode_y = str_y.encode('utf-8')
    encode_z = str_z.encode('utf-8')
    print("Encoded data type: ", type(encode_x))

    '''
    print(len(encode_x))
    print(len(encode_y))
    print(len(encode_z))
    '''

    return struct.pack("8s8s8s", encode_x, encode_y, encode_z)

# Break data into packets to send
async def send_data(data):

    accel_char.write(data)
    print("Data type of data: ", type(data))

# Scan for I2C devices
async def scan_I2C():
    print('Scanning I2C bus...')
    devices = i2c.scan() # returns all viable I2C devices on bus

    if len(devices) == 0: # if devices list is length 0, report no devices
        print('No I2C device!')
    else:
        print('I2C devices found: ', len(devices))

        for device in devices: # Run loop for every device in list, print corresponding address
            print('Decimal address: ', device, ' | Hexa address: ', hex(device))

        # Set up MPU6050 object
        global mpu
        mpu = MPU6050.MPU6050(i2c)

        # Wake up MPU6050 in case it was sleeping
        mpu.wake()

# Serially wait for connections. Don't advertise while a central is
# connected.
async def peripheral_task():
    connected = False

    while True:
        # Advertise device
        print("Advertising device, waiting for connection...")

        try:
            async with await aioble.advertise(
                _ADV_INTERVAL_MS,
                name="mpy-accel",
                services=[_ENV_SENSE_UUID],
                appearance=_ADV_APPEARANCE_CYCLING_SPEED_SENSOR,
            ) as connection:

                # Print connected device
                print("Connection from ", connection.device)
                connected = True

                await asyncio.sleep(1)

        except Exception as e:
            print("Error while advertising: ", e)

        while connected:
            # await asyncio.sleep(0.5)

            # Scan I2C devices
            await scan_I2C()

            # Retrieve measurements from accelerometer, pack and send
            await get_measuring()

            # Disconnect after measuring interval has finished
            # await connection.disconnect()

        print("Disconnected")

            #return

async def main():
    await peripheral_task()

asyncio.run(main())

Thank you!

[brianreinhold]

Personally I have always been frustrated with being able to tell what is in scope and what is not in scope in python/micropython.

accel_service and accel_char are both first defined in a try - except clause and then they are accessed later outside of that clause. Now in C and in Java, those variables would be out of scope once outside of the try clause.

Try something simple like placing them at the top of the file along with the connected = False (I type everything I can not only for my benefit but for a future reader of my code's benefit....

async def main():
    connected: bool = False
    accel_service: ClientService | None = None 
    accel_char: ClientCharacteristic | None = None

then check that they are not None before accessing them. Just because you are getting the error that what you are accessing is of NoneType suggests that they are out of scope. I recall being instructed that variables defined in a try clause should not go out of scope but that has not always been my experience.

In any case, if you have not found a solution this is an easy thing to try.