BLE advertising and scanning in IOT Protocols - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding BLE Advertising Types

Which BLE advertising type allows a device to send data without establishing a connection?

A Connectable undirected advertising

B Directed advertising

C Non-connectable undirected advertising

D Scannable undirected advertising

💡 Hint

Think about advertising that only broadcasts data but does not accept connections.

Non-connectable undirected advertising sends data without allowing connections, suitable for broadcasting information.

💻 Command Output

intermediate

Output of BLE Scan Command

What is the expected output when running a BLE scan command that finds one device named 'Sensor1' with MAC address 'AA:BB:CC:DD:EE:FF'?

IOT Protocols

sudo hcitool lescan --duplicates

A Sensor1 AA:BB:CC:DD:EE:FF

B AA:BB:CC:DD:EE:FF Sensor1

C Error: Device not found

D No devices found

💡 Hint

Check the typical output format of hcitool lescan.

The command outputs the MAC address followed by the device name for each found device.

❓ Configuration

advanced

Configuring BLE Advertising Interval

Which configuration snippet correctly sets the BLE advertising interval to 100 ms using BlueZ's hciconfig tool?

A sudo hciconfig hci0 leadv 0x03 interval 0x00A0

B sudo hciconfig hci0 leadv 0x03 interval 0x0064

C sudo hciconfig hci0 leadv 0x03 interval 0x00C8

D sudo hciconfig hci0 leadv 0x03 interval 0x0010

💡 Hint

Advertising interval is in units of 0.625 ms. Calculate 100 ms in hex units.

100 ms / 0.625 ms = 160 decimal = 0x00A0 hex, so interval 0x00A0 sets 100 ms.

❓ Troubleshoot

advanced

Troubleshooting BLE Scan Not Detecting Devices

You run a BLE scan but no devices appear, although you know devices are nearby and advertising. Which is the most likely cause?

A The scanning device's Bluetooth adapter is powered off

B The scanning device is using active scanning mode

C The advertising devices are using connectable advertising

D The advertising interval is set to 100 ms

💡 Hint

Check the state of your Bluetooth adapter before scanning.

If the Bluetooth adapter is off, scanning cannot detect any devices regardless of their advertising mode.

🔀 Workflow

expert

Correct Order of BLE Advertising and Scanning Steps

Arrange the steps in the correct order for a BLE device to advertise and another device to scan and connect.

A 2,3,1,4

B 2,1,3,4

C 1,3,2,4

D 1,2,3,4

💡 Hint

Think about which device must advertise first and when scanning starts.

Device A must start advertising before Device B can detect it during scanning, so Device B starts scanning after Device A advertises.

Practice

1. What is the main purpose of BLE advertising in Bluetooth Low Energy communication?

easy

A. To broadcast small packets of data repeatedly to nearby devices

B. To establish a full connection between devices

C. To encrypt data between devices

D. To scan for other devices' signals

Solution

1. Step 1: Understand BLE advertising role

   BLE advertising sends small data packets repeatedly to announce presence.

2. Step 2: Differentiate from scanning and connection

   Advertising is broadcasting, not scanning or connecting.

3. Final Answer:

   To broadcast small packets of data repeatedly to nearby devices -> Option A

4. Quick Check:

   Advertising = broadcast small data [OK]

Hint: Advertising means sending out info repeatedly [OK]

Common Mistakes:

• Confusing advertising with scanning
• Thinking advertising establishes connections
• Assuming advertising encrypts data

2. Which of the following is the correct command to start BLE scanning using the Linux tool bluetoothctl?

easy

A. ble scan start

B. start scan

C. scan start

D. scan on

Solution

1. Step 1: Recall bluetoothctl scan command

   The correct command to start scanning is exactly scan on.

2. Step 2: Check other options for syntax

   Other options are incorrect commands or invalid syntax in bluetoothctl.

3. Final Answer:

   scan on -> Option D

4. Quick Check:

   bluetoothctl scan on = start scanning [OK]

Hint: Use exact command 'scan on' in bluetoothctl [OK]

Common Mistakes:

• Using 'start scan' instead of 'scan on'
• Typing commands not supported by bluetoothctl
• Confusing scan commands with advertising commands

3. Given this Python snippet using a BLE library to scan devices:

devices = scanner.scan(5.0)
for dev in devices:
    print(dev.addr)

What will this code output?

medium

A. Empty list because scan time is too short

B. List of device addresses found during 5 seconds scan

C. Error because scan() needs no arguments

D. List of device names found during 5 seconds scan

Solution

1. Step 1: Understand scan() usage with timeout

   The scan method scans for devices for given seconds and returns device objects.

2. Step 2: Identify printed attribute

   Printing dev.addr outputs device MAC addresses found.

3. Final Answer:

   List of device addresses found during 5 seconds scan -> Option B

4. Quick Check:

   scan(5.0) returns devices; dev.addr prints addresses [OK]

Hint: scan(timeout) returns devices; print dev.addr for addresses [OK]

Common Mistakes:

• Thinking scan() takes no arguments
• Confusing device address with device name
• Assuming scan always returns empty list

4. You wrote this code to scan BLE devices but get no output:

scanner = Scanner()
devices = scanner.scan()
for dev in devices:
    print(dev.addr)

What is the likely problem?

medium

A. print(dev.addr) is incorrect attribute

B. Scanner() class does not exist

C. Missing scan timeout argument causes no devices found

D. scan() method should be called with 'start' keyword

Solution

1. Step 1: Check scan() method requirements

   scan() requires a timeout argument to specify scan duration.

2. Step 2: Understand effect of missing timeout

   Without timeout, scan may return immediately with no devices.

3. Final Answer:

   Missing scan timeout argument causes no devices found -> Option C

4. Quick Check:

   scan() needs timeout to find devices [OK]

Hint: Always provide scan timeout to get results [OK]

Common Mistakes:

• Omitting scan timeout argument
• Assuming dev.addr is invalid
• Thinking scan() uses 'start' keyword

5. You want to filter BLE scan results to only show devices advertising a specific service UUID. Which approach correctly applies this filter in Python?

hard

A. Use a list comprehension: [dev for dev in devices if '1234' in dev.getScanData()]

B. Check if '1234' in dev.addr for each device

C. Filter devices by comparing dev.name to '1234'

D. Use devices.filter('1234') method directly

Solution

1. Step 1: Understand filtering by service UUID

   Service UUIDs appear in scan data, not in address or name.

2. Step 2: Use list comprehension with getScanData()

   getScanData() returns advertised data; check if UUID '1234' is present.

3. Final Answer:

   Use a list comprehension: [dev for dev in devices if '1234' in dev.getScanData()] -> Option A

4. Quick Check:

   Filter by UUID in scan data using list comprehension [OK]

Hint: Filter devices by checking UUID in scan data list [OK]

Common Mistakes:

• Checking UUID in device address
• Filtering by device name instead of UUID
• Using non-existent filter() method on devices