BLE for wearables and beacons in IOT Protocols - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding BLE Advertising Interval

What is the main effect of setting a very short advertising interval in a BLE beacon?

A It disables the beacon's ability to connect to other devices.

B It decreases battery consumption and reduces device discoverability.

C It causes the beacon to stop advertising after a short time.

D It increases battery consumption but improves device discoverability.

💡 Hint

Think about how often the beacon sends signals and the impact on power.

A shorter advertising interval means the beacon sends signals more frequently, which helps devices find it faster but uses more battery power.

💻 Command Output

intermediate

BLE Scan Command Output

What output will the following BLE scan command produce on a Linux system?

sudo hcitool lescan --duplicates

A A continuous list of BLE devices including repeated entries for the same device.

B An error message indicating the command is deprecated.

C A one-time list of unique BLE devices found during the scan.

D No output because the command requires root privileges.

💡 Hint

Consider what the --duplicates flag does in scanning.

The --duplicates option allows the scan to show repeated advertisements from the same device, so the output continuously lists devices including duplicates.

❓ Configuration

advanced

Configuring a BLE Beacon's Tx Power

You want to configure a BLE beacon to have a transmission power of -12 dBm to save battery while maintaining moderate range. Which configuration snippet correctly sets this in a typical beacon config file?

A tx_power = -12

B txPower = 12

C tx_power = 12

D txPower = -12

💡 Hint

Check the typical naming convention and sign for power values in dBm.

Most beacon configs use lowercase with underscores for keys like tx_power. The value is in dBm and negative values reduce power.

❓ Troubleshoot

advanced

Troubleshooting BLE Connection Failures

A wearable device fails to connect to a smartphone via BLE. Which of the following is the most likely cause?

A The wearable's BLE advertising interval is set too long, causing the phone to miss advertisements.

B The smartphone's Bluetooth is turned off but the wearable is advertising correctly.

C The wearable is using a BLE version incompatible with the smartphone's Bluetooth version.

D The wearable's battery is fully charged.

💡 Hint

Think about what happens if the phone cannot detect any BLE signals.

If the smartphone's Bluetooth is off, it cannot scan or connect to any BLE devices, even if the wearable is advertising properly.

🔀 Workflow

expert

BLE Beacon Firmware Update Workflow

Which sequence correctly describes the steps to update firmware on a BLE beacon remotely?

A 1,3,2,4

B 2,1,3,4

C 1,2,3,4

D 2,3,1,4

💡 Hint

Think about the logical order of connecting, securing, transferring, and verifying.

The correct workflow starts with connection, then authentication, followed by data transfer, and finally verification and reboot.

Practice

1. What is the main advantage of using BLE (Bluetooth Low Energy) for wearables and beacons?

easy

A. It requires no pairing or security.

B. It provides very high data transfer speeds.

C. It uses very little power, extending battery life.

D. It works only with smartphones.

Solution

1. Step 1: Understand BLE's design goal

   BLE is designed to use minimal power to keep small devices running longer on batteries.

2. Step 2: Compare options

   High speed is not BLE's focus, pairing is often needed, and BLE works with many devices, not just smartphones.

3. Final Answer:

   It uses very little power, extending battery life. -> Option C

4. Quick Check:

   Low power = A [OK]

Hint: Remember BLE is for low power, not high speed [OK]

Common Mistakes:

• Confusing BLE with classic Bluetooth speed
• Thinking BLE needs no pairing always
• Assuming BLE only works with phones

2. Which of the following is the correct BLE advertising packet type used by beacons to broadcast data without connection?

easy

A. Connectable Directed Advertising

B. Extended Advertising

C. Scan Response Advertising

D. Non-Connectable Undirected Advertising

Solution

1. Step 1: Identify advertising types

   Beacons typically use Non-Connectable Undirected Advertising to broadcast data without needing a connection.

2. Step 2: Eliminate other options

   Connectable Directed requires connection, Scan Response is a reply to scans, Extended Advertising is newer but not typical for simple beacons.

3. Final Answer:

   Non-Connectable Undirected Advertising -> Option D

4. Quick Check:

   Beacon broadcasts = Non-Connectable Undirected [OK]

Hint: Beacons broadcast without connection using non-connectable packets [OK]

Common Mistakes:

• Choosing connectable advertising for beacons
• Confusing scan response with advertising
• Assuming extended advertising is always used

3. Given this Python snippet using a BLE library to scan for devices, what will be printed if a beacon advertising with name 'Beacon123' is found?

devices = scanner.scan(5)
for dev in devices:
    if dev.getValueText(9) == 'Beacon123':
        print(f"Found: {dev.addr}")

medium

A. Found:

B. Found: Beacon123

C. Error: getValueText is not a function

D. No output

Solution

1. Step 1: Understand the code logic

   The code scans for 5 seconds, then checks each device's advertised name (type 9) for 'Beacon123'.

2. Step 2: Analyze the print statement

   If found, it prints 'Found: ' plus the device's address, not the name itself.

3. Final Answer:

   Found: <device address> -> Option A

4. Quick Check:

   Print device address when name matches [OK]

Hint: Check what is printed: address, not name [OK]

Common Mistakes:

• Expecting the name printed instead of address
• Thinking getValueText is invalid
• Assuming no output if beacon found

4. You try to connect to a wearable device using its BLE address but get a connection timeout error. Which of these is the most likely cause?

medium

A. The device is advertising as non-connectable only.

B. The device address is invalid format.

C. The scanning duration was too long.

D. The device uses classic Bluetooth, not BLE.

Solution

1. Step 1: Understand connection timeout causes

   If a device advertises as non-connectable, it will not accept connection requests, causing timeout.

2. Step 2: Evaluate other options

   Invalid address would cause immediate error, scanning duration doesn't affect connection, classic Bluetooth devices won't appear in BLE scan.

3. Final Answer:

   The device is advertising as non-connectable only. -> Option A

4. Quick Check:

   Non-connectable device causes timeout [OK]

Hint: Non-connectable advertising means no connections allowed [OK]

Common Mistakes:

• Confusing scanning time with connection issues
• Assuming invalid address causes timeout instead of error
• Mixing classic Bluetooth with BLE scanning

5. You want to read the heart rate data from a wearable using BLE. Which sequence of steps correctly describes the process?

hard

A. Discover GATT services -> Scan for devices -> Connect to device -> Read heart rate characteristic -> Disconnect

B. Scan for devices -> Connect to device -> Discover GATT services -> Read heart rate characteristic using UUID -> Disconnect

C. Connect to device -> Scan for devices -> Read heart rate characteristic -> Discover GATT services -> Disconnect

D. Read heart rate characteristic -> Scan for devices -> Connect to device -> Discover GATT services -> Disconnect

Solution

1. Step 1: Understand BLE data reading workflow

   First, scan to find the device, then connect to it to access its data.

2. Step 2: Discover GATT services and read characteristic

   After connecting, discover services to find the heart rate characteristic by UUID, then read it.

3. Step 3: Disconnect after reading

   Once data is read, disconnect to save power and free resources.

4. Final Answer:

   Scan for devices -> Connect to device -> Discover GATT services -> Read heart rate characteristic using UUID -> Disconnect -> Option B

5. Quick Check:

   Scan -> Connect -> Discover -> Read -> Disconnect [OK]

Hint: Follow BLE steps in order: scan, connect, discover, read, disconnect [OK]

Common Mistakes:

• Trying to read before connecting
• Discovering services before connecting
• Skipping disconnect step