Bluetooth & BLE · Study deck
Bluetooth Profiles: Selection and Implementation
The profile families are understood, but a product still needs one interoperable choice.
Radio Remi is your guide for this deck.
After studying this chapter
Learning objectives
You will be able to:
- Explain: Battery life ratio (800 mAh battery):: SBC battery life: Life_SBC = 800 / 2.87 = 279 hours (radio-only estimate; Sony's rated 30 hours also includes DAC, amplifier, and ANC current that this model doesn't capture).
- Explain: The error:: A developer building a custom BLE game controller implements HID over GATT (HOGP) but hardcodes a simple report descriptor, assuming "it's just button states and joystick positions.".
- Explain: SBC compresses to 328 kbps, so Bluetooth must transmit: Radio time per second = 328,000 bits / 3,000,000 bps = 0.109 s = 10.9% duty cycle.
Major section
Technology Comparison
Mesh remains a separate many-node control choice.
- The comparison guides selection; its example ranges and rates still require device and site measurement rather than being treated as acceptance guarantees.
- Wireless earbuds: A2DP + AVRCP + HFP for music, media controls, and calls.
Major section
Common Pitfalls in Bluetooth Profile Implementation
Solution: HID requires authentication and encryption; always enable security features.
- Impact: 150-200 ms audio delay causes noticeable lip-sync issues.
- Impact: Incompatibility with operating systems and need for custom apps.
- Mistake: Assuming all Bluetooth devices support the same profiles.
- Impact: Connection failures between devices (e.g., BLE-only phone can't use SPP).
Major section
Connection: BLE GATT Profiles meet CoAP Resource Model
BLE's GATT (Generic Attribute Profile) and CoAP share a strikingly similar resource-oriented architecture.
- Both organize functionality into hierarchical resources: GATT uses Services > Characteristics > Descriptors, while CoAP uses URI paths like /sensors/temperature/current.
- Both support read/write/notify operations, and both use UUIDs or URIs as resource identifiers.
- The key difference: GATT operates at the link layer (single-hop BLE), while CoAP operates at the application layer (multi-hop IP).
Major section
Deep Dive: Attribute Tables, Handles, and UUID Evidence
BLE profile conformance is proved by the discovered attribute table, not by a screenshot of one value arriving.
- The table should expose access properties, notification descriptors, and the boundary between a standard profile and product-specific semantics.
- Standard services give generic clients shared meaning; configuration and firmware branches can use vendor UUIDs.
Major section
Deep Dive: Attribute Tables, Handles, and UUID Evidence (continued)
That hierarchy is the map for the handle, CCCD, caching, and reconnect evidence below.
- When a client connects, it performs service discovery by walking the server's attributes by handle and reading the UUIDs that live at those handles.
- It must write 0x0001 to the CCCD at handle 0x002B; after that, the server pushes each new reading from the value handle.
- The client uses handles as local addresses and UUIDs as meaning.
Major section
Deep Dive: Attribute Tables, Handles, and UUID Evidence (continued)
A good profile test records the UUID discovered, the handle used for the CCCD write, whether the characteristic property is Notify or Indicate, and what happens after reconnect.
- Handles are 16-bit addresses in this server's attribute table; the same Heart Rate Measurement can sit at handle 0x002A on one device and 0x0015 on another.
- The UUID 0x2A37, by contrast, is the universal identifier for Heart Rate Measurement.
- Reusing 16-bit SIG UUIDs for standard data and 128-bit UUIDs for private vendor data keeps generic profile clients interoperable while still leaving space for product-specific features.
Major section
Worked Example: SPP Throughput vs BLE GATT for Sensor Data Streaming
Active power: 30-50 mA continuously because the connection is maintained.
- Typical MTU: 990 bytes, so large packets reduce overhead.
- Problem:: With 7.5 ms interval, max rate is 133 notifications/sec → feasible.
- Setup complexity: SPP is simpler because it behaves like a serial port; BLE requires GATT service design.
Major section
Putting Numbers to It
SBC codec (328 kbps bitrate):: For CD-quality stereo (44.1 kHz, 16-bit), uncompressed rate is: Uncompressed = 44,100 × 16 × 2 = 1,411,200 bps = 1.41 Mbps.
- SBC compresses to 328 kbps, so Bluetooth must transmit: Radio time per second = 328,000 bits / 3,000,000 bps = 0.109 s = 10.9% duty cycle.
- Battery life ratio (800 mAh battery):: SBC battery life: Life_SBC = 800 / 2.87 = 279 hours (radio-only estimate; Sony's rated 30 hours also includes DAC, amplifier, and ANC current that this model doesn't capture).
- For casual listeners or travelers, SBC's 50% longer runtime is more valuable.
Major section
Common Mistake: Using BLE HID Without Understanding Report Descriptor Complexity
The error:: A developer building a custom BLE game controller implements HID over GATT (HOGP) but hardcodes a simple report descriptor, assuming "it's just button states and joystick positions.".
- A minimal game controller descriptor is 60-100 bytes of carefully structured data.
- Tested on Android: Worked (Android is lenient with HID descriptors).
- Tested on iOS: Worked (iOS auto-detects based on UUIDs).
- Lesson:: HID descriptors are deceptively complex.
Deck summary
Key takeaways
Mesh remains a separate many-node control choice.
- Solution: HID requires authentication and encryption; always enable security features.
- BLE's GATT (Generic Attribute Profile) and CoAP share a strikingly similar resource-oriented architecture.
- BLE profile conformance is proved by the discovered attribute table, not by a screenshot of one value arriving.
- That hierarchy is the map for the handle, CCCD, caching, and reconnect evidence below.
Retrieval practice
Recall check 1 of 2
Radio Remi says: answer from memory, then check your reasoning.
Q1You're designing a comprehensive smart home hub that needs to: (1) play music to Bluetooth speakers, (2) receive data from BLE temperature sensors, and (3) control a mesh network of smart lights. Which Bluetooth implementation strategy is required?
Show answer
Answer: C Correct!
Retrieval practice
Recall check 2 of 2
Radio Remi says: answer from memory, then check your reasoning.
Q2Place each Bluetooth profile layer where it lives so you can tell a radio transport primitive from a reusable contract and an end-user use case.
Show answer
Answer: A Build upward from radio transport through generic contracts to use-case profiles so you can select compatible roles without treating every layer as a profile.
Q3Complete the code to connect to a BLE device and read a GATT characteristic:
Show answer
Answer: A BleakClient uses an async context manager for connection management.
Print reference
Answers
Answer key.
- C · Correct!
- A · Build upward from radio transport through generic contracts to use-case profiles so you can select compatible roles without treating every layer as a profile.
- A · BleakClient uses an async context manager for connection management.