Here are the simple steps that explain the communication that happens during BLE connection process. In this process, we will know the differences between BLE scanner vs advertiser
How BLE Connection Works
Peripheral advertises - Peripherals like the Arduino Nano 33 BLE board starts BLE advertising over channels 37 to channel 39, indicating that it is ready to Connect. These are Broadcast packets.
Central Scans - In a BLE connection process, Central like mobile keeps scanning for devices to be connected
Central sees the advertisement - Finds the device like Arduino Nano 33 BLE board
Central initiates connection - Central initiates connection by sending CONNECT_REQ packet.
Connection established - Once connection is established, communication begins
Additional Notes:
- Note that Arduino Nano 33 BLE board can be a device as well as central
- The 3 channels are used for BLE advertising to avoid interference with Wi-Fi and reliable Bluetooth scanning (BLE channels 37 38 39)
| BLE Channel | Frequency | Purpose |
|---|---|---|
| 37 | 2.402 GHz | Advertising |
| 38 | 2.426 GHz | Advertising |
| 39 | 2.480 GHz | Advertising |
- BLE data channels are 0 to 36
- Arduino Nano 33 BLE advertising packet, in fact any advertising usually contains:
- Device name
- TX power
- Service UUID(s)
- Manufacturer data
- Flags (like BLE-only, classic not supported)
- Maximum Advertising payload is 31 Bytes
- BLE beacon vs connectable advertising - Not all BLE Devices sends advertising data for connection, Beacons just broadcast data to indicate presence. This is not for connection.
| Type | Purpose | Example Devices |
|---|---|---|
| Connectable Advertising | Allows BLE central to connect | Arduino Nano 33 BLE, sensors |
| Non-connectable Advertising | Only broadcasts data | Beacons, Eddystone, iBeacon |
Frequently Asked questions:
- Why does BLE use only 3 advertising channels? - Because channels 37, 38, 39 are placed to avoid Wi-Fi interference and improve discovery reliability.
- What is the size of a BLE advertising packet? - 31 bytes of advertising data + 31 bytes of scan response.
- Do all BLE devices allow connection? - No. Beacons only broadcast and do not accept connections.
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