Connection

Overview

The Armband has two types of connections: the USB connection and the Bluetooth connection.

The Bluetooth connection is chosen as default, and is used to communicate with the Armband wirelessly. It is the preferred method for most applications, as it enables a simpler setup, and more user-friendly interaction with the Armband.

The USB connection offers a direct way of connecting, allowing for a faster and more reliable exchange of data. Thus, it is the preferred method for most development applications, as it enables a stable communication channel between the Armband and the host computer.

BLE Connection

To make things clearer and closer to the BLE nomenclature we refer to the Armband as a peripheral device, and the host computer as a central device.

The wireless connection follows the standard BLE protocol to start the communication between the Armband (peripheral device) and the host computer (central device), followed by an exchange of credentials to validate the connection between them.

Only after this validation is completed, the Armband will start streaming data to the host computer.

BLE connection process:

sequenceDiagram
    participant A as Armband
    participant H as Host
    loop Every 10 seconds
        A->>H: Advertise
        H->>A: Scan
        A->>H: Connection Established
    end
    A->>H: Ask for certificate
    H->>A: Send Certificate
    alt valid credentials
        A->>H: Start Streaming
    else invalid credentials
        A->>H: Disconnect
    end
    opt unknown or timeout
        A->>H: Disconnect
    end

The credentials for each device are unique and are provided by the Neeno Team when the device is acquired. They are stored in a JSON file, which is used to authenticate the connection between the Armband and the host computer.

neeno.connect

When connecting with Python, the credentials are passed as an argument to the connect function.

This function first reads the JSON file and validates its contents. If they describe a valid BLE connection, it will create a BLEConnection class object, and asks your host device to start scanning BLE devices in the vicinity.

Once a device is found, the connection is established, and the credentials are sent to the Armband. If the credentials are valid, the Armband will start streaming data to the host computer, and the function connect will return the created BLEConnection object.

flowchart TD
    Start --> Credentials[Get credentials from JSON]
    Credentials -->|Correct Format| BLEC[create BLEConnection]
    BLEC --> Scan[Scan Peripheral devices]
    Scan -->|Found| BLEConnect[Connect to Peripheral]
    BLEConnect --> Validation[Certificate validation from Armband]
    Validation -->|Valid| ReadStream[Start reading Stream]
    Validation -->|Invalid or Timeout| Error
    Credentials -->|Invalid content| Error
    Scan -->|Not Found| Error
    BLEConnect -->|Invalid or Timeout| Error
    ReadStream --> returnOK[return BLEConnection object]
    Error --> returnError[return None]

After a successfull connection, you can start using your BLEConnection object to read the streamed data from the Armband.

The attribute data of the BLEConnection object is a byte array updated every time new data is received from the Armband.

simple_ble_connection.py

import neeno
armband_ble = neeno.connect("credentials.json")
while armband_ble.data_available():
    print(armband_ble.data)

This will print the data streamed from the Armband every time new data is received. We can stop the execution by pressing Ctrl+C. This will also finish the connection with the Armband.

$ python simple_ble_connection.py
Connected to '11:22:33:44:55:66'
[ 1.78505900e+07  9.94552487e-01  4.95322942e-02 -5.61040677e-02
 -7.25550608e-02  8.43566331e-01 -1.16930183e-02 -7.00000000e-01
  1.21614716e+00]
[ 1.78505900e+07  9.94552487e-01  4.95322942e-02 -5.61040677e-02
 -7.25550608e-02  8.43566331e-01 -1.16930183e-02 -7.00000000e-01
  1.21614716e+00]
[ 1.78506900e+07  9.88135932e-01  7.26829342e-03 -8.77417694e-02
 -1.25840903e-01  9.05164273e-01  1.01204211e-01 -7.00000000e-01
  1.10219970e+00]
[ 1.78506900e+07  9.88135932e-01  7.26829342e-03 -8.77417694e-02
 -1.25840903e-01  9.05164273e-01  1.01204211e-01 -7.00000000e-01
  1.10219970e+00]
[ 1.78507900e+07  9.94648126e-01 -8.27074411e-02 -2.49536451e-02
 -5.66736335e-02  9.59479700e-01  3.46532403e-02 -7.00000000e-01
  1.33436103e+00]
KeyboardInterrupt
^C
Disconnected from '11:22:33:44:55:66'