BLE connections use a server client model. The server contains the data of interest, while the client connects to the server to read the data. Commonly, a Bluetooth peripheral device acts as a server, while a Bluetooth central device acts as a client. Servers can contain many services, with each service containing a some set of data. Clients can send requests to read or write some data and can also subscribe to notifications so that the server can send data updates to a client.
In this example, a basic battery client is set up on the Ameba Bluetooth stack. The client connects to another Ameba board running the corresponding BLE battery service to read the battery level data.
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On the first Ameba board, upload the BLEBatteryService example code and let it run.
For the second Ameba board, open the example “Files” -> “Examples” -> “AmebaBLE” -> “BLEBatteryClient”.
Code Upload and Execution
Upload the code and press the reset button on Ameba once the upload is finished.
Open the serial monitor and observe the log messages as the Ameba board with the battery client scans, connects, and reads data from the Ameba board with the battery service.
Highlighted in yellow, the Ameba board with the battery client first scans for advertising BLE devices with the advertised device name “AMEBA_BLE_DEV” and the advertised service UUID of 0x180F representing the battery service.
After finding the target device, the Ameba board with the battery client forms a BLE connection and searches for a battery service on the connected device, highlighted in blue.
With the client connected to the service, the battery client begins to read data using both regular data reads and notifications, highlighted in green.
BLEClient is used to create a client object to discover services and characteristics on the connected device.
setNotifyCallback() is used to register a function that will be called when a battery level notification is received.
BLE.configClient() is used to configure the Bluetooth stack for client operation.
addClient(connID) creates a new BLEClient object that corresponds to the connected device.