# Using RSL Central Mobile App to Establish a Bluetooth Low Energy Connection

The RSL15 Evaluation and Development Board (EVB) comes programmed with the ble_peripheral_server sample, enabling it to establish a Bluetooth Low Energy connection with the RSL Central Android/iOS app.

Your RSL15 EVB must have the ble_peripheral_server sample loaded to connect to the RSL Central mobile app. If the ble_perhipheral_server code is modified or removed, it can be restored by following the instructions in this guide to load the blinky sample app with your preferred IDE, but load the ble_peripheral_server sample instead.

The RSL Central app scans and establishes a Bluetooth Low Energy connection with the RSL15 EVB. After establishing the connection, the app displays the battery level and button state (SW1) from the RSL15 EVB in real-time. It can also control the LED state on the RSL15 EVB by toggling the LED switch in the app.

Simply power the RSL15 EVB by connecting the USB cable and use the RSL Central app to connect. Then use the app to:

- Scan for available Bluetooth Low Energy devices, and select one.
- Use the Settings screen to filter the Bluetooth Low Energy devices and check the app version.
- Use the Device Detail screen to receive battery and button state notifications.
- Use the LED switch to toggle the LED on the RSL15 EVB.

The "Example Screenshots of the RSL Central Mobile App in Demo Mode" figure shows the Demo Mode.

Figure: Example Screenshots of the RSL Central Mobile App in Demo Mode

Demo Mode

In the default Demo Mode, a basic graphical interface is provided to interact with the connected device’s characteristics, such as Battery, Button, and LED characteristics. Demo Mode is shown only when it is enabled and the connected device has the button and LED characteristics; otherwise a Generic Data View is presented.

Generic Data View

The "Example Screenshot of the RSL Mobile Central app in Generic Data View" figure shows the Generic Data View.

Figure: Example Screenshot of the RSL Mobile Central app in Generic Data View

The Generic Data View can be enabled by disabling Demo Mode, and is automatically enabled when the connected device does not have the button and LED characteristics. The Generic Data View can used to manually read/write device characterizes.

Key Features of the RSL Central App

The RSL Central App offers the following features:

1. Device Scanning
   - The RSL Central App scans for nearby Bluetooth Low Energy devices and displays a list of connectible devices.
   - Users can filter scanned devices by name or manufacturer ID, streamlining the discovery process.
2. Device Connectivity
   - Once a device is identified, the app allows for easy connection.
   - The app supports AutoConnect, enabling automatic reconnection when the device comes back online after a disconnection.
3. Service and Characteristic Discovery
   - After connecting to the device, the app automatically discovers and lists all available services and characteristics.
   - Both standard Bluetooth SIG profiles and custom services are supported.
4. Read/Write Capabilities
   - The app enables users to interact with characteristics in two ways:
     - Read: Fetch and display characteristic values.
     - Write: Modify characteristic values with support for write types like Write Without Response.
5. Notifications and Indications
   - Notifications and indications can be enabled or disabled for supported characteristics, allowing real-time monitoring of characteristic changes.
6. RSSI Reading
   - The app can display the RSSI (Received Signal Strength Indicator) value, giving users insights into the connection strength between their device and the RSL15 EVB.
7. Data Export
   - Users can export data captured from characteristics in CSV and Excel formats.
   - This makes it easy to log or analyze information from the Bluetooth Low Energy connection.
8. PHY Management (Android Only)
   - With Android phones, the app allows users to adjust PHY settings (Physical Layer) to optimize Bluetooth Low Energy connection performance.
9. MTU Request (Android Only)
   - The app supports requesting specific MTU (Maximum Transmission Unit) sizes
   - This improves the efficiency of data transfers for certain Bluetooth Low Energy use cases.
10. Connection Interval Settings (Android Only)
    - The app provides options to adjust the connection interval between the phone and Bluetooth Low Energy device, offering settings for HIGH, LOW, and BALANCED modes.
11. Bonding (Android Only)
    - The app supports creating a bond with the device, allowing for a more secure and persistent Bluetooth Low Energy connection.