Creating BLE GATT Server (UART Service) on Raspberry Pi


In this post, I will create BLE GATT server on Raspberry Pi 3 using BlueZ dbus interface with Python. I will reuse BlueZ example code as much as possible. As an example of GATT service, I’ll create UART service (a.k.a. Nordic UART Service/NUS [1] ), so that I can test it with Nordic’s smartphone app [2].

 

Assumptions

 

Steps
1. BlueZ Update
Raspbian Stretch comes with BlueZ 5.43. BlueZ’s Advertising Manager has been officially supported from 5.48. So, let’s update BlueZ by following this post.

 

2. UART Service Implementation
I’ll use “example-advertisement” and “example-gatt-server” from the downloaded source code in Step 1. Some of the classes and functions will be reused.

2-1. First, let’s create a working directory.

 

2-2. Copy the example code with new names so that they can be imported as modules.

 

2-3. Create a new file (e.g. “uart_peripheral.py”). I’ll reuse ‘Advertisement’ class, ‘Service’ class, ‘Characteristic’ class, and callback functions from the example code. Also, combine the both main() functions from the example code into one and modify the sub-classes of Advertisement, Application, Service, and Characteristic to realize the UART service.

 

 

3. Test
3-1. Run the UART service on Raspberry Pi.

If all goes well, the output should be like this. Now, the service is running on Raspberry Pi and it’s broadcasting BLE advertising message.

3-2. Lauch nRF Toolbox app on the smartphone and tap on “UART”.

3-3. Tap on “CONNECT” button. Then the app will start scanning for nearby BLE devices.

3-4. Select your Raspberry Pi from the detected device list. It triggers the connection between the Raspberry Pi and the app.


 

 

 

 

 

* In case of iPhone, Raspberry Pi’s host name may be displayed instead of LOCAL_NAME in the code.

3-5. Tap on “Show Log”, enter some strings and tap on “Send”.

 

 

 

 

 

 

 

 

 

 

 

3-7. Check the console on Raspberry Pi. You should be able to see what you sent from the app like below.

3-8. Let’s send back something from Raspberry Pi by entering below on Raspberry Pi’s console.

3-9. Check the app screen.

 

 

 

 

 

 

 

 

 

 

 

 

References
[1] UART/Serial Port Emulation over BLE – Nordic Semiconductor 
[2] nRF Toolbox App – Nordic Semiconductor
[3] Turning a Raspberry Pi 3 into a Bluetooth Low Energy peripheral

 

 

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