December 13, 2023

Developing custom BLE profiles with the nRF52

Bluetooth Low Energy (BLE) is a popular wireless communication technology that is widely used in IoT devices. The nRF52 series of microcontrollers from Nordic Semiconductor provide excellent support for developing BLE applications. In this blog post, we will explore how to develop custom BLE profiles using the nRF52.

Understanding BLE Profiles

Before diving into developing custom BLE profiles, it’s important to understand what BLE profiles are. BLE profiles define a set of rules and structures for how devices communicate with each other over Bluetooth. They define the services, characteristics, and descriptors that devices expose to each other.

There are two main types of BLE profiles:

1. GATT (Generic Attribute Profile): This profile allows devices to expose data and functionality. It consists of services, characteristics, and descriptors.
2. HFP (Human Interface Device Profile): This profile allows devices to expose human interface devices like keyboards, mice, and game controllers.

For this blog post, we will focus on developing custom GATT-based BLE profiles using the nRF52.

Setting up the Development Environment

To develop custom BLE profiles with the nRF52, we need to set up our development environment. Here are the steps:

1. Hardware Setup: Connect the nRF52 development board to your computer via USB.

2. Software Setup: Install Nordic’s nRF5 SDK and Segger Embedded Studio (SES) or any other IDE of your choice. Make sure you have the latest version of the nRF5 SDK.

Creating a Custom BLE Profile

To create a custom BLE profile, we need to define the GATT database. The GATT database consists of services, characteristics, and descriptors. Let’s take a look at an example of a custom BLE profile that includes a single service with two characteristics.

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// Define the UUIDs for the service, characteristics, and descriptors
#define SERVICE_UUID              0x1234
#define CHARACTERISTIC_UUID_1     0x5678
#define CHARACTERISTIC_UUID_2     0x9abc
#define USER_DESCRIPTOR_UUID      0xdef0

// Create a custom service structure
ble_uuid_t service_uuid;
ble_uuid128_t base_uuid = {SERVICE_UUID};

ble_uuid_vs_add(base_uuid.uuid128, &service_uuid.type);
service_uuid.uuid = SERVICE_UUID;

// Create two characteristics
ble_uuid_t char_uuid;
ble_uuid_t char_uuid2;

char_uuid.uuid = CHARACTERISTIC_UUID_1;
char_uuid2.uuid = CHARACTERISTIC_UUID_2;

// Configure properties and permissions for the characteristics
ble_gatts_char_md_t char_md, char_md2;
ble_gatts_attr_md_t cccd_md;

memset(&char_md, 0, sizeof(char_md));
memset(&char_md2, 0, sizeof(char_md2));

char_md.char_props.read = 1;
char_md2.char_props.read = 1;

char_md.p_char_user_desc = (uint8_t*)"Characteristic 1";
char_md2.p_char_user_desc = (uint8_t*)"Characteristic 2";

// Add characteristics to the service
err_code = sd_ble_gatts_characteristic_add(service_handle, &char_md, &char_uuid, &char_handles);
err_code = sd_ble_gatts_characteristic_add(service_handle, &char_md2, &char_uuid2, &char_handles2);

In this example, we define two characteristics, each with read permissions. We also define user descriptors for each characteristic.

Once you have defined the GATT database for your custom BLE profile, you can start advertising and connecting to your device.

Testing the Custom Profile

To test your custom BLE profile, you can use a mobile application or a BLE dongle. There are several mobile applications available that allow you to explore and interact with BLE devices.

Using a mobile application, you can scan for nearby devices, connect to your device, and explore the services and characteristics exposed by your custom profile.

Conclusion

Developing custom BLE profiles with the nRF52 is a powerful feature that allows you to create unique and specialized BLE functionality for your IoT devices. In this blog post, we explored the basics of developing custom GATT-based BLE profiles. We learned how to define a GATT database and add services, characteristics, and descriptors.

With the nRF52 series and Nordic Semiconductor’s nRF5 SDK, you can easily create custom BLE profiles tailored to your specific requirements. Happy coding!

➡️ Over-the-Air (OTA) firmware updates using the nRF52

⬅️ Implementing Bluetooth Low Energy (BLE) on the nRF52

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