BLE characteristics tutorial - multiple values

[Levi]

Hello,

I am new to BLE and I'm following the solutions to the BLE characteristics tutorial for SDK 13.0.

I have successfully implemented my own external temperature sensor in place of the internal sensor provided in the solutions. I am able to see the changing external temperature value (in hex) using nRF Connect. Great!

Now I'd like to add more values to be displayed, but I can't figure out how. For example, I'd like to fill in the zeroes shown in the red box in the screenshot below with other sensor data.

I have changed the timer_timeout_handler() function to include heart rate (hr) as well as external temperature:

static void timer_timeout_handler(void * p_context)
 {		
    int32_t temperature = 0;    // Declare variable holding temperature value
    int32_t hr;
	
	start_temperature_no_hold_master();
	fetch_temperature_no_hold_master(&temperature);

	start_HR(0x01); //Request N = 1 (0x01) HR samples
    fetch_HR(&hr); 

	int32_t send_data[2] = {temperature, hr}; 

	our_termperature_characteristic_update(&m_our_service, send_data);
 }

But I have not touched the our_termperature_characteristic_update() function in our_service.c:

void our_termperature_characteristic_update(ble_os_t *p_our_service, int32_t 
*temperature_value)
{
// OUR_JOB: Step 3.E, Update characteristic value
if (p_our_service->conn_handle != BLE_CONN_HANDLE_INVALID)
{
    uint16_t               len = 4;
    ble_gatts_hvx_params_t hvx_params;
    memset(&hvx_params, 0, sizeof(hvx_params));

    hvx_params.handle = p_our_service->char_handles.value_handle;
    hvx_params.type   = BLE_GATT_HVX_NOTIFICATION;
    hvx_params.offset = 0;
    hvx_params.p_len  = &len;
    hvx_params.p_data = (uint8_t*)temperature_value;  

    sd_ble_gatts_hvx(p_our_service->conn_handle, &hvx_params);
}   
}

Can someone please point me in the right direction on what to do?

Thank you!

[Vasiliy Baryshnikov]

Adding Multiple Characteristics to your Service and updating their values, step by step:

I used "Bluetooth low energy Characteristics, a beginner's tutorial" to build on top of what they have (SDK 15)
devzone.nordicsemi.com/.../ble-characteristics-a-beginners-tutorial

Step 1.
You would need to create another 16-bit characteristic UUID

#define BLE_UUID_CHARACTERISTIC_1 0xBEEF // Just a random, but recognizable value
#define BLE_UUID_CHARACTERISTIC_2 0xB00B

Step 2.
In our_service.h navigate to Step 2.D where we define the structure ble_os_t.

We need to add the characteristic handles to our structure. We will be using these handle instances when updating a corresponding characteristic.

ble_gatts_char_handles_t char_handles_1; // Adding handles for the characteristic to our structure
ble_gatts_char_handles_t char_handles_2; // Adding handles for the characteristic to our structure

The code should look something like that:

typedef struct
{
uint16_t conn_handle; /**< Handle of the current connection (as provided by the BLE stack, is BLE_CONN_HANDLE_INVALID if not in a connection).*/ // keeps track of the current connection and has nothing to do with attribute table handles
uint16_t service_handle; /**< Handle of Our Service (as provided by the BLE stack). */
// OUR_JOB: Step 2.D, Add handles for the characteristic attributes to our struct
ble_gatts_char_handles_t char_handles_1; // Adding handles for the characteristic to our structure
ble_gatts_char_handles_t char_handles_2; // Adding handles for the characteristic to our structure

}ble_os_t;

Step 3.
Add an extra characteristic
In our_services.c create a copy of the our_char_add which will create a new characteristic. You should assign it a different name. You should assign it a unique UUID. You must assign it a unique characteristic handle (such as char_handles_1 and char_handles_2). You may choose to set different max_len depending on your application.

static uint32_t our_char_add_1(ble_os_t * p_our_service)
{
...

// OUR_JOB: Step 2.A, Add a custom characteristic UUID
char_uuid.uuid = BLE_UUID_CHARACTERISTIC_1; // specifying our characteristic UUID (16-bit)

...

// OUR_JOB: Step 2.E, Add our new characteristic to the service. 
err_code = sd_ble_gatts_characteristic_add(p_our_service->service_handle, // adding a service handle to the attribute table
&char_md, // adding characteristic metadata to the attribute table
&attr_char_value, // adding the attribute characteristic value to the attribute table
&p_our_service->char_handles_1); // adding characteristic handles to the attribute table

...
}

static uint32_t our_char_add_2(ble_os_t * p_our_service)
{
...

char_uuid.uuid = BLE_UUID_CHARACTERISTIC_2; // specifying our characteristic UUID (16-bit)

...

err_code = sd_ble_gatts_characteristic_add(p_our_service->service_handle, // adding a service handle to the attribute table
&char_md, // adding characteristic metadata to the attribute table
&attr_char_value, // adding the attribute characteristic value to the attribute table
&p_our_service->char_handles_2); // adding characteristic handles to the attribute table

...
}

Step 4.
Now we will be initialising those characteristics.

void our_service_init(ble_os_t * p_our_service)
{
...

// OUR_JOB: Call the function our_char_add() to add our new characteristic to the service. 
our_char_add_1(p_our_service);
our_char_add_2(p_our_service);

...
}

Step 5.
Now let's make a function that updates the characteristics. Basically, you would clone your update function.

void characteristic_value_update_1(ble_os_t *p_our_service, char machine_serial_number[])
{
...

hvx_params.handle = p_our_service -> char_handles_1.value_handle; // the handle needs to know what 

...
}

void characteristic_value_update_2(ble_os_t *p_our_service, char machine_serial_number[])
{
...

hvx_params.handle = p_our_service -> char_handles_2.value_handle; // the handle needs to know what 

...
}

Enjoy!!