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!

[Jørgen Holmefjord]

Hi,

Since the variable temperature is of type int32_t, it will require all the 4 bytes of the characteristic. If you want to add another 32-bit value to the characteristic, you will have to increase the size.

In our_char_add(), set:

attr_char_value.max_len = 8;

And in our_termperature_characteristic_update(), set:

uint16_t len = 8;

If your temperature value is only 1 byte, you should change the type to int8_t. Then you can fill the other 3 bytes of the characteristics using other 8-bit variables.

Best regards,

Jørgen

[Levi]

Hi Jørgen,

I went the route of filling the characteristic data with 8-bit variables using the following code:

int32_t send_data = temperature | (heart_rate << 8) | (third_variable << 16) | (fourth_variable << 24);

I can see the values were transmitted over BLE successfully in nRF Connect!

Thank you very much for your help!