Discovering problem for different 128-bit service and characteristic uuid as a central device

[secondbest]

Hello;

I am using NRF51822 with SDK12.3 as a central device. I want to discover and connect a peripheral bluetooth device by using my NRF51822 central device.

If the service and characteristic is the same, for example service uuid is "00002234-b38d-4985-720e-0f993a68ee41" and characteristic uuid is "00002235-b38d-4985-720e-0f993a68ee41" , I can enable the notification of the characteristic and NRF51 get data from this peripheral device by using this characteristic.

However, If the service and characteristic is the different, for example service uuid is "680c21d9-c946-4c1f-9c11-baa1c21329e7" and characteristic uuid is "003bbdf2-c634-4b3d-ab56-7ec889b89a37", I can connect to this device but NRF51 discovers all characteristics as 0x00 and cannot enable the notification.

Is there a way to handle this problem?

Thanks.

[tesc]

Hi,

Either if you use the Database Discovery Module or not, the underlying call is to sd_ble_gattc_primary_services_discover(). In order to make sense of the discovery, all the base UUIDs must be registered with the SoftDevice on the device doing the scanning. If not the type will be of BLE_UUID_TYPE_UNKNOWN (which is, incidentally, 0x00). May that be what you are seeing?

Do you have example projects for reproducing what you see using standard DKs or Dongles?

Regards,
Terje

[secondbest]

Thanks for response, tesc. Also, sorry for late response.

I must use NRF51822 device, so I am using SDK 12.3.0. In this SDK, I am using "ble_app_uart_c" central example. I registered my 128-bit service UUID. However, In this example, this central example discovers  the characteristic of this service by using 16-bit UUID address. For example;

Service: "00002234-b38d-4985-720e-0f993a68ee41" (This service is added inside the central code.)

Characteristic of this service: "00002235-b38d-4985-720e-0f993a68ee41" (0x2235 adress is added inside the central code.)

In this situation, there is no problem. Because, the central example code only uses the 16-bit UUID address(0x2235) to discover the characteristics. However;

Service: "680c21d9-c946-4c1f-9c11-baa1c21329e7"

Characteristic of this service: "003bbdf2-c634-4b3d-ab56-7ec889b89a37"

In this situation, I can discover the service correctly. There is no problem. But, I cannot discover characteristics of this service because they have different 128-bit UUID address. The problem arises in this case.

....

ble_gatt_db_char_t * p_chars = p_evt->params.discovered_db.charateristics;
if (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE){
			
	printf("SERVICE: %d\r\n", p_evt->params.discovered_db.srv_uuid.type);
}

if (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE &&
        p_evt->params.discovered_db.srv_uuid.uuid == BLE_UUID_SENSOR_SERVICE &&
        p_evt->params.discovered_db.srv_uuid.type == p_ble_sensor_c->uuid_type)
    {
		printf("CHAR SIZE: %d\r\n", p_evt->params.discovered_db.char_count);

        for (i = 0; i < p_evt->params.discovered_db.char_count; i++)
        {
			printf("UUID: %d\r\n", p_chars[i].characteristic.uuid.uuid);
            switch (p_chars[i].characteristic.uuid.uuid)
            {
                case BLE_UUID_SENSOR_CHARACTERISTIC:
                    sensor_c_evt.handles.sensor_rx_handle = p_chars[i].characteristic.handle_value;
                    sensor_c_evt.handles.sensor_rx_cccd_handle = p_chars[i].cccd_handle;
                    break;
                
                ...    
            } 
    ...
}    

This is my code and the output is like this.

For first situation; the log outputs are like this.

SERVICE: 00002234-b38d-4985-720e-0f993a68ee41

CHAR_SIZE: 2

UUID: 0x2435

UUID: 0x2436

For second situation; the log outputs are like this.

SERVICE: 680c21d9-c946-4c1f-9c11-baa1c21329e7

CHAR_SIZE: 5

UUID: 0x0

UUID: 0x0

....

My question is how to get 128-bit characteristic UUID by using central example. Thanks for your help and sorry for my bad english. 

Thanks.

[Bjørn Kvaale]

Sorry for the delayed response. May I first ask why you want to have a different base UUID for your service & your characteristic? If you do want to use a different base UUID for your service & the service's characteristic, you can do this. Take a look at this devzone case for more info, as well as the S130 v2.0.1 softdevice API documentation.

[Jim_huan]

Hi,

Now I just doing the same project like this, and how about your progress now?And Can I  get some advices form you ?thx.

[secondbest]

Hello Jim_huan, in my experience, it is not possible to scan different service and characteristic addresses as a central device. On the other hand, it is possible to create different service and characteristic addresses as a peripheral device.