Connecting to Custom Service/Characteristic of BLE peripheral with nRF52 acting as central.

[inspiringdev123]

I am currently connected to a BLE peripheral with the nRF52 acting as the central. I am able to scan using the device's name and connect. I created a custom file to handle the central functions including adding the custom UUID and starting the discovery. This done here

uint32_t ble_obd_c_init(ble_obd_c_t * p_obd_service_client, ble_obd_c_init_t * p_ble_obd_c_init)
{
    uint32_t      err_code;
    ble_uuid_t    obd_uuid;
    // TODO for V Link
    ble_uuid128_t obd_base_uuid = OBD_BASE_UUID;
    obd_uuid.uuid = BLE_UUID_OBD_SERVICE;
    obd_uuid.type = BLE_UUID_TYPE_VENDOR_BEGIN;

    VERIFY_PARAM_NOT_NULL(p_obd_service_client);
    VERIFY_PARAM_NOT_NULL(p_ble_obd_c_init);

    err_code = sd_ble_uuid_vs_add(&obd_base_uuid, &obd_uuid.type);
    VERIFY_SUCCESS(err_code);

    p_obd_service_client->conn_handle                    = BLE_CONN_HANDLE_INVALID;
    p_obd_service_client->evt_handler                    = p_ble_obd_c_init->evt_handler;
    p_obd_service_client->error_handler                  = p_ble_obd_c_init->error_handler;
    p_obd_service_client->obd_service_char.handle_value  = BLE_GATT_HANDLE_INVALID;
    p_obd_service_client->p_gatt_queue                   = p_ble_obd_c_init->p_gatt_queue;
    p_obd_service_client->uuid_type                      = BLE_UUID_TYPE_VENDOR_BEGIN;

    return ble_db_discovery_evt_register(&obd_uuid);
}

The discovery runs smoothly and finds the Service. The issue is that the characteristic is not there, so I am unable to read and write to the device. This is where I try and find the characteristic. The uuid type is returning as 4, but I thought there was only 0, 1, and 2 (I set it to 2, the BLE_UUID_TYPE_VENDOR_BEGIN).

void ble_obd_c_on_db_disc_evt(ble_obd_c_t * p_obd_service_client, ble_db_discovery_evt_t * p_evt)
{
    memset(&obd_c_evt,0,sizeof(ble_obd_c_evt_t));

    ble_gatt_db_char_t * p_chars = p_evt->params.discovered_db.charateristics;

    // Check if the OBD was discovered.
    if (    (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE)
        &&  (p_evt->params.discovered_db.srv_uuid.uuid == BLE_UUID_OBD_SERVICE)
        &&  (p_evt->params.discovered_db.srv_uuid.type == p_obd_service_client->uuid_type))
    {
        for (uint32_t i = 0; i < p_evt->params.discovered_db.char_count; i++)
        {
            switch (p_chars[i].characteristic.uuid.uuid)
            {
                case BLE_UUID_OBD_CHARACTERISTIC:
                    // Found OBD characteristic inside the OBD Service.
                    p_obd_service_client->obd_service_char = p_chars[i].characteristic;
                    NRF_LOG_INFO("Discovered characteristic handle: %i", p_chars[i].characteristic.handle_value);
                    break;

                default:
                    break;
            }
        }
        if (p_obd_service_client->evt_handler != NULL)
        {
            obd_c_evt.conn_handle = p_evt->conn_handle;
            obd_c_evt.evt_type    = BLE_OBD_C_EVT_DISCOVERY_COMPLETE;
            p_obd_service_client->evt_handler(p_obd_service_client, &obd_c_evt);
        }
    }
}

These are my defines for the custom service/characteristics of the OBD device 

#define OBD_BASE_UUID {{0xF2, 0xC3, 0xF0, 0xAE, 0xA9, 0xFA, 0x15, 0x8C, 0x9D, 0x49, 0xAE, 0x73, 0x71, 0x0A, 0x81, 0xE7}}

#define BLE_UUID_OBD_SERVICE 0x0A71                   //< The UUID of the OBD Service. 
#define BLE_UUID_OBD_CHARACTERISTIC 0xD6C9  // < The UUID of the RX and TX Characteristic. 

I attached an image of the service/characteristic from nRF52 connect. 

I have another OBD device that uses 16 bit UUIDS and was able to do this easily, but since these use 128 bit UUIDs, I am running into some issues.

I have attached my wireshark capture from when I establish a connection, search for the service and then search for the characteristic for a working device and the non-working one. The LE Link Capture is working while the VLINK does not.

3225.VLINK Capture from connecting.pcapng5381.LE LINK Capture from connecting.pcapngVLINK to iOS Capture from connecting.pcapng

[Tai]

Can you check if your BLE peripheral already enabled WRITE, READ, NOTIFY properties or not? You need to enable them so that the central one can be able to interact with.

[inspiringdev123]

Tai Seems to be. This is the only characteristic that returns for the given service UUID

[Tai]

Did you check if bonding process is needed? Please refer to this post. Happy to discuss if the prob is still there after you take a look at that post.

[inspiringdev123]

No bonding is needed I believe. I am going to connect to the OBD device with an iOS OBD Car Reader and get the wireshark report and post that in here tomorrow and see if there is anything useful in there that can help us find the issue. 

[Tai]

Taking a look at your wireshark report, the peripheral only sent its Characteristic UUID as highlighted in yellow. I believe it has to send its Service UUID as well to be able to talk with the central. Thus, you can check in your peripheral custom ble service init function if you configure it correctly.

[inspiringdev123]

 Tai The peripheral is from an outside source, so I do not have any control over the code. Android and iOS devices are able to connect to and talk to this device. Just wondering if you see anything else I am possibly doing wrong?

I have attached the wireshark capture from the working OBD Device too to the first message as well as an iOS app connecting to the OBD device.