How to send gyro sensor data through bluetooth(ble)?

[Gon]

Hi, all.

I want data read from gyro sensor through i2c, and then send it through bluetooth equipment.(PC or iPhone and so on) But i don'k know how to send gyro sensor data through bluetooth.

I tried to send gyro sensor data transmitted through "on_hids_evt()" and "on_hids_evt()" and "bsp_event_handler()" functions. But it did not fit.

I would like to transmit the gyro sensor data via the BLE continuously. In other words, I would like to express the mouse cursor through the sensor value. (Not use button triggering like "ble_app_hids_mouse" original example.)

My development environment is like below.

• chip : nRf51822
• example : ble_app_hids_mouse(s130) in nRF_Example 10.0.0

Please kindly comment guide or relevant Q&A issue. (I can't found relevant this issue in "Questions" tab, yet.)

[FormerMember]

In your case, the BLE device will be a peripheral/slave device. In order to transmit data continuously, I would recommend you to use notification. This message sequence chart shows the flow for transmitting a notification. As you can see, sd_ble_gatts_hvx(..) transmits notifications.

The functions "on_hids_evt()" and "on_hids_evt()" and "bsp_event_handler()" handle received events.

In order for the peripheral to transmit notifications, the central/master device will have to enable notifications. The central enables notifications by writing to the CCCD (Client Characteristic Configuration Descriptor) for the gyro characteristic.

I will try to make it clearer with an example, using ble_app_uart :

The peripheral side:

The UART RX characteristic is set up the following way, with the notification property set. The UART RX characteristic transmits data from the peripheral to the central.

static uint32_t rx_char_add(ble_nus_t * p_nus, const ble_nus_init_t * p_nus_init)
{
/**@snippet [Adding proprietary characteristic to S110 SoftDevice] */
...
...    
memset(&char_md, 0, sizeof(char_md));

char_md.char_props.notify = 1;  // Notification property set
char_md.p_char_user_desc  = NULL; 
char_md.p_char_pf         = NULL;
char_md.p_user_desc_md    = NULL;
char_md.p_cccd_md         = &cccd_md;
char_md.p_sccd_md         = NULL;

...
...
return sd_ble_gatts_characteristic_add(p_nus->service_handle,
                                       &char_md,
                                       &attr_char_value,
                                       &p_nus->rx_handles);
/**@snippet [Adding proprietary characteristic to S110 SoftDevice] */
}

The transfer of the notifications happen in ble_nus_string_send(..) if notification has been enabled.

As mentioned above, notifications are being enabled by writing to the CCCD for the characteristic in question. In ble_app_uart, a write event to the RX characteristic CCCD is handled in on_write(..):

  static void on_write(ble_nus_t * p_nus, ble_evt_t * p_ble_evt)
  {
  ble_gatts_evt_write_t * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;

// Check if the write event is addressed to the RX characteristic CCCD handle:
if (
    (p_evt_write->handle == p_nus->rx_handles.cccd_handle)  /
    &&
    (p_evt_write->len == 2)
   )
{
    // Check if the write event enables notifications:
    if (ble_srv_is_notification_enabled(p_evt_write->data))
    {
        p_nus->is_notification_enabled = true;
    }
    else
    {
        p_nus->is_notification_enabled = false;
    }
}
...
...
}

The central side: The central side enables notifications when the RX characteristic has been found:

static void ble_nus_c_evt_handler(ble_nus_c_t * p_ble_nus_c, const ble_nus_c_evt_t * p_ble_nus_evt)
{
    uint32_t err_code;
    switch (p_ble_nus_evt->evt_type)
   {
    ...
    ...
    
    case BLE_NUS_C_EVT_FOUND_NUS_RX_CHARACTERISTIC:
        err_code = ble_nus_c_rx_notif_enable(p_ble_nus_c);
        APP_ERROR_CHECK(err_code);
        APPL_LOG("The device has the device RX characteristic\r\n");
        break;
...
...
}

I hope this gives you an idea of how to implement update of the gyro data.

Update 04.03.16: It should be possible to update the data fast enough. There are several parameters that affect the throughput:

1. Connection interval: A shorter connection interval will allow the peripheral to send notifications more often, at least every connection interval.
2. Multiple packets per connection interval: When using notification, it is also possible to transmit multiple packets per connection interval.

How often do you want to transmit the gyro data?

For a continuous data update every given interval, you can use a timer. The example ble_app_hrs uses a timer to update the heart rate value at a given interval.

In order to check what is being transferred over the air, you can use the sniffer to track the BLE link.The sniffer download contains among others a sniffer firmware that you program to either the nRF51-DK or the nRF51-Dongle, and the nRF51-DK/nRF51-Dongle will be the sniffing device. Using the sniffer is very easy. It can be downloaded from the nRF51822 webpage --> "downloads" tab.

The sniffer should be used with Wireshark, and it works best with version 1.10, not one of the newer versions. Wireshark can be downloaded here:

• www.wireshark.org/.../
• www.wireshark.org/.../

[Gon]

Hi, Kristin. I'm sorry for making you wait.

I don't know about the "sniffer". Could you some guide to me for it?