Two way communication in BLE Heart Rate Sample App

[djqtsg]

Hi,

I am using nRF5_SDK_11.0.0 to learn how to use BLE stack to communicate. For the BLE HRS app, I want to achieve sth. like this: Central node can configure the sending rate of peripheral node; not only that, it can also inform peripheral to start or stop HR sending.

Can anyone enlighten me on this? It will be great with sample code, since I am new in this area.

[Petter Myhre]

You can use peripheral\ble_app_hrs and central\ble_app_hrs_c as a starting point.

[djqtsg]

yes, I've been studying those two samples. For the peripheral, I know where it sends out HR info and I could change its updating rate. But for the central, it is not clear to me where it "talks" to the peripheral. Actually I can see the heart rate sample is quite comprehensive, not only having heart rate but also two other measurements. To me the missing part is how the central talks back. Is it handle by the underlying BLE stack? Forgive my naiveness, I am new in this field.

[Petter Myhre]

The peripheral sends the heart data by using notifications, these are acknowledged by a lower layer in the stack. Every time a notification is received, the central will receive a BLE_GATTC_EVT_HVX event, and the heart rate data can be extracted. The central enables notifications by writing 0x0001 to the CCCD of the heart rate characteristic, this is done by ble_hrs_c_hrm_notif_enable().

[djqtsg]

what if there is a parameter heart rate tx rate that defines how faster sensor transmit heart rate data, which the central node can change?

[Petter Myhre]

ble_app_hrs implements the Heart Rate Service, this is a service adopted by the Bluetooth SIG. You can find a list over the adopted services here. According to the specification the central cannot change the Transmission Interval, see Section 3.1.1.5. The functionality you descirbe is easy to implement, but then you shouldn't use the UUID of the heart rate service, you should use a proprietary UUID, and implement you own service.