BLE Radio Off

[ran]

Hi, 

I am developing a product using nRF2840 which performs periodic sensor readings.

Due to the nature of the sensor I'm reading from ( sensitive to noises and placement  ) , I have to make sure radio is off during sampling. 

If timing the sampling between connection interval, does that guarantees radio is powered off ? ( no radio activity what so ever ) 

Thanks, 

Ran

[Einar Thorsrud]

Hi,

The radio will never be on between connection events provided that you do not scan or advertise. You can also use the Radio timeslot API if you want the SoftDevice to allocate time slots for you where it is guaranteed that it will not use the radio.

[ran]

Einar - as an alternative for using Radio timeslot API , can I turn off BLE ( sd-power-off ) for a brief period, and then turn it on again ( with fast advertising after power on ) - do you see a problem with that ? 

[Einar Thorsrud]

Yes, you can do that.

However, it has some downsides compared to using timeslots. The most important is probably what you mentioned already, that the connection will be terminate for a period. Also, initializing the SoftDevice after reading takes some time, leading to higher average current consumption if done often in addition to what follows from the fast advertising after re-configuring the SoftDevice. Lastly, many SDK libraries are not designed to handle SoftDevice being disabled and reinitialized, and this is not a scenario that is used while testing the SDK, so you might get some problems that you need to solve. Lastly, I do not see any benefit of disabling the SoftDevice instead of using a timeslot (unless you need a longer period of time without SoftDevice interruption, longer than what can be guaranteed with timeslots).

[ran]

Einar - I'd like to better understand  : If I use MAX connection interval ( 4 sec ) - I should be able to get a 4 sec. window of radio off . If I set slave latency to N , I can even get 4 x N window of no radio . So - how come I can get only 100ms with Timeslot API ? What am I missing here ? 

[Einar Thorsrud]

Hi,

100 ms is the maximum timeslot that can be granted, which is a limitation of the SoftDevice. However, it is possible to extend a timeslot repeatedly, up to 128 seconds. This should cover most use cases, but if you must know that you have the timeslot for more than 100 ms in advance, then it is not possible. In that case the only option is to disable the SoftDevice and reinitialize it when you are done with the other task.