Power Usage when connected to nRF Connect Android App

[Gary T]

Hi

I am testing a thermometer peripheral using the nRF52840DK. It is advertising using BT LE Coded (BT_LE_ADV_OPT_CODED) with an advertising frequency of 3 seconds.

When it is advertising it is using ~20µA of power. When I connect to the peripheral using the nRF Connect App on my Android phone the power usage of the peripheral goes up to ~235µA.

I believe the connection parameters are controlled by the "Central" which in this case would be my phone. Is this correct?

Using my PPK2 I can see that there is power usage every 45ms.

Is there any way to control the settings on the nRF Connect App to lower the power usage (perhaps by changing the 45ms communication interval)?

I also have another question related to the connection timeout for the nRF Connect Android App.

If I set my advertising interval on my peripheral to 2 seconds the app connects reliably. If I set it to 3 seconds then sometimes it connects but sometimes it times out. If I set it to 5 seconds then it never seems to connect. Is there a specific connection timeout in the app? Is there a way for me to adjust this?

Thanks for your help.

Regards,

Gary

[Kazi Afroza Sultana]

Hello Gary,

The following configs set the preferred connection interval:

CONFIG_BT_PERIPHERAL_PREF_MIN_INT=3100

CONFIG_BT_PERIPHERAL_PREF_MAX_INT=3200

However as you said that the peripheral can only have preferred connection interval settings. It is always the central that decides what you actually get.

Regarding nRF Connect for android app, you can read this link https://stackoverflow.com/questions/21398766/android-ble-connection-time-interval . It is possible to choose between a few intervals, but you are not free to set it to any value that you want.

''I also have another question related to the connection timeout for the nRF Connect Android App.

If I set my advertising interval on my peripheral to 2 seconds the app connects reliably. If I set it to 3 seconds then sometimes it connects but sometimes it times out. If I set it to 5 seconds then it never seems to connect. Is there a specific connection timeout in the app? Is there a way for me to adjust this?''

If the advertising is slow then there is a higher chance that the central will not pick the advertising packets up. 

You can read the following blog post: 

 https://devzone.nordicsemi.com/guides/short-range-guides/b/bluetooth-low-energy/posts/bluetooth-smart-and-the-nordics-softdevices-part-1 

Thanks.

Best Regards,

Kazi Afroza Sultana

[Gary T]

Hi Kazi

Thank you for your feedback. 

I was successful in changing the connection interval from the default (~45ms to around ~150ms) by adding the CONFIG's you mention below to the PRJ.conf file.

Interestingly, if I set the MAX_INT beyond 160 then I get a compile error. 

For example, if I use the exact values you provide below, it doesn't work.

According to the docs it seems I should be able to set this anywhere from 6 to 3200.

Any ideas on what's causing this?

Thankfully, setting to 160 has dropped the power usage while connected from ~235µA to ~60µA which is good enough for me (although I would like it lower).

Thanks for your help.

Regards,

Gary

[Kazi Afroza Sultana]

Hello Gary,

Is the preferred time is 1/4 of the supervision timeout in your configuration?

This is another requirement for preferred connection interval. 

Thanks.

Best Regards,

Kazi Afroza Sultana

[Gary T]

Hi Kazi

That's perfect. I hadn't set the timeout value.

I have set it now and it works correctly.

When the max is set to 500ms the power usage is 15µA. Very nice!

When set to 4s the power usage is only 7µA but the response times when pulling data are too slow.

Please let me know which file you extracted the screenshot from.

Thanks for your help.

Regards

Gary 

[Kazi Afroza Sultana]

Hello Gary,

This is the file : zephyr\subsys\bluetooth\host\gatt.c

Thanks. 

Best Regards,

Kazi Afroza Sultana