Need long battery life with fast connection interval

RE: Need long battery life with fast connection interval

mrono — Thu, 28 Oct 2021 05:06:14 GMT

Yes, that's what I was trying to say.

I'm not sure if there is a way to tell the Nordic BLE stack that you would like it to listen on every interval even if you have negotiated a high slave latency.

But one way to override this is to have something to send from the peripheral to the central. So when you'd like to override the latency, send a dummy notification from the peripheral every 100ms. That forces the peripheral to listen.

This would mean some extra communication, but it would avoid the need to renegotiate.

RE: Need long battery life with fast connection interval

Dawei — Thu, 28 Oct 2021 00:15:43 GMT

I don't totally understand this. If the peripheral has a high latency, it won't be listening for data from the central. Am I wrong? I guess what we need is some way to force the peripheral to "override" the latency.

RE: Need long battery life with fast connection interval

mrono — Wed, 27 Oct 2021 08:39:10 GMT

[quote userid="76454" url="~/f/nordic-q-a/81068/need-long-battery-life-with-fast-connection-interval/336117#336117"]So we are thinking about some scheme where maybe we can adjust the slave latency[/quote]

Hmm.. Is there a way to tell the BLE stack to wake up on every interval even if you have a nonzero slave latency? Because as far as I know the only way to really adjust it is to renegotiate the connection parameters. And that undoes much of the benefits.

If your device also sends some data to the central, then one option is to send dummy notifications. So keep a large slave latency all the time. And when you do want to wake up on every interval, send a dummy notification to force the peripheral to wake up.

RE: Need long battery life with fast connection interval

Dawei — Wed, 27 Oct 2021 07:59:14 GMT

Yes we are trying slave latency. For some of the peripherals, its fine, because they do not receive data, only send as required. We've got another peripheral however, that will need to receive data. So we are thinking about some scheme where maybe we can adjust the slave latency depending on how often its used. If there is for example, 1 hour of non-use, then we increase the latency. That will result in a small delay, or maybe even a missed command, but that's ok. After some activity then the latency goes back to 0 until there is another lapse in use.

We can't have some of the devices go to sleep, because they are not easily accessible. We must maintain some connection.

RE: Need long battery life with fast connection interval

mrono — Wed, 27 Oct 2021 07:53:43 GMT

Have you already considered slave latency? That might be enough for your power requirement.

A 100ms interval with a slave latency of 10 would mean you only need to communicate once per second. And there would be no need to renegotiate, it would be up to the peripheral to decide whether to communicate every 100ms or not.

RE: Need long battery life with fast connection interval

Simonr — Wed, 27 Oct 2021 07:43:05 GMT

Do you plan on the device being constantly connected to the central device, or to disconnect and go to sleep between connections? If the supervision timeout is lower the device will disconnect quicker, and alternatively go to sleep quicker. When the device is asleep the current consumption will be way lower (check out the sleep scenarios for the nRF52832 in the product specification).

Best regards,

Simon

RE: Need long battery life with fast connection interval

Dawei — Tue, 26 Oct 2021 09:52:15 GMT

We have a small battery in the peripheral, about 150-200mAh. If we have a 100mS connection interval, that is about 44uA (According to online power profiler), even when using all the normal power saving efforts, the life is too short. About 70 days battery half life. We would like to have at least double that.

How would the supervision timeout effect the power consumption?

RE: Need long battery life with fast connection interval

Simonr — Tue, 26 Oct 2021 09:30:46 GMT

Have you checked out my colleague Scott's current consumption guide where he goes through all the most common ways to optimize power consumption on nRF52 designs? The connection interval should not be detrimental to your current consumption, so please check out the guide for some suggestions. What is I.E. the connection supervision timeout in your application and advertising interval?

Best regards,

Simon