How to configure a very low power connection

[Jason]

Hi, I'm making a device that will probably be encapsulated In silicone, which means it won't be possible to change the battery easily. It's got to connect to android and iOS phones/tablets. It only really needs to send a value to the phones once every 2 minutes, it's really a beacon but I had problems with android background scans (discussion here devzone.nordicsemi.com/.../long-running-android-scanning-in-background)

I was advised in that post to make a connection to the device 

Hung Bui said:

For example you can configure a connection with 0.5 second interval and 1 minutes timeout. You can configure the slave latency so that you only need to wakeup and response to the central every 30 seconds. 

I posted a supplementary question a few days ago to that original devzone question, but it wasn't noticed. I would like some help modifying an example to setup the necessary parameters since I can see that there are a lot of variables and a lot of ways to get this wrong. I think I could spend weeks experimenting with all the options so and help is greatly appreciated. 

Kind Regards, 

-Jason

[Turbo J]

Jason said:

You can configure the slave latency so that you only need to wakeup and response to the central every 30 seconds. 

This would violate iOS guidelines, which only allow 4 (four) seconds of supervision timeout. That meany there MUST be communication in this 4 second window each time - otherwise there will be a disconnect. The iOS developer has no control over this timeout AFAIK.

So while BTLE specs technically allow large timeouts, actual OS limits might be much lower.

You also don't want to go much above one second connection interval, because crowded urban environments cause communication attemts to fail. There are almost always other users on the 2.4 GHz frequencies.

[Jason]

I read the apple design guidelines a few days ago and saw this mentioned but hoped maybe the slave latency, or something else, might offer a workaround. I calculated that a cr2032 will last about a week to 10 days at these transmission rates. 

I guess I need to redesign the device. 

Thank you

[Fredrik]

Did you check out the online power profiler? If you plug in your parameters I think you'll find that a CR2032 battery will happily keep your device alive for years (in theory).

[Jason]

I think my calculations were miles off. 

I tested a few months ago with an nrf52840 dongle and the power profiler but I cant find my notes from the tests. I'll test again.

THANK YOU

[Fredrik]

No problem. Please click the "verify answer" button on my comment if you consider this case solved.

Good luck with your project!

[Jason]

FYI

On my 52840 dongle I get 70uA average during advertising with one advert per second. 

This equates to only 130 days for a 220mAh CR2032. This is where my bad calculation came from. But instead of 10-14 days I should have said 100-140 days... I did similar experiments a few months ago with the dongle. This is why I concluded that I needed to keep communications to the absolute minimum. 

All of this is using +8 TX power. 

Here's the trigger view showing one of the adverts. They seem to vary between 3 big peaks like this or sometimes up to 6 peaks. 

I'm not sure if these figures are normal for the dongle or not.