nrf51 not waking to advertise (Bluetooth)

[MattFL]

I'm looking for help figuring out why my nrf51422 isn't waking up to advertise, I'm missing a detail but I don't know what it is.  It works great, until sd_power_system_off() is called, and then there is no more advertising.  

My project will run on a single button cell but it needs to always advertise so that it automatically connects to its partner device when that device comes into range.  Right now if I skip the call to sd_power_system_off() everything works great, except that it draws 2mA which will kill my button cell quickly.  If I call sd_power_system_off() it never seems to wake to advertise and the devices never connect.  Is there something specific that I need to do to enable periodic wakeup to advertise? 

[Vidar Berg]

Hi,

System OFF mode is the deepest power saving mode on the nRF51. In this mode, everything on the chip will be powered down except for reset and wakeup mechanisms, please see chapter 12 in nRF51 RM for more details. It's probably System ON mode that you want use. Just call  sd_app_evt_wait() wait from the main loop like we do in our SDK examples. 

[MattFL]

 Thank you for the reply.   sd_app_evt_wait() works great functionality wise, but it's drawing about 2mA when doing this.  Should I be expecting lower current draw using this method?  

[Vidar Berg]

Current consumption should be significantly lower if it is only advertising. Are you using any other peripherals such as UART, etc? Also note that the chip will draw more current while in debug mode (debugger attached). 

[MattFL]

Thank you, it turns out I had another sensor on the board that was always enabled and should not have been.  Now I'm sitting at about 0.15-ish mA when connected, and 0.5-ish mA when advertising.  I need to get that advertising value down, but definitely going the right direction.  :) 

[Vidar Berg]

Glad to hear that found the problem. You can always increase the advertisment interval. Tradeoff is that it takes longer time to establish a new connection. You can also get some improvements by using the built-in DCDC converter if that is supported by your design.  

[MattFL]

Thanks, I played with the advertisement interval a little but didn't see much difference in current.  I'm probably missing something.  In the end I re-worked all of the logic and basically only advertise when triggered by an external sensor, which works for this case.  Without advertising my idle current is now 12uA, and still about 0.5mA when advertising.  At some point I would like to figure out the advertising current, but for now I'm rarely advertising so it's good for now. :)