Power backup for RTC

[rvandam]

I there a way to add a backup battery for the RTC? I noticed that the RTC loses his date after a power loss. It would be great if I could prevent that with a battery or so.

[livius]

@rvandam
if you attache battery to your board it will be preserve RTC
but i do not suppose that it is possible to power up "only RTC"
When sleep modes will be enabled then you can sleep board and only RTC will be work and eat battery.

[rvandam]

Thanks for the reply.

Yes it is only meant to preserve rtc time in case of power failure, not to power the entire board.

Where and with which voltage do I connect the battery?

[abilio]

@rvandam, if you have an expansion board, there is a connector for a Lithium battery (rechargeable). If not, there are several ways you can go. Low power modes will be added in the upcoming releases, so that will also help.

[rvandam]

I meant to power the board with a net adapter. Lots of rtc chips have the possibility to have a coin cell 3V backup battery, only for memorizing the time after a power loss. I was hoping I could connect a coin cell for this purpose.

[abilio]

@rvandam, yes, you'll be able, after we enable the low power mode.

[rvandam]

@abilio thank you, I understand now. Glad this feature will be available in the future.

[abilio]

@rvandam, though still untested, most probably you'll need to wire the external coin cell to the 3.3V pin using something a schottky diode. There should also be a way to detect the power loss to put the board in low power consumption mode as soon as the main supply is gone. None of this is done automatically, as is application specific.

[rvandam]

@abilio I thought it would be possible to power only the RTC. Going with your solution (power backup for the whole board) I think I will go for a battery pack option (in combination with the schottky diode).

My intention is to power the boards with 5v so a 4,5V battey pack must do the job.

Powerlosses here are incidental, and not very long.

Thanks for the help!