9651 SOM RTC Battery Status

[Pipho]

We are using the 9651 SOM in an embedded control application. We need to know the status of the external RTC backup battery VBAT input. Is there a software method, such as status from a VI, to determine if the backup voltage is within range to reliably keep the RTC active should primary power be removed? 

[Myr.i.am.]

Hi Pipho,

Unfortunately, there is no way to programmatically determine the charge on the RTC backup battery.  That being said, the 9651 is designed to draw a very small amount of current from the battery (on the order of hundreds of nanoamperes), and it should last at least five years.  The easiest way to maintain it is probably to periodically change it.  It would also be possible to set up an analog input circuit to monitor the voltage, but this would be more work than just replacing the battery once in a while.

Thanks,

Myriam

[tannerite]

Pipho,

The functionality is not built into the SOM to be able to read the battery voltage. Since the customer carrier board is where the battery will be located, idealll the customer would implement a simply voltage sense on their carrier board then send that digitally back to the sbRIO-9651 through several of the DIO lines. LabVIEW FPGA could feed those values to LabVIEW RT. There can then be a check in RT to determine whether they can shut the system and still keep system time. This would be ideal.

We specify the RTC characteristics in our specifications guide. They can use that information and the battery they choose and its specificaitons to determine the expected lifetime of their system. They should then perform routine system maintenance to replace the battery before they expect it to die.

[Pipho]

Thanks for the reply. The ideal place is on the SOM module itself. That way the VBAT pin connection through the high density connector is also verified. A voltage comparator on the customer interface card would add more loading on the battery. This status monitoring would be a feature to consider for the future perhaps.