A20-LIME2-RTC Coin Cell Battery Option

Started by gops, October 09, 2019, 06:54:28 pm

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Dear Team,

We are looking for having RTC time stored always kept within the device, no matter device is powered off or not.

1. We do not want to have Battery Backup for the entire board, as the customer doesn't want to connect batteries on his product line.
2. We do not want to go with UEXT options with LIME2, it seems cumbersome process
3. Present documentation of LIME2 on the product page https://www.olimex.com/Products/OLinuXino/A20/A20-OLinuXino-LIME2/open-source-hardware is very poor, it doesn't talk about RTC option at all without powering entire board with battery backup.
4. But on the Olimex forum, https://www.olimex.com/forum/index.php?topic=5815.0 , I understood that AXP_BACKUP is not possible on Olimex LIME2 board due to pin non-availablity.
5. Last option is to use External RTC with I2C

Is this hold good for October 2019 or the LIME2 latest revision boards have improved to make RTC possible? For Industrial board, RTC become mandatory, we have a lot of trouble with DB, drivers and other issues without RTC, we cannot expect NTP is allowed all time, or device is connected to internet or local NTP server always. Can you please provide an reasonable advise to solve RTC issue with Olimex LIME2 boards?


October 10, 2019, 12:37:31 pm #1 Last Edit: October 10, 2019, 12:44:53 pm by LubOlimex
The information from https://www.olimex.com/forum/index.php?topic=5815.0 is no longer correct. The BACKUP pin is lead out to a 2-pin connector footprint at the bottom edge of the board starting hardware revision I (and all subsequent hardware revisions).

You can place a connector similar to the Li-Po one, or solder wires or pins and access the 3V additional backup battery.

Inspect the schematics for the exact location. Look for pin #30 of the AXP209 (named "BACKUP"). Search near the big holes meant for placing for two pins with BACKUP label over them - one is 3V, the other - GND.

Refer to the datasheet of AXP209 and search for "30" and "BACKUP" for more information: http://dl.linux-sunxi.org/AXP/AXP209_Datasheet_v1.0en.pdf
Technical support and documentation manager at Olimex


Thank you for the clarification.

this means, if we place 3 v battery cell in our mounting, connect the pins as you suggested,  are we good with Olimex boards with RTC? That is super cool, I am happy to know this.

Would you mind take a snap of Olimex board, put a round/marker on exact pin you were recommending as image, that would serve as nice documentation and visuals. Can you please attach image of board with pins and marking them? We have one board from customer, we don't want to screw that till we have backup board from customer.


Technical support and documentation manager at Olimex