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Hi!
First of all thanks for the great compact Arduino platform you're providing.

I'm using a ASM2001 with coin cell holder with the TinyRTC module to store timestamps in EEPROM when a given (interrupt driven) event (push button) occurs. When the stack is powered from USB the application works flawlessly. However, when powered on the coin cell, the timestamps are either

• correct (only once right after unplugging from USB) or,
• bogus values (most of the time),

After doing several tests, I think the culprit is the DS1339 being in power fail mode (or transitioning to power fail). In fact, the part marking shows that you are using the 1339-A3-33 which has a power fail voltage range of [2.7 2.85 2.97]V (min,typ,max). When using a CR1632 coin cell (3V) the power voltage I measure on the VCC rail is 2.8V.

Can you provide the tinyRTC board with a DS1339-3 part on it ?
Do you have any suggestions ?

Best regards
Claudio

Claudio, I think you're correct, good detective work- I must have picked that particular DS1339 for use with the lithium ion cell without thinking about coin cell use. I think that's our fault- are you able to use a lithium ion cell in your project?

Hi Ben, thank you for the reply.
We ordered the lithium battery base boards last Monday and we'll switch to using those. I'll let you know if there are any issues with it.

As a side note, when one orders the basic kit on your website (https://www.tiny-circuits.com/tiny-duino-basic-kit-171.html)
there's no choice of which battery (coin cell or lithium ion) holder is included. That's why we ended up with the coin cell boards when actually we wanted the lithium battery in the first place...

Sorry about that. In the future, you can always email us beforehand if there's something missing on the store. If there are still problems with the RTC, we'll sort something out- we are definitely not intending to force people to buy things twice.

Lithium kits are supposed to be part of our future store upgrade, but we keep hitting delays with the changeover.