Wednesday, April 10, 2013

CR2032 vs LIR2032

These past few days I have been doing basic bringup and initial firmware load on the new 'integrated' remote board.  And it is looking good.  (Arduino libs make quick work of simple projects).
LIR2032?   Nope, not here.
Need a CR2032 for this project.

But I was having difficulties with the DS1307 RTC, it just would not respond...  Long story short - turns out the problem was the coin cell I had installed.    The DS1307 RTC 'shuts down' when Vcc drops below 1.25x the coin cell voltage.  And using the designed in CR2032 at 3.2v, and the resulting 4v threshold should be no problem.   But I had instead installed the coin cell that came with a sample Chinese DS1307 module.  And it turned out to be a rechargeable Lithium-Ion coin cell, with a fully charged voltage of over 4v.  In fact, it measured just at 4v, putting the threshold just at 5v.  And hence at times the DS1307 would stop.

Swapping out the coin cell to the current CR2032 and all is well.   Given Dallas states a coin cell should last 10+ years, I see little need to do a rechargeable design.  Adding a few more parts in.

But it did come back and reaffirm:  Never Assume something!

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