An unexpected request arose for needing to send two texts at 1000H and 1600H everyday 24/7 from my current Arduino project. I have done my research and believe that my best bet is to use an external RTC powered by a coin cell battery. This will avoid the 'clock reset' problem when power is lost.
While that will obviously work, I think that replacing the coin cell battery with a rechargeable 3.7V Lithium polymer battery recharged with a solar panel would be a better solution in many repects. Replacing the coin cell battery (in an enclosure) is a concern because I may not be around to replace this battery and no one else will know how or be willing to do this. Non-technical types tend to break things when they go where they should not.
The problem I face is learning how to code the recharging of the LiPo battery from the solar panel. The board I use (Adafruit Feather MO WIFI) has a built-in charging circuit that keeps its LiPo battery charged when not in use. That said, I wonder if this charging circuit can charge TWO LiPo batteries??
The DS3231 RTC (among others) will run on a coin cell for several years. You probably can't expect more reliable operation from anything you build yourself.
Presently there are no proven, reliable methods for hobbyists to recharge LiPo cells connected to other active circuits (as you expect from your phone).
Since I could find zero useful info on this subject I assumed what you just noted. I will save myself a lot of stress and just go with the coin cell RTC setup.
I do have to wonder why it would not be possible to 'GET' real time from the internet and use that time to trigger texts with. I am looking into that possibility and avoid the external RTC altogether.
I think all those ZS-042 modules have the recharge circuit built in. So you would need the rechargeable version of the battery, which I think is the LIR2032. If you use a regular cell, you're supposed to disable the charging circuit by removing the diode or resistor, or cutting a trace.
But I think you would find that a regular CR2032 would last a long time, and the LIR2032 will be expensive. The DS3231 draws about 1.2uA when on battery power. You're probably looking at years of battery life.
I had never heard of such a thing but that may solve my coin-cell-replacing by not-technical types worry. If I can make this breakout board accessible EXTERNAL to my project enclosure, then I'm good to go.
I could mount a small external enclosure on the right side of the main enclosure as shown above to house the coin cell breakout board. This is not fool proof, but is a better alternative to having someone poking about in my main enclosure.
This will also eliminate having to tie into a timeAPI to keep the time current.
I think you are correct in the longevity of the CR2032 batteries. I think this is the best solution and saves me the time of having to code up a link to a timeAPI.
I would just add that if you use an RTC you'll have to deal with daylight saving time if you want to report data at the same times every day. However, it looks like they're about to eliminate leap seconds, so you won't have to worry about that.
The RTC's all drift to one extent or the other. Youll have to re-sync occassionally. Manual or automatic is up to you, but it will become necessary eventually. Plan for it.
