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Topic: Making an external RTC redundant (Read 734 times) previous topic - next topic

odometer

The way I see it, if your oscillator is a crystal rather than a ceramic resonator, then a DS1307 is redundant.
The only reason I can think of to keep a DS1307 around would be in case you have some kind of battery backup for it.
But then, why not just have a battery backup for the microprocessor? Such a backup would have other uses as well.

James C4S

The battery back is already the #1 reason to use an external RTC.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

odometer

So, why not just battery-back the microprocessor?

James C4S

A DS1307 draws less than 500nA when running off battery.

The ATmega328 can draw in the neighborhood of 200-400uA (about 50 times more) when sleeping.  Then you have to add the power wasted to wake up the processor to deal with the time.  So if your battery backs up the DS1307 for 1 year, it'll backup the ATmega for about 7 days (365/50).

Not to mention, the Arduino board has linear regulators and (except for Leonardo) another Microprocessor on-board.  So creating a battery back up system is going to be incredibly complex to something that the DS1307 already solves.

There might be applications for a battery-backed board, but I doubt it is a mainstream need. 
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

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