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[on:]

so i made a solar charger ,which charges a 6v battery with a 12v panel...my question is that i would like to have some kind of indication,which could tell me when the battery's full / empty...but how can i feed a reference voltage to the comparator because the voltage from the panel will vary upon light,and so that would change the reference voltage...similarly when the battery's low(ill use a voltage divider from the battery to the comparator), the reference voltage again would vary...

how can i have a constant reference voltage,when the voltage of the panel varys upon light?

[Reply #1 on:]

You can use a voltage regulator to get a reference voltage (such as the 3.3v regulator already on most Arduino boards), or use the internal 1.1v (approx) reference in the mcu itself.

[Reply #2 on:]

There are also "voltage reference" chips that work like a voltage regulator but only handle a tiny amount of power, their purpose is to generate a stable accurate voltage precisely for this sort of purpose.  A standard voltage regulator may take a lot more idle current, or actually require there be a load current in order to be stable. 

[Reply #3 on:]

I would recommend the MAX6029 as a voltage reference chip.  Very low voltage, and pretty accurate