Another thread here, someone asking about a circuit to test the condition of a battery, got me wondering about this. What I'm getting at is this: how do you measure a voltage, when the voltage source of the measuring circuit is that same voltage?
What I'm guessing (could be way off here, I know) is that one would want to derive a reference voltage from the battery, then compare the reference against the battery voltage. Correct? Of course, the reference voltage would have to be a lot smaller than the battery voltage when fully charged, maybe somewhere below Vcc for whatever measuring circuit is used. And obviously, it'll only work down to the point where the battery is still capable of powering the measuring circuit.
So how is this done in real life? It seems somewhat of a circular (or recursive) problem.
How far down a battery's charge can such a circuit (more or less) accurately measure that charge?
What I'm guessing (could be way off here, I know) is that one would want to derive a reference voltage from the battery, then compare the reference against the battery voltage. Correct? Of course, the reference voltage would have to be a lot smaller than the battery voltage when fully charged, maybe somewhere below Vcc for whatever measuring circuit is used. And obviously, it'll only work down to the point where the battery is still capable of powering the measuring circuit.
So how is this done in real life? It seems somewhat of a circular (or recursive) problem.
How far down a battery's charge can such a circuit (more or less) accurately measure that charge?