Let's Make Robots!

Optimized voltage divider for low power application?

Well, I'm (trying) to build a low power node which is powered by a tiny 80mAh NiMH battery pack which in turn is recharged (kept charged) by a small photovoltaic panel.

I want to measure the voltages at both panel and battery, so I'm thinking of using a couple of voltage dividers. Usually I wouldn't think too much on it and would just use a couple of resistors, that would divide the max Vin to the voltage at which my chip would be running. 

In this case I intend to run an Atmega8 (if everything fits -- else atmega328p) at 3.3V...

hence 6.5V (max I read from the photocell) ---> 3.3V

and 4.35V (theoretical max of 3 NiMH in series) --> 3.3V

now, I'm not asking for that math (algebra) of resolving the equations, I'm asking for the REASONING of picking, say R1, the first resistor, or even if it's more important to choose R2 first (or indiferent).

All this taking into account that this is a low-power application where I'll periodically monitor the voltages, but don't want to waste a lot of current on that.


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I am not doing the math since it's all available: http://www.raltron.com/cust/tools/voltage_divider.asp and http://www.random-science-tools.com/electronics/divider.htm

That works on my Desktop Companion Bot quite good, reading the voltage from the divder and compare it with the reference voltage of the chip.

Actually, it might be Mac as well...

Download and install the Electrodroid app. It not only has everything you would ever need, it has an incredible voltage divider calculator. Will tell you amp draw and watts and just about every other resistor bridge calculation you could possibly need.

Hmm, good to know, going to check it out :) Thanks