I have made a simple voltage divider using the diagram and calculator on THIS Web Site
The idea is to make the voltage from my 3s (12.6v) readable by my arduino analog pin, basically divide it by 3ish and then read it and scale it back up in the code.
So I looked at what resistors I had lying around, I have used a 33k (Ra) and a 15k (Rb) according to the calculator it should be a ratio of 3.125.
I hooked it up to my voltage supply at 5.14 volts and measured the output, I need a factor of 2.57 to scale it back up, no problem, that's what I put in my code.
But now I have tried it with a 12v input and with a scaling factor of 2.57 it only shows 10.5 volts? I can change the code but..
![Confused :?](./images/smilies/icon_e_confused.gif)
My question is..... Should I be using a certain range of resistor values for the range of voltage that I propose to divide?