Potential divider


I am looking to build a small device using an Uno to monitor three different battery voltages on a 12v vehicle. I've been looking at options to reduce the input voltage to the digital pins on the Uno, but can't seem to find anything that will take into consideration the cranking voltage which can peak at around 13.5 to 15v.

I would like to be able to log overvoltage with this project so it would not be practical to regulate the input to the Uno, so I need something that would measure anything from around 17v to 0.

Does anyone have any ideas on how I can accurately achieve this?

Thank you

Use a potential divider, consisting of 75k on 25k.

This will give you 5v on the ADC when you have 20v, 3v when you have 12v.

Then why not make a voltage divider that reduces the 17V to 5V?

Thanks for the replies, I will give this a try.

Because mentally multiplying read values by 4 is a lot easier than multiplying by 3.4

I'd surmise cranking voltage on a 12V system is more likely to be 9 to 12 rather than 13 to 15

True. But you do lose a bit of resolution then.

And yeah, cranking voltage is going to be low. But with a running engine and alternator a voltage of 15V isn't weird.

Are we confusing "cranking" with "running" since they are not the same (in English)