Hi if you wanted to log your fuel pump voltage for example with your XFI, but you only have a 5 volt input you need to build a voltage divider network, and connect to your analog inputs to lets say 16 volts in =5volts out
You can use the following online tool to build this...
http://tuxgraphics.org/toolbox/circuit-design-calculator.html
You can use the following online tool to build this...
http://tuxgraphics.org/toolbox/circuit-design-calculator.html