Sorry I read your post before I had my morning coffee... The device you chose is a Bi-lateral current sensor so its output voltage will be 1/2 of the supply voltage and swing positive for current flow shown by the arrow on the sensing device. The Arrow points to the load... If the current flow was the other way (from the load to the source) then the voltage will drop... That's the EASY part. You chose a 25A sensor and on the data sheet there is a formula for determining the voltage represented by a specific current... READ the Data sheet first and work through the calculations first. It is very likely that you will need either an Op-Amp or better a comparator as the voltage change is going to be small, on the order of 10mV/A and likely the sensor isn't going to be very workable for small current changes < 1A.. There are other devices that are probably more suitable. All those devices are hall effect type devices and you should be able to find one better suited to what you need. Match the sensor to the MAX expected load current. You WILL however have to make the output ground referenced or sense the increase from mid point that represents the load and of course the sense pin Must be analog, or use a comparator [better] because then you can use a 'digital' input as the comparator output will swing from Vsource to ground) when your load changes. IMO
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