I have a school project which it requires me to design a logical circuit that tests a 12v battery if it is full or not or half-full and light the corresponding LED, but, I am having a trouble because I want a component that only allow a voltage to pass if it is above 12v in first branch and 6v in second branch and 0.5v in third branch, but, I don't know what to component to use to achieve my goal. I am thinking to use resistors but I do not know what are the values to assign to it to achieve my goal. NOTE: I am using Proutuse isis
This is a possible solution. As Passerby stated comparators (or op amps) could be used.
If the voltage (from the battery) is more than the voltage at the minus-pin on the comparator then there is positive output from the comparator (i.e the voltage "passes").
The voltage at the minus-pin of the comparators can be constructed with simple voltage dividers.
The XORs at the end makes sure that only one lights up at a time.
This solution needs an external voltage source of at least 12V to power the comparators, XORs and also create the voltage dividers connected to the minus-pins of the comparators.