no sir i have your reply but i know the car alternate produce more than 12 volt, 14,5 or less,
so i said i want to use 7805 for this,
after your reply i have do some search and found that i can use some this like 4-PIN PHOTOTRANSISTOR OPTOCOUPLERS
and i got this http://www.alldatasheet.com/datasheet-pdf/pdf/52896/FAIRCHILD/H11A817C.300.html
can i ask you how to connect it?
how i can use it with 12volt or more, and how to connect it to arduino?
or if you have any advice how to do this,