Hello,
thank you for the answers!
To measure the time between two interrupts, I will calculate "micros()-last_micros" wherby "last_micros" is a variable, that is set at the end of the interrupt function.
However, is this the same?!
An alternative could be checking in the loop digitalRead() status of a pin and save it in a variable.
Always compare digitalRead with the variable's value from the loop's execution before. If it is different (that means change from 0->1 or from 1->0), then do something.