i want to run a green laser with a 9v battery but i don't know what resistor to get radio shack has no clue does anybody know a web site that calculates resistors buy in/out voltage? the laser needs 4.5v so i need to go from 9v-4.5v. is that a 1/4w 45ohm resistor or a 50ohm resistor? just want to make sure i don't fry my module.