Hi guys i just wanted to replace my lian li power led to a blue one so i went ahead and bought a few blue leds from farnell. Now the leds are rated at forward current of 30mA and typical voltage of 3.5v. I dont know what my mobo header voltage output is and i dont have a multimeter so to play it safe i want to connect it to the 5v output on the molex. I cant seem to calculate what resistor i need for this led. I know the formula V=IR but what do u put for the voltage the running voltage of led i.e 3.5 or the voltage of the molex 5v. Also where do i connect the resistor to the longer or shorter leg of the led. Cheers guys Any help appreciated.
R=V/I (V= Vin-Vtypical=5v-3,5v=1,5v) R=1,5v/30mA R=50ohms It doesnt matter where you put the resistor as long it is in series with the led
