Need Help on resistors

[nox13666]

I bought some LEDs and im not really good on what resistor i should use. I have the specs of the leds below

Technical Spec
Source Material: InGaN
Emitting Colour: Blue
Emitting Wavelength (nm): 465-470
Size: 5mm
Intensity (mcd): 6000-8000
Viewing Angle (deg): 20
Forward Voltage (mA): 3.0-3.2
Forward Current (V): 20-30

I want to connect them to the 5V source from the 360 HDD and I was just wondering what resistors i should use. Would and 82 Ohm be ok? or 100ohm or am I completely off?

[802Chives]

Ok, 5V source - 3.2V LED forward voltage = 1.8V

according to ohms law V=IR  we know the V is 1.8V and I is 20mA or 0.02A so using algebra you re-arange to solve for R....    R = V/I

1.8V / 0.02A =  90 ohm


so ya.. ur right on the money with 82-100 ohm limiting resisors on ur LEDs

[nox13666]

Woah... That was impressive. And thanks, ive bought some 82Ohm resistors. Also rather random question I just didn't want to make a new topic for it but for the Rapid Fire mod (using the rumble method) you would need a "push-to-make" switch right? As there isn't an existing connection anyway (hope that made some sense, im not very gd at explaining stuff lol).

[802Chives]

that is correct, you will need a push to make switch, also known as a Normally Open Momentary Push Button.  as all you are doing is connecting the signal from the rumble motor to the button and essentially that signal will rapidly clip the signal that the controller reads on the trigger... giving you rapidfire.

I think the thread in rapidfire section that details that mod is called:
"New Rapidfire Method"

[phenoptix]

I bought some LEDs and im not really good on what resistor i should use. I have the specs of the leds below

Technical Spec
Source Material: InGaN
Emitting Colour: Blue
Emitting Wavelength (nm): 465-470
Size: 5mm
Intensity (mcd): 6000-8000
Viewing Angle (deg): 20
Forward Voltage (mA): 3.0-3.2
Forward Current (V): 20-30

I want to connect them to the 5V source from the 360 HDD and I was just wondering what resistors i should use. Would and 82 Ohm be ok? or 100ohm or am I completely off?

Those LEDs are from me! You can tell as the Voltage and Current units are the wrong way around!
Are you all sorted with the resistors now nox13666?

[802Chives]

Those LEDs are from me! You can tell as the Voltage and Current units are the wrong way around!

lol... i noticed the units were swapped, but didnt want to confuse anything.

[phenoptix]

All due to writing a script to generate all my listings and webpages. Can't believe I didn't notice until I'd uploaded 500 ebay listings!!

As they say, the devil is in the detial.

[802Chives]

ah.... now I know who you are! hahaha a man with the LED connection. good to know, espeacially for our UK guys.  Welcome to the site!