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kayson
05-20-05, 07:01 PM
For my first mod, I'm gonna put an external cd activity led. I bought the led, some 15-ohms resistors, and some led holders. I used a led calculator to figure out the right resistor to get, but now I have no idea which way to connect them? Which sides of the led do I hook up to the ground and power? Where does the resistor go? I'd assume it goes between the power and the led, but which way?

Thanks
Borisw37
05-21-05, 06:56 PM
The packaging of the LED should say which leg is + which one is -. On most LEDs the long leg is +
connect +---/\/\/\/\----LED--- -
Electron Chaser
05-22-05, 01:08 AM
This pic may help you a bit.

http://home.comcast.net/~electronchaser/LED_Mod1.JPG

connect the resistor to the LEDs longer lead the Anode (+) and the connect your ground to the shorter lead the Cathode(-). I obviously cut the Anode shorter so I could make both leads the same length.
noxqzs
06-02-05, 12:25 AM
if you know the resistance you need, then use these formulas to calculate total resistance for them.


where n = the number of resistors used.

SERIES:

R(Total) = R (1) + R (2) + R (n).......


ex. R (1) = 2 Ohm, R (2) = 4 Ohm.

R(T) = 2 + 4

R(T) = 6 Ohm

PARALLEL:

1/R(T) = 1/R(1) + 1/R(2) +1/R(n)

ex. R (1) = 2 Ohm, R (2) = 4 Ohm.

1/R(T) = 1/2 + 1/4

1/R(T) = (1/2)2 + 1/4

1/R(T) = 2/4 + 1/4

1/R(T) = 3/4

R(T) = 1.33 Ohm
Lunar_Lamp
06-07-05, 01:56 PM
Usually one side of the LED is flattened at the base, and it is the side of the negative leg (cathode). That's useful to know when you have chopped the legs down and then drop it, hehe!
wannaoc
06-07-05, 01:59 PM
I did a couple things using these a while back and if I remember right you put the resistor on the longer leg.
Lunar_Lamp
06-07-05, 02:06 PM
I'm reasonably confident that a lot of the time it doesn't matter really. At least, that's what my memory of GCSE electronics from 4years or so ago says.
noxqzs
06-09-05, 12:49 AM
the resistor location does not matter. It will limit current the same way, if its before the LED of after. It really is a preference, but usually its put closest to ground or lowest potential.

As far as the polarity of the LED, inside the plastic housing there are 2 small plates. The larger one is the Anode. In the picture of the LED above, you can see it just barely.