Blue LED too bright - questions

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FoolOnTheHill

Limp Gawd
Joined
Aug 2, 2001
Messages
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Okay, I own a Lian-Li PC-65, which has a high-intensity blue LED installed as the stock power LED. I've been fine with it for a year or two, but recently, I've decided that it's just too bright, as it lights up my room at night. I plan on just putting a simple resistor in line with the LED to take down the brightness. Anyone tried something similar?

Basically, the things I want to know are:
-What voltage does the power LED run at?
-What value of resistor should I use for this mod to take down the brightness so that it's an indicator, not a beacon?

Thanks in advance :)
 
the LED that's Blue probably runs at v2.5-3.5

as for resistor.... i have no idear...
 
If you can get to the resistor I'm sure you can find what the colors of the lines mean in terms of resistance. Just go to your local radioshack and get a pack of resistors with a higher resistance (higher level of ohms).
 
resistors are color coded usually with four stripes. The resistor value is read with the silver or gold stripe on the far right.

1st stripe - first digit
2nd stripe - second digit
3rd stripe - if there are only four total stripes, this is the number of zeros after the first and second digit. If there are five stripes total, this is the third digit
4th stripe - if there are five total stripes, this one indicates the number of zeros after all the preceding digits
last stripe - tolerance. gold is better than silver, although I don't remember exactly what the accuracy is.

The color codes are as follows
black - 0
brown - 1
red - 2
orange - 3
yellow - 4
green - 5
blue - 6
purple - 7
grey - 8
white - 9

Example:
blue-grey-yellow: 6-8-3 so 68 followed by 3 zeros - 68kohms
brown-black-black-red: 1-0-0-2 so 100 followed by 2 zeros = 10kohms
yellow-white-brown: 3-9-1 so 39 followe by 1 zero = 390 ohms

Hope this helps
 
Well, hey, thanks for the replies and the mini lesson. Unfortunately, I already knew the resistor color codes. I learned it last year in Physics, and again this year in my digital electronics class. ;)

Anyways, the help is appreciated anyway. I was actually looking for a specific resistor value, perhaps someone has done this before and has some experience doing it. (I was looking for a specific value, like 100K... etc)

Thanks:D
 
A better investment at RadioShack would be a cheap digital multimeter if you plan on doing more electronics-type modifications. You will never have to 'count colors' again; just set the dial and connect the leads to the resistor and it will give you the resistor's actual Ohm rating.

For your particular LED, most are around 20mA, so plug it into Ohm's Law to figure out how many Ohms you need out of your resistor. There is a minimum starting voltage that you will need. Let's say for starters that you wanted to take .5V off the LED. Put it into Ohm's Law, and you get .5 = R x .02A, which is 25 Ohms. Usually you have to buy your resistors in packs of 5 at the Shack, so I'd start with 25 Ohms and work your way up.
 
I feel that way about my PC6077. I just put my chair in front of it at night.

James
 
Being at college can be a wonderful thing. I can just go to the analog circuit lab and I have all the equipment I need to build any circuit I want. Anyway....put a potentiometer in series with the LED and adjust it until you get the amount of light you want. Then measure the resistance and get a normal resistor with a similar value. Voila!

You may have a hard time getting a POT that will be in the range you want. In that case, take a normal resistor somewhat larger than the value you currently have, and put the POT in parallel with it. Then adjust the pot like before, and measure the resistance of the two in parallel when you get the brightness you want.

Since every LED is slightly different, you'll have to do your own experimenting to figure out exactly what you need.
 
i find it surprising that no one's mentioned that LEDs don't really 'dim' all that well... I think you're better off just buying a new LED at ratshack, considering the ones at the shack aren't very bright (IMO). In my experience, LEDs just change hues a bit and then shut off completely. As far as a resister, the motherboard probably supplies 5v to it, but you can go as far as 3.3v

http://bit-tech.net/article/68/

Bit-tech's got a nice LED calculator

100 ohms seems to be what you need
(5v supply voltage, 3.3 forward, 20ma) = 85, nearest up is 100 which would give you slightly less than 3.3v, which would probably 'dim' your LED a bit, but i dont think you'll be pleased with the results either way...
 
I would recomend sunglasses for your led. Get something that will dim it by only letting a % of the light emitted pass through. Some tinted celophane, a dark marker, or something similar should do.
 
Find the LED voltage and the LED current. Use a multimeter. If you don't have one, get one.

find the "resistance" of the LED (it's not really a resistance)
Find a real resistor to effectively equal about 40-50% of the LED's "resistance." Put it in series with the resistor.

Anything more than that and your voltage will be too low, and it will barely light at all.

BTW, this is horribly ghetto.

LEDs are properly dimmed using pulse width modulation.
 
I have the Antec Sonata and the front blue LED's are cool but annoying as hell when the lights are out, way too bright. I was just thinking about modifying the circuit and adding a resistor to make the voltage drop... Thanks for the tips.

Maybe there is a practical use for Physics.
 
Hey, thanks for all the replies

So today I went into my digi electronics class and dragged out my computer. I set the lab-volt to 3.3v and hooked it up to the LED. I tried a few different values, but I ended up using a 150ohm resistor. You are right about it not dimming very far, but it did manage to take the edge off, so at least now I wont be able to signal airplanes at night.

If I get it home and see it at night, and it still is too bright, i'll just end up tinting the LED light guide on the front of the case. I suppose the situation is in control, so thanks to everyone for the help. :cool:
 
Originally posted by matoch
I feel that way about my PC6077. I just put my chair in front of it at night.

James
Click to expand...

Hehe, i do that too, i HAVE to leave my comp on at night, its my alarm clock:)

When I did my 'ghetto' fan switch, i accidently used two diff resistors on the LEDs, so they are two diff color/intensities of blue :p

did the res. make the hue change in yours? i can't remember, but i think i used a 2.2k res. on one and a 1k on the other, but these are rated lower volatage, and i was lazy and just used the 12v rail on the molex

edit: my drunk ass can't type
 
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