Instructables

USB LED Backlight

Picture of USB LED Backlight
Really simple build for a USB accent light utilising a generic type "A" USB cable end (the wide one), a 100ohm 1/4 watt resistor, 1/4 inch shrink wrap, and a 3.5 volt LED (I used blue to be different).
 
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Step 1: I can't believe it's so easy...

Picture of I can't believe it's so easy...
C:\Documents and Settings\DGray\Desktop\messydesk.jpg
C:\Documents and Settings\DGray\Desktop\xboxlight.jpg
Image is pretty self explanitory, just solder the LED as close to the USB connector as possible with the resistor on the anode (+) leg of the LED. Slip on the heat shrink tubing, heat until golden brown, and diffuse the tip of the LED with some sandpaper or a disposable nailfile. These work really well behind my desktop, laptop, xbox360, cable box, and dvr.
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I linked to your instructable in an article about led lighting. The idea is really nice and the picture showing the led wired in is very helpful for showing people the simplicity. Thanks!

PC Bias Lighting Kit Comparison
Big jermini6 years ago
Ok resisters are not that easily explained. resistors in series with anything drops Voltage. resistors in parallel with anything drops current. Think of your circuits like a water hose. voltage is how much water is flowing and current is how fast. put a resistor in series and it is like stepping on the hose voltage goes down current goes up. now try adding another piece of hose in parallel with the first hose. (a resistor in parallel). The voltage stays the same but the current goes down. So if you wanted to take down the current you would need to put the resitor in parallel with the LED. IF your limiting Voltage Put it in series. I am taking EET/CET and have just passed AC/DC(no pun intended) digital and hardware. Now after break its on to communications. yeah! Just trying to help by the way.
are you sure? cause I tested this with my multimeter with the resistor in series and still got 5v but like ~25 mA (LED was rated at 20mA but still within max range) When I put the resistor in parallel, my current kept going up, but my voltage was at 4.2 volts and my LED got hot and started to turn a reddish green, then popped. So in conclusion, i believe running a resistor in series limits current, hence its name, RESISTS CURRENT! Ohms Law states I=V/R, Voltage is constant (5v) the greater the denominator(resistor) the lower the current

ex. I=5/100, I=.05 | I=5/120, I=.041667
In replying to myself, i just did another experiment, and I should know this from wiring speakers, a resistor in parallel, will actually draw more current for the LED but keep the same voltage causing my pop. Wire two 100 ohm resistors and you get 50ohms with double the current draw. and LED has resistance, putting it in parallel with a resistor is a bad idea unless you want to blow it.
The reason for the 4.2v is because of the forward voltage drop of any typical diode (light emitting or not), which is about .7v. This will always be a near constant. Resistances wired in parallel REDUCE overall resistance, thus current increases. To calculate resistors in series, simply add the values. If the resistors are in parallel, add the inverse values of all the resistors (1/x) together, and then take the inverse of THAT number as well. On a scientific calculator, typical entry for 4 50ohm resistors would like this: 1 / (1 /50+1/50+1/50+1/50) = 12.5ohms.
I would not use the electrical tape instead of the heat shrink tubing because I would want it to look nicer, but it would work. I just got heat exchangers and some heat shrink tubing a week or so ago, so it is available to me, but I would suggest buying some and using that.
 Instead of heat shrink tubing, electrical tape would work, right?
Of course, shrink tubing just looks nicer.
 Yes, in fact depending on the application many things could be used. Cardboard for instance.
bobtannica5 years ago
Thanks for your 'ible. Even with my limited skills it was a snap!
sk83rjosh5 years ago
what is the point of the resistor? i tied with out one and the led got hot i mean relly hot! is that normal?
You need to use resistor, if you don't want to take a risk that the LED'll go hot or explode. I exploded my best led by using not a resistor ;'(
lol nvr mind itll burn up i have on hooked up to a 10 watt for now itll last 10-20 mins if i leave it on how long would 100 one last thats a 10 p resitor correct i had one but it dimed my light way to much an mines an ultra bright green you think itll be safe if i leave it on for extended periods say 30 min-1 hour??
you need a resistor
you know how you cant believe it so easy? i cant believe its not butter.
i cant believe its not butter

i can
lol, No kidding.
drderek6 years ago
Does it matter if the resistor is 1/2 or 1/4?
nope
sk83rjosh5 years ago
hey is that just a 100ohm or is it like 100 k 100 m ??
100 ohm, not anything more
Kasm2795 years ago
i noticed that you can also us a 5v LED and no resistor. (radioshack says 6v on the package)
un0 Kasm2795 years ago
Are you sure the LED has a forward volatge of 5v? Some places claim to have 5/12v LED's when they are 3v oens and have a byrn out rating of 5v
Kasm279 un05 years ago
well, its sitting on my desk, powered by USB from my laptop right now
i dont have a resistor can i make it without one??
you could also use a 5v LED
if you have a 3.5 volt regulator. But in that case, you would have resistors. So, no. You can always remove it from something else. Otherwise, you will burn out your led.
(removed by author or community request)
prototype27 (author)  IW5 Industries5 years ago
Good eye, yes that is 2 computers. One is my workstation and the other is a small business server with exchange for syncing my desktop outlook and iphone/windows mobile phones. I'm an IT consultant so it helps to have an online demo for potential clients. Thanks for looking at my little contribution to instructables!
WOW! I just now came across this tutorial and made this a while back and it looks EXACTLY like yours! Blue LED too! odd?!?! another one i built, i stripped the usb casing off and desoldiered the wires. Then using a 1/8w resistor and a 3mm LED, soldiered that sucker right on the pins. Anyone know how to send RAW 1s&0s out the USB data ports? (make the LED blink if soldered to data)
haha... forget that first part of the comment. I must of forgot i visited this. :-/
Hi, I've made a custom set of speakers, with woofers and all, but would like it to light up (from the inside, from holes and grooves) when switched on... Also, I'm making a Guitar, with EMG-81 pickups. Behind the guitar, on the underside, I would like the grooves of the Floyd Rose to light up with a blue glow... Could you help me...?
just put lots of leds in it and find god power. Hot glue works quite well to hold leds in.

http://www.youtube.com/watch?v=OkLHhuCT_00

all those are held in with hot glue.
Darkshot6 years ago
ok i got the risistor and everything but i cant freakin get the hooking up right do i hook up the risitor to the red wire then hook it up to the short side of usb? or what...i need HELP get back ASAP plz thanks
wow. one end of the resistor (doesnt matter) hook it to the red wire on the usb cable and solder, next solder the other end of the resistor to the + on the LED then the black to black
mbx28146 years ago
i tried this out with a blue led which for some reason was emitting a green color... maybe i just got my leds mixed up, but its barely lighting up, what am i doing wrong? i followed the steps :(
hmm... maybe the LED was receiving too much power, and has burnt out. Not quite sure if that would turn it green but it certainly makes them very dull. If this is the case you will need a resistor with a higher resistance (that is if you use that kind of LED again) BTW if it is burnt out it's stuffed
mbx28146 years ago
When i took apart my USB cable it had 4 different colors and greyish stuff around those wires, which ones do the positive and negative legs go into? (sry im a n00b at this)
red is +5, black is -(ground) the yellow and green, maybe white, are data wires, you dont need them, the grey stuff is shielding, you dont need that either.
Mr.KC6 years ago
Can you make the cord longer for this, or does that cause ill-effects?
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