USB LED Backlight

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Introduction: 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).

Step 1: I Can't Believe It's So Easy...

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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    55 Discussions

    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.

    3 replies

    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.

     Yes, in fact depending on the application many things could be used. Cardboard for instance.

    Thanks for your 'ible. Even with my limited skills it was a snap!

    what is the point of the resistor? i tied with out one and the led got hot i mean relly hot! is that normal?

    3 replies

    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??