can i take a usb cable then hook it into a rig that i make up inside the case then power a bunch of leds off of it? if so what resistor would I have to run on the leds because I am not sure how much power the usb cable will give me, this would be sweet because it would be plug and play leds lol. anyway the leds would be standard 5mm ones, actually I got them off l337hax0r (thanks man) any suggestions anyone?
Well first off the USB puts out +5 volts. Most max out at 500ma, check our motherboard manual to find out how much it can handle. Depending on how many amps you LED's take each will limit how many you can connect to your USB port.
Test leds? Just take couple of 1.5 volt batteries and use them for testing. No need for multimeters etc. Some people are using USB to power up their leds in their GlowPads. Easy to do but like Zap said you shouldn't go over that 500mA. 300-400mA max. should be enough for most led setups.
What he is saying is he doesn't know the forward voltage drop of his LED's so he's not sure how to find this out. (Which is why you need a diode tester) What type of LED are they? Normal or dim =1.2volt drop @ 20mA Bright = 2.2-2.6volt drop @ 30mA Super bright = 2.4-3volt drop @ 30mA
that sure is what I ment. If any one has gotten blue or aqua leds off l33thax0r they may be able to help me, I just need to find out what resistor to use for them when it comes to putting usb power to them I would like to be able to plug a usb cable into a box that supplies power to a bunch of plugs for a bunch of leds, though I don't know if it will have enough power to power over 6 of them.
any more suggestions for this setup? poor me needs to know more about electronics besides setting it up.
well this is what i though too until I plugged one right into a usb plug and i found that it got dimmer over the course of a week. any suggestions on that one?
aye it burned out. it will stop working completely shortly, dont worry For some reason a 5v led on just a straightup usb cable frys out.
Very unlikely they have a built in resistor if blue and if so - 5V WILL kill them..!! LEDs always need a current limiting resistor - when on a case LED the Mobo already does the current limiting - if direct from a 5V source then the LED will suck more than 30ma and crash and burn!! If a blue LED and unsure of voltage just whack a 56ohm resistor in - most blues will draw enough ma to be very bright.. Thats per LED? You can use one resistor for several LEDs in parallel?
Don't confuse a maximum rating with the voltage that you should operate your LED at. For blue/white/aqua/true green/UV, a decent guess is 3.7V @ 20 mA, mainly due to the physical properties of the junction material (these are InGaN). I recommend a 68 ohm, 1/4W resistor for each blue LED running from USB. This will limit them to 20 mA, so you can parallel up to 25 LEDs if you feel the urge. As noted, running them at 5V without a resistor will cause them to fail quite prematurely.
Yes, you can use a single resistor for a parallel array of LEDs, but things I've seen recently have convinced me that's not the best way to do it. If the difference in the forward voltage is significant enough, one leg of the parallel circuit may take essentially all the current, and you can release the magic smoke. I know in the past I have indicated one resistor can serve a whole parallel array (especially series/parallel combinations of blue LEDs reunning from 12V) but I now want to revise my opinion and say that best practice is to have one resistor per parallel string.
I just looked at radioshack.ca and they don't show a 68 ohm 1/4 watt resistor. I am going to go up there tomorrow if they don't have any I am going to be so pissed it is not even funny. So if I can not get them from there where can I get them. And can anyone suggest a good way of splitting off the power from a usb plug in and have connectors to plug wires into for leds? I was thinking maybe the really small headphone jack wires (the ones that go in cellphones) But i don't know how well that would work. Also I want to make this in like a project box so does anyone know of a good way of making this? should I make a small board with this all wired up ?
Due to peoples suggestions I am going to go with molex, apparently I will be able to power a lot more leds with it.
