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Old 06-15-2008, 11:54 AM   #11
muz
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Default Re: USB LED's ?

if you link 3 3V led's in series it will require 9V to operate and unlike bulbs led's dont light until the voltage across them was at a certain point
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Old 06-15-2008, 12:02 PM   #12
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Default Re: USB LED's ?

If you have them one after another i.e. in Series, the first one takes some current to work, then the other takes some more current but less is available because oif the first and so on...

You could have done it like this:



Which is putting them in Parallel to each other, where they all get the same amount of current

This is a good site for calculating the resistor you need for series or parallel LED's.
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Old 06-15-2008, 12:02 PM   #13
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Default Re: USB LED's ?

You can get usb cables already put together with led's in the head. ThinkGeek has them.
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Old 06-15-2008, 12:04 PM   #14
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Default Re: USB LED's ?

at the moment you have done this


yer wire them up like this and it will work fine
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Old 06-15-2008, 02:23 PM   #15
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Default Re: USB LED's ?

right i think i get it how bout resistors ?

i really have no idea where to place them in a circuit how many or n e thing at all treat me as a complete noob is there any pages you have that could guide me, i just use 3V batteries with 3V LEDs lol simple
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Old 06-15-2008, 02:50 PM   #16
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Default Re: USB LED's ?

If the battery (or batteries) are 3v, and the LED's 3v, you wont need a resistor

If you need a resistor, then this is how you would connected them (imagine red/black lines)

Picture

An LED has one leg slightly longer than the other, the longer leg is the + side, the shorter led the - side. The wires go from the + of the battery, to the resistor (but only if its more than 3v from the battery) and then from the other side of the resistor, the wires go to the longest leg of each LED, and then the wires go from the other leg of the LED to the - of the battery...
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Old 06-16-2008, 01:24 AM   #17
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Default Re: USB LED's ?

LEDs are current sensitive. Too much current will over drive them either leading to a shortened life time or end it abruptly and with a bang. The dropping resistor is to limit the amount of current the led draws. It doesn't matter if it's a battery or 110 from the wall, you'll need to limit the current. How you wire them can bypass the need for a dropping resistor. A series/parallel connection would normally do the trick. Most will light up at around 20miliamps and get brighter as the current ramps up. But if you over drive one you better be standing back from it. They have a nasty habit of exploding like a popcorn kernel spewing hot shards of plastic.
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Old 06-16-2008, 05:18 AM   #18
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Default Re: USB LED's ?

nice sounds like fun exploding
LEDS

right i think for now im gonna stick with 5V LEDS for my usb LEDS and then im gonna do soem reading on resistors im still not 100% about them

i get that if you had a 5V power source and 3V LEDS at 25 milliamps id need a 80OHMS 0.05 Watts resistor ? is that right ?

1 of these http://www.rapidonline.com/productin...catRef=63-2398 but i dont get which 1 i dont see OHMS there, "4.7R 0.5W CARBON COMP RESISTOR RC" what is 4.7R ? looks like the wattage is right but how do i now how much OHMS i need or doesnt it matter ?? lol noob alert
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Old 06-16-2008, 07:46 AM   #19
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Default Re: USB LED's ?

Check this site out. http://www.superbrightleds.com/

The resistor you're asking about is 4.7 ohms. It's an odd value.
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Old 06-16-2008, 08:41 AM   #20
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Default Re: USB LED's ?

Quote:
Originally Posted by muz View Post
at the moment you have done this


yer wire them up like this and it will work fine
crocodile technologies?


long an short.
yes this is possible.
someone alreay gave the pinnout.

you can run the LEDs (assuming that you use 5v LEDs) straight from the power lines.
though LEDs have quite a low forward bias resistance and will draw a lot of current from the bus.
so it's really recommended that you use a current limiting resistor regardles of whether you use 3.3v or 5v (or 12v LEDs).
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