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Old 06-16-2008, 02:53 PM   #21
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Join Date: Oct 2006
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Default Re: USB LED's ?

Originally Posted by root View Post
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).
Yer that is crocodile technologies thought it would be easier to show what i meant using actual pics of the batteries and led's
and yes if they are 5v i would still just put a smallish current limiting resistor in just to protect the LED's from too much current

Originally Posted by ssc456 View Post
nice sounds like fun exploding

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
Exploding wouldnt be fun if you got a small bit of that hot plastic in your eye it would hurt a lot , i remember once when i mis calculated a protection resisotr on one of my circuits at college and the LED exploded it scared the crap out of me

4.7R is 4.7ohms ,
and yes if you had a 5V power source and 3V leds at 25 milliamps you would need about 80ohms although i usually put just a lil bit over 80ohms in just to be safe , say 100phms see if it works , and depending on the spec of the led but i would say 25 milliamps is a bit high
even if your powering them from the 5v power lines put a small resistor in just to limit the current through the led

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