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Led Not Working?!


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#1 Canada_Dry

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Posted 16 January 2005 - 09:42 AM

Hello, I'm trying to hook up a simple LED, but it wont work for the hell of me.


Ok heres how I have it set up. The led has the 220k resistor on the positive in the leg directly soldered to the pin off of the resistor. Then the other end of the resistor has a red cable that is attached to a 5v power source (red hdd molex cable). The cathode (shorter) end of the led has a black wire directly soldered to it. It goes to the black molex cable next to the red (5v) one. I turn on the xbox and it wouldnt light up. So I then thought maybe the cathode should be grounded...so I took out the black wire and left the red one in the 5v power cable. Turned on the xbox and touched the black wire to the metal chassis on the xbox (grounding it).... no luck.

What could be causing this? The only thing I could possibly see whats wrong is that I'm using the wrong kind of wire to connect it with? I know it is rated for 600w, but nothing else. I have an old ide cable lying around, will that work?

I've hooked up 8 leds in a paralell circuit with 1 100ohm resistor and it worked with this wire before.

the resistor is a 220k ohm 1/2 volt 5%

I did the calculator and this is what I got:

Supply Voltage: 5 volts
Voltage Drop: 3 volts (is that right?)
Desired LED Current: 20 ma

RESULT:

Calulated limiting resistor: 100 ohm
Nearest higher rated 10% resistor: 120 ohm
Calculated resistor voltage: 0.04 Watts
Safe Pick is a resistor with: 0.067 Watts

#2 Bezel

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Posted 16 January 2005 - 01:01 PM

You need a 220 ohm resistor 0.6watt to power one led form a 5 volt supply. You say you are using a 220k ohm resistor, which is to high a value to power the led. Assuming the value you typed was not a typo.

Hope it helps Bezel biggrin.gif


#3 Canada_Dry

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Posted 16 January 2005 - 05:49 PM

haha i overlooked the K at the store and said, well no-one would need this so it must be the right one. They sell 1/2 watt 1/4th watt and 1 watt resistors. Which one would work since there is no .6 watt resistor? (i'm thinking 1 watt)

#4 Canada_Dry

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Posted 16 January 2005 - 06:58 PM

i got a 220 ohm one and it worx ...Thx alot guys biggrin.gif

#5 Bezel

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Posted 16 January 2005 - 07:03 PM

No problem.
A 1/2 watt resistor is more than adequate for the job.

Enjoy Bezel biggrin.gif

Edited by Bezel, 16 January 2005 - 07:08 PM.





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