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Basic LED Questions

neon

Oct 21, 2006
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to get them to flush you only need a current source of 20ma a 555 will only interup the flushing is it what you want?
 

Waynetarm

Nov 17, 2009
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Question from a beginner-

Preface I am a "sub novice" and have no electronics experience or training.

I am building a halloween costume for my son as a Robot and have set up some basic LEDs. I found a beginner's tutorial on instructables.com which was very helpful in explaining things from the ground up.


While at radio shack I found the blinking LEDs, which of course I thought would look cool. From what I have read online so far, I sense that setting up the flashing LEDs is beyond my knowledge base (or time frame!) right now, so I am going to only use regular LEDs for the costume. However, I find this stuff very interesting so maybe you can shed some light for me.

My questions:

-The led has three leads instead of two. What is the third for?
- I hooked one up with the appropriate calculated resistor. It blinked for about a minute or less and then stopped. What is the reason it stops?
-My web research talks about using a timer circuit ("555"), which I wiki'd but obviously alot of the technical description is beyond me. Is a timer part of using these flashing LEDs?

Thanks alot to anyone willing to explain these fundamentals.
An LED has only two leads - pay attention to the + terminal because reverse voltage is usually low.
The 555 timer is a classic multistable multivibrator which can be wired as a square wave oscillator - plenty of circuits on the web. Good one for a beginner to wire up.
If you are wiring up many LEDs make sure not to exceed the 555 output current limit. If you do, use an output pass transistor - again look on the web for this kind of addition.
 

Gerbil

Nov 4, 2009
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I'd delayed posting pictures hoping to find better ones, but apparently the event was attended by people with the photographic skills of a blind platypus. Here's the best I could find :(

attachment.php
attachment.php


Again, my thanks for the help in this thread, it was very much appreciated :)
 

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Resqueline

Jul 31, 2009
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Hey, that's absolutely fantastic! Congrat's on a great job!
Glad to have been able to be of assistance. :)
 

Gerbil

Nov 4, 2009
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I assure you the lights showed up a lot better than in the photos - everyone automatically stuck the flashes on to take pics :(
I'll definately be playing with lights again in the future, it was very cool to do something physical for a change (I'm a games programmer by trade).
 

neon

Oct 21, 2006
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LEDS NEEDS A NOMINAL CURRENT OF 20ma and the minimal voltage to see them they are not a linear devices sodimmers will not work as good as incandence devices.LIKE ALL DEVICES THERE IS POWER DISSIPATION TO CONSIDER.
 

nay27uk

Dec 19, 2009
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the answer to your first question is three legs useualy meen that the LED is a color changing LED like the ones you have in a TV when the TV is in stanbdby the LED will be RED when you turn on the tv taking it out of standby the LED turns GREEN this hapens with three lead LED's as one lead will detect a drop in voltage causing the led to alter its color, esentialy iit is two LED's in one.

Or a LED with three leads could be a flashing variant you can purchas an LED that will flash and they to usualy have three leads, so this may answer your second question.

Two of the leads will be cathode while one will be anode + or -
 
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