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Glowing LED Warning Lights, Too Dark Now-LM317

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CardinalNSB(at)aol.com
Guest

Posted: Mon Oct 02, 2006 8:15 am Post subject: Glowing LED Warning Lights, Too Dark Now-LM317

 	  Quote: 	
		  MikeEasley wrote: 



My LED voltage warning lights are now too    dark to see in daylight after  

adding the resistors in the    drawing.



Smaller resistors? 	
 I have been "playing" with leds on a breadboard, controlling them with a  LM317.  The LM317 supplies constant voltage, determined by a resistance to  (the control leg, I don't know the real term).  I have used a rheostat and  been able to control multiple or single leds, from very bright to very  dim/off.  I am planning to make an annunciator for a 300xl gps, which  always has 2 leds on, sometimes 3, sometimes 4.   I have the LM317  between the battery positive and the leds, the leds taking power from the LM317  with their other leg grounded.  The leds are in parallel.

  

 A value to me of the LM317 is to be able to maintain constant brightness of  multiple leds (I plan to use all the same white leds with colored lenses  for colors).  The LM317 is from Radio Shack and I have only used the  circuit on the back of the box-LM317, a resistor, and a rheostat, 3  parts.  Could I wire a backup with a zener diode for a constant  brightness?

  

 

 However, I have been told this LM317 won't work, that I need Pulse Width  Modulation.  I'm not sure why, the LM317 seems to do what I want at least  on my desk at home, is cheap and low parts count.  I would appreciate any  reasons this would not be a proper way to control multiple identical leds-rf  production?  Skip Simpson

  [quote][b]

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klehman(at)albedo.net
Guest

Posted: Mon Oct 02, 2006 6:36 pm Post subject: Glowing LED Warning Lights, Too Dark Now-LM317

The brightness of an LED is proportional to the current going through 

it.  You need a resistor in series with each LED to limit the max 

current and max brightness. Connecting all those resistors to the output 

of your LM317 should do what you want. When you dim (lower the voltage 

ouput of the LED) there will be less voltage drop through each resistor 

and the brightness will reduce. That brightness should not change 

regardless of how many LED's are on because each LED has its own 

resistor.  I think that is your answer - a separate resistor for each 

LED.  Of course with this description, it is assumed that individual 

LED's are turned on by connecting its negative lead to ground.

Ken L.



CardinalNSB(at)aol.com wrote:



 	  Quote: 	
		       MikeEasley wrote:



     My LED voltage warning lights are now too dark to see in daylight

     after 

     adding the resistors in the drawing.



     Smaller resistors?



 I have been "playing" with leds on a breadboard, controlling them with 

 a LM317.  The LM317 supplies constant voltage, determined by a 

 resistance to (the control leg, I don't know the real term).  I have 

 used a rheostat and been able to control multiple or single leds, from 

 very bright to very dim/off.  I am planning to make an annunciator for 

 a 300xl gps, which always has 2 leds on, sometimes 3, sometimes 4.   I 

 have the LM317 between the battery positive and the leds, the leds 

 taking power from the LM317 with their other leg grounded.  The leds 

 are in parallel.

  

 A value to me of the LM317 is to be able to maintain constant 

 brightness of multiple leds (I plan to use all the same white 

 leds with colored lenses for colors).  The LM317 is from Radio Shack 

 and I have only used the circuit on the back of the box-LM317, a 

 resistor, and a rheostat, 3 parts.  Could I wire a backup with a zener 

 diode for a constant brightness?

  

 However, I have been told this LM317 won't work, that I need Pulse 

 Width Modulation.  I'm not sure why, the LM317 seems to do what I want 

 at least on my desk at home, is cheap and low parts count.  I would 

 appreciate any reasons this would not be a proper way to control 

 multiple identical leds-rf production?  Skip Simpson



=================

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