varying control of leds

Comments

• Vern Graner Posts: 337

  2006-07-25 23:13 edited 2006-07-25 23:13

  al cooke said...
  I'm having trouble controlling brightness of led banks , 24 each RGB, each color connected in parallel. Hoped to use digital pots into op-amps - transistors/w feedback to vary incrementally. I'd appreciate any help - which op-amp, dig-pot, transistor tp use. Or where can I look for info? Using LM358, 2N2222, tried 10K and 100K pots, 5 & 12 volts but very little control between LED on - off. Thanks for any suggestions. Al

  It would appear from your description that you would be using a "resistive" approach to dimming the LEDs. If this is the case it's going to be much less efficient (i.e. turning a lot of energy into heat) than using Pulse Width Modulation. There was a posting to the ParallaxEFX board a few days back that detailed using PWM code to vary the brightness of LEDS:
  
  http://forums.parallax.com/showthread.php?p=591981
  
  Hope this helps [noparse]:)[/noparse]
  
  Vern
  
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• al cooke Posts: 8

  2006-07-26 16:11 edited 2006-07-26 16:11

  Thanks for the reference Vern. I think you are right about PWM. Al Cooke