Linear or logarithmic or exponential

Comments

• bobledoux Posts: 187

  2005-09-21 14:18 edited 2005-09-21 14:18

  I think you are trying to replicate the curve found in an "audio taper" potentiometer. This is found in the volume controls on radios. Turning the knob creates a proportional increase in volume. Try to Google that topic.
• Tracy Allen Posts: 6,667

  2005-09-21 18:15 edited 2005-09-21 18:15

  To get a logarithm, there is the NCD function.
  
  log2x=NCD x - 1 ' log2x goes from 0 to 15 in powers of 2 as x goes from 1 to 65535
  
  I'm not sure that is the function you want. A square law might be more appropriate.
  
  Subjective luminosity of a source depends greatly on the background light level. It is one thing to view the LED in a dark room and another outdoors. For that reason, your setup might have an ambient light sensor.
  
  As one counter goes from full off at 0 to full on at 255, say, the PWM values could take on a value that changes by constant proportions, not linearly, something like this...
  
  

      rateFactor CON 64      ' larger value for larger step.  64 is x-> x^0.75 or x^1.25
      fadeFactor CON 256 - rateFactor
      growFactor CON 256 + rateFactor
      DO
          DO     ' increase level in steps
             PWM 0,x,100
             x = x */ growFactor
          LOOP UNTIL x>255
         DO       ' decrease level in steps
            PWM 0, x  ,100
            x = x */ fadeFactor
          LOOP UNTIL x=0
       LOOP
  
  

  
  
  
  The low end would only be perceptable in a dark room, though, hence necessity for ambient light compensation, or simply truncation at the low end.
  
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  Tracy Allen
  www.emesystems.com