git.piffa.net Git - sketchbook_andrea/blob - basic/pwm/pwm_7_states_lum_correction_256/pwm_7_states_lum_correction_256.ino

   1 /*
   2   Change brightness of LED linearly to Human eye
   3   256 step brightness using 8 bit PWM of Arduino
   4   with slight correction at base.
   5
   6   https://ledshield.wordpress.com/2012/11/13/led-brightness-to-your-eye-gamma-correction-no/
   7   https://learn.adafruit.com/led-tricks-gamma-correction/the-quick-fix
   8 */
   9
  10
  11 #include <avr/pgmspace.h>
  12 #define CIELPWM(a) (pgm_read_byte_near(CIEL8 + a)) // CIE Lightness lookup table function
  13
  14 /*
  15   5 bit CIE Lightness to 8 bit PWM conversion
  16   https://ledshield.wordpress.com/2012/11/13/led-brightness-to-your-eye-gamma-correction-no/
  17   L* = 116(Y/Yn)^1/3 - 16 , Y/Yn > 0.008856
  18   L* = 903.3(Y/Yn), Y/Yn <= 0.008856
  19 */
  20
  21 const uint8_t CIEL8[] PROGMEM = {
  22    0,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,
  23    2,2,2,2,2,3,3,3,3,3,3,3,3,3,4,4,
  24    4,4,4,4,4,5,5,5,5,5,5,5,6,6,6,6,
  25    7,7,7,7,8,8,8,8,9,9,9,10,10,10,10,11,
  26    11,11,12,12,12,13,13,13,14,14,15,15,15,16,16,17,
  27    17,17,18,18,19,19,20,20,21,21,22,22,23,23,24,24,
  28    25,25,26,26,27,28,28,29,29,30,31,31,32,32,33,34,
  29    34,35,36,37,37,38,39,39,40,41,42,43,43,44,45,46,
  30    47,47,48,49,50,51,52,53,54,54,55,56,57,58,59,60,
  31    61,62,63,64,65,66,67,68,70,71,72,73,74,75,76,77,
  32    79,80,81,82,83,85,86,87,88,90,91,92,94,95,96,98,
  33    99,100,102,103,105,106,108,109,110,112,113,115,116,118,120,121,
  34    123,124,126,128,129,131,132,134,136,138,139,141,143,145,146,148,
  35    150,152,154,155,157,159,161,163,165,167,169,171,173,175,177,179,
  36    181,183,185,187,189,191,193,196,198,200,202,204,207,209,211,214,
  37    216,218,220,223,225,228,230,232,235,237,240,242,245,248,252,255
  38 };
  39
  40 int brightness = 0;             // initial brightness of LED
  41 int fadeAmount = 1;
  42 int led1Pin = 1;
  43
  44 unsigned long startTime = 0;    // timing variables
  45 const long interval = 4;        // pause between each interval (256)
  46
  47
  48 void setup()  {
  49   pinMode(led1Pin, OUTPUT);     // declare pin 9 to be an output:
  50 }
  51
  52 void loop()  {
  53   unsigned long currentTime = millis();
  54   if (currentTime - startTime >= interval)
  55   {
  56     startTime += interval;                         // increment timing sequence
  57     analogWrite(led1Pin, CIELPWM(brightness));     // set the brightness of pin 9:, 0-31, 5 bit steps of brightness
  58     brightness += fadeAmount;                      // change the brightness for next time through the loop:
  59     if (brightness == 0 || brightness == 255)       // reverse the direction of the fading at the ends of the fade:
  60     {
  61       fadeAmount = -fadeAmount ;
  62     }
  63   }
  64 }