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.
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
11 #include <avr/pgmspace.h>
12 #define CIELPWM(a) (pgm_read_byte_near(CIEL8 + a)) // CIE Lightness lookup table function
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
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
40 int brightness = 0; // initial brightness of LED
44 unsigned long startTime = 0; // timing variables
45 const long interval = 4; // pause between each interval (256)
49 pinMode(led1Pin, OUTPUT); // declare pin 9 to be an output:
53 unsigned long currentTime = millis();
54 if (currentTime - startTime >= interval)
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:
61 fadeAmount = -fadeAmount ;