Breathing

//breath effect implementation
//fastled ledstrip demo
//Yaroslaw Turbin 25.08.2020
//https://vk.com/ldirko
//https://www.reddit.com/user/ldirko/

#include "FastLED.h"
// LEDs pin
#define DATA_PIN 3
// LED brightness
#define BRIGHTNESS 255
#define NUM_LEDS 60  // number of leds in strip
// Define the array of leds
CRGB leds[NUM_LEDS];

#define SMOOTHERSTEP(x) ((x) * (x) * (x) * ((x) * ((x) * 6 - 15) + 10))  // https://en.wikipedia.org/wiki/Smoothstep#Variations
#define min_bright 40
#define max_bright BRIGHTNESS
float a = 0;

void setup() {
  FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);
  FastLED.setBrightness(BRIGHTNESS);
}

float inverse_smoothstep(float x) {               // https://en.wikipedia.org/wiki/Smoothstep#Variations
return 0.5 - sin(asin(1 - 2 * x) / 3);}

void loop() {
float b = (sin (a)+1)/2;   //get 0-1 cycle value
float v = SMOOTHERSTEP(b);  //SMOOTHERSTEP it
//float v = inverse_smoothstep(b);  //uncomment this for inverse smoothstep. very nice looking breath!
int color = (50 * v) + (255 * (1 - v)); //interpolate beetween min and max value
fill_solid(leds, NUM_LEDS, CHSV(0, 255, color));
a+=0.03;
FastLED.delay(15);
} //loop