Candle Flicker

In this lesson we will try to simulate the behavior of a flickering candle using the randint() function. To do this we will need a function that generates a mostly yellow-orange color, but the actual color and and brightness will vary. This will give the impression of a candle flame with a flicker.

A pure yellow color has both the red and green values on and the blue value off:

yellow = (255, 255, 0)
orange = (255, 150, 0)

Our goal is to generate variations in both color and brightness. We can do this by starteding out with a green that varies from 50 to 200 and a red that varies above this value by 25 to 50.

Sample Candle Function

Our function will draw the new value on a random location on the LED strip. It will take a single parameter of the delay on how often the values are updated, typically about 1/100th of a second.

def candle(delay):
    for i in range(0, NUMBER_PIXELS):
         green = 50 + randint(0,155)
         red = green + randint(25,50)
         strip[randint(0,NUMBER_PIXELS - 1)] = (red, green, 0)
         strip.write()
         sleep(delay)

Full Demonstration Program

from machine import Pin
from neopixel import NeoPixel
from utime import sleep
from urandom import randint
# https://docs.micropython.org/en/latest/library/random.html

NEOPIXEL_PIN = 0
NUMBER_PIXELS = 60
strip = NeoPixel(machine.Pin(NEOPIXEL_PIN), NUMBER_PIXELS)

def candle(delay):
    for i in range(0, NUMBER_PIXELS):
         green = 50 + randint(0,155)
         red = green + randint(25,50)
         strip[randint(0,NUMBER_PIXELS - 1)] = (red, green, 0)
         strip.write()
         sleep(delay)

counter = 0
while True:
   candle(.01)
   # wrap
   counter = counter % (NUMBER_PIXELS-1)
   counter += 1