while loops
Light up the first 10 lights.
We can do this with a for i in range(10): loop, but we can also use a while loop.
The while loop checks to see if a condition is true each time before it goes throught the loop. In this case we'll create a variable, i, give it an initial value (0), and increase it by 1 every time we loop.
i = 0 # initialize variable
while (i < 10): # loop with check
pixels[i] = (10,0,0)
i = i + 1 # increase the value of i
this makes a loop that repeats 10 times, but every time we have to tell i to increase by 1 (line 4).
The full program looks like:
import board
import neopixel
pixels = neopixel.NeoPixel(board.GP0, 20)
i = 0 # iniatialize variable
while (i < 10): # loop with check
pixels[i] = (10,0,0)
i = i + 1 # increase the value of i
Assignment 1
Use awhile loop light up ever other pixel in the strip (green).
import board
import neopixel
import time
pixels = neopixel.NeoPixel(board.GP0, 20)
i = 0 # initialize variable
while (i < 20): # loop
pixels[i] = (0,10,0)
i = i + 2 # increment i
time.sleep(0.1)
Assignment 2
Use awhile loop to light up the last 10 lights (green), going backwards with a 0.1 second delay between each one.
import board
import neopixel
import time
pixels = neopixel.NeoPixel(board.GP0, 20)
i = 19 # initialize variable
while (i > 10): # loop while greater than 10
pixels[i] = (0,10,0)
i = i - 1 # decrement i
time.sleep(0.1)
Assignment 5
Light up each light that is a Fibonacci Number.The Fibonacci sequence starts with 0, 1, and then increases by adding the two previous numbers together to get the next number. So the sequence goes 0, 1, 1, 2, 3, 5, 8, 13, 21 ....
import board
import neopixel
pixels = neopixel.NeoPixel(board.GP0, 20)
n1 = 0
n2 = 1
while (n2 < 20):
pixels[n2] = (0,10,10) # set pixel color
# save the old value of n2
n2Old = n2
# update n2 (Fibonacci sequence)
n2 = n1 + n2
# make n1 the old value of n2
n1 = n2Old
Unpacking (Tuples and Arrays)
(n1, n2) = (n2, n1 + n2)
In Assignment 2, that lights up the Fibonacci sequence, the code example takes three lines (13, 15, and 17) to update the two numbers in the Fibonacci sequence (n1 and n2).
import board
import neopixel
pixels = neopixel.NeoPixel(board.GP0, 20)
n1 = 0
n2 = 1
while (n2 < 20):
pixels[n2] = (0,10,10) # set pixel color
# save the old value of n2
n2Old = n2
# update n2 (Fibonacci sequence)
n2 = n1 + n2
# make n1 the old value of n2
n1 = n2Old
In python, you can avoid having to save the old value of n2 by updating both numbers at the same time using something called tuple assignment/unpacking tuples.
# update n2 and n2 (Fibonacci sequence)
(n1, n2) = (n2, n1+n2)
import board
import neopixel
pixels = neopixel.NeoPixel(board.GP0, 20)
n1 = 0
n2 = 1
while (n2 < 20):
pixels[n2] = (0,10,10) # set pixel color
# update n2 and n2 (Fibonacci sequence)
(n1, n2) = (n2, n1+n2)
Infinite Loops
Sometimes you want your program to run forever. Then you can create an infinite loop using a while condition that is always true, such as:
while True:
import board
import neopixel
import time
pixels = neopixel.NeoPixel(board.GP0, 20)
i = 0 # initialize variable
while (i < 20): # loop
pixels[i] = (0,10,0)
i = i + 2 # increment i
time.sleep(0.1)
Now to make it run forever, we stick it into an infinite loop (line 7). And we also need reset the pixels (make them black) in-between each iteration of the infinite loop (lines 14-16):
import board
import neopixel
import time
pixels = neopixel.NeoPixel(board.GP0, 20)
while True:
i = 0 # initialize variable
while (i < 20): # loop
pixels[i] = (0,10,0)
i = i + 2 # increment i
time.sleep(0.1)
# reset leds
for n in range(20):
pixels[n] = (0,0,0)