Lesson 1: Lighting Lights

Examine the test1.py file:

            import board
            import neopixel

            pixels = neopixel.NeoPixel(board.D18, 20)

            pixels[2] = (10,0,0)
            

Looking through the code line by line:

Lines 1 and 2:

                import board
                import neopixel
              

Import two modules that we need to light the LED's.

• import board: The board module helps control the general purpose input/output (GPIO) pins on the Pi.
• import neopixel: The neopixel module specifically focuses on operating this type (WS2811) of individually addressable LED lights.

Line 4:

              pixels = neopixel.NeoPixel(board.D18, 20)
              

This activates the LED strip. Specifically it indicates that:

• pixels =: It gives the strip a variable name, pixels so we can refer to it later.
• neopixel.NeoPixel(): it uses an object called NeoPixel from the neopixel library we imported on line 2.
• board.D18: indicates that the strip is being controlled by the GPIO 18 pin, (you can look at the Pi and see that the data wire of the LED is connected to Pin 18)
• 20: there are 20 LED's in the strip.

Line 6:

              pixels[2] = (10,0,0)
              

This makes the third light red.

• pixels: this is the variable that refers to the LED strip that we created on Line 4 that comes from the neopixel library we imported on Line 2.
• [2]: the pixels variable has an array that refers to each LED light, all 20 of them. However, the array indices starts at 0 so the 2 here refers to the third LED.
• (10,0,0): sets the color. Colors are RGB--(red, blue, green). The color values range from 0 to 255, so (10,0,0) indicates a low level of red, but no green or blue. Thus the third light shows a faint red.

                import board
                import neopixel

                pixels = neopixel.NeoPixel(board.D18, 20)

                pixels[4] = (10,0,0)
              

Colors are RGB (red, blue, green). With light, you get yellow when you mix red and green. You can search for "color picker" if you'd like to find your own custom color, just note that some colors are not represented accurately by the LED's.

                import board
                import neopixel

                pixels = neopixel.NeoPixel(board.D18, 20)

                pixels[3] = (255,255,0)
              

You could do this all by hand with copy and paste, but it's easier with a loop. With the simplest form of a for loop you can give it a range that it will itterate through: basically the loop will repeat so many times. To repeat something 5 times do:

              for i in range(5):
            

Don't forget the colon (:), otherwise this will not work. In python, you indicate what gets repeated by tabbing it over like so:

              for i in range(5):
                pixels[i] = (10,0,0)
            

Notice how the index in pixels[i] is the variable i. The variable is created in the for loop (you can use any variable name you like, it does not have to be i)

                import board
                import neopixel

                pixels = neopixel.NeoPixel(board.D18, 20)

                for i in range(5):
                  pixels[i] = (10,0,0)
              

The range() function can do more than just create a set of numbers starting from zero. You can give it a starting number and a stopping number. Say you wanted to get the numbers 4 through 8, you could write:

              for i in range(4, 9):
            

Notice that the second number ("9"), is one more than the last number we want.

                import board
                import neopixel

                pixels = neopixel.NeoPixel(board.D18, 20)

                # red
                for i in range(6):
                  pixels[i] = (10,0,0)

                # blue
                for i in range(5, 20):
                  pixels[i] = (0,0,10)
              

Here you just need to wait a moment (0.25 seconds to be exact) before lighting up the next light. We can do this by using the time module and the sleep function.

First import time:

              import time
            

Then use the sleep function like so:

              time.sleep(0.25)
            

                import board
                import neopixel
                import time

                pixels = neopixel.NeoPixel(board.D18, 20)

                for i in range(20):
                  pixels[i] = (10,0,0)
                  time.sleep(0.25)
              

How to turn off a light? Make it black (0,0,0).