Introducing CircuitPython: Adafruit Circuit Playground Express

Button Press

Circuit Playground Express comes with 10 onboard RGB (red, green, blue) Neopixel LEDs capable of displaying any color individually or together. They are numbered 0 – 9 counter-clockwise on the board.
Contained within each Neopixel LED is three LEDs of different colors, one red, one blue and one green. The full spectrum of color is created by varying the levels of each LED within the Neopixel. To make a red light you only turn on the red portion of the Neopixel and leave the blue and green off. To create purple, you turn on red and blue, and to create white you turn on all three. If you’re not sure what combination of colors will give you the desired result you can.

For this example, we are going to start by making the Neopixel 0-4 turn red while the B button is pressed, and Neopixel 5-9 turn blue when button A is pressed.

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The Code

From within Mu, we want to create a new file and name it code.py. This is the file that the Circuit Playground Express will run whenever it starts up. Save the file to your CIRCUITPY drive. Whenever you make a change and save, the Circuit Playground Express will reboot and start the program immediately. Remember that code.py is where the code lives. Whenever you make changes to your code you will overwrite this file.

The following code activates half of the lights with each button press:

 
from adafruit_circuitplayground.express import cpx  # imports the CPX library from its subfolder

cpx.pixels.brightness = 0.1                     # set pixel brightness
cpx.pixels.fill((0, 0, 0))                          # turns all pixels off
cpx.pixels.show()                                   # sends data to pixels


while True:                            # loop
    if cpx.button_b:                   # if button is pushed then everything in hanging indent is executed
        print("Button B Pressed!")     # prints text in the serial monitor
        cpx.pixels[0] = (255, 0, 0)    # sets a single neopixel to given color pixel[number] = (R,G,B)
        cpx.pixels[1] = (255, 0, 0)
        cpx.pixels[2] = (255, 0, 0)
        cpx.pixels[3] = (255, 0, 0)
        cpx.pixels[4] = (255, 0, 0)
    if cpx.button_a:                   # button is pushed
        print("Button A Pressed!")
        cpx.pixels[5] = (0, 0, 255)
        cpx.pixels[6] = (0, 0, 255)
        cpx.pixels[7] = (0, 0, 255)
        cpx.pixels[8] = (0, 0, 255)
        cpx.pixels[9] = (0, 0, 255)
    if not(cpx.button_a or cpx.button_b):
        cpx.pixels.fill((0, 0, 0))              # will turn the lights off when buttons arent pressed

    cpx.pixels.show()                       # sends accumulated data to pixels

 

Let’s break down the code and explain the parts. One of the ways that CircuitPython simplifies code is with indentation. In most programming language the indentation is used to organize code and keep it easy to understand, but {} are used to show the constraints of operators. For example, in CircuitPython there are no brackets used to show what is included in an "if” statement, instead everything that is included in an if statement will have a hanging indent from the "if” statement. This helps keep the code clean and removes unnecessary characters.

The first step to writing a program in CircuitPython is to import Libraries. We need just one library to run this program, the CPX (Circuit Playground Express)  library. The CPX library allows us to make use of the on-board buttons easily. The CPX library is in a subfolder in lib, so to add it we must include the folder as well. 

from adafruit_circuitplayground.express import cpx  # imports the CPX library from its subfolder

The next section of our code sets the conditions for the NeoPixels. 
The next two lines set all the NeoPixels to off, just in case they were somehow illuminated at the start of the program. This is mostly precautionary as its very unlikely that this would be the case.

cpx.pixels.brightness = 0.1                         # set pixel brightness
cpx.pixels.fill((0, 0, 0))                            # turns all pixels off
cpx.pixels.show()                                   # sends data to pixels

The main body of our code contains our loop, in this case, a “while True” loop. Notice how everything contained within the while true loop is indented once. For the logic of this program, we are using if statements. The first if statement looks for a press of button B. To use an onboard button we use the cpx.button_a command. CircuitPython allows you to keep your code simple here by not requiring an if true/false statement. Within our If statement we print “Button B Pressed!” in the serial monitor or the REPL if you are using Mu, and set the color of NeoPixel 0-4. We then do the same for button A. We then have an If statement to turn off the NeoPixels if neither button A or B is being pressed. Finally we write the commands to the NeoPixels with cpx.pixel.show(). 

while True:                            # loop
    if cpx.button_b:                   # if button is pushed then everything in hanging indent is executed
        print("Button B Pressed!")     # prints text in the serial monitor
        cpx.pixels[0] = (255, 0, 0)    # sets a single neopixel to given color pixel[number] = (R,G,B)
        cpx.pixels[1] = (255, 0, 0)
        cpx.pixels[2] = (255, 0, 0)
        cpx.pixels[3] = (255, 0, 0)
        cpx.pixels[4] = (255, 0, 0)
    if cpx.button_a:                   # button is pushed
        print("Button A Pressed!")
        cpx.pixels[5] = (0, 0, 255)
        cpx.pixels[6] = (0, 0, 255)
        cpx.pixels[7] = (0, 0, 255)
        cpx.pixels[8] = (0, 0, 255)
        cpx.pixels[9] = (0, 0, 255)
    if not(cpx.button_a or cpx.button_b):
        cpx.pixels.fill((0, 0, 0))              # will turn the lights off when buttons arent pressed

    cpx.pixels.show()                       # sends accumulated data to pixels

Uploading your program to your board is as easy as saving the program as code.py on the Circuit Playground Express! The Circuit Playground Express will look for a program file and run the first one it finds, starting with code.py, then main.py. Now you are free to take your button press lights anywhere you want! Check out our tutorials section if you want to learn more about the Adafruit Circuit Playground Express. We also have tutorials about programming the Circuit Playground Express using MakeCode. Let's not forget about Arduino! If you want to learn about programming the Circuit Playground Express using Arduino check out our dedicated Arduino tutorials!