CircuitPython

Let’s get something happening on your Gemma.

All of these examples are complete programs, so make sure you copy them into Mu (or whatever editor you’re using) and run them as you go through this page.

Flash the built-in LED

The first thing you try to get working on any embedded system is flashing a light. It’s amazing how much information you can convey with just a light if you get a little creative!

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import board
import digitalio
import time

led = digitalio.DigitalInOut(board.LED)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    time.sleep(0.5)
    led.value = False
    time.sleep(0.5)

Lines 1-3 import various libraries that we will use. All of your Gemma programs will start with one or more of these import lines.

Line 5 gives us a reference to the pin that the built-in LED (the red one) is connected to. We store that reference in a variable called led. Line 6 tells the Gemma that we want to use the pin we’ve called led as an output (to drive the red LED).

Lines 8-12 are an infinite loop. We turn the LED on, wait for half a second, turn it off, and wait another half second. Then we do it all again, and again, and so on.

If you’ve written this in Mu, it should look like this:

Flash the built-in RGB LED

Now we’ve got something happening, let’s explore the built-in RGB LED. This model of LED is a Dotstar. The LEDs on the strip we’ll be using are a model called Neopixel.

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import board
import adafruit_dotstar as dotstar
import time

dot = dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1, brightness=0.2)

while True:
    dot[0] = (255, 255, 0)
    time.sleep(0.5)
    dot[0] = (0, 0, 255)
    time.sleep(0.5)

Notice that we on line 5 we call the dotstar dot, but to use it we say dot[0]. Dotstars and Neopixels are designed to be chained together on a strip with common wires, so dot actually refers to a list of LEDs, not just one. Counting in computers usually begins at zero, so the LED at the end closest to the signal source is numbered dot[0] and the others numbered dot[1], dot[2] and so on. Since there is only one built-in dotstar, we only use dot[0].

Respond to the capacitive input

You can use pin A2 as a capacitive input, meaning it will detect your finger touching it.

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import board
import digitalio
from touchio import TouchIn

touch2 = TouchIn(board.A2)

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = touch2.value

Capacitive input and the RGB LED

If we want to control the RGB led with with the touch input, we need to do a bit more work, and use an if statement.

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import board
import adafruit_dotstar as dotstar
from touchio import TouchIn

touch2 = TouchIn(board.A2)

dot = dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1, brightness=0.2)

while True:
    if touch2.value:
        dot[0] = (255, 255, 0)
    else:
        dot[0] = (0, 0, 255)