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CircuitPython Cheatsheet

Digital I/O

import board
from digitalio import DigitalInOut, Direction, Pull

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

switch = DigitalInOut(board.D5)
switch.direction = Direction.INPUT
switch.pull = Pull.UP   # Pull.Down is available on some MCUs

while True:
    led.value = not switch.value
    time.sleep(0.01)

Analog Input

import time
import board
from analogio import AnalogIn

analog_in = AnalogIn(board.A1)

def get_voltage(pin):
    return (pin.value * 3.3) / 65536

while True:
    print((get_voltage(analog_in),))
    time.sleep(0.1)

Analog input values are always 16 bit (i.e. in range(0, 65535)), regardless of the converter's resolution. The get_voltage function converts the analog reading into a voltage, assuming the default 3.3v reference voltage.

Analog Output

import board
from analogio import AnalogOut

analog_out = AnalogOut(board.A0)

while True:
    # Count up from 0 to 65535
    for i in range(0, 65536):
        analog_out.value = i

Analog output values are always 16 bit (i.e. in range(0, 65535)). Depending on the underlying hardware those values will get scaled to match the resolution of the converter. The example will generate a stairstepped signal, the number of steps depends on the resolution of the converter. E.g. the 10-bit converter in the SAMD21 will create 1024 steps, while the 12-bit converter on the SAMD51 will create 4096 steps.

PWM

You can use a PWM in one of two ways.

  1. With fixed frequency PWM with variable duty cycle. This is useful for controllign the brightness of a LED or the speed of a motor.

    import time import board import pulseio

    led = pulseio.PWMOut(board.D13, frequency=5000, duty_cycle=0)

    while True: for i in range(100): # PWM LED up and down if i < 50: led.duty_cycle = int(i * 2 * 65535 / 100) # Up else: led.duty_cycle = 65535 - int((i - 50) * 2 * 65535 / 100) # Down time.sleep(0.01)

  2. With variable frequency as well. This is handy for producing tones. The duty cycle effects the sound (as opposed to the note).

    import time import board import pulseio

    piezo = pulseio.PWMOut(board.A1, duty_cycle=0, frequency=440, variable_frequency=True)

    while True: for f in (262, 294, 330, 349, 392, 440, 494, 523): piezo.frequency = f piezo.duty_cycle = 65536 // 2 # On 50% time.sleep(0.25) # On for 1/4 second piezo.duty_cycle = 0 # Off time.sleep(0.05) # Pause between notes time.sleep(0.5)

Servo

import time
import board
import pulseio
from adafruit_motor import servo

# create a PWMOut object on Pin A2.
pwm = pulseio.PWMOut(board.A2, duty_cycle=2 ** 15, frequency=50)

# Create a servo object, my_servo.
my_servo = servo.Servo(pwm)

while True:
    for angle in range(0, 180, 5):  # 0 - 180 degrees, 5 degrees at a time.
        my_servo.angle = angle
        time.sleep(0.05)
    for angle in range(180, 0, -5): # 180 - 0 degrees, 5 degrees at a time.
        my_servo.angle = angle
        time.sleep(0.05)

Cap Touch

import time

import board
import touchio

touch_pad = board.A1  # For Circuit Playground Express

touch = touchio.TouchIn(touch_pad)

while True:
    if touch.value:
        print("Touched!")
    time.sleep(0.05)

NeoPixels

import time
import board
import neopixel

RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)

pixel_pin = board.A1
num_pixels = 8

pixels = neopixel.NeoPixel(pixel_pin, num_pixels, brightness=0.3, auto_write=False)

pixels.fill(RED)
pixels.show()

#The usual slicing operations can be used
pixels[1:6:2] = GREEN
pixels[7] = BLUE
pixels.show()

DotStar

import time
import adafruit_dotstar
import board

RED = (255, 0, 0)
num_pixels = 30

# DotStars use 2 pins instead of 1 that NeoPixels take
pixels = adafruit_dotstar.DotStar(board.A1, board.A2, num_pixels, brightness=0.1, auto_write=False)
pixels.fill(0) # all off
pixels[::2] = [RED] * (num_pixels // 2) # every other pixel red
pixels.show()

UART Serial

import board
import busio
import digitalio

uart = busio.UART(board.TX, board.RX, baudrate=9600)

while True:
    data = uart.read(32)  # read up to 32 bytes

    if data is not None:
        # convert bytearray to string
        data_string = ''.join([chr(b) for b in data])
        print(data_string, end="")
        uart.write(data_string)

I2C

import time
import adafruit_tsl2561
import board
import busio

i2c = busio.I2C(board.SCL, board.SDA)

# Create library object on our I2C port
tsl2561 = adafruit_tsl2561.TSL2561(i2c)

# Use the object to print the sensor readings
while True:
    print("Lux:", tsl2561.lux)
    time.sleep(1.0)

SPI

import board
import busio
import digitalio
import adafruit_bme280

spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
cs = digitalio.DigitalInOut(board.D5)
bme280 = adafruit_bme280.Adafruit_BME280_SPI(spi, cs)
print("\nTemperature: %0.1f C" % bme280.temperature)
print("Humidity: %0.1f %%" % bme280.humidity)
print("Pressure: %0.1f hPa" % bme280.pressure)

HID Keyboard

from adafruit_circuitplayground.express import cpx
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keycode import Keycode

kbd = Keyboard()

while True:
    if cpx.button_a:
        kbd.send(Keycode.SHIFT, Keycode.A)  # Type capital 'A'
        while cpx.button_a: # Wait for button to be released
            pass

    if cpx.button_b:
        kbd.send(Keycode.CONTROL, Keycode.X)  # control-X key
        while cpx.button_b: # Wait for button to be released
            pass

HID Mouse

from adafruit_circuitplayground.express import cpx
from adafruit_hid.mouse import Mouse

m = Mouse()
cpx.adjust_touch_threshold(200)

while True:
    if cpx.touch_A4:
        m.move(-1, 0, 0)
    if cpx.touch_A3:
        m.move(1, 0, 0)
    if cpx.touch_A7:
        m.move(0, -1, 0)
    if cpx.touch_A1:
        m.move(0, 1, 0)

    if cpx.button_a:
        m.press(Mouse.LEFT_BUTTON)
        while cpx.button_a:    # Wait for button A to be released
            pass
        m.release(Mouse.LEFT_BUTTON)

    if cpx.button_b:
        m.press(Mouse.RIGHT_BUTTON)
        while cpx.button_b:    # Wait for button B to be released
            pass
        m.release(Mouse.RIGHT_BUTTON)
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