QT Py Tricks

Some things to do on a stock Adafruit QT Py running CircuitPython 6. This list is mostly to help me remmeber how to do things in CircuitPython. Fore more general CircuitPython tricks, check out my CircuitPython Tricks page.

These code snippets will also work on a Trinket M0 and really just about CircuitPython-compatible board, but you may need to adjust some of the board pins.

Notes:

• You will need to copy needed libraries from the CircuitPython libraries bundle to your CIRCUITPY drive
• When copying files to QT Py or Trinket M0, and you're on a Mac, be sure to use the xattr trick described here to save flash space
• Or, just use circup to install libraries. It's very nice! (on Mac, do pip3 install circup)

Table of Contents

• Print "time" on OLED display
• Disco Party on built-in Neopixel
• Output Farty Noises to DAC
• Capsense Touch to Colors on Built-in LED
• Rotary Encoder to Built-in LED
• Fire Simulation on External Neopixel Strip
• Two servos with Python Class for Easing / Sequencing
• Spooky Eyes with Dual SSD1306 OLED displays
• Use Capsense as Proximity Detector to Make Spooopy Ghost
• Get Size of Device's Flash Disk
• Capsense Touch Sensor to USB keyboard

Print "time" on OLED display

[Note: as of CircuitPython 7, this only works on QTPy RP2040, not QTPy M0 or QTPY M0 Haxpress]

import time
import board 
import adafruit_ssd1306 # requires: adafruit_bus_device and adafruit_framebuf
i2c = board.I2C()
oled = adafruit_ssd1306.SSD1306_I2C(width=128, height=32, i2c=i2c)
while True:
    oled.fill(0)
    oled.text( "hello world", 0,0,1) # requires 'font5x8.bin'
    oled.text("time:"+str(time.monotonic()), 0,8,1)
    oled.show()
    time.sleep(1.0)

Disco Party on built-in Neopixel

import time
import board
import neopixel
from random import randint
pixel = neopixel.NeoPixel(board.NEOPIXEL, 1, brightness=0.2)
while True:
    pixel.fill( (randint(0,255), randint(0,255), randint(0,255) ))
    time.sleep(0.1)

Output Farty Noises to DAC

import time
import board 
import analogio
import random
dac = analogio.AnalogOut(board.A0)
i = 0
di = 40000
lasttime = 0
while True:
    dac.value = i
    i = (i+di) & 0xffff
    if time.monotonic() - lasttime > 1:
        lasttime = time.monotonic()
        di = random.randrange(40000,80000)

(hear it in action)

Capsense Touch to Colors on Built-in LED

import board
from touchio import TouchIn
import neopixel
pixel = neopixel.NeoPixel(board.NEOPIXEL, 1, brightness=0.2)
touchA = TouchIn(board.A1)
touchB = TouchIn(board.A2)
print("hello")
while True:
  pixel[0] = (int(touchA.value*255), 0, int(touchB.value*255))

Rotary Encoder to Built-in LED

import board
import time
import neopixel
import rotaryio
pixel = neopixel.NeoPixel(board.NEOPIXEL, 1, brightness=1.0)
encoder = rotaryio.IncrementalEncoder( board.MOSI, board.MISO ) # any two pins
while True:
    b = (encoder.position % 32) * 8
    print(encoder.position,b)
    pixel.fill((0,0,b))
    time.sleep(0.1)

Fire Simulation on External Neopixel Strip

Uses Python array operations and list comprehensions for conciseness.

import board
import time
import neopixel
from random import randint
# External Neopixel strip, can be on any pin
leds = neopixel.NeoPixel(board.RX,8,brightness=0.2,auto_write=False)
while True:
    # reduce brightness of all pixels by (30,30,30)
    leds[:] = [[max(i-30,0) for i in l] for l in leds]
    # shift LED values up by one (0->1, 1->2, etc)
    leds[1:] = leds[0:-1] # '-1' means len-1 here
    # pick new random fire color for LED 0
    leds[0] = (randint(150,255),randint(50,100),0) 
    leds.show()
    time.sleep(0.1)

If you want it "flipped", so the fire goes from the top LED down to LED 0:

import time, board, neopixel
from random import randint
leds = neopixel.NeoPixel(board.RX,8,brightness=0.2,auto_write=False)
while True:
    leds[:] = [[max(i-30,0) for i in l] for l in leds] # reduce brightness of all pixels by (30,30,30)
    leds[0:-1] = leds[1:]                              # shift LED values down by one
    leds[-1] = (randint(150,255),randint(50,100),0)    # pick new random fire color for LED N
    leds.show()
    time.sleep(0.1)

Two servos with Python Class for Easing / Sequencing

import board
import time
from pulseio import PWMOut
from adafruit_motor import servo
from random import random

servoA = servo.Servo(PWMOut(board.RX, duty_cycle=2**15, frequency=50))
servoB = servo.Servo(PWMOut(board.TX, duty_cycle=2**15, frequency=50))

class AngleSequence:
    def __init__(self,angles,speed):
        self.angles = angles
        self.aindex = 0
        self.angle = angles[0]
        self.speed = speed
    def next_angle(self):
        self.aindex = (self.aindex + 1) % len(self.angles)
    def update(self):
        new_angle = self.angles[self.aindex]
        self.angle += (new_angle - self.angle) * self.speed  # simple easing
        return self.angle

seqA = AngleSequence( [90,70,90,90,90,90,60,80,100], 0.1) # set speed to taste
seqB = AngleSequence( [90,90,90,80,70,90,120], 0.1) # set angles for desired animation

lasttime = time.monotonic()
while True:
    if time.monotonic() - lasttime > (0.2 + random()*4.0  ):  # creepy random timing
        lasttime = time.monotonic()
        seqA.next_angle() # go to next angle in list
        seqB.next_angle()
    servoA.angle = seqA.update() # get updated (eased) servo angle
    servoB.angle = seqB.update()
    time.sleep(0.02) # wait a bit, note this affects 'speed'

Spooky Eyes with Dual SSD1306 OLED displays

Displays are at same address, so code can be much simpler

[Note: as of CircuitPython 7, this only works on QTPy RP2040, not QTPy M0 or QTPY M0 Haxpress]

import time
import board 
import random
import adafruit_ssd1306 # requires: adafruit_bus_device, adafruit_framebuf
i2c = board.I2C()
oled = adafruit_ssd1306.SSD1306_I2C(width=128, height=64, i2c=i2c)
i=0; inc=30
while True:
    oled.fill(0)
    for d in (31,30,14,12,10,8):  # various diameters
        oled.circle( 64+i,32, d,1)
    i = random.randint(-30,30)
    oled.show()
    time.sleep( 0.1 + random.random() )

Use Capsense as Proximity Detector to Make Spooopy Ghost

Computing the difference between current touch raw value anda baseline minimum provides a kind of proximity detector, if your antenna is big enough.

import time
import board
import digitalio
import touchio
from pulseio import PWMOut
from adafruit_motor import servo

touchA = touchio.TouchIn(board.A2)
servoA = servo.Servo(PWMOut(board.RX, duty_cycle=2**15, frequency=50))
touch_min = touchA.raw_value  # baseline for proximity
servo_pos_last = 160

while True:
    # get proximity value, set within servo bounds (30-160)
    proximity_val = (touchA.raw_value - touch_min)
    servo_pos = 160 - min(160, max(30, proximity_val))
    servo_pos_last += (servo_pos - servo_pos_last) * 0.01  # easing/smoothing
    servoA.angle = servo_pos_last

Get Size of Device's Flash Disk

see os.statvfs() docs

import os
print("\nHello World!")
fs_stat = os.statvfs('/') 
print("Disk size in MB", fs_stat[0] * fs_stat[2] / 1024 / 1024)
print("Free space in MB", fs_stat[0] * fs_stat[3] / 1024 / 1024)
while True: pass

Capsense Touch Sensor to USB keyboard

import time
import board 
import neopixel
import touchio
import usb_hid
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keycode import Keycode
touchA= touchio.TouchIn(board.A0)
pixel = neopixel.NeoPixel(board.NEOPIXEL, 1, brightness=0.2, auto_write=False)
pixel[0] = (0,0,0)
time.sleep(1)  # Sleep for a bit to avoid a race condition on some systems
kbd = Keyboard(usb_hid.devices)
while True:
    if touchA.value:
        print("A press")
        pixel[0] = (255,0,0)
        kbd.send(Keycode.RIGHT_ARROW)
    pixel.show()
    pixel[0] = (0,0,0)
    time.sleep(0.2)

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Really Helpful CircuitPython Links

• https://circuitpython.readthedocs.io/projects/bundle/en/latest/drivers.html
• https://circuitpython.readthedocs.io/en/latest/shared-bindings/support_matrix.html
• https://learn.adafruit.com/circuitpython-essentials/circuitpython-essentials
• https://learn.adafruit.com/welcome-to-circuitpython/overview