Sensors with CircuitPython: Background

The purpose of this lesson is to provide background about microcontroller hardware and CircuitPython. The goal is to provide the necessary information you’ll need to start playing with a QT Py 2040 board and sensors.

Learning objectives At the end of this lesson, the learner will be able to:

describe how CircuitPython is different from normal CPython.
list three ways execution of the code.py file can be initiated in CircuitPython.
describe a module.
import a module into a script.
explain how importing modules in CircuitPython is different from standard Python.
describe the Blinka distribution and state what kinds of devices can use it.
explain what makes the I2C communications protocol so simple.
describe how Stemma QT connectors make the process of connecting sensors easy.
explain the syntax of a statement that instantiates a custom object.
use a while True: loop to keep a Python script running indefinitely.
describe the coding strategy used to initiate data collection using a button press.

Total video time: 31 min 56 s

Links

Lesson slides

DiSC CircuitPython code on GitHub

Introduction to QT Py RP2040 (0m42s)

QT Py RP 2040 information page

Introduction to CircuitPython (5m21s)

CircuitPython landing page

RP2040 chip specifications

The code.py script (2m16s)

Circumstances under which code.py begins execution:

board power up
saving to the memory chip (the pseudo flash drive seen by your laptop file system)
soft reset by CTRL-D via the serial console (REPL)
hard reset by pressing the reset button on the board

Example code.py script for QT Py RP2040:

import time
import board
import busio
import adafruit_vcnl4040

i2c = busio.I2C(board.SCL1, board.SDA1)
sensor = adafruit_vcnl4040.VCNL4040(i2c)

while True:
    print("Proximity:", sensor.proximity)
    print("Light: %d lux" % sensor.lux)
    time.sleep(1.0)

Modules in CircuitPython (5m25s)

CircuitPython library bundle download page

CircuitPython libraries installation instructions

Blinka landing page

Connecting sensors (4m18s)

I2C protocol specification

QT Py RP2040 pinouts description

CircuitPython objects (5m26s)

Microsoft learning module on Python object-oriented programming

VCNL4040 breakout board CircuitPython reference page

Sensor code (7m06s)

Lesson on for and while loops

Code examples:

Execute loop 10 times:

count = 0
while count < 10:
    count += 1
    print(count, 'yaaaa!')

Execute loop 1 time:

count = 0
if True:
    count += 1
    print(count, 'yaaaa!')

Infinite loop:

count = 0
while True:
    count += 1
    print(count, 'yaaaa!')

digitalio module reference

CircuitPython digital inputs learn page

code.py example with triggering data collection using the button:

import time
import board
import busio
import digitalio
import adafruit_vcnl4040

i2c = busio.I2C(board.SCL1, board.SDA1)

# humidity/temperature sensor
sensor = adafruit_vcnl4040.VCNL4040(i2c)

# Code to use the built-in boot button on the board. Pressed is False (grounded)
button = digitalio.DigitalInOut(board.BUTTON)
button.switch_to_input(pull=digitalio.Pull.UP)

# Program will do nothing until the button is pressed.
while button.value: # button.value will be True when not pressed
    pass

# read the relative humidity and temperature every second indefinitely
while True:
    print("Proximity:", sensor.proximity)
    print("Light: %d lux" % sensor.lux)
    time.sleep(1.0)