DIY Trinkey No-Soldering USB Air Quality Monitor

published December 22, 2021, last edited January 22, 2025

posted in Sensors/ Temperature & Humidity CircuitPython STEMMA

Beginner

Project guide

Direct Reading with U2IF

This approach allows for direct reading of the sensors. Instead of reading and parsing from a serial stream, the sensor libraries are used directly in Python running on the host PC. This is done by having specialized firmware called U2IF running on the Trinkey QT2040. On the host PC, Blinka is installed to provide access to the Trinkey running U2IF and allow use of CircuitPython libraries.

This approach has a lot of setup. However, if your goal is to get sensor values into a Python application running on the host PC, this approach offers the most direct route.

Install U2IF Firmware onto Trinkey

This step is pretty easy. Just download the firmware file and copy to Trinkey. To download a copy of the U2IF firmware for the Trinkey QT2040, go here:

U2IF Firmware for Trinkey QT2040

To install the UF2 file:

Put the Trinkey QT2040 in bootloader mode by holding the BOOT button while pressing the RST (reset) button.
A folder named RPI-RP2 should appear.
Drag the UF2 file to the RPI-RP2 folder.
Once copied, board should reset and code is now running.

Install Blinka onto PC

This step has more to it. The installation process is different for each operating system. Use this guide to install Blinka and the associated supporting software on to your PC:

Setup on PC

Make sure the post install checks pass before proceeding. Skip the check for the Pico, since were using a different board:

Post Install Checks

Install Libraries onto PC

Now we can install the specific CircuitPython libraries needed for talking to the sensors. For the SCD40, install this library:

SCD4x Library Install

For the BME280, install this library:

BME280 Library Install

Read Sensors via Python

Once all the setup is done, actually reading the sensors is easy.

Make sure you've set the BLINKA_U2IF environment variable.

Here is a basic "hello world" example of simply reading and printing the sensor values in a loop.

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# SPDX-FileCopyrightText: 2021 Carter Nelson for Adafruit Industries
#
# SPDX-License-Identifier: MIT

import time
import board
import adafruit_scd4x
from adafruit_bme280 import basic as adafruit_bme280

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
scd = adafruit_scd4x.SCD4X(i2c)
scd.start_periodic_measurement()

bme = adafruit_bme280.Adafruit_BME280_I2C(i2c)

while True:
    time.sleep(5)
    print("CO2 =", scd.CO2)
    print("Pressure = {:.1f} hPa".format(bme.pressure))
    print("Temperature = {:.1f} degC".format(bme.temperature))
    print("Humidity = {:.1f}%".format(bme.humidity))

# SPDX-FileCopyrightText: 2021 Carter Nelson for Adafruit Industries
#
# SPDX-License-Identifier: MIT

import time
import board
import adafruit_scd4x
from adafruit_bme280 import basic as adafruit_bme280

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
scd = adafruit_scd4x.SCD4X(i2c)
scd.start_periodic_measurement()

bme = adafruit_bme280.Adafruit_BME280_I2C(i2c)

while True:
    time.sleep(5)
    print("CO2 =", scd.CO2)
    print("Pressure = {:.1f} hPa".format(bme.pressure))
    print("Temperature = {:.1f} degC".format(bme.temperature))
    print("Humidity = {:.1f}%".format(bme.humidity))

Make sure you've set the BLINKA_U2IF environment variable.

Running that code should produce output similar to this: