Turn Cytron MOTION 2350 Pro as air quality scanner using circuitpython

In this tutorial we will use CircuitPython to turn a Cytron MOTION 2350 Pro into a HibouAir scanner. The board’s RP2350 has no Bluetooth radio of its own. A BleuIO dongle in the board’s USB-A host port provides Bluetooth Low Energy, and a short CircuitPython program talks to it with ordinary AT commands.

Everything runs on the board. No computer is needed once the code is in place, and the HibouAir sensors do not need to be paired.

With circup installed on your computer, one command copies both:

circup install asyncio

Everything else the program uses is built into CircuitPython: usb_host, usb.core, json, binascii, microcontroller, pwmio and time. The servo is driven with pwmio directly, so it needs no extra library. No boot.py is needed.

The MOTION 2350 Pro’s USB-A port is driven by the RP2350’s PIO. CircuitPython starts it with usb_host.Port on GPIO24 and GPIO25. The board definition has no named pins for this port, so the program uses the raw pins.

The program waits until a device with vendor ID 0x2DCF and product ID 0x6002 appears, which is BleuIO. It selects the dongle’s configuration and sets DTR and RTS, so that BleuIO starts sending its output.

BleuIO remembers what it was doing, so a scan from an earlier run may still be going. The program first sends Ctrl-C three times to stop it. It then throws away everything the dongle sends until it has been quiet for 0.3 seconds. After that it sends:

If you have more than one PM sensor, set PM_SENSOR_ID to the one pm10 should follow. If nothing has been heard for 15 seconds, the program starts the scan again.

The MOTION 2350 Pro has eight servo ports, on GP0 to GP7, each with a PWM channel of its own. The program drives a servo on GP0 as a needle: 0 µg/m³ at 0 degrees, and 100 µg/m³ or more at 180 degrees.

With that full scale, the PM10 limits the HibouAir app uses fall at simple angles. That is where to draw the bands on a paper scale behind the servo arm:

The gauge is its own asyncio task, beside the reader and the command logic:

Connect the servo to the GP0 servo header, matching the servo cable to the markings next to the header. Check Cytron’s datasheet for how the servo ports are supplied before connecting a larger servo.

The board’s four DC motor drivers, on GP8 to GP15 (board.M1A to board.M4B in CircuitPython), would suit a different use of the same value, such as running a fan faster as PM10 rises.

Ctrl-C stops the scan, but whatever BleuIO had already queued still arrives afterwards. Often the last piece is a line cut off in the middle, sometimes with a byte that is not valid UTF-8.

In early versions of this program, a reader that tried to decode that line before removing it from its buffer stuck on it. Every later piece of data was appended behind the same broken line, and the program heard nothing more, in about half of all restarts.

With both in place, the start-up worked every time in repeated tests, whether the dongle was fresh (echo on, verbose off) or left in verbose mode by an earlier run.

Download the CircuitPython UF2 for the Cytron MOTION 2350 Pro and put the board into its UF2 bootloader mode. On RP2350 boards this is done by holding BOOT while pressing RESET, or while connecting the USB cable. Copy the UF2 to the RP2350 drive that appears. The board restarts as a drive named CIRCUITPY.

Run circup install asyncio, or copy the asyncio folder and adafruit_ticks.mpy from the library bundle into CIRCUITPY/lib.

Save the code at the end of this post as code.py on the CIRCUITPY drive. CircuitPython starts it as soon as the file is saved.

Insert the BleuIO dongle into the board’s USB-A port. Do not connect BleuIO to the computer for this setup.

Plug the servo into the GP0 servo header. It sweeps once from 0 to 180 degrees and back when the program starts, then follows PM10, and goes quiet whenever the needle is still.

Open the board’s serial console at 115200 baud. Use Mu, Thonny or the CircuitPython web workflow, or on macOS and Linux:

screen /dev/cu.usbmodem2101 115200

The device name differs from computer to computer. If the console shows raw REPL; CTRL-B to exit, an editor has left it in raw REPL mode: press Ctrl-B, then Ctrl-D to start code.py.

BleuIO dongle found! (0x2dcf:0x6002) CDC Control Lines (DTR/RTS) enabled. Starting background USB reader task... Starting the HibouAir scan... [Sending]: ATE0 [Sending]: ATV1 [Sending]: AT+FINDSCANDATA=FF5B07 [HibouAir 22026A] PM10 0.1 ug/m3 PM2.5 0.1 PM1 0.0 21.8 C [HibouAir 22008C] board 0x04, 21.5 C, 39.8 %rh, CO2 459 ppm [HibouAir 220095] board 0x04, 20.8 C, 42.9 %rh, CO2 411 ppm [HibouAir 22005A] board 0x04, 19.6 C, 44.2 %rh, CO2 721 ppm [HibouAir 220265] board 0x09, 19.8 C, 45.5 %rh, CO2 533 ppm

Every HibouAir sensor in range appears with its ID. Lines from the PM sensor show the particle readings; the others show temperature, humidity and CO2. Each new PM line also updates pm10.

Source code is available to download from

https://github.com/smart-sensor-devices-ab/hibouair-with-circuitpython

This project is a practical example of how BleuIO can bring Bluetooth Low Energy connectivity to development boards without built-in Bluetooth support. Using the Cytron MOTION 2350 Pro and CircuitPython, we demonstrated how to scan for HibouAir sensors, read real-time data, and use that data to control a servo motor.

The complete source code is available for developers to explore, modify, and integrate into their own projects. Whether you’re building sensor monitoring systems, automation solutions, or custom IoT applications, this example provides a starting point for using BleuIO with compatible development boards.

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