pico-scd4x

Raspberry Pi Pico W and SCD4X sensor

Connecting a SCD4X sensor (temperature, humidity, CO2)* to a Rpi Pico 2W and publish the measurements to an MQTT broker. I used the MicroPython_SCD4X driver from peter-l5, which is based on the adafruit_scd4x.py.

Steps:

1. Download the .uf2 firmware from MicroPython
2. Connect the Pico via USB and drag .uf2 to RPI-RP2 drive (flashes the firmware and reboots the Pico)
3. Access Pico via CLI (or use an IDE like Thonny).
   • On Linux OS: apt install picocom
   • picocom /dev/ttyACM0 -b 115200 to start the MicroPython REPL on the Pico
   • Check if install works:

     >>> import machine
     >>> led = machine.Pin("LED", machine.Pin.OUT)
     >>> led.toggle()

4. Upload the MicroPython MQTT client library simple.py and robust.py
   • via Thonny:
     1. Open the Files pane (View → Files).
     2. Navigate to the Pico device.
     3. Right-click → New Directory → name it: "umqtt"
     4. Upload simple.py and robust.py into that folder
5. Add a configuration file (config.py) and create variables for Wifi and MQTT connections:
   • wifi_ssid = local WIFI name
   • wifi_password = local WIFI password
   • mqtt_server = the server address running the MQTT broker
   • mqtt_topic = the MQTT topic to publish the sensor readings to
   • mqtt_username = MQTT user (optional, depending on MQTT setup)
   • mqtt_password = MQTT password -"-
6. Connect the sensor to the Pico and upload the main.py to the device in order to read/publish the sensor data (via MQTT)

Useful resources:

• Rpi Pico W-Series Documentation
• Rpi Pico GPIO-Connections diagram
• SCD4X sensor datasheets
• Mosquitto (Open-source MQTT broker)

Additional helper scripts:

• I2Cscan.py checks if sensor can be found on I2C bus
• sample_read_sensor_data.py simple script to test read sensor data

* I used an SCD41 sensor from SEED-Studio