Sensirion SCD30 Particulate Matter Sensor

This is a library to interact with the Sensirion SCD30 Sensor Module for CO2, humidity and temperature. Currently, only the Modbus interface is implemented. The SCD30 also supports I2C, but requires clock stretching, which is currently not supported in the .NET Nanoframework ESP32 implementation.

Documentation

• For this implementation the official datasheet and interface description have been used.

Usage for the Modbus interface

Important: make sure you properly setup the UART pins for ESP32 before creating the SerialPort. For this, make sure you install the nanoFramework.Hardware.Esp32 NuGet and use the Configuration class to configure the pins:

Configuration.SetPinFunction(5, DeviceFunction.COM3_TX);
Configuration.SetPinFunction(27, DeviceFunction.COM3_RX);

Initialize the SerialPort and pass it to the Scd30Sensor. You'll stay in control of the SerialPort for any exotic situations (i.e. InvertSignalLevels or multiplexing scenarios). The constructor of the Scd30Sensor will configure the SerialPort to the expected BaudRate and other settings:

var scd30 = new Scd30Sensor(new SerialPort("COM3"));

Use the scd30 to interact with the sensor, e.g.:

var firmware = scd30.ReadFirmwareVersion();
Debug.WriteLine($"SCD30 detected: Firmware version={firmware}");

Collect a measurement reliably:

scd30.SetMeasurementInterval(TimeSpan.FromSeconds(2));
scd30.StartContinuousMeasurement();
Thread.Sleep(5000);
if (scd30.GetDataReadyStatus())
{
    var measurement = scd30.ReadMeasurement();
    Debug.WriteLine($"Measurement: {measurement}");
}

The above would output the following:

SCD30 detected: Firmware version=3.66
Measurement: Co2Concentration=400.8741 ppm, Temperature=27.10421752 °C, RelativeHumidity=32.75756835 %RH

Check out the sample for more information.

I don't get any measurements and GetDataReadyStatus never returns true!

When this happens, make sure you provide enough current/voltage to your sensor. In my particular case I was providing power from the 3v3 of my Pycom WiPy to both the vin and sel pins on the SCD30. However, the measurements never worked.

Instead, connecting the 5v to the vin and the 3v3 to sel made the SCD30 work as expected. The sel must be pulled high to enable the Modbus interface.

DO NOT CONNECT 5V TO sel, it is only tolerant up to 4v so you must use a voltage divider if you do not have 3v3 available