Rust SCD4x Crate

A Rust crate to query CO₂ concentration, temperature and humidity from sensor SCD4x

https://gitlab.com/claudiomattera/scd4x-rs/

This crate supports both embedded-hal and embedded-hal-async.

See the changelog for this project.

Usage

Add the dependency to Cargo.toml.

[dependencies.scd4x-rs]
version = "0.1.0"

Optionally enable the desired features.

A Scd4x structure can be created from an I²C interface and a delay function.

use scd4x_rs::Scd4x;

let i2c = ...
let delay = ...

let sensor = Scd4x::new(i2c, delay);

let mut sensor = sensor.stop_periodic_measurement()?;
sensor.reinit()?;

let serial_number = sensor.get_serial_number()?;
println!("Serial number: 0x{serial_number:x}");

let mut sensor = sensor.start_periodic_measurement()?;

for _ in 0..5 {
    println!("Waiting before next measurement");
    delay.delay_ms(5_000);

    let sample = sensor.read_measurement()?;

    println!("Sample: ┳ CO₂: {} ppm", sample.co2);
    println!("        ┣ Temperature: {} C", sample.temperature);
    println!("        ┗ Humidity: {} %", sample.humidity);

    Ok(sample)
}

let sensor = sensor.stop_periodic_measurement()?;

An AsyncScd4x structure can be used with asynchronous HALs. Its API is completely identical to Scd4x, just with .async at the end of function calls.

use scd4x_rs::AsyncScd4x;

let i2c = ...
let delay = ...

let sensor = AsyncScd4x::new(i2c, delay);

let mut sensor = sensor.stop_periodic_measurement().await?;
sensor.reinit().await?;

let serial_number = sensor.get_serial_number().await?;
println!("Serial number: 0x{serial_number:x}");

let mut sensor = sensor.start_periodic_measurement().await?;

for _ in 0..5 {
    println!("Waiting before next measurement");
    delay.delay_ms(5_000);

    let sample = sensor.read_measurement().await?;

    println!("Sample: ┳ CO₂: {} ppm", sample.co2);
    println!("        ┣ Temperature: {} C", sample.temperature);
    println!("        ┗ Humidity: {} %", sample.humidity);

    Ok(sample)
}

let sensor = sensor.stop_periodic_measurement().await?;

See the examples for more information.

Sensor State

The sensor is implemented using the type-state pattern, i.e. its state is part of the type Scd4x<..., State>. The sensor can be in two states: idle or measuring. Functions that can only be executed when the sensor is idling are only implemented on type Scd4x<..., Idle>, and functions that can only be executed when the sensor is actively measuring are only implemented on type Scd4x<..., Measuring>.

The sensor is normally created in idle state with Scd4d::new(). Calling functions such as start_periodic_measurement(), start_low_power_periodic_measurement(), measure_single_shot() or measure_single_shot_rht_only() will consume the variable and return an new one of type Scd4x<..., Measuring>. Function stop_periodic_measurement() will again consume the variable and return an new one of type Scd4x<..., Idle>.

Alternatively, the sensor can be created directly in measuring state with Scd4d::new_in_measuring(). This is useful, for instance, when the sensor is left measuring while the controller is put to sleep. When the controller awakes again, it should not call start_periodic_measurement() again, but instead it should create the sensor directly in measuring state and start reading samples.

Unit of Measurements

By default, this crate uses f32 values for all the measurements CO₂ concentration, temperature and humidity, and the operating quantities altitude and pressure. When instead enabling the Cargo feature uom, it uses quantities from crate uom. CO₂ concentration values have type uom::si::f32::Ratio, temperature values have type uom::si::f32::ThermodynamicTemperature, humidity values have type uom::si::f32::Ratio, altitude values have type uom::si::f32::Length, and pressure values have type uom::si::f32::Pressure.

License

Copyright Claudio Mattera 2024

You are free to copy, modify, and distribute this application with attribution under the terms of either

• Apache License, Version 2.0 (file LICENSE-APACHE-2.0.txt or https://opensource.org/licenses/Apache-2.0)
• MIT license (file LICENSE-MIT.txt or https://opensource.org/licenses/MIT)

at your option.

This project is entirely original work, and it is not affiliated with nor endorsed in any way by Sensirion.