Crate sgp30

source ·
Expand description

A platform agnostic Rust driver for the Sensirion SGP30 gas sensor, based on the embedded-hal traits.

The Device

The Sensirion SGP30 is a low-power gas sensor for indoor air quality applications with good long-term stability. It has an I²C interface with TVOC (Total Volatile Organic Compounds) and CO₂ equivalent signals.

Usage

Instantiating

Import this crate and an embedded_hal implementation, then instantiate the device:

use linux_embedded_hal as hal;

use hal::{Delay, I2cdev};
use sgp30::Sgp30;

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let address = 0x58;
let mut sgp = Sgp30::new(dev, address, Delay);

Fetching Device Information

You can fetch the serial number of your sensor as well as the feature set:

use sgp30::FeatureSet;

let serial_number: [u8; 6] = sgp.serial().unwrap();
let feature_set: FeatureSet = sgp.get_feature_set().unwrap();

Doing Measurements

Before you do any measurements, you need to initialize the sensor.

sgp.init().unwrap();

The SGP30 uses a dynamic baseline compensation algorithm and on-chip calibration parameters to provide two complementary air quality signals. Calling this method starts the air quality measurement. After initializing the measurement, the measure() method must be called in regular intervals of 1 second to ensure proper operation of the dynamic baseline compensation algorithm. It is the responsibility of the user of this driver to ensure that these periodic measurements are being done!

use embedded_hal::blocking::delay::DelayMs;
use hal::Delay;
use sgp30::Measurement;

loop {
    let measurement: Measurement = sgp.measure().unwrap();
    println!("CO₂eq parts per million: {}", measurement.co2eq_ppm);
    println!("TVOC parts per billion: {}", measurement.tvoc_ppb);
    Delay.delay_ms(1000u16 - 12);
}

(Note: In the example we’re using a delay of 988 ms because the measurement takes up to 12 ms according to the datasheet. In reality, it would be better to use a timer-based approach instead.)

For the first 15 s after initializing the air quality measurement, the sensor is in an initialization phase during which it returns fixed values of 400 ppm CO₂eq and 0 ppb TVOC. After 15 s (15 measurements) the values should start to change.

A new init command has to be sent after every power-up or soft reset.

Restoring Baseline Values

The SGP30 provides the possibility to read and write the values of the baseline correction algorithm. This feature is used to save the baseline in regular intervals on an external non-volatile memory and restore it after a new power-up or soft reset of the sensor.

The get_baseline() method returns the baseline values for the two air quality signals. After a power-up or soft reset, the baseline of the baseline correction algorithm can be restored by calling init() followed by set_baseline().

use sgp30::Baseline;

let baseline: Baseline = sgp.get_baseline().unwrap();
// …
sgp.init().unwrap();
sgp.set_baseline(&baseline).unwrap();

Humidity Compensation

The SGP30 features an on-chip humidity compensation for the air quality signals (CO₂eq and TVOC) and sensor raw signals (H2 and Ethanol). To use the on-chip humidity compensation, an absolute humidity value from an external humidity sensor is required.

use sgp30::Humidity;

// This value must be obtained from a separate humidity sensor
let humidity = Humidity::from_f32(23.42).unwrap();

sgp.init().unwrap();
sgp.set_humidity(Some(&humidity)).unwrap();

After setting a new humidity value, this value will be used by the on-chip humidity compensation algorithm until a new humidity value is set. Restarting the sensor (power-on or soft reset) or calling the function with a None value sets the humidity value used for compensation to its default value (11.57 g/m³) until a new humidity value is sent.

Structs

Enums

  • Error
    All possible errors in this crate
  • ProductType
    The product types compatible with this driver.