devices/scd4x

Sensirion SCD4x CO₂ Sensors

Overview

This package provides a driver for the Sensirion SCD4x CO₂ sensors. This is a compact sensor that provides temperature, humidity, and CO₂ concentration readings. The datasheet for this device is available at:

https://sensirion.com/media/documents/48C4B7FB/66E05452/CD_DS_SCD4x_Datasheet_D1.pdf

Testing

The unit tests can function with either a live sensor, or in playback mode. If the environment variable SCD4X is set, then the self test code will use a live sensor on the default I²C bus. For example:

$> SCD4X=1 go test -v

If the environment variable is not present, then unit tests will be conducted using playback values.

Notes

Acquisition Time

The minimum acquisition time for the sensor is 5 seconds. If you call Sense() more frequently, it will block until a reading is ready.

Forced Calibration and Self-Test

These functions are not implemented. From examining the datasheet, and experimenting, it appears that these two calls require the i2c communication driver to wait a specified period before initiating the read. The periph.io I²C library doesn't support this functionality. This means that attempts to call these functions will always fail so they're not implemented.

Acquisition Mode

Only certain commands can be issued while the device is running in acquisition mode. If you're working on the low-level code, be aware that attempts to send a non-allowed command while in acquisition mode will return an i2c remote io-error.

Automatic Self Calibration

When Automatic Self Calibration is enabled, and the sensor has run for the required period, it will adjust itself so that the LOWEST recorded reading during the period yields the value set for ASC Target. The factory default target is 400PPM, but the current PPM is ~425PPM. To get a more accurate value for CO2 concentration in Earth's atmosphere, refer to:

https://www.co2.earth/daily-co2

For more details, refer to the datasheet.