scd4x

A Go module for reading CO2, temperature, and humidity data from the Sesirion SCD4x family of sensors. Example sensors are the Adafruit SCD-40 and Adafruit SCD-41. The former was used during the development of this module.

Scope

The module implements the following sensor functions through an i2c bus:

• Starting periodic measurements
• Reading the current sensor values
• Stopping periodic measurements

Once the sensor has started periodic measurements, it automatically records new sensor data every 5 seconds into its internal buffer. A ReadMeasurement call retrieves the most recent sensor data from SCD4x.

Example CLI Monitor

The example_monitor.go provides a simple CLI monitor with syntax similar to other CLI tools like iostat and vmstat.

Installation

Clone this repository and navigate to the examples/ directory. Then build with go.

go build example_monitor.go

You should now have an executable file called example_monitor

Syntax

pi@sliceofpi:~/scd4x/examples $ ./example_monitor -h
Usage:
 ./example_monitor [options] [delay [count]]
  -f	Use degrees Fahrenheit (default: Celsius)
  -init
    	Get sensor in state ready for measurements.
  -v	Verbose output

Like other system tools, delay is the number of seconds to wait between measurements, and count is the total number of measurements to take. Both field are optional. Not specifying the delay will take one measurement and exit. Specifying a delay but not a count will run the monitor indefinitely, until it receives an interrupt (e.g. Ctrl+C).

If you're not sure what state the sensor is in, i.e. whether its in an idle state or already in a periodic measurement state, you can use the --init flag, which will issue a StopMeasurement followed by a StartMeasurement command. The --init operation takes about 7 seconds to complete. You should only ever need to use the flag once.

Output

Verbose output:

pi@sliceofpi:~/scd4x/examples $ ./example_monitor -f -v 10
Time                            CO2   Temp    RH
[2022-01-30T10:31:10-07:00]  801ppm 71.0*F 18.9%
[2022-01-30T10:31:20-07:00]  782ppm 70.9*F 19.0%
[2022-01-30T10:31:30-07:00]  780ppm 70.9*F 19.0%
[2022-01-30T10:31:40-07:00]  780ppm 70.9*F 18.9%
[2022-01-30T10:31:50-07:00]  780ppm 70.9*F 18.9%

Minimal output:

pi@sliceofpi:~/scd4x/examples $ ./example_monitor -f 10
665 71.0 18.1
665 71.0 18.1
663 71.0 18.0
663 71.0 18.0
663 71.0 18.0
663 71.1 18.0