SCD30 I2C

Software to read out Sensirion SCD30 CO₂ Sensor values over I2C on Raspberry Pi.

This software is licenced under GPLv3 by UnravelTEC OG (https://unraveltec.com), 2018.

Prerequisites

You might need to run the following commands as root e.g. by typing sudo before running a specific command.

Enable I2C interface on Raspberry Pi

raspi-config navigate to P5 I2C and select <Yes>.

Wiring SCD30 to Raspberry Pi 3 B

• SCD30: RX/SDA -> Pi: I2C1 SDA (GPIO2)
• SCD30: TX/SCL -> Pi: I2C1 SCL (GPIO3)
• SCD30: VIN -> Pi: 3.3V/5.5V (use one of PWR pinouts)
• SCD30: GND -> Pi: GND (use one of GND pinouts)

Python

Install the following python-libraries:

aptitude install python-crcmod

(for Python3, use the appropriate prefix)

Pigpiod

As the SCD30 needs complex i2c-commands, the Linux standard i2c-dev doesn't work. A working alternative is pigpiod.

aptitude install pigpio python-pigpio

Atm, IPv6 doesn't work on Raspbian correctly with pigpiod, so:

sed -i "s|^ExecStart=.*|ExecStart=/usr/bin/pigpiod -l -n 127.0.0.1|" /lib/systemd/system/pigpiod.service
systemctl restart pigpiod
# Test (should return an int)
pigs hwver

I2C Clock stretching

Master needs to support Clock Stretching up to 150ms. The default in Raspbian is too low, we have to increase it:

To set it, download from here:

https://github.com/raspihats/raspihats/tree/master/clk_stretch

Compile:

gcc -o i2c1_set_clkt_tout i2c1_set_clkt_tout.c
gcc -o i2c1_get_clkt_tout i2c1_get_clkt_tout.c

execute (add to /etc/rc.local to run on every boot):

./i2c1_set_clkt_tout 20000 # for 200ms

Remember: Maximum I2C speed for SCD30 is 100kHz.

Run program

You might need to run the following as root e.g. by typing sudo before running the script.

For a one-time output:

python scd30-once.py

installing as a service

./install.sh

the service writes a file /run/sensors/scd30/last and updates it every second (which resides in RAM) - it is meant to be read out by prometheus.

To use pressure compensation, provide the pressure in a file named e.g. /run/sensors/bme280/last - for details see the source code in the service.py