Air Quality Monitor Reference Design

This repository contains the firmware source code and pre-built release firmware images for the Golioth Air Quality Monitor reference design.

The full project details are available on the Air Quality Monitor Project Page, including follow-along guides for building an IoT Air Quality Monitor yourself using widely available off-the-shelf development boards.

We call this Follow-Along Hardware, and we think it's one of the quickest and easiest ways to get started building an IoT proof-of-concept with Golioth. In the follow-along guides, you will learn how to assemble the hardware, flash a pre-built firmware image onto the device, and connect to the Golioth cloud in minutes.

Once you have completed a follow-along guide for one of our supported hardware platforms, the instructions below will walk you through how to build and configure the firmware yourself.

Supported Hardware

This firmware can be built for a variety of supported hardware platforms.

In Zephyr, each of these different hardware variants is given a unique "board" identifier, which is used by the build system to generate firmware for that variant.

When building firmware using the instructions below, make sure to use the correct Zephyr board identifier that corresponds to your follow-along hardware platform.

Follow-Along Hardware

Hardware	Zephyr Board	Follow-Along Guide
	nrf9160dk_nrf9160_ns	nRF9160 DK Follow-Along Guide

Custom Golioth Hardware

Hardware	Zephyr Board	Project Page
	aludel_mini_v1_sparkfun9160_ns	Air Quality Monitor Project Page
	aludel_elixir_ns

Firmware Overview

This reference design firmware demonstrates how to measure ambient air quality within an indoor environment using the Golioth IoT platform.

Specifically, the following environmental parameters can be monitored:

• 🦠 Airborne particulate matter (μg/m³ and #/cm³)
• 😷 CO₂ (ppm)
• 💦 Relative humidity (%RH)
• 🌡️ Temperature (°C)
• 💨 Pressure (kPa)

The sensor values are uploaded to the LightDB stream database in the Golioth Cloud. The sensor sampling frequency and other sensor parameters are remotely configurable via the Golioth Settings service.

Supported Golioth Zephyr SDK Features

This firmware implements the following features from the Golioth Zephyr SDK:

• Device Settings Service
• LightDB State Client
• LightDB Stream Client
• Logging Client
• Over-the-Air (OTA) Firmware Upgrade
• Remote Procedure Call (RPC)

Device Settings Service

The following settings can be set in the Device Settings menu of the Golioth Console.

LOOP_DELAY_S

Adjusts the delay between sensor readings. Set to an integer value (seconds).

Default value is 60 seconds.

CO2_SENSOR_TEMPERATURE_OFFSET

Adjusts the temperature offset setting for the SCD4x CO₂ sensor. Set to an integer value (milli °C).

Default value is 0 m°C.

CO2_SENSOR_ALTITUDE

Adjusts the altitude setting for the SCD4x CO₂ sensor. Set to an integer value(meters above sea level).

Default value is 0 meters.

CO2_SENSOR_ASC_ENABLE

Enables or disables the automatic self-calibration setting for the SCD4x CO₂ sensor. Set to a boolean value.

Default value is true.

PM_SENSOR_SAMPLES_PER_MEASUREMENT

Adjusts the number of samples averaged together when fetching a measurement from the particulate matter sensor. Set to an integer value (samples).

Note that each sample requires ~1s to fetch, so there is a tradeoff between getting a good average sample and the time required to fetch the measurement.

Default value is 30 samples per measurement.

PM_SENSOR_AUTO_CLEANING_INTERVAL

Adjusts the automatic fan cleaning interval setting for the SPS30 particulate matter sensor. Set to an integer value (seconds).

Default value is 604800 seconds (168 hours or 1 week).

LightDB Stream Service

Sensor data is periodically sent to the following sensor/* endpoints of the LightDB Stream service:

• sensor/tem: Temperature (°C)
• sensor/pre: Pressure (kPa)
• sensor/hum: Humidity (%RH)
• sensor/co2: CO₂ (ppm)
• sensor/mc_1p0: Particulate Matter Mass Concentration 1.0 (μg/m³)
• sensor/mc_2p5: Particulate Matter Mass Concentration 2.5 (μg/m³)
• sensor/mc_4p0: Particulate Matter Mass Concentration 4.0 (μg/m³)
• sensor/mc_10p0: Particulate Matter Mass Concentration 10.0 (μg/m³)
• sensor/nc_0p5: Particulate Matter Number Concentration 0.5 (#/cm³)
• sensor/nc_1p0: Particulate Matter Number Concentration 1.0 (#/cm³)
• sensor/nc_2p5: Particulate Matter Number Concentration 2.5 (#/cm³)
• sensor/nc_4p0: Particulate Matter Number Concentration 4.0 (#/cm³)
• sensor/nc_10p0: Particulate Matter Number Concentration 10.0 (#/cm³)
• sensor/tps: Typical Particle Size (μm)

On hardware platforms with support for battery monitoring, battery voltage and level readings are periodically sent to the following battery/* endpoints:

• battery/batt_v: Battery Voltage (V)
• battery/batt_lvl: Battery Level (%)

LightDB State Service

The concept of Digital Twin is demonstrated with the LightDB State example_int0 and example_int1 variables that are members of the desired and state endpoints.

• desired values may be changed from the cloud side. The device will recognize these, validate them for [0..65535] bounding, and then reset these endpoints to -1
• state values will be updated by the device whenever a valid value is received from the desired endpoints. The cloud may read the state endpoints to determine device status, but only the device should ever write to the state endpoints.

Remote Procedure Call (RPC) Service

The following RPCs can be initiated in the Remote Procedure Call menu of the Golioth Console.

get_network_info

Query and return network information.

reboot

Reboot the system.

set_log_level

Set the log level.

The method takes a single parameter which can be one of the following integer values:

• 0: LOG_LEVEL_NONE
• 1: LOG_LEVEL_ERR
• 2: LOG_LEVEL_WRN
• 3: LOG_LEVEL_INF
• 4: LOG_LEVEL_DBG

clean_pm_sensor

Initiate the SPS30 particulate matter fan-cleaning procedure manually. The fan cleaning procedure takes approximately 10s to complete.

reset_pm_sensor

Reset the SPS30 particulate matter sensor.

Building the firmware

The firmware build instructions below assume you have already set up a Zephyr development environment and have some basic familiarity with building firmware using the Zephyr Real Time Operating System (RTOS).

If you're brand new to building firmware with Zephyr, you will need to follow the Zephyr Getting Started Guide to install the Zephyr SDK and related dependencies.

We also provide free online Developer Training for Zephyr at:

https://training.golioth.io/docs/zephyr-training

Do not clone this repo using git. Zephyr's west meta-tool should be used to set up your local workspace.

Create a Python virtual environment (recommended)

cd ~
mkdir golioth-reference-design-air-quality
python -m venv golioth-reference-design-air-quality/.venv
source golioth-reference-design-air-quality/.venv/bin/activate

Install west meta-tool

pip install wheel west

Use west to initialize the workspace and install dependencies

cd ~/golioth-reference-design-air-quality
west init -m git@github.com:golioth/reference-design-air-quality.git .
west update
west zephyr-export
pip install -r deps/zephyr/scripts/requirements.txt

Build the firmware

Build the Zephyr firmware from the top-level workspace of your project. After a successful build you will see a new build/ directory.

Note that this git repository was cloned into the app folder, so any changes you make to the application itself should be committed inside this repository. The build and deps directories in the root of the workspace are managed outside of this git repository by the west meta-tool.

Prior to building, update CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION in the prj.conf file to reflect the firmware version number you want to assign to this build.

When running the commands below, make sure to replace the placeholder <your_zephyr_board_id> with the actual Zephyr board from the table above that matches your follow-along hardware.

$ (.venv) west build -p -b <your_zephyr_board_id> app

For example, to build firmware for the Nordic nRF9160 DK-based follow-along hardware:

$ (.venv) west build -p -b nrf9160dk_nrf9160_ns app

Flash the firmware

$ (.venv) west flash

Provision the device

In order for the device to securely authenticate with the Golioth Cloud, we need to provision the device with a pre-shared key (PSK). This key will persist across reboots and only needs to be set once after the device firmware has been programmed. In addition, flashing new firmware images with west flash should not erase these stored settings unless the entire device flash is erased.

Configure the PSK-ID and PSK using the device UART shell and reboot the device:

uart:~$ settings set golioth/psk-id <my-psk-id@my-project>
uart:~$ settings set golioth/psk <my-psk>
uart:~$ kernel reboot cold

External Libraries

The following code libraries are installed by default. If you are not using the custom hardware to which they apply, you can safely remove these repositories from west.yml and remove the includes/function calls from the C code.

• golioth-zephyr-boards includes the board definitions for the Golioth Aludel-Mini
• libostentus is a helper library for controlling the Ostentus ePaper faceplate
• zephyr-network-info is a helper library for querying, formatting, and returning network connection information via Zephyr log or Golioth RPC

Pulling in updates from the Reference Design Template

This reference design was forked from the Reference Design Template repo. We recommend the following workflow to pull in future changes:

• Setup
  • Create a template remote based on the Reference Design Template repository
• Merge in template changes
  • Fetch template changes and tags
  • Merge template release tag into your main (or other branch)
  • Resolve merge conflicts (if any) and commit to your repository

# Setup
git remote add template https://github.com/golioth/reference-design-template.git
git fetch template --tags

# Merge in template changes
git fetch template --tags
git checkout your_local_branch
git merge template_v1.0.0

# Resolve merge conflicts if necessary
git add resolved_files
git commit