Archive for category Raspberry Pi
IoT Data Analytics at the Edge: Exploring the convergence of IoT, Data Analytics, and Edge Computing with Grafana, Mosquitto, and TimescaleDB on ARM-based devices
Posted by Gary A. Stafford in Analytics, AWS, Cloud, IoT, Python, Raspberry Pi, Software Development on April 15, 2021
This post is a revised version of an earlier post, featuring major version updates of TimescaleDB (v1.7.4-pg12 to v2.0.0-pg12), Grafana (v7.1.5 to v7.5.2), and Mosquitto (v1.6.12 to v2.0.9). All source code and SQL scripts are revised. Note that TimeScaleDB has a current limitation/bug with Docker on ARM later than v2.0.0.
The Edge
Edge computing is a fast-growing technology trend, which involves pushing compute capabilities to a network’s edge. Wikipedia describes edge computing as a distributed computing paradigm that brings computation and data storage closer to the location needed to improve response times and save bandwidth. The term edge commonly refers to a compute node at the edge of a network (edge device), sitting close to the data source and between that data source and external system such as the Cloud. In his recent post, 3 Advantages (And 1 Disadvantage) Of Edge Computing, well-known futurist Bernard Marr argues reduced bandwidth requirements, reduced latency, and enhanced security and privacy as three primary advantages of edge computing.
David Ricketts, Head of Marketing at Quiss Technology PLC, in his post, Cloud and Edge Computing — The Stats You Need to Know for 2018, estimates that the global edge computing market is expected to reach USD 6.72 billion by 2022 at a compound annual growth rate of a whopping 35.4 percent. Realizing the market potential, many major Cloud providers, edge device manufacturers, and integrators are rapidly expanding their edge compute capabilities. AWS, for example, currently offers more than a dozen services in their edge computing category.
Internet of Things
Edge computing is frequently associated with the Internet of Things (IoT). IoT devices, industrial equipment, and sensors generate data transmitted to other internal and external systems, often by way of edge nodes, such as an IoT Gateway. IoT devices typically generate time-series data. According to Wikipedia, a time series is a set of data points indexed in time order — a sequence taken at successive equally spaced points in time. IoT devices typically generate continuous high-volume streams of time-series data, often on a scale of millions of data points per second. IoT data characteristics require IoT platforms to minimally support temporal accuracy, high-volume ingestion and processing, efficient data compression and downsampling, and real-time querying capabilities.
Edge devices such as IoT Gateways, which aggregate and transmit IoT data from these devices to external systems, are generally lower-powered, with limited processors, memory, and storage. Accordingly, IoT platforms must satisfy all the requirements of IoT data while simultaneously supporting resource-constrained environments.
IoT Analytics at the Edge
Leading Cloud providers AWS, Azure, Google Cloud, IBM Cloud, Oracle Cloud, and Alibaba Cloud all offer IoT services. Many offer IoT services with edge computing capabilities. AWS offers AWS IoT Greengrass. Greengrass provides local compute, messaging, data management, sync, and machine learning (ML) inference capabilities to edge devices. Azure offers Azure IoT Edge. Azure IoT Edge provides the ability to run artificial intelligence (AI), Azure and third-party services, and custom business logic on edge devices using standard containers. Google Cloud offers Edge TPU. Edge TPU (Tensor Processing Unit) is Google’s purpose-built application-specific integrated circuit (ASIC), designed to run AI at the edge.
IoT Analytics
Many Cloud providers also offer IoT analytics as part of their suite of IoT services, although not at the edge. AWS offers AWS IoT Analytics, while Azure has Azure Time Series Insights. Google provides IoT analytics, indirectly, through downstream analytic systems and ad hoc analysis using Google BigQuery or advanced analytics and machine learning with Cloud Machine Learning Engine. These services generally all require data to be transmitted to the Cloud for analytics.
The ability to analyze real-time, streaming IoT data at the edge is critical to a rapid feedback loop. IoT edge analytics can accelerate anomaly detection and remediation, improve predictive maintenance capabilities, and expedite proactive inventory replenishment.
IoT Edge Analytics Stack
In my opinion, the ideal IoT edge analytics stack is comprised of lightweight, purpose-built, easily deployable and manageable, platform- and programming language-agnostic, open-source software components. The minimal IoT edge analytics stack should include:
- Lightweight message broker;
- Purpose-built time-series database;
- ANSI-standard SQL ad-hoc query engine;
- Data visualization tool;
- Simple deployment and management framework;
Each component should be purpose-built for IoT.
Lightweight Message Broker
We will use Eclipse Mosquitto as our message broker. According to the project’s description, Mosquitto is an open-source message broker that implements the Message Queuing Telemetry Transport (MQTT) protocol versions 5.0, 3.1.1, and 3.1. Mosquitto is lightweight and suitable for use on all devices, from low-power single-board computers (SBCs) to full-powered servers.
MQTT Client Library
We will interact with Mosquitto using Eclipse Paho. According to the project, the Eclipse Paho project provides open-source, mainly client-side implementations of MQTT and MQTT-SN in a variety of programming languages. MQTT and MQTT for Sensor Networks (MQTT-SN) are light-weight publish/subscribe messaging transports for TCP/IP and connectionless protocols, such as UDP, respectively.
We will be using Paho’s Python Client. The Paho Python Client provides a client class with support for both MQTT v3.1 and v3.1.1 on Python 2.7 or 3.x. The client also provides helper functions to make publishing messages to an MQTT server straightforward.
Time-Series Database
Time-series databases are optimal for storing IoT data. According to InfluxData, makers of a leading time-series database, InfluxDB, a time-series database (TSDB), is a database optimized for time-stamped or time-series data. Time series data are simply measurements or events that are tracked, monitored, downsampled, and aggregated over time. Jiao Xian of Alibaba Cloud has authored an insightful post on the time-series database ecosystem, What Are Time Series Databases? A few leading Cloud providers offer purpose-built time-series databases, though they are not available at the edge. AWS offers Amazon Timestream, and Alibaba Cloud offers Time Series Database.
InfluxDB is an excellent choice for a time-series database. It was my first choice, along with TimescaleDB, when developing this stack. However, InfluxDB Flux’s apparent incompatibilities with some ARM-based architecture ruled it out for inclusion in the stack for this particular post.
We will use TimescaleDB as our time-series database. TimescaleDB is the leading open-source relational database for time-series data. Described as ‘PostgreSQL for time-series,’ TimescaleDB is based on PostgreSQL, which provides full ANSI SQL, rock-solid reliability, and a massive ecosystem. TimescaleDB claims to achieve 10–100x faster queries than PostgreSQL, InfluxDB, and MongoDB, with native optimizations for time-series analytics.
TimescaleDB is designed for performing analytical queries, both through its native support for PostgreSQL’s full range of SQL functionality and additional functions native to TimescaleDB. These time-series optimized functions include Median/Percentile, Cumulative Sum, Moving Average, Increase, Rate, Delta, Time Bucket, Histogram, and Gap Filling.
Ad-hoc Data Query Engine
We have the option of using psql, the terminal-based front-end to PostgreSQL, to execute ad-hoc queries against TimescaleDB. The psql front-end enables you to enter queries interactively, issue them to PostgreSQL, and see the query results.
We also have the option of using pgAdmin, specifically the biarms/pgadmin4 Docker version, to execute ad-hoc queries and perform most other database tasks. pgAdmin is the most popular open-source administration and development platform for PostgreSQL. While several popular Docker versions of pgAdmin only support Linux AMD64 architectures, the biarms/pgadmin4 Docker version supports ARM-based devices.
Data Visualization
For data visualization, we will use Grafana. Grafana allows you to query, visualize, alert on, and understand metrics no matter where they are stored. With Grafana, you can create, explore, and share dashboards, fostering a data-driven culture. Grafana allows you to define thresholds visually and get notified via Slack, PagerDuty, and more. Grafana supports dozens of data sources, including MySQL, PostgreSQL, Elasticsearch, InfluxDB, TimescaleDB, Graphite, Prometheus, Google BigQuery, GraphQL, and Oracle. Grafana is extensible through a large collection of plugins.
Edge Deployment and Management Platform
Docker introduced the current industry standard for containers in 2013. Docker containers are a standardized unit of software that allows developers to isolate apps from their environment. We will use Docker to deploy the IoT edge analytics stack, referred to herein as the GTM Stack, composed of containerized versions of Grafana, TimescaleDB, Eclipse Mosquitto, and pgAdmin, to an ARMv7-based edge node. The acronym, GTM, comes from the three primary OSS projects composing the stack. The abbreviation also suggests Greenwich Mean Time, relating to the precise time-series nature of IoT data.
Running Docker Engine in swarm mode, we can use Docker to deploy the complete IoT edge analytics stack to the swarm, running on the edge node. The deploy command accepts a stack description in the form of a Docker Compose file, a YAML file used to configure the application’s services. With a single command, we can create and start all the services from the configuration file.
Source Code
All source code for this post is available on GitHub. Use the following command to git clone a local copy of the project. Note that the updated version of the source code for this post is in the v2021–03 branch.
git clone --branch v2021-03 --single-branch --depth 1 \
https://github.com/garystafford/iot-analytics-at-the-edge.git
IoT Devices
For this post, I have deployed three Linux ARM-based IoT devices, each connected to a sensor array. Each sensor array contains multiple analog and digital sensors. The sensors record temperature, humidity, air quality (liquefied petroleum gas (LPG), carbon monoxide (CO), and smoke), light, and motion. For more information on the IoT device and sensor hardware involved, please see my previous post.Getting Started with IoT Analytics on AWS
Analyze environmental sensor data from IoT devices in near real-time with AWS IoT Analyticstowardsdatascience.com
Each ARM-based IoT device runs a small Python3-based script, sensor_data_to_mosquitto.py, shown below.
The IoT devices’ script implements the Eclipse Paho MQTT Python client library. An MQTT message containing simultaneous readings from each sensor is sent to a Mosquitto topic on the edge node at a configurable frequency.
Below are the actual sensor readings sent by the IoT device as an MQTT message to the Mosquitto topic.
IoT Edge Node
For this post, I have deployed a single Linux ARM-based edge node. The three IoT devices containing sensor arrays communicate with the edge node over Wi-Fi. IoT devices could easily use an alternative communication protocol, such as BLE, LoRaWAN, or Ethernet. For more information on BLE and LoRaWAN, please see some of my previous posts:LoRa and LoRaWAN for IoT: Getting Started with LoRa and LoRaWAN Protocols for Low Power, Wide Area Networking of IoT and BLE and GATT for IoT: Getting Started with Bluetooth Low Energy (BLE) and Generic Attribute Profile (GATT) Specification for IoT.
The edge node also runs a small Python3-based script, mosquitto_to_timescaledb.py, shown below.
Like the IoT devices, the edge node’s script implements the Eclipse Paho MQTT Python client library. The script pulls MQTT messages off a Mosquitto topic(s), serializes the message payload to JSON, and writes the payload’s data to the TimescaleDB database. The edge node’s script accepts several arguments, which allow you to configure the necessary Mosquitto and TimescaleDB connection settings.
Why not use Telegraf?
Telegraf is a plugin-driven agent that collects, processes, aggregates, and writes metrics. There is a Telegraf output plugin, the PostgreSQL and TimescaleDB Output Plugin for Telegraf, produced by TimescaleDB. The plugin can replace the need to manage and maintain the above script. However, I chose not to use it because it is not yet an official Telegraf plugin. If the plugin was included in a Telegraf release, I would certainly encourage its use.
Script Management
Both Linux-based IoT devices and edge nodes run systemd system and service manager. To ensure the Python scripts keep running in the case of a system restart, we define a systemd unit. Units are objects that systemd knows how to manage. This is a standardized representation of system resources that can be managed by the suite of daemons and manipulated by the provided utilities. Each script has a systemd unit file. Below, we see the gtm_stack_mosquitto unit file, gtm_stack_mosquitto.service.
The gtm_stack_mosq_to_tmscl unit file, gtm_stack_mosq_to_tmscl.service, is nearly identical.
To install the gtm_stack_mosquitto.service systemd unit file on each IoT device, use the following commands:
Installing the gtm_stack_mosq_to_tmscl.service unit file on the edge node is nearly identical.
Docker Stack
The edge node runs the GTM Docker stack, stack.yml, in a swarm. As discussed earlier, the stack contains four containers: Eclipse Mosquitto, TimescaleDB, Grafana, and pgAdmin. The Mosquitto, TimescaleDB, and Grafana containers have paths within the containers bind-mounted to directories on the edge device. With bind-mounting, the container’s configuration and data will persist if the containers are removed and re-created. The containers are running on an isolated overlay network.
The GTM Docker stack is installed using the following commands on the edge node. We will assume Docker and git are pre-installed on the edge node for this post.
First, we will create several local directories on the edge device, which will be used to bind-mount to the Docker container’s directories. Below, we see the bind-mounted local directories with the eventual container’s contents stored within them.
Next, we copy the custom Mosquitto configuration file, mosquitto.conf, included in the project to the edge device’s correct location.
Lastly, we initialize the Docker swarm and deploy the stack.
docker service ls' command, showing the running GTM Stack containersTimescaleDB Setup
With the GTM stack running, we need to create a single Timescale hypertable, sensor_data, in the TimescaleDB demo_iot database to hold the incoming IoT sensor data. Hypertables, according to TimescaleDB, are designed to be easy to manage and to behave like standard PostgreSQL tables. Hypertables are comprised of many interlinked “chunk” tables. Commands made to the hypertable automatically propagate changes down to all of the chunks belonging to that hypertable.
I suggest using psql to execute the required DDL statements, which will create the hypertable and the proceeding views and database user permissions. All SQL statements are included in the project’s statements.sql file. One way to use psql is to install it on your local workstation, then use psql to connect to the remote edge node. I prefer to instantiate a local PostgreSQL Docker container instance running psql. I then use the local container’s psql client to connect to the edge node’s TimescaleDB database. For example, from my local machine, I run the following docker run command to connect to the edge node’s TimescaleDB database on the edge node, located locally at 192.168.1.12.
Although not as practical, you can also access psql from within the TimescaleDB Docker container, running on the actual edge node, using the following docker exec command.
TimescaleDB Continuous Aggregates
For this post’s demonstration, we will create four TimescaleDB materialized views, which will be queried from a Grafana Dashboard. The materialized views are TimescaleDB Continuous Aggregates. According to Timescale, aggregate queries which touch large swathes of time-series data can take a long time to compute because the system needs to scan large amounts of data on every query execution. To make these queries faster, a continuous aggregate allows materializing the computed aggregates, while also providing means to continuously, and with low overhead, keep them up-to-date as the underlying source data changes.
For example, we generate sensor data every five seconds from the three IoT devices in this post. When visualizing a 24-hour period in Grafana, using continuous aggregates with an interval of one minute, we would reduce the total volume of data queried from 51,840 rows to 4,320 rows, a reduction of over 91%. The larger the time period or the number of IoT devices being analyzed, the more significant these savings will positively impact query performance.
A time_bucket on the time partitioning column of the hypertable is required for all continuous aggregate views. The time_bucket function, in this case, has a bucket width (interval) of 1 minute. The interval is configurable.
To automatically refresh the four materialized views, we will create four corresponding continuous aggregate policies. In this demonstration, the continuous aggregate policies create a refresh window between one week ago and one hour ago, with a refresh interval of one hour.
Advanced Analytic Queries
The ability to perform ad-hoc queries on time-series IoT data is an essential feature of the IoT edge analytics stack. We can use psql, pgAdmin, or even our own IDE to perform ad-hoc queries against the TimescaleDB database on the edge node. Below are examples of typical ad-hoc queries a data analyst might perform on IoT sensor data. These example queries demonstrate TimescaleDB’s advanced analytical capabilities for working with time-series data, including Moving Average, Delta, Time Bucket, and Histogram.
Data Visualization with Grafana
Using the TimescaleDB continuous aggregates we have created, we can quickly build a richly featured dashboard in Grafana. Below we see a typical IoT Dashboard you might build to monitor the post’s IoT sensor data in near real-time. An exported version, dashboard_external_export.json, is included in the GitHub project.
Limiting Grafana’s Access to IoT Data
Following the Grafana recommendation for database user permissions, we create a grafanareader PostgresSQL user, and limit the user’s access to the sensor_data table and the four views we created. Grafana will use this user’s credentials to perform SELECT queries of the TimescaleDB demo_iot database.
Using PostgreSQL in Grafana
Grafana’s documentation includes a comprehensive set of instructions for Using PostgreSQL in Grafana. To connect to the TimescaleDB database from Grafana, we use the PostgreSQL data source plugin.
The data displayed in each Panel in the Grafana Dashboard is based on a SQL query. For example, the Average Temperature Panel might use a query similar to the example below. This particular query also converts Celsius to Fahrenheit. Note the use of Grafana Macros (e.g., $__time(), $__timeFilter()). Macros can be used within a query to simplify syntax and allow for dynamic parts.
SELECT
$__time(bucket),
device_id AS metric,
((avg_temp * 1.9) + 32) AS avg_temp
FROM temperature_humidity_summary_minute
WHERE
$__timeFilter(bucket)
ORDER BY 1,2
Below, we see another example from the Average Humidity Panel. In this particular query, we might choose to limit the humidity data to a valid range of 0%–100%.
SELECT
$__time(bucket),
device_id AS metric,
avg_humidity
FROM temperature_humidity_summary_minute
WHERE
$__timeFilter(bucket)
AND avg_humidity >= 0.0
AND avg_humidity <= 100.0
ORDER BY 1,2
Mobile Friendly
Grafana dashboards are mobile-friendly. Below we see two views of the dashboard, using the Chrome mobile browser on an Apple iPhone.
Grafana Alerts
Grafana allows Alerts to be created based on the Rules you define in each Panel. If data values match the Rule’s conditions, which you pre-define, such as a temperature reading above a certain threshold for a set amount of time, an alert is sent to your choice of destinations. According to the Rule shown below, If the average temperature exceeds 75°F for a period of 5 minutes, an alert is sent.
As demonstrated below, when the laboratory temperature began to exceed 75°F, the alert entered a ‘Pending’ state. If the temperature exceeded 75°F for the pre-determined period of 5 minutes, the alert status changes to ‘Alerting’, and an alert is sent. When the temperature dropped back below 75°F for the pre-determined period of 5 minutes, the alert status changed from ‘Alerting’ to ‘OK’, and a subsequent notification was sent.
There are currently twenty alert notifiers available out-of-the-box with Grafana, including Slack, email, PagerDuty, webhooks, VictorOps, Opsgenie, and Microsoft Teams. We can use Grafana Alerts to notify the proper resources, in near real-time, if an issue is detected based on the data. Below, we see an actual series of high-temperature alerts sent by Grafana to the Slack channel, followed by subsequent notifications as the temperature returned to normal.
Conclusion
This post explored the development of an IoT edge analytics stack comprised of lightweight, purpose-built, easily deployable and manageable platform- and programming language-agnostic, open-source software components. These components included Docker containerized versions of Grafana, TimescaleDB, Eclipse Mosquitto, and pgAdmin, referred to as the GTM Stack. Using the GTM stack, we collected, analyzed, and visualized IoT data without first shipping the data to Cloud or other external systems.
This blog represents my own viewpoints and not of my employer, Amazon Web Services (AWS). All product names, logos, and brands are the property of their respective owners.
GTM Stack: Exploring IoT Data Analytics at the Edge with Grafana, Mosquitto, and TimescaleDB on ARM-based Architectures
Posted by Gary A. Stafford in Big Data, IoT, Python, Raspberry Pi, Software Development on October 12, 2020
In the following post, we will explore the integration of several open-source software applications to build an IoT edge analytics stack, designed to operate on ARM-based edge nodes. We will use the stack to collect, analyze, and visualize IoT data without first shipping the data to the Cloud or other external systems.
The Edge
Edge computing is a fast-growing technology trend, which involves pushing compute capabilities to the edge. Wikipedia describes edge computing as a distributed computing paradigm that brings computation and data storage closer to the location needed to improve response times and save bandwidth. The term edge commonly refers to a compute node at the edge of a network (edge device), sitting in close proximity to the source a data and between that data source and external system such as the Cloud.
In his recent post, 3 Advantages (And 1 Disadvantage) Of Edge Computing, well-known futurist Bernard Marr argues reduced bandwidth requirements, reduced latency, and enhanced security and privacy as three primary advantages of edge computing. Due to techniques like data downsampling, Marr advises one potential disadvantage of edge computing is that important data could end up being overlooked and discarded in the quest to save bandwidth and reduce latency.
David Ricketts, Head of Marketing at Quiss Technology PLC, estimates in his post, Cloud and Edge Computing — The Stats You Need to Know for 2018, the global edge computing market is expected to reach USD 6.72 billion by 2022 at a compound annual growth rate of a whopping 35.4 percent. Realizing the market potential, many major Cloud providers, edge device manufacturers, and integrators are rapidly expanding their edge compute capabilities. AWS, for example, currently offers more than a dozen services in the edge computing category.
Internet of Things
Edge computing is frequently associated with the Internet of Things (IoT). IoT devices, industrial equipment, and sensors generate data, which is transmitted to other internal and external systems, often by way of edge nodes, such as an IoT Gateway. IoT devices typically generate time-series data. According to Wikipedia, a time series is a set of data points indexed in time order — a sequence taken at successive equally spaced points in time. IoT devices typically generate continuous high-volume streams of time-series data, often on the scale of millions of data points per second. IoT data characteristics require IoT platforms to minimally support temporal accuracy, high-volume ingestion and processing, efficient data compression and downsampling, and real-time querying capabilities.
The IoT devices and the edge devices, such as IoT Gateways, which aggregate and transmit IoT data from these devices to external systems, are generally lower-powered, with limited processor, memory, and storage capabilities. Accordingly, IoT platforms must satisfy all the requirements of IoT data while simultaneously supporting resource-constrained environments.
IoT Analytics at the Edge
Leading Cloud providers AWS, Azure, Google Cloud, IBM Cloud, Oracle Cloud, and Alibaba Cloud all offer IoT services. Many offer IoT services with edge computing capabilities. AWS offers AWS IoT Greengrass. Greengrass provides local compute, messaging, data management, sync, and ML inference capabilities to edge devices. Azure offers Azure IoT Edge. Azure IoT Edge provides the ability to run AI, Azure and third-party services, and custom business logic on edge devices using standard containers. Google Cloud offers Edge TPU. Edge TPU (Tensor Processing Unit) is Google’s purpose-built application-specific integrated circuit (ASIC), designed to run AI at the edge.
IoT Analytics
Many Cloud providers also offer IoT analytics as part of their suite of IoT services, although not at the edge. AWS offers AWS IoT Analytics, while Azure has Azure Time Series Insights. Google provides IoT analytics, indirectly, through downstream analytic systems and ad hoc analysis using Google BigQuery or advanced analytics and machine learning with Cloud Machine Learning Engine. These services generally all require data to be transmitted to the Cloud for analytics.
The ability to analyze IoT data at the edge, as data is streamed in real-time, is critical to a rapid feedback loop. IoT edge analytics can accelerate anomaly detection, improve predictive maintenance capabilities, and expedite proactive inventory replenishment.
The IoT Edge Analytics Stack
In my opinion, the ideal IoT edge analytics stack is comprised of lightweight, purpose-built, easily deployable and manageable, platform- and programming language-agnostic, open-source software components. The minimal IoT edge analytics stack should include a lightweight message broker, a time-series database, an ANSI-standard ad-hoc query engine, and a data visualization tool. Each component should be purpose-built for IoT.
Lightweight Message Broker
We will use Eclipse Mosquitto as our message broker. According to the project’s description, Mosquitto is an open-source message broker that implements the Message Queuing Telemetry Transport (MQTT) protocol versions 5.0, 3.1.1, and 3.1. Mosquitto is lightweight and suitable for use on all devices from low power single board computers (SBCs) to full servers.
MQTT Client Library
We will interact with Mosquitto using Eclipse Paho. According to the project, the Eclipse Paho project provides open-source, mainly client-side implementations of MQTT and MQTT-SN in a variety of programming languages. MQTT and MQTT for Sensor Networks (MQTT-SN) are lightweight publish/subscribe messaging transports for TCP/IP and connectionless protocols, such as UDP, respectively.
We will be using Paho’s Python Client. The Paho Python Client provides a client class with support for both MQTT v3.1 and v3.1.1 on Python 2.7 or 3.x. The client also provides helper functions to make publishing messages to an MQTT server straightforward.
Time-Series Database
Time-series databases are optimal for storing IoT data. According to InfluxData, makers of a leading time-series database, InfluxDB, a time-series database (TSDB), is a database optimized for time-stamped or time-series data. Time series data are simply measurements or events that are tracked, monitored, downsampled, and aggregated over time. Jiao Xian, of Alibaba Cloud, has authored an insightful post on the time-series database ecosystem, What Are Time Series Databases? A few leading Cloud providers offer purpose-built time-series databases, though they are not available at the edge. AWS offers Amazon Timestream and Alibaba Cloud offers Time Series Database.
InfluxDB is an excellent choice for a time-series database. It was my first choice, along with TimescaleDB, when developing this stack. However, InfluxDB Flux’s apparent incompatibilities with some ARM-based architectures ruled it out for inclusion in the stack for this particular post.
We will use TimescaleDB as our time-series database. TimescaleDB is the leading open-source relational database for time-series data. Described as ‘PostgreSQL for time-series,’ TimescaleDB is based on PostgreSQL, which provides full ANSI SQL, rock-solid reliability, and a massive ecosystem. TimescaleDB claims to achieve 10–100x faster queries than PostgreSQL, InfluxDB, and MongoDB, with native optimizations for time-series analytics.
TimescaleDB claims to achieve 10–100x faster queries than PostgreSQL, InfluxDB, and MongoDB, with native optimizations for time-series analytics.
TimescaleDB is designed for performing analytical queries, both through its native support for PostgreSQL’s full range of SQL functionality, as well as additional functions native to TimescaleDB. These time-series optimized functions include Median/Percentile, Cumulative Sum, Moving Average, Increase, Rate, Delta, Time Bucket, Histogram, and Gap Filling.
Ad-hoc Data Query Engine
We have the option of using psql, the terminal-based front-end to PostgreSQL, to execute ad-hoc queries against TimescaleDB. The psql front-end enables you to enter queries interactively, issue them to PostgreSQL, and see the query results.
We also have the option of using pgAdmin, specifically the biarms/pgadmin4 Docker version, to execute ad-hoc queries and perform most other database tasks. pgAdmin is the most popular open-source administration and development platform for PostgreSQL. While several popular Docker versions of pgAdmin only support Linux AMD64 architectures, the biarms/pgadmin4 Docker version supports ARM-based devices.
Data Visualization
For data visualization, we will use Grafana. Grafana allows you to query, visualize, alert on, and understand metrics no matter where they are stored. With Grafana, you can create, explore, and share dashboards, fostering a data-driven culture. Grafana allows you to define thresholds visually and get notified via Slack, PagerDuty, and more. Grafana supports dozens of data sources, including MySQL, PostgreSQL, Elasticsearch, InfluxDB, TimescaleDB, Graphite, Prometheus, Google BigQuery, GraphQL, and Oracle. Grafana is extensible through a large collection of plugins.
Edge Deployment and Management Platform
Docker introduced the current industry standard for containers in 2013. Docker containers are a standardized unit of software that allows developers to isolate apps from their environment. We will use Docker to deploy the IoT edge analytics stack, referred to herein as the GTM Stack, composed of containerized versions of Eclipse Mosquitto, TimescaleDB, and Grafana, and pgAdmin, to an ARM-based edge node. The acronym, GTM, comes from the three primary OSS projects composing the stack. The acronym also suggests Greenwich Mean Time, relating to the precise time-series nature of IoT data.
Running Docker Engine in swarm mode, we can use Docker to deploy the complete IoT edge analytics stack to the swarm, running on the edge node. The deploy command accepts a stack description in the form of a Docker Compose file, a YAML file used to configure the application’s services. With a single command, we can create and start all the services from the configuration file.
Source Code
All source code for this post is available on GitHub. Use the following command to git clone a local copy of the project.
IoT Devices
For this post, I have deployed three Linux ARM-based IoT devices, each connected to a sensor array. Each sensor array contains multiple analog and digital sensors. The sensors record temperature, humidity, air quality (liquefied petroleum gas (LPG), carbon monoxide (CO), and smoke), light, and motion. For more information on the IoT device and sensor hardware involved, please see my previous post: Getting Started with IoT Analytics on AWS.
Each ARM-based IoT device is running a small Python3-based script, sensor_data_to_mosquitto.py, shown below.
The IoT devices’ script implements the Eclipse Paho MQTT Python client library. An MQTT message containing simultaneous readings from each sensor is sent to a Mosquitto topic on the edge node, at a configurable frequency.
IoT Edge Node
For this post, I have deployed a single Linux ARM-based edge node. The three IoT devices, containing sensor arrays, communicate with the edge node over Wi-Fi. The IoT devices could easily use an alternative communication protocol, such as BLE, LoRaWAN, or Ethernet. For more information on BLE and LoRaWAN, please see some of my previous posts: LoRa and LoRaWAN for IoT: Getting Started with LoRa and LoRaWAN Protocols for Low Power, Wide Area Networking of IoT and BLE and GATT for IoT: Getting Started with Bluetooth Low Energy (BLE) and Generic Attribute Profile (GATT) Specification for IoT.
The edge node is also running a small Python3-based script, mosquitto_to_timescaledb.py, shown below.
Similar to the IoT devices, the edge node’s script implements the Eclipse Paho MQTT Python client library. The script pulls MQTT messages off a Mosquitto topic(s), serializes the message payload to JSON, and writes the payload’s data to the TimescaleDB database. The edge node’s script accepts several arguments, which allow you to configure necessary Mosquitto and TimescaleDB variables.
Why not use Telegraf?
Telegraf is a plugin-driven agent that collects, processes, aggregates, and writes metrics. There is a Telegraf output plugin, the PostgreSQL and TimescaleDB Output Plugin for Telegraf, produced by TimescaleDB. The plugin could replace the need to manage and maintain the above script. However, I chose not to use it because it is not yet an official Telegraf plugin. If the plugin was included in a Telegraf release, I would certainly encourage its use.
Script Management
Both the Linux-based IoT devices and the edge node run systemd system and service manager. To ensure the Python scripts keep running in the case of a system restart, we define a systemd unit. Units are the objects that systemd knows how to manage. These are basically a standardized representation of system resources that can be managed by the suite of daemons and manipulated by the provided utilities. Each script has a systemd unit files. Below, we see the gtm_stack_mosquitto unit file, gtm_stack_mosquitto.service.
The gtm_stack_mosq_to_tmscl unit file, gtm_stack_mosq_to_tmscl.service, is nearly identical.
To install the gtm_stack_mosquitto.service systemd unit file on each IoT device, use the following commands.
Installing the gtm_stack_mosq_to_tmscl.service unit file on the edge node is nearly identical.
Docker Stack
The edge node runs the GTM Docker stack, stack.yml, in a swarm. As discussed earlier, the stack contains four containers: Eclipse Mosquitto, TimescaleDB, and Grafana, along with pgAdmin. The Mosquitto, TimescaleDB, and Grafana containers have paths within the containers, bind-mounted to directories on the edge device. With bind-mounting, the container’s data will persist if the containers are removed and re-created. The containers are running on their own isolated overlay network.
The GTM Docker stack is installed using the following commands on the edge node. We will assume Docker and git are pre-installed on the edge node for this post.
First, we create the proper local directories on the edge device, which will be used to bind-mount to the container’s directories. Below, we see the bind-mounted local directories with the eventual container’s contents stored within them.
Next, we copy the custom Mosquitto configuration file, mosquitto.conf, included in the project, to the correct location on the edge device. Lastly, we initialize the Docker swarm and deploy the stack.
docker container ls command, showing the running GTM Stack containers
docker stats command, showing the resource consumption of GTM Stack containersTimescaleDB Setup
With the GTM stack running, we need to create a single Timescale hypertable, sensor_data, in the TimescaleDB demo_iot database, to hold the incoming IoT sensor data. Hypertables, according to TimescaleDB, are designed to be easy to manage and to behave like standard PostgreSQL tables. Hypertables are comprised of many interlinked “chunk” tables. Commands made to the hypertable automatically propagate changes down to all of the chunks belonging to that hypertable.
I suggest using psql to execute the required DDL statements, which will create the hypertable, as well as the proceeding views and database user permissions. All SQL statements are included in the project’s statements.sql file. One way to use psql is to install it on your local workstation, then use psql to connect to the remote edge node. I prefer to instantiate a local PostgreSQL Docker container instance running psql. I then use the local container’s psql client to connect to the edge node’s TimescaleDB database. For example, from my local machine, I run the following docker run command to connect to the edge node’s TimescaleDB database, on the edge node, located locally at 192.168.1.12.
Although not always practical, could also access psql from within the TimescaleDB Docker container, running on the actual edge node, using the following docker exec command.
TimescaleDB Continuous Aggregates
For this post’s demonstration, we need to create four TimescaleDB database views, which will be queried from an eventual Grafana Dashboard. The views are TimescaleDB Continuous Aggregates. According to Timescale, aggregate queries that touch large swathes of time-series data can take a long time to compute because the system needs to scan large amounts of data on every query execution. TimescaleDB continuous aggregates automatically calculate the results of a query in the background and materialize the results.
For example, in this post, we generate sensor data every five seconds from the three IoT devices. When visualizing a 24-hour period in Grafana, using continuous aggregates with an interval of one minute, we would reduce the total volume of data queried from ~51,840 rows to ~4,320 rows, a reduction of over 91%. The larger the time period or the number of IoT devices being analyzed, the more significant these savings will positively impact query performance.
A time_bucket on the time partitioning column of the hypertable is required in all continuous aggregate views. The time_bucket function, in this case, has a bucket width (interval) of 1 minute. The interval is configurable.
Limiting Grafana’s Access to IoT Data
Following the Grafana recommendation for database user permissions, we create a grafanareader PostgresSQL user, and limit the user’s access to the sensor_data table and the four views we created. Grafana will use this user’s credentials to perform SELECT queries of the TimescaleDB demo_iot database.
Grafana Dashboards
Using the TimescaleDB continuous aggregates we have created, we can quickly build a richly-featured dashboard in Grafana. Below we see a typical IoT Dashboard you might build to monitor the post’s IoT sensor data in near real-time. An exported version, dashboard_external_export.json, is included in the GitHub project.
Grafana’s documentation includes a comprehensive set of instructions for Using PostgreSQL in Grafana. To connect to the TimescaleDB database from Grafana, we use a PostgreSQL data source.
The data displayed in each Panel in the Grafana Dashboard is based on a SQL query. For example, the Average Temperature Panel might use a query similar to the example below. This particular query also converts Celcius to Fahrenheit. Note the use of Grafana Macros (e.g., $__time(), $__timeFilter()). Macros can be used within a query to simplify syntax and allow for dynamic parts.
SELECT
$__time(bucket),
device_id AS metric,
((avg_temp * 1.9) + 32) AS avg_temp
FROM temperature_humidity_summary_minute
WHERE
$__timeFilter(bucket)
ORDER BY 1,2
Below, we see another example from the Average Humidity Panel. In this particular query, we might choose to validate the humidity data is within an acceptable range of 0%–100%.
SELECT
$__time(bucket),
device_id AS metric,
avg_humidity
FROM temperature_humidity_summary_minute
WHERE
$__timeFilter(bucket)
AND avg_humidity >= 0.0
AND avg_humidity <= 100.0
ORDER BY 1,2
Mobile Friendly
Grafana dashboards are mobile-friendly. Below we see two views of the dashboard, using the Chrome mobile browser on an Apple iPhone.
Grafana Alerts
Grafana allows Alerts to be created based on Rules you define in each Panel. If data values match the Rule’s conditions, which you pre-define, such as a temperature reading above a certain threshold for a set amount of time, an alert is sent to your choice of destinations. According to the Rule shown below, If the average temperature exceeds 75°F for a period of 5 minutes, an alert is sent.
As demonstrated below, when the temperature in the laboratory began to exceed 75°F, the alert entered a ‘Pending’ state. If the temperature exceeded 75°F for the pre-determined period of 5 minutes, the alert status changed to ‘Alerting’, and an alert was sent. When the temperature dropped back below 75°F for the pre-determined period of 5 minutes, the alert status changed from ‘Alerting’ to ‘OK’, and a subsequent notification was sent.
There are currently 18 destinations available out-of-the-box with Grafana, including Slack, email, PagerDuty, webhooks, HipChat, and Microsoft Teams. We can use Grafana Alerts to notify the proper resources, in near real-time, if an issue is detected, based on the data. Below, we see an actual series of high-temperature alerts sent by Grafana to a Slack channel, followed by subsequent notifications as the temperature returned to normal.
Ad-hoc Queries
The ability to perform ad-hoc queries on the time-series IoT data is an essential feature of the IoT edge analytics stack. We can use psql or pgAdmin to perform ad-hoc queries against the TimescaleDB database. Below are examples of typical ad-hoc queries we might perform on the IoT sensor data. These example queries demonstrate TimescaleDB’s advanced analytical capabilities for working with time-series data, including Moving Average, Delta, Time Bucket, and Histogram.
Conclusion
In this post, we have explored the development of an IoT edge analytics stack, comprised of lightweight, purpose-built, easily deployable and manageable, platform- and programming language-agnostic, open-source software components. These components included Docker containerized versions of Eclipse Mosquitto, TimescaleDB, Grafana, and pgAdmin, referred to as the GTM Stack. Using the GTM stack, we collected, analyzed, and visualized IoT data, without first shipping the data to Cloud or other external systems.
This blog represents my own viewpoints and not of my employer, Amazon Web Services. All product names, logos, and brands are the property of their respective owners.
Collecting and Analyzing IoT Data in Near Real-Time with AWS IoT, LoRa, and LoRaWAN
Posted by Gary A. Stafford in AWS, Bash Scripting, IoT, Python, Raspberry Pi, Serverless, Software Development on August 26, 2020
Introduction
In a recent post published on ITNEXT, LoRa and LoRaWAN for IoT: Getting Started with LoRa and LoRaWAN Protocols for Low Power, Wide Area Networking of IoT, we explored the use of the LoRa (Long Range) and LoRaWAN protocols to transmit and receive sensor data, over a substantial distance, between an IoT device, containing several embedded sensors, and an IoT gateway. In this post, we will extend that architecture to the Cloud, using AWS IoT, a broad and deep set of IoT services, from the edge to the Cloud. We will securely collect, transmit, and analyze IoT data using the AWS cloud platform.
LoRa and LoRaWAN
According to the LoRa Alliance, Low-Power, Wide-Area Networks (LPWAN) are projected to support a major portion of the billions of devices forecasted for the Internet of Things (IoT). LoRaWAN is designed from the bottom up to optimize LPWANs for battery lifetime, capacity, range, and cost. LoRa and LoRaWAN permit long-range connectivity for IoT devices in different types of industries. According to Wikipedia, LoRaWAN defines the communication protocol and system architecture for the network, while the LoRa physical layer enables the long-range communication link.
AWS IoT
AWS describes AWS IoT as a set of managed services that enable ‘internet-connected devices to connect to the AWS Cloud and lets applications in the cloud interact with internet-connected devices.’ AWS IoT services span three categories: Device Software, Connectivity and Control, and Analytics.
In this post, we will focus on three AWS IOT services, one from each category, including AWS IoT Device SDKs, AWS IoT Core, and AWS IoT Analytics. According to AWS, the AWS IoT Device SDKs include open-source libraries and developer and porting guides with samples to help you build innovative IoT products or solutions on your choice of hardware platforms. AWS IoT Core is a managed cloud service that lets connected devices easily and securely interact with cloud applications and other devices. AWS IoT Core can process and route messages to AWS endpoints and other devices reliably and securely. Finally, AWS IoT Analytics is a fully-managed IoT analytics service, designed specifically for IoT, which collects, pre-processes, enriches, stores, and analyzes IoT device data at scale.
To learn more about AWS IoT, specifically the AWS IoT services we will be exploring within this post, I recommend reading my recent post published on Towards Data Science, Getting Started with IoT Analytics on AWS.
Hardware Selection
In this post, we will use the following hardware.
IoT Device with Embedded Sensors
An Arduino single-board microcontroller will serve as our IoT device. The 3.3V AI-enabled Arduino Nano 33 BLE Sense board (Amazon: USD 36.00), released in August 2019, comes with the powerful nRF52840 processor from Nordic Semiconductors, a 32-bit ARM Cortex-M4 CPU running at 64 MHz, 1MB of CPU Flash Memory, 256KB of SRAM, and a NINA-B306 stand-alone Bluetooth 5 low energy (BLE) module.
The Sense contains an impressive array of embedded sensors:
- 9-axis Inertial Sensor (LSM9DS1): 3D digital linear acceleration sensor, a 3D digital
angular rate sensor, and a 3D digital magnetic sensor - Humidity and Temperature Sensor (HTS221): Capacitive digital sensor for relative humidity and temperature
- Barometric Sensor (LPS22HB): MEMS nano pressure sensor: 260–1260 hectopascal (hPa) absolute digital output barometer
- Microphone (MP34DT05): MEMS audio sensor omnidirectional digital microphone
- Gesture, Proximity, Light Color, and Light Intensity Sensor (APDS9960): Advanced Gesture detection, Proximity detection, Digital Ambient Light Sense (ALS), and Color Sense (RGBC).
The Arduino Sense is an excellent, low-cost single-board microcontroller for learning about the collection and transmission of IoT sensor data.
IoT Gateway
An IoT Gateway, according to TechTarget, is a physical device or software program that serves as the connection point between the Cloud and controllers, sensors, and intelligent devices. All data moving to the Cloud, or vice versa, goes through the gateway, which can be either a dedicated hardware appliance or software program.
LoRa Gateways, to paraphrase The Things Network, form the bridge between devices and the Cloud. Devices use low power networks like LoRaWAN to connect to the Gateway, while the Gateway uses high bandwidth networks like WiFi, Ethernet, or Cellular to connect to the Cloud.
A third-generation Raspberry Pi 3 Model B+ single-board computer (SBC) will serve as our LoRa IoT Gateway. This Raspberry Pi model features a 1.4GHz Cortex-A53 (ARMv8) 64-bit quad-core processor System on a Chip (SoC), 1GB LPDDR2 SDRAM, dual-band wireless LAN, Bluetooth 4.2 BLE, and Gigabit Ethernet (Amazon: USD 42.99).
LoRa Transceiver Modules
To transmit the IoT sensor data between the IoT device, containing the embedded sensors, and the IoT gateway, I have used the REYAX RYLR896 LoRa transceiver module (Amazon: USD 19.50 x 2). The transceiver modules are commonly referred to as a universal asynchronous receiver-transmitter (UART). A UART is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable.
According to the manufacturer, REYAX, the RYLR896 contains the Semtech SX1276 long-range, low power transceiver. The RYLR896 module provides ultra-long range spread spectrum communication and high interference immunity while minimizing current consumption. Each RYLR896 module contains a small, PCB integrated, helical antenna. This transceiver operates at both the 868 and 915 MHz frequency ranges. In this demonstration, we will be transmitting at 915 MHz for North America.
The Arduino Sense (IoT device) transmits data, using one of the RYLR896 modules (shown below front). The Raspberry Pi (IoT Gateway), connected to the other RYLR896 module (shown below rear), receives the data.
LoRaWAN Security
The RYLR896 is capable of AES 128-bit data encryption. Using the Advanced Encryption Standard (AES), we will encrypt the data sent from the IoT device to the IoT gateway, using a 32 hex digit password (128 bits / 4 bits/hex digit).
Provisioning AWS Resources
To start, we will create the necessary AWS IoT and associated resources on the AWS cloud platform. Once these resources are in place, we can then proceed to configure the IoT device and IoT gateway to securely transmit the sensor data to the Cloud.
All the source code for this post is on GitHub. Use the following command to git clone a local copy of the project.
git clone --branch master --single-branch --depth 1 --no-tags \
https://github.com/garystafford/iot-aws-lora-demo.git
AWS CloudFormation
The CloudFormation template, iot-analytics.yaml, will create an AWS IoT CloudFormation stack containing the following resources.
- AWS IoT Thing
- AWS IoT Thing Policy
- AWS IoT Core Topic Rule
- AWS IoT Analytics Channel, Pipeline, Data store, and Data set
- AWS Lambda and Lambda Permission
- Amazon S3 Bucket
- Amazon SageMaker Notebook Instance
- AWS IAM Roles
Please be aware of the costs involved with the AWS resources used in the CloudFormation template before continuing. To create the AWS CloudFormation stack from the included CloudFormation template, execute the following AWS CLI command.
The resulting CloudFormation stack should contain 16 AWS resources.
Additional Resources
Unfortunately, AWS CloudFormation cannot create all the AWS IoT resources we require for this demonstration. To complete the AWS provisioning process, execute the following series of AWS CLI commands, aws_cli_commands.md. These commands will create the remaining resources, including an AWS IoT Thing Type, Thing Group, Thing Billing Group, and an X.509 Certificate.
IoT Device Configuration
With the AWS resources deployed, we can configure the IoT device and IoT Gateway.
Arduino Sketch
For those not familiar with Arduino, a sketch is the name that Arduino uses for a program. It is the unit of code that is uploaded into non-volatile flash memory and runs on an Arduino board. The Arduino language is a set of C and C++ functions. All standard C and C++ constructs supported by the avr-g++ compiler should work in Arduino.
For this post, the sketch, lora_iot_demo_aws.ino, contains the code necessary to collect and securely transmit the environmental sensor data, including temperature, relative humidity, barometric pressure, Red, Green, and Blue (RGB) color, and ambient light intensity, using the LoRaWAN protocol.
AT Commands
Communications with the RYLR896’s long-range modem is done using AT commands. AT commands are instructions used to control a modem. AT is the abbreviation of ATtention. Every command line starts with AT. That is why modem commands are called AT commands, according to Developer’s Home. A complete list of AT commands can be downloaded as a PDF from the RYLR896 product page.
To efficiently transmit the environmental sensor data from the IoT sensor to the IoT gateway, the sketch concatenates the sensor ID and the sensor values together in a single string. The string will be incorporated into an AT command, sent to the RYLR896 LoRa transceiver module. To make it easier to parse the sensor data on the IoT gateway, we will delimit the sensor values with a pipe (|), as opposed to a comma. According to REYAX, the maximum length of the LoRa payload is approximately 330 bytes.
Below, we see an example of an AT command used to send the sensor data from the IoT sensor and the corresponding unencrypted data received by the IoT gateway. Both contain the LoRa transmitter Address ID, payload length (62 bytes in the example), and the payload. The data received by the IoT gateway also has the Received signal strength indicator (RSSI), and Signal-to-noise ratio (SNR).
Receiving Data on IoT Gateway
The Raspberry Pi will act as a LoRa IoT gateway, receiving the environmental sensor data from the IoT device, the Arduino, and sending the data to AWS. The Raspberry Pi runs a Python script, rasppi_lora_receiver_aws.py, which will receive the data from the Arduino Sense, decrypt the data, parse the sensor values, and serialize the data to a JSON payload, and finally, transmit the payload in an MQTT-protocol message to AWS. The script uses the pyserial, the Python Serial Port Extension, which encapsulates the access for the serial port for communication with the RYLR896 module. The script uses the AWS IoT Device SDK for Python v2 to communicate with AWS.
Running the IoT Gateway Python Script
To run the Python script on the Raspberry Pi, we will use a helper shell script, rasppi_lora_receiver_aws.sh. The shell script helps construct the arguments required to execute the Python script.
To run the helper script, we execute the following command, substituting the input parameter, the AWS IoT endpoint, with your endpoint.
sh ./rasppi_lora_receiver_aws.sh \
a1b2c3d4e5678f-ats.iot.us-east-1.amazonaws.com
You should see the console output, similar to the following.
The script starts by configuring the RYLR896 module and outputting that configuration to a log file, output.log. If successful, we should see the following debug information logged.
DEBUG:root:Connecting to a1b2c3d4e5f6-ats.iot.us-east-1.amazonaws.com with client ID 'lora-iot-gateway-01'
DEBUG:root:Connecting to REYAX RYLR896 transceiver module
DEBUG:root:Connected!
DEBUG:root:Address set? +OK
DEBUG:root:Network Id set? +OK
DEBUG:root:AES-128 password set? +OK
DEBUG:root:Module responding? +OK
DEBUG:root:Address: +ADDRESS=116
DEBUG:root:Network id: +NETWORKID=6
DEBUG:root:UART baud rate: +IPR=115200
DEBUG:root:RF frequency: +BAND=915000000
DEBUG:root:RF output power: +CRFOP=15
DEBUG:root:Work mode: +MODE=0
DEBUG:root:RF parameters: +PARAMETER=12,7,1,4
DEBUG:root:AES128 password of the network: +CPIN=92A0ECEC9000DA0DCF0CAAB0ABA2E0EF
That sensor data is also written to the log file for debugging purposes. This first line in the log (shown below) is the raw decrypted data received from the IoT device via LoRaWAN. The second line is the JSON-serialized payload, sent securely to AWS, using the MQTT protocol.
DEBUG:root:b'+RCV=116,59,0447383033363932003C0034|23.46|41.89|99.38|230|692|833|1116,-48,39\r\n'
DEBUG:root:{'ts': 1598305503.7041512, 'data': {'humidity': 41.89, 'temperature': 23.46, 'device_id': '0447383033363932003C0034', 'gateway_id': '00000000f62051ce', 'pressure': 99.38, 'color': {'red': 230.0, 'blue': 833.0, 'ambient': 1116.0, 'green': 692.0}}}
DEBUG:root:b'+RCV=116,59,0447383033363932003C0034|23.46|41.63|99.38|236|696|837|1127,-49,35\r\n'
DEBUG:root:{'ts': 1598305513.7918658, 'data': {'humidity': 41.63, 'temperature': 23.46, 'device_id': '0447383033363932003C0034', 'gateway_id': '00000000f62051ce', 'pressure': 99.38, 'color': {'red': 236.0, 'blue': 837.0, 'ambient': 1127.0, 'green': 696.0}}}
DEBUG:root:b'+RCV=116,59,0447383033363932003C0034|23.44|41.57|99.38|232|686|830|1113,-48,32\r\n'
DEBUG:root:{'ts': 1598305523.8556132, 'data': {'humidity': 41.57, 'temperature': 23.44, 'device_id': '0447383033363932003C0034', 'gateway_id': '00000000f62051ce', 'pressure': 99.38, 'color': {'red': 232.0, 'blue': 830.0, 'ambient': 1113.0, 'green': 686.0}}}
DEBUG:root:b'+RCV=116,59,0447383033363932003C0034|23.51|41.44|99.38|205|658|802|1040,-48,36\r\n'
DEBUG:root:{'ts': 1598305528.8890748, 'data': {'humidity': 41.44, 'temperature': 23.51, 'device_id': '0447383033363932003C0034', 'gateway_id': '00000000f62051ce', 'pressure': 99.38, 'color': {'red': 205.0, 'blue': 802.0, 'ambient': 1040.0, 'green': 658.0}}}
AWS IoT Core
The Raspberry Pi-based IoT gateway will be registered with AWS IoT Core. IoT Core allows users to connect devices quickly and securely to AWS.
Things
According to AWS, IoT Core can reliably scale to billions of devices and trillions of messages. Registered devices are referred to as things in AWS IoT Core. A thing is a representation of a specific device or logical entity. Information about a thing is stored in the registry as JSON data.
Below, we see an example of the Thing created by CloudFormation. The Thing, lora-iot-gateway-01, represents the physical IoT gateway. We have assigned the IoT gateway a Thing Type, LoRaIoTGateway, a Thing Group, LoRaIoTGateways, and a Thing Billing Group, IoTGateways.
In a real IoT environment, containing hundreds, thousands, even millions of IoT devices, gateways, and sensors, these classification mechanisms, Thing Type, Thing Group, and Thing Billing Group, will help to organize IoT assets.
Device Gateway and Message Broker
IoT Core provides a Device Gateway, which manages all active device connections. The Gateway currently supports MQTT, WebSockets, and HTTP 1.1 protocols. Behind the Message Gateway is a high-throughput pub/sub Message Broker, which securely transmits messages to and from all IoT devices and applications with low latency. Below, we see a typical AWS IoT Core architecture containing multiple Topics, Rules, and Actions.
AWS IoT Security
AWS IoT Core provides mutual authentication and encryption, ensuring all data is exchanged between AWS and the devices are secure by default. In the demonstration, all data is sent securely using Transport Layer Security (TLS) 1.2 with X.509 digital certificates on port 443. Below, we see an example of an X.509 certificate assigned to the Thing, lora-iot-gateway-01, which represents the physical IoT gateway. The X.509 certificate and the private key, generated using the AWS CLI, previously, are installed on the IoT gateway.
Authorization of the device to access any resource on AWS is controlled by AWS IoT Core Policies. These policies are similar to AWS IAM Policies. Below, we see an example of an AWS IoT Core Policy, LoRaDevicePolicy, which is assigned to the IoT gateway.
AWS IoT Core Rules
Once an MQTT message is received from the IoT gateway (a thing), we use AWS IoT Rules to send message data to an AWS IoT Analytics Channel. Rules give your devices the ability to interact with AWS services. Rules are analyzed, and Actions are performed based on the MQTT topic stream. Below, we see an example rule that forwards our messages to an IoT Analytics Channel.
Rule query statements are written in standard Structured Query Language (SQL). The datasource for the Rule query is an IoT Topic.
AWS IoT Analytics
AWS IoT Analytics is composed of five primary components: Channels, Pipelines, Data stores, Data sets, and Notebooks. These components enable you to collect, prepare, store, analyze, and visualize your IoT data.
Below, we see a typical AWS IoT Analytics architecture. IoT messages are received from AWS IoT Core, thought a Rule Action. Amazon QuickSight provides business intelligence, visualization. Amazon QuickSight ML Insights adds anomaly detection and forecasting.
IoT Analytics Channel
An AWS IoT Analytics Channel pulls messages or data into IoT Analytics from other AWS sources, such as Amazon S3, Amazon Kinesis, or Amazon IoT Core. Channels store data for IoT Analytics Pipelines. Both Channels and Data store support storing data in your own Amazon S3 bucket or an IoT Analytics service-managed S3 bucket. In the demonstration, we are using a service managed S3 bucket.
When creating a Channel, you also decide how long to retain the data. For the demonstration, we have set the data retention period for 21 days. Channels are generally not used for long term storage of data. Typically, you would only retain data in the Channel for the period you need to analyze. For long term storage of IoT message data, I recommend using an AWS IoT Core Rule to send a copy of the raw IoT data to Amazon S3, using a service such as Amazon Kinesis Data Firehose.
IoT Analytics Pipeline
An AWS IoT Analytics Pipeline consumes messages from one or more Channels. Pipelines transform, filter, and enrich the messages before storing them in IoT Analytics Data stores. A Pipeline is composed of an ordered list of activities. Logically, you must specify both a Channel (source) and a Datastore (destination) activity. Optionally, you may choose as many as 23 additional activities in the pipelineActivities array.
In our demonstration’s Pipeline, iot_analytics_pipeline, we have specified three additional activities, including DeviceRegistryEnrich, Filter, and Lambda. Other activity types include Math, SelectAttributes, RemoveAttributes, and AddAttributes.
The Filter activity ensures the sensor values are not Null or otherwise erroneous; if true, the message is dropped. The Lambda Pipeline activity executes an AWS Lambda function to transform the messages in the pipeline. Messages are sent in an event object to the Lambda. The message is modified, and the event object is returned to the activity.
The Python-based Lambda function easily handles typical IoT data transformation tasks, including converting the temperature from Celsius to Fahrenheit, pressure from kilopascals (kPa) to inches of Mercury (inHg), and 12-bit RGBA values to 8-bit color values (0–255). The Lambda function also rounds down all the values to between 0 and 2 decimal places of precision.
The demonstration’s Pipeline also enriches the IoT data with metadata from the IoT device’s AWS IoT Core Registry. The metadata includes additional information about the device that generated the IoT data, including the custom attributes such as LoRa transceiver manufacturer and model, and the IoT gateway manufacturer.
A notable feature of Pipelines is the ability to reprocess messages. If you make changes to the Pipeline, which often happens during the data preparation stage, you can reprocess any or all the IoT data in the associated Channel, and overwrite the IoT data in the Data set.
IoT Analytics Data store
An AWS IoT Analytics Data store stores prepared data from an AWS IoT Analytics Pipeline, in a fully-managed database. Both Channels and Data store support storing IoT data in your own Amazon S3 bucket or an IoT Analytics managed S3 bucket. In the demonstration, we are using a service-managed S3 bucket to store the IoT data in our Data store, iot_analytics_data_store.
IoT Analytics Data set
An AWS IoT Analytics Data set automatically provides regular, up-to-date insights for data analysts by querying a Data store using standard SQL. Periodic updates are implemented using a cron expression. For the demonstration, we are updating our Data set, iot_analytics_data_set, at a 15-minute interval. The time interval can be increased or reduced, depending on the desired ‘near real-time’ nature of the IoT data being analyzed.
Below, we see messages in the Result preview pane of the Data set. Note the SQL query used to obtain the messages, which queries the Data store. The Data store, as you will recall, contains the transformed messages from the Pipeline.
IoT Analytics Data sets also support sending content results, which are materialized views of your IoT Analytics data, to an Amazon S3 bucket.
The CloudFormation stack created an encrypted Amazon S3 Bucket. This bucket receives a copy of the messages from the IoT Analytics Data set whenever the cron expression runs the scheduled update.
IoT Analytics Notebook
An AWS IoT Analytics Notebook allows users to perform statistical analysis and machine learning on IoT Analytics Data sets using Jupyter Notebooks. The IoT Analytics Notebook service includes a set of notebook templates that contain AWS-authored machine learning models and visualizations. Notebook Instances can be linked to a GitHub or other source code repository. Notebooks created with IoT Analytics Notebook can also be accessed directly through Amazon SageMaker. For the demonstration, the Notebooks Instance is cloned from our project’s GitHub repository.
The repository contains a sample Jupyter Notebook, LoRa_IoT_Analytics_Demo.ipynb, based on the conda_python3 kernel. This preinstalled environment includes the default Anaconda installation and Python 3.
The Notebook uses pandas, matplotlib, and plotly to manipulate and visualize the sample IoT data stored in the IoT Analytics Data set.
The Notebook can be modified, and the changes pushed back to GitHub. You could easily fork the demonstration’s GitHub repository and modify the CloudFormation template to point to your source code repository.
Amazon QuickSight
Amazon QuickSight provides business intelligence (BI) and visualization. Amazon QuickSight ML Insights adds anomaly detection and forecasting. We can use Amazon QuickSight to visualize the IoT message data, stored in the IoT Analytics Data set.
Amazon QuickSight has both a Standard and an Enterprise Edition. AWS provides a detailed product comparison of each edition. For the post, I am demonstrating the Enterprise Edition, which includes additional features, such as ML Insights, hourly refreshes of SPICE (super-fast, parallel, in-memory, calculation engine), and theme customization.
Please be aware of the costs of Amazon QuickSight if you choose to follow along with this part of the demo. Although there is an Amazon QuickSight API, Amazon QuickSight is not automatically enabled or configured with CloudFormation or using the AWS CLI in this demonstration.
QuickSight Data Sets
Amazon QuickSight has a wide variety of data source options for creating Amazon QuickSight Data sets, including the ones shown below. Do not confuse Amazon QuickSight Data sets with IoT Analytics Data sets; they are two different service features.
For the demonstration, we will create an Amazon QuickSight Data set that will use our IoT Analytics Data set, iot_analytics_data_set.
Amazon QuickSight gives you the ability to view and modify QuickSight Data sets before visualizing. QuickSight even provides a wide variety of functions, enabling us to perform dynamic calculations on the field values. For this demonstration, we will leave the data unchanged since all transformations were already completed in the IoT Analytics Pipeline.
QuickSight Analysis
Using the QuickSight Data set, built from the IoT Analytics Data set as a data source, we create a QuickSight Analysis. The QuickSight Analysis console is shown below. An Analysis is primarily a collection of Visuals (aka Visual types). QuickSight provides several Visual types. Each visual is associated with a Data set. Data for the QuickSight Analysis or each visual within the Analysis can be filtered. For the demo, I have created a simple QuickSight Analysis, including a few typical QuickSight visuals.
QuickSight Dashboards
To share a QuickSight Analysis, we can create a QuickSight Dashboard. Below, we see a few views of the QuickSight Analysis, shown above, as a Dashboard. Although viewers of the Dashboard cannot edit the visuals, they can apply filtering and interactively drill-down into data in the Visuals.
Amazon QuickSight ML Insights
According to Amazon, ML Insights leverages AWS’s machine learning (ML) and natural language capabilities to gain deeper insights from data. QuickSight’s ML-powered Anomaly Detection continuously analyze data to discover anomalies and variations inside of the aggregates, giving you the insights to act when business changes occur. QuickSight’s ML-powered Forecasting can be used to predict your business metrics accurately, and perform interactive what-if analysis with point-and-click simplicity. QuickSight’s built-in algorithms make it easy for anyone to use ML that learns from your data patterns to provide you with accurate predictions based on historical trends.
Below, we see the ML Insights tab (left) in the demonstration’s QuickSight Analysis. Individually detected anomalies can be added to the QuickSight Analysis, like Visuals, and configured to tune the detection parameters. Observe the temperature, humidity, and barometric pressure anomalies, identified by ML Insights, based on their Anomaly Score, which is higher or lower, given a minimum delta of five percent. These anomalies accurately reflected an actual failure of the IoT device, caused by overheated during testing, which resulted in abnormal sensor readings.
Receiving the Messages on AWS
To confirm the IoT gateway is sending messages, we can use a packet analyzer, like tcpdump, on the IoT gateway. Running tcpdump on the IoT gateway, below, we see outbound encrypted MQTT messages being sent to AWS on port 443.
To confirm those messages are being received from the IoT gateway on AWS, we can use the AWS IoT Core Test feature and subscribe to the lora-iot-demo topic. We should see messages flowing in from the IoT gateway at approximately 5-second intervals.
The JSON payload structure of the incoming MQTT messages will look similar to the below example. The device_id is the unique id of the IoT device that transmitted the message using LoRaWAN. The gateway_id is the unique id of the IoT gateway that received the message using LoRaWAN and sent it to AWS. A single IoT gateway would usually manage messages from multiple IoT devices, each with a unique id.
The SQL query used by the AWS IoT Rule described earlier, transforms and flattens the nested JSON payload structure, before passing it to the AWS IoT Analytics Channel, as shown below.
We can measure the near real-time nature of the IoT data using the ts and msg_received data fields. The ts data field is date and time when the sensor reading occurred on the IoT device, while the msg_received data field is the date and time when the message was received on AWS. The delta between the two values is a measure of how near real-time the sensor readings are being streamed to the AWS IoT Analytics Channel. In the below example, the difference between ts (2020–08–27T11:45:31.986) and msg_received (2020–08–27T11:45:32.074) is 88 ms.
Final IoT Data Message Structure
Once the message payload passes through the AWS IoT Analytics Pipeline and lands in the AWS IoT Analytics Data set, its final data structure looks as follows. Note that the device’s attribute metadata has been added from the AWS IoT Core device registry. Regrettably, the metadata is not well-formatted JSON and will require additional transformation to be usable.
A set of sample messages is included in the GitHub project’s sample_messages directory.
Conclusion
In this post, we explored the use of the LoRa and LoRaWAN protocols to transmit environmental sensor data from an IoT device to an IoT gateway. Given its low energy consumption, long-distance transmission capabilities, and well-developed protocols, LoRaWAN is an ideal long-range wireless protocol for IoT devices. We then demonstrated how to use AWS IoT Device SDKs, AWS IoT Core, and AWS IoT Analytics to securely collect, analyze, and visualize streaming messages from the IoT device, in near real-time.
This blog represents my own viewpoints and not of my employer, Amazon Web Services.
LoRa and LoRaWAN for IoT: Getting Started with LoRa and LoRaWAN Protocols for Low Power, Wide Area Networking of IoT
Posted by Gary A. Stafford in C++ Development, IoT, Python, Raspberry Pi, Software Development, Technology Consulting on August 10, 2020
Introduction
According to the LoRa Alliance, Low-Power, Wide-Area Networks (LPWAN) are projected to support a major portion of the billions of devices forecasted for the Internet of Things (IoT). LoRaWAN is designed from the bottom up to optimize LPWANs for battery lifetime, capacity, range, and cost. LoRa and LoRaWAN permit long-range connectivity for the Internet of Things (IoT) devices in different types of industries. According to Wikipedia, LoRaWAN defines the communication protocol and system architecture for the network, while the LoRa physical layer enables the long-range communication link.
LoRa
Long Range (LoRa), the low-power wide-area network (LPWAN) protocol developed by Semtech, sits at layer 1, the physical layer, of the seven-layer OSI model (Open Systems Interconnection model) of computer networking. The physical layer defines the means of transmitting raw bits over a physical data link connecting network nodes. LoRa uses license-free sub-gigahertz radio frequency (RF) bands, including 433 MHz, 868 MHz (Europe), 915 MHz (Australia and North America), and 923 MHz (Asia). LoRa enables long-range transmissions with low power consumption.
LoRaWAN
LoRaWAN is a cloud-based medium access control (MAC) sublayer (layer 2) protocol but acts mainly as a network layer (layer 3) protocol for managing communication between LPWAN gateways and end-node devices as a routing protocol, maintained by the LoRa Alliance. The MAC sublayer and the logical link control (LLC) sublayer together make up layer 2, the data link layer, of the OSI model.
LoRaWAN is often cited as having greater than a 10-km-wide coverage area in rural locations. However, according to other sources, it is generally more limited. According to the Electronic Design article, 11 Myths About LoRaWAN, a typical LoRaWAN network range depends on numerous factors—indoor or outdoor gateways, the payload of the message, the antenna used, etc. On average, in an urban environment with an outdoor gateway, you can expect up to 2- to 3-km-wide coverage, while in the rural areas it can reach beyond 5 to 7 km. LoRa’s range depends on the “radio line-of-sight.” Radio waves in the 400 MHz to 900 MHz range may pass through some obstructions, depending on their composition, but will be absorbed or reflected otherwise. This means that the signal can potentially reach as far as the horizon, as long as there are no physical barriers to block it.
In the following hands-on post, we will explore the use of the LoRa and LoRaWAN protocols to transmit and receive sensor data, over a substantial distance, between an IoT device, containing a number of embedded sensors, and an IoT gateway.
Recommended Hardware
For this post, I have used the following hardware.
IoT Device with Embedded Sensors
I have used an Arduino single-board microcontroller as an IoT sensor, actually an array of sensors. The 3.3V AI-enabled Arduino Nano 33 BLE Sense board (Amazon: USD 36.00), released in August 2019, comes with the powerful nRF52840 processor from Nordic Semiconductors, a 32-bit ARM Cortex-M4 CPU running at 64 MHz, 1MB of CPU Flash Memory, 256KB of SRAM, and a NINA-B306 stand-alone Bluetooth 5 low energy (BLE) module.
The Sense also contains an impressive array of embedded sensors:
- 9-axis Inertial Sensor (LSM9DS1): 3D digital linear acceleration sensor, a 3D digital
angular rate sensor, and a 3D digital magnetic sensor - Humidity and Temperature Sensor (HTS221): Capacitive digital sensor for relative humidity and temperature
- Barometric Sensor (LPS22HB): MEMS nano pressure sensor: 260–1260 hectopascal (hPa) absolute digital output barometer
- Microphone (MP34DT05): MEMS audio sensor omnidirectional digital microphone
- Gesture, Proximity, Light Color, and Light Intensity Sensor (APDS9960): Advanced Gesture detection, Proximity detection, Digital Ambient Light Sense (ALS), and Color Sense (RGBC).
The Arduino Sense is an excellent, low-cost single-board microcontroller for learning about the collection and transmission of IoT sensor data.
IoT Gateway
An IoT Gateway, according to TechTarget, is a physical device or software program that serves as the connection point between the Cloud and controllers, sensors, and intelligent devices. All data moving to the Cloud, or vice versa goes through the gateway, which can be either a dedicated hardware appliance or software program.
I have used an a third-generation Raspberry Pi 3 Model B+ single-board computer (SBC), to serve as an IoT Gateway. This Raspberry Pi model features a 1.4GHz Cortex-A53 (ARMv8) 64-bit quad-core processor System on a Chip (SoC), 1GB LPDDR2 SDRAM, dual-band wireless LAN, Bluetooth 4.2 BLE, and Gigabit Ethernet (Amazon: USD 42.99).
To follow along with the post, you could substitute the Raspberry Pi for any Linux-based machine to run the included sample Python script.
LoRa Transceiver Modules
To transmit the IoT sensor data between the IoT device, containing the embedded sensors, and the IoT gateway, I have used the REYAX RYLR896 LoRa transceiver module (Amazon: USD 19.50 x 2). The transceiver modules are commonly referred to as a universal asynchronous receiver-transmitter (UART). A UART is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable.
According to the manufacturer, REYAX, the RYLR896 contains the Semtech SX1276 long-range, low power transceiver. The RYLR896 module provides ultra-long range spread spectrum communication and high interference immunity while minimizing current consumption. This transceiver operates at both the 868 and 915 MHz frequency ranges. We will be transmitting at 915 MHz for North America, in this post. Each RYLR896 module contains a small, PCB integrated, helical antenna.
Security
The RYLR896 is capable of the AES 128-bit data encryption. Using the Advanced Encryption Standard (AES), we will encrypt the data sent from the IoT device to the IoT gateway, using a 32 hex digit password (128 bits / 4 bits/hex digit = 32 hex digits). Using hexadecimal notation, the password is limited to digits 0–9 and characters A–F.
USB to TTL Serial Converter Adapter
Optionally, to configure, test, and debug the RYLR896 LoRa transceiver module directly from your laptop, you can use a USB to TTL serial converter adapter. I currently use the IZOKEE FT232RL FTDI USB to TTL Serial Converter Adapter Module for 3.3V and 5V (Amazon: USD 9.49 for 2). The 3.3V RYLR896 module easily connects to the USB to TTL Serial Converter Adapter using the TXD/TX, RXD/RX, VDD/VCC, and GND pins. We use serial communication to send and receive data through TX (transmit) and RX (receive) pins. The wiring is shown below: VDD to VCC, GND to GND, TXD to RX, and RXD to TX.
The FT232RL has support for baud rates up to 115,200 bps, which is the speed we will use to communicate with the RYLR896 module.
Arduino Sketch
For those not familiar with Arduino, a sketch is the name that Arduino uses for a program. It is the unit of code that is uploaded into non-volatile flash memory and runs on an Arduino board. The Arduino language is a set of C and C++ functions. All standard C and C++ constructs supported by the avr-g++ compiler should work in Arduino.
For this post, the sketch, lora_iot_demo.ino, contains all the code necessary to collect and securely transmit the environmental sensor data, including temperature, relative humidity, barometric pressure, RGB color, and ambient light intensity, using the LoRaWAN protocol. All code for this post, including the sketch, can be found on GitHub.
| /* | |
| Description: Transmits Arduino Nano 33 BLE Sense sensor telemetry over LoRaWAN, | |
| including temperature, humidity, barometric pressure, and color, | |
| using REYAX RYLR896 transceiver modules | |
| http://reyax.com/wp-content/uploads/2020/01/Lora-AT-Command-RYLR40x_RYLR89x_EN.pdf | |
| Author: Gary Stafford | |
| */ | |
| #include <Arduino_HTS221.h> | |
| #include <Arduino_LPS22HB.h> | |
| #include <Arduino_APDS9960.h> | |
| const int UPDATE_FREQUENCY = 5000; // update frequency in ms | |
| const float CALIBRATION_FACTOR = –4.0; // temperature calibration factor (Celsius) | |
| const int ADDRESS = 116; | |
| const int NETWORK_ID = 6; | |
| const String PASSWORD = "92A0ECEC9000DA0DCF0CAAB0ABA2E0EF"; | |
| const String DELIMITER = "|"; | |
| void setup() | |
| { | |
| Serial.begin(9600); | |
| Serial1.begin(115200); // default baud rate of module is 115200 | |
| delay(1000); // wait for LoRa module to be ready | |
| // needs all need to be same for receiver and transmitter | |
| Serial1.print((String)"AT+ADDRESS=" + ADDRESS + "\r\n"); | |
| delay(200); | |
| Serial1.print((String)"AT+NETWORKID=" + NETWORK_ID + "\r\n"); | |
| delay(200); | |
| Serial1.print("AT+CPIN=" + PASSWORD + "\r\n"); | |
| delay(200); | |
| Serial1.print("AT+CPIN?\r\n"); // confirm password is set | |
| if (!HTS.begin()) | |
| { // initialize HTS221 sensor | |
| Serial.println("Failed to initialize humidity temperature sensor!"); | |
| while (1); | |
| } | |
| if (!BARO.begin()) | |
| { // initialize LPS22HB sensor | |
| Serial.println("Failed to initialize pressure sensor!"); | |
| while (1); | |
| } | |
| // avoid bad readings to start bug | |
| // https://forum.arduino.cc/index.php?topic=660360.0 | |
| BARO.readPressure(); | |
| delay(1000); | |
| if (!APDS.begin()) | |
| { // initialize APDS9960 sensor | |
| Serial.println("Failed to initialize color sensor!"); | |
| while (1); | |
| } | |
| } | |
| void loop() | |
| { | |
| updateReadings(); | |
| delay(UPDATE_FREQUENCY); | |
| } | |
| void updateReadings() | |
| { | |
| float temperature = getTemperature(CALIBRATION_FACTOR); | |
| float humidity = getHumidity(); | |
| float pressure = getPressure(); | |
| int colors[4]; | |
| getColor(colors); | |
| String payload = buildPayload(temperature, humidity, pressure, colors); | |
| // Serial.println("Payload: " + payload); // display the payload for debugging | |
| Serial1.print(payload); // send the payload over LoRaWAN WiFi | |
| displayResults(temperature, humidity, pressure, colors); // display the results for debugging | |
| } | |
| float getTemperature(float calibration) | |
| { | |
| return HTS.readTemperature() + calibration; | |
| } | |
| float getHumidity() | |
| { | |
| return HTS.readHumidity(); | |
| } | |
| float getPressure() | |
| { | |
| return BARO.readPressure(); | |
| } | |
| void getColor(int c[]) | |
| { | |
| // check if a color reading is available | |
| while (!APDS.colorAvailable()) | |
| { | |
| delay(5); | |
| } | |
| int r, g, b, a; | |
| APDS.readColor(r, g, b, a); | |
| c[0] = r; | |
| c[1] = g; | |
| c[2] = b; | |
| c[3] = a; | |
| } | |
| void displayResults(float t, float h, float p, int c[]) | |
| { | |
| Serial.print("Temperature: "); | |
| Serial.println(t); | |
| Serial.print("Humidity: "); | |
| Serial.println(h); | |
| Serial.print("Pressure: "); | |
| Serial.println(p); | |
| Serial.print("Color (r, g, b, a): "); | |
| Serial.print(c[0]); | |
| Serial.print(", "); | |
| Serial.print(c[1]); | |
| Serial.print(", "); | |
| Serial.print(c[2]); | |
| Serial.print(", "); | |
| Serial.println(c[3]); | |
| Serial.println("———-"); | |
| } | |
| String buildPayload(float t, float h, float p, int c[]) | |
| { | |
| String readings = ""; | |
| readings += t; | |
| readings += DELIMITER; | |
| readings += h; | |
| readings += DELIMITER; | |
| readings += p; | |
| readings += DELIMITER; | |
| readings += c[0]; | |
| readings += DELIMITER; | |
| readings += c[1]; | |
| readings += DELIMITER; | |
| readings += c[2]; | |
| readings += DELIMITER; | |
| readings += c[3]; | |
| String payload = ""; | |
| payload += "AT+SEND="; | |
| payload += ADDRESS; | |
| payload += ","; | |
| payload += readings.length(); | |
| payload += ","; | |
| payload += readings; | |
| payload += "\r\n"; | |
| return payload; | |
| } |
AT Commands
Communications with the RYLR896’s long-range modem is done using AT commands. AT commands are instructions used to control a modem. AT is the abbreviation of ATtention. Every command line starts with “AT”. That is why modem commands are called AT commands, according to Developer’s Home. A complete list of AT commands can be downloaded as a PDF from the RYLR896 product page.
To efficiently transmit the environmental sensor data from the IoT sensor to the IoT gateway, the sketch concatenates the sensor values together in a single string. The string will be incorporated into AT command to send the data to the RYLR896 LoRa transceiver module. To make it easier to parse the sensor data on the IoT gateway, we will delimit the sensor values with a pipe (|), as opposed to a comma. The maximum length of the payload (sensor data) is 240 bytes.
Below, we see an example of an AT command used to send the sensor data from the IoT sensor and the corresponding unencrypted data received by the IoT gateway. Both strings contain the LoRa transmitter Address ID, payload length, and the payload. The data received by the IoT gateway also contains the Received signal strength indicator (RSSI), and Signal-to-noise ratio (SNR).
Configure, Test, and Debug
As discussed earlier, to configure, test, and debug the RYLR896 LoRa transceiver modules without the use of the IoT gateway, you can use a USB to TTL serial converter adapter. The sketch is loaded on the Arduino Sense (the IoT device) and actively transmits data through one of the RYLR896 modules (shown below right). The other RYLR896 module is connected to your laptop’s USB port, via the USB to TTL serial converter adapter (shown below left). Using a terminal and the screen command, or the Arduino desktop application’s Serial Terminal, we can receive the sensor data from the Arduino Sense.
Using a terminal on your laptop, we first need to locate the correct virtual console (aka virtual terminal). On Linux or Mac, the virtual consoles are represented by device special files, such as /dev/tty1, /dev/tty2, and so forth. To find the virtual console for the USB to TTL serial converter adapter plugged into the laptop, use the following command.
ls -alh /dev/tty.*
We should see a virtual console with a name similar to /dev/tty.usbserial-.
... /dev/tty.Bluetooth-Incoming-Port ... /dev/tty.GarysBoseQC35II-SPPDev ... /dev/tty.a483e767cbac-Bluetooth- ... /dev/tty.usbserial-A50285BI
To connect to the RYLR896 module via the USB to TTL serial converter adapter, using the virtual terminal, we use the screen command and connect at a baud rate of 115,200 bps.
screen /dev/tty.usbserial-A50285BI 115200
If everything is configured and working correctly, we should see data being transmitted from the Arduino Sense and received by the local machine, at five second intervals. Each line of unencrypted data transmitted will look similar to the following, +RCV=116,25,22.18|41.57|99.74|2343|1190|543|4011,-34,47. In the example below, the AES 128-bit data encryption is not enabled on the Arduino, yet. With encryption turned on the sensor data (the payload) would appear garbled.
Even easier than the screen command, we can also use the Arduino desktop application’s Serial Terminal, as shown in the following short screen recording. Select the correct Port (virtual console) from the Tools menu and open the Serial Terminal. Since the transmitted data should be secured using AES 128-bit data encryption, we need to send an AT command (AT+CPIN) containing the transceiver module’s common password, to correctly decrypt the data on the receiving device (e.g., AT+CPIN=92A0ECEC9000DA0DCF0CAAB0ABA2E0EF).
Receiving Data on IoT Gateway
The Raspberry Pi will act as an IoT gateway, receiving the environmental sensor data from the IoT device, the Arduino. The Raspberry Pi will run a Python script, rasppi_lora_receiver.py, which will receive and decrypt the data payload, parse the sensor values, and display the values in the terminal. The script uses the pyserial, the Python Serial Port Extension. This Python module encapsulates the access for the serial port.
| import logging | |
| import time | |
| from argparse import ArgumentParser | |
| from datetime import datetime | |
| import serial | |
| from colr import color as colr | |
| # LoRaWAN IoT Sensor Demo | |
| # Using REYAX RYLR896 transceiver modules | |
| # Author: Gary Stafford | |
| # Requirements: python3 -m pip install –user -r requirements.txt | |
| # To Run: python3 ./rasppi_lora_receiver.py –tty /dev/ttyAMA0 –baud-rate 115200 | |
| # constants | |
| ADDRESS = 116 | |
| NETWORK_ID = 6 | |
| PASSWORD = "92A0ECEC9000DA0DCF0CAAB0ABA2E0EF" | |
| def main(): | |
| logging.basicConfig(filename='output.log', filemode='w', level=logging.DEBUG) | |
| args = get_args() # get args | |
| payload = "" | |
| print("Connecting to REYAX RYLR896 transceiver module…") | |
| serial_conn = serial.Serial( | |
| port=args.tty, | |
| baudrate=int(args.baud_rate), | |
| timeout=5, | |
| parity=serial.PARITY_NONE, | |
| stopbits=serial.STOPBITS_ONE, | |
| bytesize=serial.EIGHTBITS | |
| ) | |
| if serial_conn.isOpen(): | |
| set_lora_config(serial_conn) | |
| check_lora_config(serial_conn) | |
| while True: | |
| serial_payload = serial_conn.readline() # read data from serial port | |
| if len(serial_payload) > 0: | |
| try: | |
| payload = serial_payload.decode(encoding="utf-8") | |
| except UnicodeDecodeError: # receiving corrupt data? | |
| logging.error("UnicodeDecodeError: {}".format(serial_payload)) | |
| payload = payload[:–2] | |
| try: | |
| data = parse_payload(payload) | |
| print("\n———-") | |
| print("Timestamp: {}".format(datetime.now())) | |
| print("Payload: {}".format(payload)) | |
| print("Sensor Data: {}".format(data)) | |
| display_temperature(data[0]) | |
| display_humidity(data[1]) | |
| display_pressure(data[2]) | |
| display_color(data[3], data[4], data[5], data[6]) | |
| except IndexError: | |
| logging.error("IndexError: {}".format(payload)) | |
| except ValueError: | |
| logging.error("ValueError: {}".format(payload)) | |
| # time.sleep(2) # transmission frequency set on IoT device | |
| def eight_bit_color(value): | |
| return int(round(value / (4097 / 255), 0)) | |
| def celsius_to_fahrenheit(value): | |
| return (value * 1.8) + 32 | |
| def display_color(r, g, b, a): | |
| print("12-bit Color values (r,g,b,a): {},{},{},{}".format(r, g, b, a)) | |
| r = eight_bit_color(r) | |
| g = eight_bit_color(g) | |
| b = eight_bit_color(b) | |
| a = eight_bit_color(a) # ambient light intensity | |
| print(" 8-bit Color values (r,g,b,a): {},{},{},{}".format(r, g, b, a)) | |
| print("RGB Color") | |
| print(colr("\t\t", fore=(127, 127, 127), back=(r, g, b))) | |
| print("Light Intensity") | |
| print(colr("\t\t", fore=(127, 127, 127), back=(a, a, a))) | |
| def display_pressure(value): | |
| print("Barometric Pressure: {} kPa".format(round(value, 2))) | |
| def display_humidity(value): | |
| print("Humidity: {}%".format(round(value, 2))) | |
| def display_temperature(value): | |
| temperature = celsius_to_fahrenheit(value) | |
| print("Temperature: {}°F".format(round(temperature, 2))) | |
| def get_args(): | |
| arg_parser = ArgumentParser(description="BLE IoT Sensor Demo") | |
| arg_parser.add_argument("–tty", required=True, help="serial tty", default="/dev/ttyAMA0") | |
| arg_parser.add_argument("–baud-rate", required=True, help="serial baud rate", default=1152000) | |
| args = arg_parser.parse_args() | |
| return args | |
| def parse_payload(payload): | |
| # input: +RCV=116,29,23.94|37.71|99.89|16|38|53|80,-61,56 | |
| # output: [23.94, 37.71, 99.89, 16.0, 38.0, 53.0, 80.0] | |
| payload = payload.split(",") | |
| payload = payload[2].split("|") | |
| payload = [float(i) for i in payload] | |
| return payload | |
| def set_lora_config(serial_conn): | |
| # configures the REYAX RYLR896 transceiver module | |
| serial_conn.write(str.encode("AT+ADDRESS=" + str(ADDRESS) + "\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("Address set?", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+NETWORKID=" + str(NETWORK_ID) + "\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("Network Id set?", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+CPIN=" + PASSWORD + "\r\n")) | |
| time.sleep(1) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("AES-128 password set?", serial_payload.decode(encoding="utf-8")) | |
| def check_lora_config(serial_conn): | |
| serial_conn.write(str.encode("AT?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("Module responding?", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+ADDRESS?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("Address:", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+NETWORKID?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("Network id:", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+IPR?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("UART baud rate:", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+BAND?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("RF frequency", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+CRFOP?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("RF output power", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+MODE?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("Work mode", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+PARAMETER?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("RF parameters", serial_payload.decode(encoding="utf-8")) | |
| serial_conn.write(str.encode("AT+CPIN?\r\n")) | |
| serial_payload = (serial_conn.readline())[:–2] | |
| print("AES128 password of the network", | |
| serial_payload.decode(encoding="utf-8")) | |
| if __name__ == "__main__": | |
| main() |
Prior to running the Python script, we can test and debug the connection from the Arduino Sense to the Raspberry Pi using a general application such as Minicom. Minicom is a text-based modem control and terminal emulator program. To install Minicom on the Raspberry Pi, use the following command.
sudo apt-get install minicom
To run Minicom or the Python script, we will need to know the virtual console of the serial connection (Serial1 in the script) used to communicate with the RYLR896 module, wired to the Raspberry Pi. This can found using the following command.
dmesg | grep -E --color 'serial|tty'
Search for a line, similar to the last line, shown below. Note the name of the virtual console, in my case, ttyAMA0.
[ 0.000000] Kernel command line: coherent_pool=1M bcm2708_fb.fbwidth=656 bcm2708_fb.fbheight=416 bcm2708_fb.fbswap=1 vc_mem.mem_base=0x1ec00000 vc_mem.mem_size=0x20000000 dwc_otg.lpm_enable=0 console=tty1 root=PARTUUID=509d1565-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles [ 0.000637] console [tty1] enabled [ 0.863147] uart-pl011 20201000.serial: cts_event_workaround enabled [ 0.863289] 20201000.serial: ttyAMA0 at MMIO 0x20201000 (irq = 81, base_baud = 0) is a PL011 rev2
To view the data received from the Arduino Sense, using Minicom, use the following command, substituting the virtual console value, found above.
minicom -b 115200 -o -D /dev/ttyAMA0
If successful, we should see output similar to the lower right terminal window. Data is being transmitted by the Arduino Sense and being received by the Raspberry Pi, via LoRaWAN. In the below example, the AES 128-bit data encryption is not enabled on the Arduino, yet. With encryption turned on the sensor data (the payload) would appear garbled.
IoT Gateway Python Script
To run the Python script on the Raspberry Pi, use the following command, substituting the name of the virtual console (e.g., /dev/ttyAMA0).
python3 ./rasppi_lora_receiver.py \ --tty /dev/ttyAMA0 --baud-rate 115200
The script starts by configuring the RYLR896 and outputting that configuration to the terminal. If successful, we should see the following informational output.
Connecting to REYAX RYLR896 transceiver module... Address set? +OK Network Id set? +OK AES-128 password set? +OK Module responding? +OK Address: +ADDRESS=116 Firmware version: +VER=RYLR89C_V1.2.7 Network Id: +NETWORKID=6 UART baud rate: +IPR=115200 RF frequency +BAND=915000000 RF output power +CRFOP=15 Work mode +MODE=0 RF parameters +PARAMETER=12,7,1,4 AES-128 password of the network +CPIN=92A0ECEC9000DA0DCF0CAAB0ABA2E0EF
Once configured, the script will receive the data from the Arduino Sense, decrypt the data, parse the sensor values, and format and display the values within the terminal.
The following screen recording shows a parallel view of both the Arduino Serial Monitor (upper right window) and the Raspberry Pi’s terminal output (lower right window). The Raspberry Pi (receiver) receives data from the Arduino (transmitter). The Raspberry Pi successfully reads, decrypts, interprets, and displays the sensor data, including displaying color swatches for the RGB and light intensity sensor readings.
Conclusion
In this post, we explored the use of the LoRa and LoRaWAN protocols to transmit environmental sensor data from an IoT device to an IoT gateway. Given its low energy consumption, long-distance transmission capabilities, and well-developed protocols, LoRaWAN is an ideal long-range wireless protocol for IoT devices.
This blog represents my own viewpoints and not of my employer, Amazon Web Services (AWS). All product names, logos, and brands are the property of their respective owners.
BLE and GATT for IoT: Getting Started with Bluetooth Low Energy and the Generic Attribute Profile Specification for IoT
Posted by Gary A. Stafford in C++ Development, Python, Raspberry Pi, Software Development, Technology Consulting on August 4, 2020
Introduction
According to Wikipedia, Bluetooth is a wireless technology standard used for exchanging data between fixed and mobile devices over short distances. Bluetooth Low Energy (Bluetooth LE or BLE) is a wireless personal area network (WPAN) technology designed and marketed by the Bluetooth Special Interest Group (Bluetooth SIG). According to the Bluetooth SIG, BLE is designed for very low power operation. BLE supports data rates from 125 Kb/s to 2 Mb/s, with multiple power levels from 1 milliwatt (mW) to 100 mW. Several key factors influence the effective range of a reliable Bluetooth connection, which can vary from a kilometer down to less than a meter. The newer generation Bluetooth 5 provides a theoretical 4x range improvement over Bluetooth 4.2, from approximately 200 feet (60 meters) to 800 feet (240 meters).
Wikipedia currently lists 36 definitions of Bluetooth profiles defined and adopted by the Bluetooth SIG, including the Generic Attribute Profile (GATT) Specification. According to the Bluetooth SIG, GATT is built on top of the Attribute Protocol (ATT) and establishes common operations and a framework for the data transported and stored by the ATT. GATT provides profile discovery and description services for the BLE protocol. It defines how ATT attributes are grouped together into sets to form services.
Given its low energy consumption and well-developed profiles, such as GATT, BLE is an ideal short-range wireless protocol for Internet of Things (IoT) devices, when compared to competing protocols, such as ZigBee, Bluetooth classic, and Wi-Fi. In this post, we will explore the use of BLE and the GATT specification to transmit environmental sensor data from an IoT Sensor to an IoT Gateway.
IoT Sensor
In this post, we will use an Arduino single-board microcontroller to serve as an IoT sensor, actually an array of sensors. The 3.3V AI-enabled Arduino Nano 33 BLE Sense board, released in August 2019, comes with the powerful nRF52840 processor from Nordic Semiconductors, a 32-bit ARM Cortex-M4 CPU running at 64 MHz, 1MB of CPU Flash Memory, 256KB of SRAM, and a NINA-B306 stand-alone Bluetooth 5 low energy module.
The Sense also contains an impressive array of embedded sensors:
- 9-axis Inertial Sensor (LSM9DS1): 3D digital linear acceleration sensor, a 3D digital
angular rate sensor, and a 3D digital magnetic sensor - Humidity and Temperature Sensor (HTS221): Capacitive digital sensor for relative humidity and temperature
- Barometric Sensor (LPS22HB): MEMS nano pressure sensor: 260–1260 hectopascal (hPa) absolute digital output barometer
- Microphone (MP34DT05): MEMS audio sensor omnidirectional digital microphone
- Gesture, Proximity, Light Color, and Light Intensity Sensor (APDS9960): Advanced Gesture detection, Proximity detection, Digital Ambient Light Sense (ALS), and Color Sense (RGBC).
The Sense is an excellent, low-cost single-board microcontroller for learning about collecting and transmitting IoT sensor data.
IoT Gateway
An IoT Gateway, according to TechTarget, is a physical device or software program that serves as the connection point between the Cloud and controllers, sensors, and intelligent devices. All data moving to the Cloud, or vice versa goes through the gateway, which can be either a dedicated hardware appliance or software program.
In this post, we will use a recent Raspberry Pi 3 Model B+ single-board computer (SBC), to serve as an IoT Gateway. This Raspberry Pi model features a 1.4GHz Cortex-A53 (ARMv8) 64-bit quad-core processor System on a Chip (SoC), 1GB LPDDR2 SDRAM, dual-band wireless LAN, Bluetooth 4.2 BLE, and Gigabit Ethernet. To follow along with the post, you could substitute the Raspberry Pi for any Linux-based machine to run the included sample Python script.
The Arduino will transmit IoT sensor telemetry, over BLE, to the Raspberry Pi. The Raspberry Pi, using Wi-Fi or Ethernet, is then able to securely transmit the sensor telemetry data to the Cloud. In Bluetooth terminology, the Bluetooth Peripheral device (aka GATT Server), which is the Arduino, will transmit data to the Bluetooth Central device (aka GATT Client), which is the Raspberry Pi.
Arduino Sketch
For those not familiar with Arduino, a sketch is the name that Arduino uses for a program. It is the unit of code that is uploaded into non-volatile flash memory and runs on an Arduino board. The Arduino language is a set of C/C++ functions. All standard C and C++ constructs supported by the avr-g++ compiler should work in Arduino.
For this post, the sketch, combo_sensor_ble.ino, contains all the code necessary to collect environmental sensor telemetry, including temperature, relative humidity, barometric pressure, and ambient light and RGB color. All code for this post, including the sketch, can be found on GitHub.
The sensor telemetry will be advertised by the Sense, over BLE, as a GATT Environmental Sensing Service (GATT Assigned Number 0x181A) with multiple GATT Characteristics. Each Characteristic represents a sensor reading and contains the most current sensor value(s), for example, Temperature (0x2A6E) or Humidity (0x2A6F).
Each GATT Characteristic defines how the data should be represented. To represent the data accurately, the sensor readings need to be modified. For example, using ArduinoHTS221 library, the temperature is captured with two decimal points of precision (e.g., 22.21 °C). However, the Temperature GATT Characteristic (0x2A6E) requires a signed 16-bit value (-32,768–32,767). To maintain precision, the captured value (e.g., 22.21 °C) is multiplied by 100 to convert it to an integer (e.g., 2221). The Raspberry Pi will then handle converting the value back to the original value with the correct precision.
The GATT specification has no current predefined Characteristic representing ambient light and RGB color. Therefore, I have created a custom Characteristic for the color values and assigned it a universally unique identifier (UUID).
According to the documentation, ambient light and RGB color are captured as 16-bit values (a range of 0–65,535). However, using the ArduinoAPDS9960 library, I have found the scale of the readings to be within a range of 0–4097. Without diving into the weeds, the maximum count (or saturation) value is variable. It can be calculated based upon the integration time and the size of the count register (e.g., 16-bits). The ADC integration time appears to be set to 10 ms in the library’s file, Arduino_APDS9960.cpp.
RGB values are typically represented as 8-bit color. We could convert the values to 8-bit before sending or handle it later on the Raspberry Pi IoT Gateway. For the sake of demonstration purposes versus data transfer efficiency, the sketch concatenates the 12-bit values together as a string (e.g., 4097,2811,1500,4097). The string will be converted from 12-bit to 8-bit on the Raspberry Pi (e.g., 255,175,93,255).
| /* | |
| Description: Transmits Arduino Nano 33 BLE Sense sensor readings over BLE, | |
| including temperature, humidity, barometric pressure, and color, | |
| using the Bluetooth Generic Attribute Profile (GATT) Specification | |
| Author: Gary Stafford | |
| Reference: Source code adapted from `Nano 33 BLE Sense Getting Started` | |
| Adapted from Arduino BatteryMonitor example by Peter Milne | |
| */ | |
| /* | |
| Generic Attribute Profile (GATT) Specifications | |
| GATT Service: Environmental Sensing Service (ESS) Characteristics | |
| Temperature | |
| sint16 (decimalexponent -2) | |
| Unit is in degrees Celsius with a resolution of 0.01 degrees Celsius | |
| https://www.bluetooth.com/xml-viewer/?src=https://www.bluetooth.com/wp-content/uploads/Sitecore-Media-Library/Gatt/Xml/Characteristics/org.bluetooth.characteristic.temperature.xml | |
| Humidity | |
| uint16 (decimalexponent -2) | |
| Unit is in percent with a resolution of 0.01 percent | |
| https://www.bluetooth.com/xml-viewer/?src=https://www.bluetooth.com/wp-content/uploads/Sitecore-Media-Library/Gatt/Xml/Characteristics/org.bluetooth.characteristic.humidity.xml | |
| Barometric Pressure | |
| uint32 (decimalexponent -1) | |
| Unit is in pascals with a resolution of 0.1 Pa | |
| https://www.bluetooth.com/xml-viewer/?src=https://www.bluetooth.com/wp-content/uploads/Sitecore-Media-Library/Gatt/Xml/Characteristics/org.bluetooth.characteristic.pressure.xml | |
| */ | |
| #include <ArduinoBLE.h> | |
| #include <Arduino_HTS221.h> | |
| #include <Arduino_LPS22HB.h> | |
| #include <Arduino_APDS9960.h> | |
| const int UPDATE_FREQUENCY = 2000; // Update frequency in ms | |
| const float CALIBRATION_FACTOR = –4.0; // Temperature calibration factor (Celsius) | |
| int previousTemperature = 0; | |
| unsigned int previousHumidity = 0; | |
| unsigned int previousPressure = 0; | |
| String previousColor = ""; | |
| int r, g, b, a; | |
| long previousMillis = 0; // last time readings were checked, in ms | |
| BLEService environmentService("181A"); // Standard Environmental Sensing service | |
| BLEIntCharacteristic tempCharacteristic("2A6E", // Standard 16-bit Temperature characteristic | |
| BLERead | BLENotify); // Remote clients can read and get updates | |
| BLEUnsignedIntCharacteristic humidCharacteristic("2A6F", // Unsigned 16-bit Humidity characteristic | |
| BLERead | BLENotify); | |
| BLEUnsignedIntCharacteristic pressureCharacteristic("2A6D", // Unsigned 32-bit Pressure characteristic | |
| BLERead | BLENotify); // Remote clients can read and get updates | |
| BLECharacteristic colorCharacteristic("936b6a25-e503-4f7c-9349-bcc76c22b8c3", // Custom Characteristics | |
| BLERead | BLENotify, 24); // 1234,5678, | |
| BLEDescriptor colorLabelDescriptor("2901", "16-bit ints: r, g, b, a"); | |
| void setup() { | |
| Serial.begin(9600); // Initialize serial communication | |
| // while (!Serial); // only when connected to laptop | |
| if (!HTS.begin()) { // Initialize HTS221 sensor | |
| Serial.println("Failed to initialize humidity temperature sensor!"); | |
| while (1); | |
| } | |
| if (!BARO.begin()) { // Initialize LPS22HB sensor | |
| Serial.println("Failed to initialize pressure sensor!"); | |
| while (1); | |
| } | |
| // Avoid bad readings to start bug | |
| // https://forum.arduino.cc/index.php?topic=660360.0 | |
| BARO.readPressure(); | |
| delay(1000); | |
| if (!APDS.begin()) { // Initialize APDS9960 sensor | |
| Serial.println("Failed to initialize color sensor!"); | |
| while (1); | |
| } | |
| pinMode(LED_BUILTIN, OUTPUT); // Initialize the built-in LED pin | |
| if (!BLE.begin()) { // Initialize NINA B306 BLE | |
| Serial.println("starting BLE failed!"); | |
| while (1); | |
| } | |
| BLE.setLocalName("ArduinoNano33BLESense"); // Set name for connection | |
| BLE.setAdvertisedService(environmentService); // Advertise environment service | |
| environmentService.addCharacteristic(tempCharacteristic); // Add temperature characteristic | |
| environmentService.addCharacteristic(humidCharacteristic); // Add humidity characteristic | |
| environmentService.addCharacteristic(pressureCharacteristic); // Add pressure characteristic | |
| environmentService.addCharacteristic(colorCharacteristic); // Add color characteristic | |
| colorCharacteristic.addDescriptor(colorLabelDescriptor); // Add color characteristic descriptor | |
| BLE.addService(environmentService); // Add environment service | |
| tempCharacteristic.setValue(0); // Set initial temperature value | |
| humidCharacteristic.setValue(0); // Set initial humidity value | |
| pressureCharacteristic.setValue(0); // Set initial pressure value | |
| colorCharacteristic.setValue(""); // Set initial color value | |
| BLE.advertise(); // Start advertising | |
| Serial.print("Peripheral device MAC: "); | |
| Serial.println(BLE.address()); | |
| Serial.println("Waiting for connections…"); | |
| } | |
| void loop() { | |
| BLEDevice central = BLE.central(); // Wait for a BLE central to connect | |
| // If central is connected to peripheral | |
| if (central) { | |
| Serial.print("Connected to central MAC: "); | |
| Serial.println(central.address()); // Central's BT address: | |
| digitalWrite(LED_BUILTIN, HIGH); // Turn on the LED to indicate the connection | |
| while (central.connected()) { | |
| long currentMillis = millis(); | |
| // After UPDATE_FREQUENCY ms have passed, check temperature & humidity | |
| if (currentMillis – previousMillis >= UPDATE_FREQUENCY) { | |
| previousMillis = currentMillis; | |
| updateReadings(); | |
| } | |
| } | |
| digitalWrite(LED_BUILTIN, LOW); // When the central disconnects, turn off the LED | |
| Serial.print("Disconnected from central MAC: "); | |
| Serial.println(central.address()); | |
| } | |
| } | |
| int getTemperature(float calibration) { | |
| // Get calibrated temperature as signed 16-bit int for BLE characteristic | |
| return (int) (HTS.readTemperature() * 100) + (int) (calibration * 100); | |
| } | |
| unsigned int getHumidity() { | |
| // Get humidity as unsigned 16-bit int for BLE characteristic | |
| return (unsigned int) (HTS.readHumidity() * 100); | |
| } | |
| unsigned int getPressure() { | |
| // Get humidity as unsigned 32-bit int for BLE characteristic | |
| return (unsigned int) (BARO.readPressure() * 1000 * 10); | |
| } | |
| void getColor() { | |
| // check if a color reading is available | |
| while (!APDS.colorAvailable()) { | |
| delay(5); | |
| } | |
| // Get color as (4) unsigned 16-bit ints | |
| int tmp_r, tmp_g, tmp_b, tmp_a; | |
| APDS.readColor(tmp_r, tmp_g, tmp_b, tmp_a); | |
| r = tmp_r; | |
| g = tmp_g; | |
| b = tmp_b; | |
| a = tmp_a; | |
| } | |
| void updateReadings() { | |
| int temperature = getTemperature(CALIBRATION_FACTOR); | |
| unsigned int humidity = getHumidity(); | |
| unsigned int pressure = getPressure(); | |
| getColor(); | |
| if (temperature != previousTemperature) { // If reading has changed | |
| Serial.print("Temperature: "); | |
| Serial.println(temperature); | |
| tempCharacteristic.writeValue(temperature); // Update characteristic | |
| previousTemperature = temperature; // Save value | |
| } | |
| if (humidity != previousHumidity) { // If reading has changed | |
| Serial.print("Humidity: "); | |
| Serial.println(humidity); | |
| humidCharacteristic.writeValue(humidity); | |
| previousHumidity = humidity; | |
| } | |
| if (pressure != previousPressure) { // If reading has changed | |
| Serial.print("Pressure: "); | |
| Serial.println(pressure); | |
| pressureCharacteristic.writeValue(pressure); | |
| previousPressure = pressure; | |
| } | |
| // Get color reading everytime | |
| // e.g. "12345,45678,89012,23456" | |
| String stringColor = ""; | |
| stringColor += r; | |
| stringColor += ","; | |
| stringColor += g; | |
| stringColor += ","; | |
| stringColor += b; | |
| stringColor += ","; | |
| stringColor += a; | |
| if (stringColor != previousColor) { // If reading has changed | |
| byte bytes[stringColor.length() + 1]; | |
| stringColor.getBytes(bytes, stringColor.length() + 1); | |
| Serial.print("r, g, b, a: "); | |
| Serial.println(stringColor); | |
| colorCharacteristic.writeValue(bytes, sizeof(bytes)); | |
| previousColor = stringColor; | |
| } | |
| } |
Previewing and Debugging BLE Device Services
Before looking at the code running on the Raspberry Pi, we can use any number of mobile applications to preview and debug the Environmental Sensing service running on the Arduino and being advertised over BLE. A commonly recommended application is Nordic Semiconductor’s nRF Connect for Mobile, available on Google Play. I have found the Android version works better at correctly interpreting and displaying GATT Characteristic values than the iOS version of the app.
Below, we see a scan of my local vicinity for BLE devices being advertised, using the Android version of the nRF Connect mobile application. Note the BLE device, ArduinoNano33BLESense (indicated in red). Also, note the media access control address (MAC address) of that BLE device, in my case, d1:aa:89:0c:ee:82. The MAC address will be required later on the IoT Gateway.
Connecting to the device, we see three Services. The Environmental Sensing Service (indicated in red) contains the sensor readings.
Drilling down into the Environmental Sensing Service (0x181A), we see the four expected Characteristics: Temperature (0x2A6E), Humidity (0x2A6F), Pressure (0x2A6D), and Unknown Characteristic (936b6a25-e503-4f7c-9349-bcc76c22b8c3). Since nRF Connect cannot recognize the color sensor reading as a registered GATT Characteristic (no GATT Assigned Number), it is displayed as an Unknown Characteristic. Whereas the temperature, humidity, and pressure values (indicated in red) are interpreted and displayed correctly, the color sensor reading is left as raw hexadecimal text (e.g., 30-2c-30-2c-30-2c-30-00 or 0,0,0,0).
These results indicate everything is working as expected.
BLE Client Python Code
To act as the BLE Client (aka central device), the Raspberry Pi runs a Python script. The script, rasppi_ble_receiver.py, uses the bluepy Python module for interfacing with BLE devices through Bluez, on Linux.
| import sys | |
| import time | |
| from argparse import ArgumentParser | |
| from bluepy import btle # linux only (no mac) | |
| from colr import color as colr | |
| # BLE IoT Sensor Demo | |
| # Author: Gary Stafford | |
| # Reference: https://elinux.org/RPi_Bluetooth_LE | |
| # Requirements: python3 -m pip install –user -r requirements.txt | |
| # To Run: python3 ./rasppi_ble_receiver.py d1:aa:89:0c:ee:82 <- MAC address – change me! | |
| def main(): | |
| # get args | |
| args = get_args() | |
| print("Connecting…") | |
| nano_sense = btle.Peripheral(args.mac_address) | |
| print("Discovering Services…") | |
| _ = nano_sense.services | |
| environmental_sensing_service = nano_sense.getServiceByUUID("181A") | |
| print("Discovering Characteristics…") | |
| _ = environmental_sensing_service.getCharacteristics() | |
| while True: | |
| print("\n") | |
| read_temperature(environmental_sensing_service) | |
| read_humidity(environmental_sensing_service) | |
| read_pressure(environmental_sensing_service) | |
| read_color(environmental_sensing_service) | |
| # time.sleep(2) # transmission frequency set on IoT device | |
| def byte_array_to_int(value): | |
| # Raw data is hexstring of int values, as a series of bytes, in little endian byte order | |
| # values are converted from bytes -> bytearray -> int | |
| # e.g., b'\xb8\x08\x00\x00' -> bytearray(b'\xb8\x08\x00\x00') -> 2232 | |
| # print(f"{sys._getframe().f_code.co_name}: {value}") | |
| value = bytearray(value) | |
| value = int.from_bytes(value, byteorder="little") | |
| return value | |
| def split_color_str_to_array(value): | |
| # e.g., b'2660,2059,1787,4097\x00' -> 2660,2059,1787,4097 -> | |
| # [2660, 2059, 1787, 4097] -> 166.0,128.0,111.0,255.0 | |
| # print(f"{sys._getframe().f_code.co_name}: {value}") | |
| # remove extra bit on end ('\x00') | |
| value = value[0:–1] | |
| # split r, g, b, a values into array of 16-bit ints | |
| values = list(map(int, value.split(","))) | |
| # convert from 16-bit ints (2^16 or 0-65535) to 8-bit ints (2^8 or 0-255) | |
| # values[:] = [int(v) % 256 for v in values] | |
| # actual sensor is reading values are from 0 – 4097 | |
| print(f"12-bit Color values (r,g,b,a): {values}") | |
| values[:] = [round(int(v) / (4097 / 255), 0) for v in values] | |
| return values | |
| def byte_array_to_char(value): | |
| # e.g., b'2660,2058,1787,4097\x00' -> 2659,2058,1785,4097 | |
| value = value.decode("utf-8") | |
| return value | |
| def decimal_exponent_two(value): | |
| # e.g., 2350 -> 23.5 | |
| return value / 100 | |
| def decimal_exponent_one(value): | |
| # e.g., 988343 -> 98834.3 | |
| return value / 10 | |
| def pascals_to_kilopascals(value): | |
| # 1 Kilopascal (kPa) is equal to 1000 pascals (Pa) | |
| # to convert kPa to pascal, multiply the kPa value by 1000 | |
| # 98834.3 -> 98.8343 | |
| return value / 1000 | |
| def celsius_to_fahrenheit(value): | |
| return (value * 1.8) + 32 | |
| def read_color(service): | |
| color_char = service.getCharacteristics("936b6a25-e503-4f7c-9349-bcc76c22b8c3")[0] | |
| color = color_char.read() | |
| color = byte_array_to_char(color) | |
| color = split_color_str_to_array(color) | |
| print(f" 8-bit Color values (r,g,b,a): {color[0]},{color[1]},{color[2]},{color[3]}") | |
| print("RGB Color") | |
| print(colr('\t\t', fore=(127, 127, 127), back=(color[0], color[1], color[2]))) | |
| print("Light Intensity") | |
| print(colr('\t\t', fore=(127, 127, 127), back=(color[3], color[3], color[3]))) | |
| def read_pressure(service): | |
| pressure_char = service.getCharacteristics("2A6D")[0] | |
| pressure = pressure_char.read() | |
| pressure = byte_array_to_int(pressure) | |
| pressure = decimal_exponent_one(pressure) | |
| pressure = pascals_to_kilopascals(pressure) | |
| print(f"Barometric Pressure: {round(pressure, 2)} kPa") | |
| def read_humidity(service): | |
| humidity_char = service.getCharacteristics("2A6F")[0] | |
| humidity = humidity_char.read() | |
| humidity = byte_array_to_int(humidity) | |
| humidity = decimal_exponent_two(humidity) | |
| print(f"Humidity: {round(humidity, 2)}%") | |
| def read_temperature(service): | |
| temperature_char = service.getCharacteristics("2A6E")[0] | |
| temperature = temperature_char.read() | |
| temperature = byte_array_to_int(temperature) | |
| temperature = decimal_exponent_two(temperature) | |
| temperature = celsius_to_fahrenheit(temperature) | |
| print(f"Temperature: {round(temperature, 2)}°F") | |
| def get_args(): | |
| arg_parser = ArgumentParser(description="BLE IoT Sensor Demo") | |
| arg_parser.add_argument('mac_address', help="MAC address of device to connect") | |
| args = arg_parser.parse_args() | |
| return args | |
| if __name__ == "__main__": | |
| main() |
To run the Python script, execute the following command, substituting the MAC address argument for your own BLE device’s advertised MAC address.
python3 ./rasppi_ble_receiver.py d1:aa:89:0c:ee:82
Unlike the nRF Connect app, the bluepy Python module is not capable of correctly interpreting and displaying the GATT Characteristic values. Hence, the script takes the raw, incoming hexadecimal text from the Arduino and coerces it to the correct values. For example, a temperature reading must be transformed from bytes, b'\xb8\x08\x00\x00', to a byte array, bytearray(b'\xb8\x08\x00\x00'), then to an integer, 2232, then to a decimal, 22.32, and finally to the Fahrenheit scale, 72.18°F.
Sensor readings are retrieved from the BLE device every two seconds. In addition to displaying the numeric sensor readings, the Python script also displays a color swatch of the 8-bit RGB color, as well as a grayscale swatch representing the light intensity using the colr Python module.
The following screen recording shows a parallel view of both the Arduino Serial Monitor and the Raspberry Pi’s terminal output. The Raspberry Pi (central device) connects to the Arduino (peripheral device) when the Python script is started. The Raspberry Pi successfully reads and interprets the telemetry data from the Environmental Sensing Service.
Conclusion
In this post, we explored the use of BLE and the GATT specification to transmit environmental sensor data from a peripheral device to a central device. Given its low energy consumption and well-developed profiles, such as GATT, Bluetooth Low Energy (BLE) is an ideal short-range wireless protocol for IoT devices.
This blog represents my own viewpoints and not of my employer, Amazon Web Services.
Prevent Motion From Running Without a Camera Connected
Posted by Gary A. Stafford in Bash Scripting, Raspberry Pi, Software Development on July 19, 2013
Introduction
If you read my post, Raspberry Pi-Powered Dashboard Video Camera Using Motion and FFmpeg, you know Motion with FFmpeg on a Raspberry Pi makes an ideal dashboard camera system. However, an issue I still struggled with when using the dash-cam was Motion running without a webcam connected.
When I start my car, the Raspberry Pi boots-up, and subsequently, Motion starts. No interaction with the Pi is required. The dash-cam starts capturing images and making the time-lapse video. However, when I get home and plug my Pi back into my local network, Motion starts up again and starts recording blank images and creating the time-lapse video, even though there is no webcam connected.
To get prevent Motion from starting up without a webcam connected, I’ve added a simple function to the Motion startup script. When the system calls Motion on startup, the new function checks if a webcam is connected. If not, it immediately exits the script, without ever starting Motion. No blank images or empty time-lapse videos are created. This saves a lot of wasted processing on the Pi. It also saves a lot of wasted time moving videos and images off the Pi that end up being blank, because no webcam was connected.
Find Your Webcam
First, attach your webcam to the Raspberry Pi. Run the following command to list the USB devices connected to the Pi:
lsusb
You should see similar output to the example below. Note your webcam’s ID(s). I ran the command twice in this example, to identify both of my webca