Packt+ | Advance your knowledge in tech

You're reading from Hands-On Embedded Programming with C++17

Product typeBook

Published inJan 2019

Reading LevelIntermediate

PublisherPackt

ISBN-139781788629300

Edition1st Edition

Languages

C++

Tools

Concepts

Embedded Systems

Author (1)

Maya Posch

Chapter 9. Example - Building Monitoring and Control

The monitoring of conditions within a building, including the temperature, humidity, and CO₂ levels is becoming increasingly more common, with the goal being to adjust heating, cooling, and ventilation systems to keep the occupants of the building as comfortable as possible. In this chapter, such a system is explored and implemented. The following topics will be covered:

Creating complex firmware for the ESP8266
Integrating an MCU into an IP-based network
Adding CO₂ and I2C-based sensors
Using GPIO and PWM to control relays and DC voltage-controlled fans
Connecting networked nodes using a central controller

Plants, rooms, and beyond

In Chapter 5, Example - Soil Humidity Monitor with Wi-Fi, we looked at developing firmware for the ESP8266 MCU to complement a soil humidity sensor and pump, to ensure that a connected plant would be provided with sufficient water from the water tank.

As we noted in that chapter, the firmware used is highly modular and has the highly flexible MQTT-based interface so that it can be used for a wide variety of modules. This chapter covers the system in which the firmware originated: Building Management and Control (BMaC), originally developed just to monitor rooms for their temperature, humidity, and CO² levels, but later expanded to keep tabs on coffee machines and meeting room occupancy, and ultimately to control the air-conditioning throughout the building.

The BMaC project's current development status can be found at the author's GitHub account at https://github.com/MayaPosch/BMaC. The version we are covering here is as it exists at this point, with us covering...

Developmental history

The BMaC project started when sensors were to be added around an office building in order to measure temperature and other parameters, such as relative humidity. After deciding to use ESP8266 MCUs along with DHT22 temperature and humidity sensors, a simple prototype was put together, using a basic firmware written using the Sming framework.

It was found that DHT22 sensors were generally rather bulky and not very precise. The breakout boards used also had an improper resistor mounted on them, leading to the wrong temperature being reported. This sensor type also had the disadvantage of using its own one-wire protocol, instead of a standard interface method.

The DHT22 sensors got swapped out with BME280 MEMS sensors, which measure temperature, humidity, and also air pressure. A CO₂ sensor was added as well, in the form of the MH-Z19. This required the firmware to support these additional sensors too. The sensor readings would be sent as MQTT messages, with a backend service...

Functional modules

Here is a list of modules in this firmware:

Firmware source

In this section, we look at the source code for the ESP8266 firmware as used with the BMaC system.

Core

The core of the firmware we already looked at in Chapter 5, Example - Soil Humidity Monitor with Wi-Fi, including the entry point, the OtaCore class, and the BaseModule class, which provide all of the functionality needed to make individual modules initialize and to allow them to be enabled and disabled using the MQTT interface.

Modules

Of the firmware modules, we already looked at the plant module inChapter 5, Example - Soil Humidity Monitor with Wi-Fi. Here we will look at the remaining modules, starting with the THP module:

#include "base_module.h"
class THPModule {
    public:
    static bool initialize();
    static bool start();
    static bool shutdown();
};
#include "thp_module.h"
#include "dht_module.h"
#include "bme280_module.h"
bool THPModule::initialize() {
    BaseModule::registerModule(MOD_IDX_TEMPERATURE_HUMIDITY, 
    THPModule::start, THPModule::shutdown);...

Command and control server

As alluded to earlier in this chapter, a so-called command and control (C&C) server is essentially a database containing information on individual nodes and their configuration, for use by the nodes themselves and administration tools like the one in the next section.

It also includes an HTTP server, for use with HTTP-based over-the-air (OTA) updates. Since the BMaC system is MQTT-based, this server is also written as an MQTT client:

#include "listener.h"  
#include <iostream> 
#include <string> 
 
using namespace std; 
 
#include <Poco/Util/IniFileConfiguration.h> 
#include <Poco/AutoPtr.h> 
#include <Poco/Net/HTTPServer.h> 
 
using namespace Poco::Util; 
using namespace Poco; 
using namespace Poco::Net; 
 
#include "httprequestfactory.h" 
  
int main(int argc, char* argv[]) { 
   cout << "Starting MQTT BMaC Command & Control server...\n"; 
    
   int rc; 
   mosqpp::lib_init(); 
    
   cout << "Initialised C+...

Administration tool

Using the APIs implemented by the C&C server, a GUI-based administration tool was created using the Qt5 framework and the Mosquitto MQTT client library was developed, allowing for the basic management of nodes. They were overlaid on top of a layout graphic of buildings.

While basically usable, it was found that a graphical tool was fairly complicated to develop. It was also limited to a single floor of a building, unless one were to have a really large map containing all of the floors with the nodes mapped onto this. This would have been quite clumsy, obviously.

In the source code provided with this chapter, the administration tool can be found as well, to serve as an example of how one could implement it. For the sake of brevity, the code for it has been omitted here.

Air-conditioning service

To control air-conditioning units, a service much like the C&C one was developed, using the same basic template. The interesting parts of its source are the following:

#include <string>
 #include <vector>

 using namespace std;

 #include <Poco/Data/Session.h>
 #include <Poco/Data/SQLite/Connector.h>

 #include <Poco/Net/HTTPClientSession.h>
 #include <Poco/Net/HTTPSClientSession.h>

 #include <Poco/Timer.h>

 using namespace Poco;
 using namespace Poco::Net;

 class Listener;


 struct NodeInfo {
    string uid;
    float posx;
    float posy;
    float current;    
    float target;
    bool ch0_state;
    UInt8 ch0_duty;
    bool ch0_valid;
    bool ch1_state;
    UInt8 ch1_duty;
    bool ch1_valid;
    bool ch2_state;
    UInt8 ch2_duty;
    bool ch2_valid;
    bool ch3_state;
    UInt8 ch3_duty;
    bool ch3_valid;
    UInt8 validate;
 };


 struct ValveInfo {
    string uid;
    UInt8 ch0_valve;
    UInt8 ch1_valve...

InfluxDB for recording sensor readings

Recording the sensor readings and later the statistics read from the coffee machines was a priority from the beginning. The ideal database for this kind of data is a time series database, of which Influx is a common one. The biggest problem with this database is that it does not support MQTT, only offering its HTTP and native interface.

To fix this, a simple MQTT-to-Influx HTTP line protocol bridge was written, again using the Mosquitto client library as well as the POCO framework's HTTP functionality:

#include "mth.h"

#include <iostream>

using namespace std;

#include <Poco/Net/HTTPRequest.h>
#include <Poco/Net/HTTPResponse.h>
#include <Poco/StringTokenizer.h>
#include <Poco/String.h>

using namespace Poco;


MtH::MtH(string clientId, string host, int port, string topics, string influxHost, 
                int influxPort, string influxDb, string influx_sec) : mosquittopp(clientId.c_str()) {
    this->topics  = topics...

Security aspects

During the development of this system it became soon obvious that security would be a paramount aspect of the system. For that reason we looked at adding transport layer security (TLS) encryption. This would use the integrated axTLS encryption library in the Sming framework together with AES certificates (host and client) to provide both verification that the host (servers) and clients (nodes) are who they say they are, but also provide a secure encrypted link.

In Chapter 5, Example - Soil Humidity Monitor with Wi-Fi, we already looked at the handling of these client certificates and setting up of an encrypted MQTT connection. One detail which is not obvious from that were the troubles which we encountered while setting up this certificate system. As mentioned in Chapter 5, Example - Soil Humidity Monitor with Wi-Fi, the ESP8266 does not have enough memory to allocate the default TLS handshake buffers and requires the use of the SSL fragment size extension on the side of...

Future developments

There are still many additions that can be made to this system. From the number of sensors that could be supported, further GPIO expander chips, air-conditioning system configurations, room occupancy detection linked into a calendar backend, to clearing out scheduled meetings at an office where nobody showed up, and so on.

There is also the option of switching from ESP8266 as the MCU to a different one, such as ARM-based MCUs, to get wired Ethernet options, along with better debug and development tools. As convenient as it is to have an MCU with Wi-Fi, which one can just stick anywhere and theoretically have it work, the development tools for the ESP8266 aren't that great, and the lack of wired communication options (without using external chips) means that everything either works or doesn't depending on the quality of the Wi-Fi network.

As BMaC involves the automation of a building, it is desirable to have a certain level of reliability, which is hard to guarantee with...

Summary

In this chapter, we looked at how a building-wide monitoring and management system was developed, what its components looked like, and what lessons were learned during its development.

The reader is expected to understand now how such a large-scale embedded system is constructed and functions, and should be able either to use the BMaC system themselves or implement a similar system.

In the next chapter we will look at developing embedded projects using the Qt framework.

The rest of the chapter is locked

You have been reading a chapter from

Hands-On Embedded Programming with C++17

Published in: Jan 2019Publisher: PacktISBN-13: 9781788629300

A free Packt account unlocks extra newsletters, articles, discounted offers, and much more. Start advancing your knowledge today.

undefined

Unlock this book and the full library FREE for 7 days

Get unlimited access to 7000+ expert-authored eBooks and videos courses covering every tech area you can think of

Start free trial

Renews at $15.99/month. Cancel anytime

Author (1)

Maya Posch

Maya Posch is a senior C++ developer with more than 15 years of experience. Discovering the joys of programming early on, and later the joys of electronics, she has always expressed a profound interest in technology, a passion that she gladly shares with others. Describing herself as a C developer who happens to like C++ and Ada, she likes to seek the limits of what can be done with the minimum of code and hardware to accomplish everything that is cool, new, and exciting. She also enjoys FPGA development, AI, and robotics research, in addition to creative writing, music, and drawing.
Read more about Maya Posch

Other recommended products

Related to this chapter

ESP8266 Home Automation Projects

The ESP8266 is a low-cost yet powerful Wi-Fi chip that is becoming more popular at an alarming rate, and people have adopted it to create interesting projects. This book shows readers how to build autonomous home automation projects, create entire home automation systems, and monitor/access their homes from the cloud. You will learn how to read values from sensors, how to send them to your cloud platform over Wi-Fi, and how to receive them on your mobile application.

BookNov 2017196 pages

Hands-On RTOS with Microcontrollers

This book covers important real-time operating systems concepts used in microcontroller-based embedded systems. You will use an STM32 board, SEGGER debugging tools, and STM32Cube IDE to build and analyze real-world embedded projects. After completing this book, you will have gained advanced techniques to implement robust real-time embedded systems.

BookMay 2020496 pages

Developing IoT Projects with ESP32

ESP32 is a low-cost, low-power MCU series by Espressif systems that can be used in wireless IoT applications. With Wi-Fi and Bluetooth technologies as well as security features, it's a full-fledged SoC for developing IoT products for consumer and industrial markets. This book will help you get up to speed with ESP32 using interesting projects.

BookSep 2021474 pages

Mastering C++ Multithreading

Multithreaded applications execute multiple threads in a single processor environment, allowing developers achieve concurrency. Moden day programming requires data to be fetched at incredible speed. Multithreading allows developers to deal with asynchronous data so their programming needs are met. This book will teach you the finer points of multithreading and concurrency concepts and how to apply them efficiently in C++.

BookJul 2017244 pages

Architecting High-Performance Embedded Systems

This book takes embedded system developers through the complete process of developing systems based on field-programmable gate arrays (FPGAs). You’ll not only understand the concepts underlying embedded systems and FPGAs but also explore the powerful free FPGA tools to design electronic circuits and construct and debug prototype embedded devices.

BookFeb 2021376 pages4

Embedded Programming with Modern C++ Cookbook

This book is a collection of practical examples for understanding how embedded development is different from other desktop application development. You’ll learn to build an embedded application and use specialized memory and custom allocators. By the end of the book, you’ll be able to build robust and secure embedded applications with C++20.

BookApr 2020412 pages

Embedded Systems Architecture

Embedded systems are self-contained units that have a dedicated purpose within a device. We come across a variety of applications of embedded systems in navigation tools, telecom applications, and networking equipment, to name just a few. This book will help you create your own parallel and distributed embedded systems.

BookMay 2018324 pages

Practical Hardware Pentesting

Hardware security has become a major concern in recent times making it crucial for companies and end users to focus on protecting hardware. If you’re a security practitioner who is more familiar with software and binary hacking or someone looking to repurpose devices, this book will demonstrate how to approach hardware hacking of embedded devices.

BookApr 2021382 pages

Personalised recommendations for you

Based on your interests and search pattern

Architectural Patterns and Techniques for Developing IoT Solutions

This book covers all the patterns and considerations that give you both the power and flexibility to build scalable, secure, and performant IoT solutions by combining various patterns in interesting ways. It also lists the benefits of combining IoT with technologies like blockchain, 3D-printing, 5G, Generative AI, quantum computing, and LLMs.

BookSep 2023304 pages

Arduino Data Communications

Arduino Data Communication focuses on IoT’s Internet aspect, guiding you in setting up your own infrastructure for storing and managing the data collected from sensors. This book goes beyond microcontroller basics, equipping you with the knowledge essential for building real-world projects.

BookNov 2023286 pages5

Arduino IoT Cloud for Developers

From fundamental principles to advanced techniques, this comprehensive book equips you with the knowledge and skills needed to design and deploy IoT applications seamlessly. Explore cloud integration, best practices, and real-world projects to harness the full potential of IoT application development with the Arduino IoT Cloud.

BookNov 2023402 pages

The Azure IoT Handbook

Building IoT Systems with Azure IoT is a comprehensive introduction for those who are new to the Internet of Things and looking to get up to speed in no time. This book will teach you how to create and develop IoT solutions with intelligent edge-to-cloud technologies in the Azure cloud.

BookDec 2023248 pages

Name	Feature	Description
THP	Temperature, Humidity, Pressure	Central class for THP sensors. Enables BME280 functionality by default.
CO₂	CO₂ value	Measures CO₂ <indexentry content="functional modules, Building Management and Control (BMaC):CO₂">values using an MH-Z19 or compatible sensor.
Jura	TopTronics EEPROM counters	Reads out the counters for various products from the EEPROM.
JuraTerm	TopTronics remote control	Allows a remote service to send TopTronics (classic, v5-style) commands to a supported coffee machine.
Motion	Motion detection	Uses an HC-SR501 PIR motion sensor or compatible to detect motion.
PWM	PWM output	Sets a pulse-width modulation output on one or more pins.
I/O	I/O expansion	Supports the MCP23008 eight-channel I/O expander module via I2C.
Switch	Persistent switch	Controls a switch that uses a latching relay or equivalent for switching.
Plant	Watering plants	Reads out an analog soil sensor to determine soil humidity, activating a pump...