Sensors are the most important components of the internet of things. They are used to collect data from the physical world and send it to the cloud for analysis. Sensors enable IoT devices to measure temperature, humidity, pressure and other environmental conditions. They also help in monitoring activities like motion detection, facial recognition and sound detection. Sensors are also used in smart homes and smart cities to remotely control and monitor their activities, improving efficiency and safety. The use of sensors in the IoT is expected to grow exponentially in the coming years as more users and municipalities adopt them in their environments.
IoT sensors in the smart home
Unlike traditional homes, where electronic devices operate independently of each other, in a smart home, there is an infrastructure that connects all the sensors and can access the internet via dedicated routers or radio modules.
The introduction of an automation system allows remote control and monitoring of connected devices, resulting in less need for human interaction, while providing increased comfort, safety and energy efficiency, which in turn helps to reduce the carbon footprint.
Sensors used in a smart home can perform a variety of functions, including:
• Presence detection: These sensors have the task of detecting the presence and movement of people or animals within their coverage area. Two main technologies are used to implement these sensors: passive infrared (PIR) and microwave (MW). The former are passive sensors that detect presence by measuring the heat emitted by a body. For this purpose, the sensor uses specific materials (such as gallium nitride, cesium nitrate and polyvinyl fluoride) that generate energy when exposed to heat. Even though PIR technology has evolved—for instance, introducing temperature compensation—it still has limitations that can cause false detections. MW sensors, on the other hand, are active devices and use a high-frequency signal (some in the gigahertz range) that is radiated along the sensor coverage area. Using the same operating principle as radar, these sensors have both a transmitter and a receiver. Based on the Doppler effect, these sensors detect presence by measuring the variation in the frequency of the received signal, compared with the transmitted one. This technique is very reliable and is not affected by temperature.
• Lighting control: Using presence-detection sensors, the lights can be turned on or off only when the rooms are occupied, saving energy. Furthermore, current lighting systems allow users to dim the brightness or even change the temperature of the light (color of the light). With a smart-home system, it is possible to control each lamp individually or divide them into groups according to the user’s needs, program the on and off times and define customized lighting profiles.
• HVAC monitoring: Using smart thermostats, it is possible to program the on/off switching of the heating or air conditioning unit based on the current temperature, on the presence of people in the home or at a specific time. In the case of radiator heating, the use of thermostatic valves equipped with a wireless interface makes it possible to customize the use of each heating unit, heating only when and where it is desired.
• Security system: This category ranges from the simplest sensors, such as presence detectors and reed contacts applied to doors and windows, to remote-controlled dome cameras and video surveillance systems. In addition to burglar alarm systems, sensors for detecting gas, flames or water leaks play an important role, as they are capable of sending an alert notification when a potentially dangerous event occurs.
• Weather sensors: Special sensors capable of detecting rainfall intensity, humidity and wind speed are essential for the management of garden irrigation systems. They can also automatically retract awnings and lower the shutters.
• Power sensors: A wireless smart socket connected to each power device (household appliances, air conditioners, washers, dryers, dishwashers, etc.) allows users to monitor both instantaneous power consumption and analyze historical data, helping them to identify any energy inefficiencies in their home and to reduce energy waste. To manage all of these functions most efficiently and reliably as possible, integrated solutions are now available that simplify the design process, also reducing the time to market. A general-purpose example is shown in Figure 1. A system-on-chip integrates all the required functionalities: wireless connectivity, memory (flash and RAM), security engine, analog-to-digital converter and I/O signals.
Figure 1: Block diagram of a general smart-home sensor (Source: Silicon Labs)
An appropriate signal-conditioning circuit allows for the interface with analog sensors by performing the required signal amplification, sampling and filtering processing. Devices are available today that comply with the Wi-Fi 6 standard or are equipped with a BLE, sub-gigahertz or even LoRa radio interface. Devices of this type can guarantee operation for 10 years, powered by a normal coin-cell battery.
Matter protocol
According to a McKinsey & Company study, by 2030, the potential economic value of the IoT is expected to reach up to $12.6 trillion. Such a huge amount of IoT devices and services poses design challenges related to security and interoperability. This need led to the birth of the Connectivity Standards Alliance (formerly the Zigbee Alliance), which released the Matter 1.0 standard.
The foundation of the Matter project is a shared conviction that smart-home appliances, such as thermostats, lightbulbs and smart TVs, should be safe, dependable and easy to use. To streamline development for manufacturers and boost the compatibility of various IoT devices for customers, Matter was developed to be a global IoT standard focused on the application layer.
IoT and the smart city
Applied to the wider scenario of a smart city, IoT sensors can monitor air quality, noise and water pollution. For example, these sensors can monitor soil moisture to ensure that parks and gardens are watered efficiently, cutting down on waste and unplanned maintenance.
Typical use cases in smart cities include the following:
• Street lighting: Smart cities can quickly and efficiently identify outages, broken lights and supply interruptions. Security in metropolitan areas can be increased, while the safety of walkers, cyclists and other road users is achieved by strategically regulating illumination. Utilizing real-time data analytics and usage tracking, smart-lighting solutions assist towns in energy conservation and safety enhancement.
• Waste management: Understanding bin status enables city service providers to respond to fill levels in real time, which prevents containers from spilling over and creating litter. It also enables more effective garbage collection and lowers needless pickups of half-empty bins, saving fuel and lowering pollution.
• Traffic and parking management: Parking spaces are better monitored and controlled, resulting in increased revenue by helping parking providers adjust prices to reflect actual usage patterns. The city can keep an eye on “no parking” areas to guarantee that emergency services like fire, police and ambulances always have access. With connected cars and intelligent parking solutions, IoT sensors increase safety and decrease traffic congestion. Real-time data is gathered by sensors and shared with local authorities and drivers. In addition to providing information on parking availability and the best routes to take, it also activates traffic warnings.
An example smart-lighting solution is the smart pole for a college campus shown in Figure 2. Besides providing highly efficient lighting, this device can meet a variety of requirements of a smart city, including environmental sensors, emergency phone and security camera. Smart poles from Valmont Industries Inc., in combination with Digi International Inc.’s wireless communications devices, enable a variety of smart features from turning lights on and off with changing environmental conditions to security cameras for real-time visibility for safety.
Figure 2: Valmont smart-pole project for a university campus (Source: Digi International Inc.)
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