The IoT has rapidly saturated every industry vertical, introducing wireless sensor networks in order to connect “things” — from everyday objects to large industrial equipment — to the cloud. From 2.4-GHz industrial, scientific, and medical (ISM) protocols such as Bluetooth and Wi-Fi to sub-gigahertz low-power wide-area networks (LPWANs), IoT modules can utilize a variety of RF front ends, modulation techniques, and radio protocols with the specific processing required to fit a particular application. When first attempting to design and implement an IoT module, the level of complexity can rapidly increase between design, optimization, interoperability, compliance, certification, testing, and product release — often while meeting a tight design schedule.
Breakdown of an IoT module
IoT development boards involve several basic facets, including the following:
● Data monitoring (e.g., sensor technologies)
● Data control and storage (e.g., MCU + RAM)
● Radio module (e.g., IoT protocol)
● Power management (e.g., corded, battery-powered, energy-harvesting method)
Each of these parameters comes with their own respective benefits and considerations. Figure 1 shows the basic layout of an IoT module. Development boards attempt to serve these varied interfaces with system-on-chip (SoC) multi-protocol radio modules and an MCU for processing or with more complex processing accomplished by popular MCUs such as the Arduino or by single-board computers such as the Raspberry Pi. Development boards have become the go-to platform for IoT device prototyping for several reasons that will be visited later in this article. Understanding the various IoT protocols and sensing technologies as well as their applications can help an engineer begin their IoT design.
Figure 1: Functional block diagram of an IoT module
Understanding the landscape of IoT protocols
The landscape for IoT protocols is almost as varied as the applications — there is a plethora of protocols to choose from for any particular use case (Figure 2). This can vary between the following major IoT applications:
● Smart home (e.g., video doorbell, smart thermostat, smart speaker);
● Smart city (e.g., smart grid, smart parking, smart lighting, waste management);
● Industrial IoT (e.g., asset/fleet management, process monitoring, predictive maintenance); and
● Smart health (e.g., smartwatch, wearables).
Commonly used protocols for commercial, industrial, and mission-critical health applications have often included cellular (5G, LTE/LTE-A, and 2G/3G-GPS), Wi-Fi/WiMAX, and Bluetooth (BLE) due to their dominance for wireless connectivity and ease of use — the bulk of wirelessly enabled devices readily connects to these wireless networks and therefore does not require the cost of an additional radio module.
Commercial IoT applications have often included the use of wireless personal area networks with Zigbee (IEEE 802.15.4a) and Z-wave. The Zigbee protocol leverages the 2.4-GHz unlicensed ISM band, while Z-wave uses the unlicensed sub-gigahertz, 800-MHz to 900-MHz band. The benefit of using a lower frequency is the lack of interference, as the 2.4-GHz spectrum is used by both Wi-Fi and Bluetooth. Moreover, there is an inherently longer range of a lower-frequency signal due to the longer wavelength of the signal. Regardless of their respective pros and cons, both are commonly used and matured mesh protocols that are often used in smart-home applications. Moreover, many development boards feature a multi-radio platform that is often compatible with both protocols.
A recent contender in niche, low-power, long-range use cases are LPWANs. These typically leverage the sub-gigahertz spectrum as well as specific narrowband (NB) and ultra-narrowband (UNB) modulation schemes. Commonly leveraged LPWANs include LoRa, Sigfox, Weightless, and cellular variants such as NB-IoT and LTE-M. These protocols have dominated applications that transmit small payloads, intermittently, over vast distances — for instance, in oil and gas industrial applications for checking the integrity of an oil pipeline, or in an agricultural application for monitoring the moisture levels of the soil for scheduled watering.
Figure 2: IoT protocols can serve short-, medium-, and long-range applications through the use of gateways, base stations, or satellite connectivity.
Common sensing technologies used in modules and their applications
Data acquisition for wireless sensor networks can include measurements on temperature, humidity, vibration, current, voltage, pressure, liquid level, proximity, airflow, motion detection, light detection, CO2, and VOC. Many development boards will include some of the most commonly used sensors for these measurements, including the following:
● Passive infrared (PIR) (motion) sensor
● GPS/BLE beacons
Smart meters, for instance, will include current or voltage sensors to measure the amount of electricity being supplied to a residence. Motion sensors used in video doorbells as well as in various security/lighting applications will often employ PIR sensors and/or cameras for visual motion detection. Accelerometers can collect vibration data for industrial machines that use motors such as cranes, conveyor belts, or CNC machines. Pressure, level, and airflow sensors often rely on the same underlying principles/technologies. Use cases for these sensors can include, for example, a liquid-level measurement in a tank for a water management, food processing, or pharmaceutical application in which a change in liquid levels can be monitored precisely. Commercial HVAC systems or air-filtration systems would require airflow sensors to adequately monitor incoming and outgoing air. Proximity sensing is often accomplished via GPS; however, BLE beacons can also be leveraged for this purpose in asset-tracking/real-time location systems for medium-accuracy, short-range applications. Fleet management, however, would require more long-range connectivity.
Benefits and considerations of prototyping with a development board
Compliance and certification
Some IoT protocols require compliance and testing to be able to put the IoT device on the market. For instance, Bluetooth requires an extensive qualification process to promote interoperability and ensure compliance with the Bluetooth patent and copyright agreement, the Bluetooth trademark license agreement, and Bluetooth’s specifications. This qualification process requires testing unless a previously qualified Bluetooth end product or subsystem is used. Naturally, the testing process incurs additional cost upon the manufacturer as well as an added time to market of a product. IoT devices leveraging cellular connectivity undergo a certification process in order to ensure the device works accordingly with 3GPP specifications. Different layers of certification can be used, including telecom industry certifications such as Global Certification Forum (GCF) and PTCRB, as well as operator-specific certification (see Figure 3). A pre-certified product is therefore desirable for its cost-effectiveness — the designer is allowed to focus on design, prototyping, and optimization as opposed to an in-depth certification process.
Figure 3: Various levels of certification for cellular-enabled devices
Interoperability and compatibility with the network
As stated earlier, leveraging pre-existing, well-proven SoCs allows for guaranteed interoperability as well as functionality of the radio module. For IoT-based cellular protocols such as LTE-M and NB-IoT, high-performance functionality is required in nominal and extreme deployment scenarios. Interoperability is important to ensure that devices can be configured to function from one region of connectivity to the next, with different network configurations varying based upon local requirements and market conditions. Various network configurations can be leveraged for all of these LTE-M and NB-IoT features to function properly, regardless of the deployment scenario. Bluetooth-qualified chipset interoperability requires that devices connect with grandfathered devices, or devices that do not require a requalification. The majority of Bluetooth vendors are well-acquainted with the software adjustments needed in order to make this work for their Bluetooth devices. Protocols such as LoRa require that the designer purchase vendor-specific chips from Semtech in order to be employed. The various protocols have their own respective considerations that rapidly become very involved and therefore incur a great deal of time and cost to adequately function.
For instance, the design work that goes into the RF front end of a radio module involves not only the selection of the proper antenna for a guaranteed link as a specified distance but also the proper signal chain to go along with it. In development boards, the various subsystems readily interface with commonly used MCUs and interfaces (e.g., USB, HDMI, serial RS232, SIM card, coaxial connector), so the engineer can focus on optimizing the size and connectivity of IoT interaction as opposed to the integrity of the connection and protocol.
Cloud integration and security
In some cases, boards may need to connect directly to the cloud for more enhanced data processing. This may require an IoT device to be able to readily upload data to the cloud. In many IoT applications, this occurs via a gateway in a star topology that is connected via a hardwired Ethernet connection. However, other devices may need to connect to the internet with a Wi-Fi connection. In these cases, multi-protocol development boards with a Wi-Fi module should be considered.
Some iterations of development boards integrate security features such as secure firmware updates, secure storage, tamper detection, payload verification, and a cryptographic engine to add a layer of hardware security to the IoT device. Embedded firmware, keys, and other security-critical assets can be protected through abstraction APIs. These security development boards allow engineers to integrate security into their IoT device at the beginning of the design cycle as opposed to in a later stage of development — a common occurrence when meeting tight design deadlines. Regardless of the IoT application, the IoT marketplace is more or less flooded with options to fit a designer’s prototyping needs.
Development boards: A simplified way to connect sensor data to the cloud
Development boards provide a platform to simplify IoT device prototyping and design. Understanding their benefits, IoT protocols, sensors, and the technologies used by the various dev boards can allow a designer to select the optimal board. Ultimately, these products lower barriers for the design and development of an IoT module, ensuring that the device functions properly.
