Connected Complexities
The IoT has been with us long enough now that it’s easy to think we know everything about it. But designing an IoT product is vastly different from other electronic products. Just the presence of wireless components adds new layers of complexity in terms of testing certifications, PCB design and other hurdles. In this article, Nishant discusses these and other challenges embedded system developers can face during the design cycle of an IoT product.
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The intersection of the Internet and wireless technology has changed significantly with the advancement of embedded systems, optical fiber and VLSI. The term Internet of Things (IoT) has gained tremendous momentum as convexity technologies continue to proliferate—including FTH (fiber to home) technology, Li-Fi (light fidelity), Wi-Fi, Bluetooth, voice-controlled beaming devices and many others. That’s driven engineers across a wide variety of market segments to create innovative products for the IoT.
All that said, the system design process of an IoT product is vastly different compared to other electronic products. Every part of an IoT design—including hardware, software, testing and certification—are more difficult simply due to the presence of wireless components on board. Such components increase the design challenges tenfold and adds time-to-market pressures. In this article, I’ll talk about all these hurdles engineers can face during the design cycle of an IoT product.
IoT vs. NON IoT DESIGN
To better understand the difference between an IoT and non-IoT product, let’s examine a use case. Consider a home automation example. Family A has a home automation system that provides a variety of functions. The user has an IR remote that controls switching lights on and off. It has an infrared sensor that detects the presence and absence of people, and switches lights on or off accordingly. There is an entry door, which is controlled using a switch connected using wire through the walls to the bedroom to open the door. Note that in this example that most of the automation is done either wired point-to-point or using analog or digital sensors. It involves no wireless technologies or the Internet.
Now let’s consider an example where Family B has a home automation system where the user controls the light using an android phone that has a Bluetooth transmitter. There are sensors used to detect entries to home. Entries to the home are tracked and emailed to the owner using Wi-Fi technology. The homeowner can use the Internet to switch off the lights in the home even when he or she is several miles away. And, last but not the least, the homeowner can even use voice commands to control the lights. This is a typical example of an IoT product. We’ll be discussing the more technical aspects of such products as we go.
DESIGN AND CHALLENGES
Let’s look closer at the design of an IoT-based home automation system. Figure 1 shows the block diagram of the probable system for an Internet connected home. A typical home automation system consists of a controller which provides Bluetooth or Wi-Fi functionality. For our example, I’ve selected a Cypress Semiconductor PSoC 6 microcontroller (MCU) BLE with Wi-Fi module on-chip. Although I’ve selected this device, it’s very important to understand the budget requirements of an implementation. The Cypress PSoC 6 comes packed with Bluetooth built-in, but it comes at a cost. There are other low-cost solutions—including an MCU combined with an external Bluetooth module. Either way, the selection of this central controller device is very important because it affects the system’s power requirements, interfacing capabilities, feature sets and number of external components required.
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Choosing the controller even involves knowing the scope of the interfaces and applications of the system. For example, if the requirement is to only control a light, then a smaller solution could be used—interfaced with a Bluetooth module and then controlled using a relay. In our use case, we’re looking at a system that has a lot of interfaces along with Wi-Fi. As a result, we need a somewhat complex controller that can handle wireless as well as ADCs and DACs for sensors processing. Because the PSoC MCU also has elements like all the required analog and digital components built in, it is quite cost effective for our use case.
All that said, as a system designer, we need to consider the question of whether such a powerful device is really required? You could go for a simpler Atmel chip powered by Arduino with some basic relays and a cheaper Bluetooth module and Wi-Fi module. It all comes down to budget vs. the requirements.
Up until now we were only talking about the board that we’re designing to integrate into our home automation system. Beyond this, there are multiple subsystems to be integrated in order to make a home automation a true IoT-powered system. For instance, to implement a computer vision-controlled system to track humans, we could integrate the system with Xilinx’s Ultra96 board. The Ultra96 is an Arm-based, Xilinx Zynq UltraScale+ MPSoC development board based on the Linaro 96Boards specification. Because we want a completely real-time system, using an AI-based, trained real-time solution to detect a variety of stuff could be a game changer. With that in mind, we would connect the Xilinx Ultra96 board with intel’s Movidius device which has a VPU to train the system real time. Figure 2 shows a typical connection of the two systems.
PCB DESIGN CHALLENGES
A board design containing wireless components must follow very restricted guidelines. A poor PCB design could cause radiation from traces to interfere with the analog components onboard causing lot of noise interference. Moreover, a bad PCB design of a wireless system could fail to pass radiation certifications.
A typical PCB could look like as shown in Figure 2. At minimum, the board design would have the MCU (PSoC BLE) as close to the antenna as possible. To provide power, there is a regulator circuit localized on one side. We have added some WS2812 LEDs in several places around the board’s edge for aesthetic purposes (to light up the unit when operating, for example). Beam microphones are placed in multiple directions so that an audio response system can be implemented by the system. Such an added feature could be replaced with an Alexa device to avoid the need for additional complex coding. There are also motor control circuits for controlling various areas of house like doors or relays or switches.
There are few guidelines that should be reviewed when designing a PCB with a radiating element. An antenna designed into a PCB is generally a quarter-wave antenna. A quarter-wave antenna looks something like what’s shown in Figure 3. These types of antennas take up less space than external antennas. While these aren’t the best antennas in terms of omnidirectional radiation patterns, they solve many problems in terms of design and interference. Placement of these antennas is a very important factor in determining what your radiation pattern will look like. The PCB antenna should be placed on the edge of the PCB for the least interference with the neighboring components or the rails. Antennas should be far off the ground plane because the ground attracts a lot of the radiation, causing the Bluetooth range to be reduced, for example.
For these applications, a Meandered Inverted-F Antenna (MIFA) or a Planar Inverted-F antenna (PIFA) are the two most recommended antennas because they are designed using multiple turns—which helps in achieving a lambda-by-4 value (λ/4) in a smaller space. There are even guidelines for the height an antenna or a Bluetooth module, which should be above the PCB’s surface. The deeper details of this subject are outside the scope of this article. But NXP Semiconductors provides a document called “RF Design Considerations for 802.15.4 Hardware Development” [1] which gives a good short training tutorial on designing antennas on PCBs. A link is provided in RESOURCES at the end of the article.
Once the hardware design is complete, it’s important to analyze the power budgeting of the system—especially given that Bluetooth consumes a lot of power. For a battery-powered application, such power “sponges” could be dangerous on a board. Software should be written such that the Bluetooth circuitry is used only when required and is placed in a deep sleep mode the rest of the time. Reserving Bluetooth for burst transfers could help with lowering power consumption and extending battery life.
TESTS AND CERTIFICATIONS
Testing and certification are important parts of the process of designing any product related to IoT. Any board that has a wireless component—or any radiating component—must undergo strict certification processes before they are permitted to be sold in different parts of the world. These certification rules may vary from continent to continent or even from country to country. Aside from being a tedious process, this requires a good amount of cost—costs that the system designer should include when planning budgets for their circuit designs. For any Bluetooth module or chip present onboard, several certifications are required—from the FCC (for the US), CE (for European countries), IC (for Canada) and the list goes on.
To provide the setup for certification, special preparations must be done. Certification companies provide specifications to help you configure your board design so that the certification process is easier—for example, they may require you to make all the pins high impedance so that only the radiating element is the Bluetooth circuitry. They could also ask you to program certain behaviors of code so that they can more easily test for expected results. You may also have to provide some visualization components like LEDs, an LCD or some other device to indicate operations. Those are needed because these setups are tested for EMI and EMC in a radiative environment. They generally keep a camera in the setup room and then track the activities that occur because of radiation and how the radiation affects operation. Other certifications are needed for boards containing a Wi-Fi—such as WPA2 (Wi-Fi Protected Setup) and WMM (Wi-Fi Multimedia) to name a few.
Apart from these mandatory tests required for selling the products, there are many others that are necessary for ensuring the safety of the customer. Among these are Head SAR and Body SAR calculations, which measure the amount of radiation that can penetrate from the device to the human body. There are maximum limits allowed that are set by responsible bodies. Selling products that exceed such limits could be declared illegal.
Performance testing is another pillar of testing that’s important. In this article, I won’t discuss about how to test for error free performance of a board. I have discussed that in my previous articles on manufacturing tests including “Designing Manufacturing Test Systems” (Circuit Cellar 352, November 2019) [2] and “System Controller Manufacturing Test (Part 1 and Part 2) (Circuit Cellar 354 and 355, January and February 2020) [3] [4].
If there are wireless components like Bluetooth on a board, it follows that it also has a radiating antenna. A properly designed antenna should give a uniform lobe and should ideally have an omnidirectional radiation pattern. It should have practically a circular loop in one direction and non-uniform lobe against that direction. This can be tested using an anechoic chamber with one side containing a transmitter that has a rotating handle. The other side has a receiver antenna. The transmitter antenna rotates 360 degrees at a certain speed. The receiver gets the signal and plots the radiation pattern. This is an effective way of testing and designing a good performance antenna. Figure 4 shows one of such setup [5].
With advancement in technology comes lot of responsibility for engineers and system designers—responsivities to society, to nature and to the environment. Electronic waste and radiation have been ongoing concerns with regard to the environment. Radiation is known to have affected a lot of wildlife and bird life. Proper limits to electromagnetic radiations should be taken into concern. It is true that more radiation will provide better performance for the user, but it comes at the cost of environmental troubles. Meanwhile, electronic waste accumulations add a lot of cancerous and non-renewable agents to environment. With that in mind, we should be responsible engineers while making prototypes as well, and not create unnecessary prototype units.
CONCLUSION
In this article, we explored the key factors in designing an IoT product—challenges in design lifecycle, production challenges, testing and certifications. Such IoT designs can be complemented with multiple sensors, gesture recognition and so on. The innovations that are possible are beyond the limits of imagination. While doing so, we need to be responsible for how our designs affect and interact with the environment. We also examined the cost challenges as well as the important testing strategies required to create the ideal IoT board/product.
Editor’s Note: All Circuit Cellar articles from 1988 to present can be found on the CC Vault, a pocket-sized USB available from
www.cc-webshop.com. 
RESOURCES
References:
[1] RF Design Considerations for 802.15.4 Hardware Development
https://www.nxp.com/files-static/training_pdf/WBNR_FTF10_ENT_F0515.pdf
[2] “Designing Manufacturing Test Systems” (Circuit Cellar 352, November 2019)
[3] “System Controller Manufacturing Test (Part 1)” (Circuit Cellar 354, January 2020)
[4] “System Controller Manufacturing Test (Part 2)” (Circuit Cellar 355, February 2020)
[5] Figure 4. Anechoic chamber setup (Image Courtesy: http://www.antenna-theory.com/measurements/antenna.php )
Cypress Semiconductor | www.cypress.com
Intel | www.intel.com
NXP Semiconductors | www.nxp.com
Xilinx | www.xilinx.com
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • JULY 2020 #360 – Get a PDF of the issue
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Nishant Mittal is a Hardware Systems Engineer in Hyderabad, India.
