Many new designers love to use microcontroller modules and Wi-Fi modules to build their designs. Some of the most popular microcontroller boards and modules are Arduino, ESP32 and STM32, to name but a few. There are many other modules that have become popular recently, such as the RP2040 microcontroller. Modules aren't limited to Wi-Fi and Bluetooth; there are also single-board computer modules that can plug into a main board with a variety of circuitry. No matter which module you prefer, modules are very convenient for designers and can eliminate some of the design risks.
While it is true that modules eliminate some of the design risk from a system, EMC is still a major concern in module-based systems. Depending on what goes onto the main board for your system, there is still no guarantee that your design will pass EMC testing. Here are some of the advantages and disadvantages of using microcontroller modules or other modules to build a new electronic system.
EMC myths
Some of the most popular microcontroller modules or IoT modules are found in hobby projects, student projects and commercial systems. Just because a module is popular with hobbyists or students doesn't mean that it is kept out of the commercial or industrial space. Indeed, some vendors produce versions of their modules specifically for these application areas. As long as the rest of the system is designed accordingly, modules can be reliable options for building an IoT product or embedded computing products.
Some of the popular modules used in these areas include:
- ESP32 (Espressif Systems)
- STM32 (ST Microelectronics)
- RP2040 Dev Boards (Raspberry Pi)
- Atmel MCUs (Arduino)
These modules can include many useful features, such as Wi-Fi, Bluetooth, 10/100 Ethernet, USB and serial protocols or pin headers. Many designers will make their data open source, and there is plenty of vendor support for application developers, so it's no surprise that there has been significant adoption of these products, especially by students.
Although these modules are very popular with hobbyists and students, commercial products using these modules must still pass EMC testing before products can be sold at volume. Module pre-certification is not sufficient for guaranteeing successful EMC testing.
There are a few major factors that will impact a system's EMI test results:
- Design of the enclosure and its level of electromagnetic leakage
- Connector transitions from the module to the main board
- PCB stack-up and trace routing on the main board
- Power distribution scheme and circuit design of the power regulator
Product designers who get these aspects of the design correct are more likely to pass EMC testing for the entire system.
Advantages of off-the-shelf modules
When we start to look at some of the clear advantages of off-the-shelf modules, it should be obvious why they are so attractive for professionals and hobbyists alike.
RF design effort and risk are eliminated. The RF front ends, impedance matching filter and layouts of the RF section are challenging for many designers, even if the system operates in the MHz range or lower. Off-the-shelf wireless MCUs essentially eliminate this risk.
The other factor that is sometimes overlooked is the design of the antenna itself. Some RF modules will have the antenna integrated into the module package, which eliminates the design effort for an engineer. This is quite substantial as the design and simulation of these antennas can require specialized software that carries significant cost.
Simpler software deployment. While vendor support varies among IoT and wireless module manufacturers, some of the most popular vendors provide significant software support for their products. Software support comes in many forms, such as
- A vendor IDE, either on the web or desktop
- Free availability of libraries and application examples
- Phone or desktop applications for configuring a device and testing code
- Support for popular programmer modules and applications
Module vendors may also provide evaluation kits for their products, and some vendors will put those kits online as reference designs. This is another route toward quickly building a custom main board PCB that contains all the supporting components and peripherals needed for a new product.
Open-source support. Arguably one of the biggest benefits of using off the shelf modules, despite the EMC challenges, is the level of support from the open-source community. Any designers will put their projects online and freely available so the community can build new applications. This could include application code as well as PCB layout data for the main board. As long as the open-source design can be validated to work as intended, it could conceivably form the basis for a new commercial product.
Summary
Although there are clear advantages of using wireless modules for a new product, there are still EMC challenges to be addressed in the design of the main board. Due to module pre-certification, EMC challenges become problematic from power and IO connections on the main board. For example, power regulator circuit design and interconnect for single and power are the main sources of conducted or radiated emissions. Systems designers must still have a thorough understanding of PCB layout practices that reduce EMI to ensure successful EMC testing on the first run.
