Edge AI Evangelist’s Thoughts Vol. 13: Bluetooth Microcontrollers

October 19, 2021
AI Lab, Articles

Hello everyone, I’m Haruyuki Tago, Edge Evangelist at HACARUS Tokyo R&D center.

In this series of articles, I will share some insights from my decades of experience in the semiconductor industry and I will comment on various AI industry-related topics from my unique perspective.

In today’s article, we are on the hunt for a microcontroller with Bluetooth functionality that is suitable for data collection in edge AI systems.

Bluetooth Enabled Microcontrollers

Bluetooth technology has been around since 1999, and now it is a common feature in all smart devices. Bluetooth enables wireless communication for exchanging data communications between digital devices over short distances. Bluetooth technology can be found in a wide range of products including computer mice, earphones, smartwatches, speakers, and healthcare devices.

Bluetooth technology also has a plethora of industrial applications. It can be used by administrators for factory and building management. Utilizing Bluetooth, it is possible to collect and control sensor data from remote locations (e.g., temperature and humidity readings in various locations in a building) to a controller without wiring. This type of sensor reading technology is also incorporated into medical equipment.

Recently, there have been several microprocessor products that have been released with Bluetooth communication functionality. In the remainder of this article, I will refer to these microcontrollers as BT-MCUs. since these microcontrollers will be used to collect data for edge AI systems, we will look at BT-MCUs that meet the following criteria.

The device must comply with the radio laws of each country it will be operated in since Bluetooth devices emit radio waves. Each country has different laws regarding radio wave compliance, but certain BT-MCUs have already received the Technical Regulations Conformity Certification (GITEKI) in Japan, the Fcc/ISD certification in North America, and the CE certification in Europe [2].
The device must have a way to predict the battery life. Most Bluetooth microcontrollers are designed to run on batteries (e.g., coin cell batteries), which have low power consumption and a wide operating voltage range. The battery life of a Bluetooth microcontroller depends largely on the amount of data transmission and reception and the frequency of operation. It is important to measure the power consumption under actual operating conditions to predict the battery life.
The device must run on Bluetooth 5.0 or higher and meet low energy standards.
The device must be available for purchase at electronic component sales sites. It must also be purchasable in single-unit orders.

SoC, Module, & Development Boards

Now that our evaluation criteria are set, let’s begin to look at the design and components of a BT-MCU. Figure 1 shows the block diagrams and example designs for the Bluetooth microcontroller, module, and development board for the BT-MCU.

A 3 part figure that shows the block diagram and an example image of microprocessor SoC, modules, and development boards.

Figure 1. Block Diagram & product Examples of Soc, Module, & Development Board [3][4][7]

Moving from left to right, SoC is a single-chip microcontroller that consists of a Bluetooth radio circuit (Bluetooth Radio). It also contains an MCU Core, program memory (Flash ROM), data memory (RAM), and peripheral circuits.

Moving on, the module consists of an SoC and an antenna attached to a small printed circuit board. The antenna can be made using either a PCB traced pattern or a dielectric antenna chip. When using an external antenna, a connector or pins are required on the module.

Finally, the development board on the right is made up of the aforementioned module, a power circuit, an emulator circuit, an I/O connector (for connecting an external I/O board), switches, LEDs, and a USB connector (for connecting to a host PC).

Silicon Lab’s Bluetooth Microcontroller

One product that we can look at is the Gecko Module Starter Kit from Silicon Labs. The kit, outlined in Figure 2, contains the BG220P module, a 76.8 MHz ARM Cortex M33 microprocessor (with DSP and FPU), 512 kB of flash memory, and 32kB of RAM. The kit is also equipped with a Bluetooth radio subsystem and a variety of peripheral functions.

A diagram outlining all of the different subsystems in the EFR32BG22 Wireless Gecko SoC. It also shows all of the different components that makes up each subsystem.

Figure 2 Silicon Labs, EFR32BG22 Wireless Gecko SoC Block diagram [3]

Silicon Labs currently offers three different types of development boards in their starter kits. Each of these kits has its own unique set of features. In this article, we will focus on the BGM220P kit shown in Figure 3.

BGM220 Explorer Kit – A small and simple starter kit [5].

Thunderboard EFR32BG22 – A small, cost-effective starter kit [6].

BGM220P Wireless Gecko Module Starter Kit – A high-performance version of the explorer kit with temperature and humidity sensors, LCD, and more [7].

A visual image of the BGM220P Wireless Gecko Module Starter Kit.

Figure 3 Silicon Labs BGM220P Wireless Gecko Module Starter Kit

As mentioned in the criteria above, a suitable BT-MCU must have a way to monitor battery life and power consumption. Silicon Lab’s BGM220P Wireless Gecko Module starter Kit is equipped with a current measurement circuit displayed in Figure 4. Using this circuit, it is possible to calculate the power consumption by multiplying the current by the supply voltage. Silicon Labs has coined the name Advanced Energy Monitor, or AEM, for this power consumption measurement function. AEM runs using Simplicity Studio and is shown in Figure 5.

A detailed diagram showing the power consumption measurement circuit for the Gecko Module Starter Kit.

Figure 4 Circuit for Measuring Power Consumption of the Silicon Labs Gecko Module Starter Kit

The image shows energy consumption graphs for microcontroller using Simplicity Studio. On the right and underneath this image is the code and program details for the measurements.

Figure 5 Silicon Labs Simplicity Studio Power Consumption Measurements

Renesas’ Bluetooth Microcontrollers

Another company that has released a Bluetooth Microcontroller is Renesas, a Japanese company located in Kyoto, Japan. Today, we will take a closer look at their RX23W group which offers three different types of modules shown in figure 6 [9][10]. Looking back at the evaluation criteria, the only module that comes with a certificate of compliance with radio laws is the PTLG0083KA-A. The other two modules are also unique since they do not contain an antenna, only containing SoC.

A table showing the three different modules for the RX23W group and their specifications for antenna and radio-law compliance.

Figure 6 Renesas RX23W group [9]

Going into further detail, the block diagram for the Renesas RX23W SoC system is shown in figure 7. This system is extremely powerful, housing a 54MHZ RXv2 microcontroller core with DSP and FPU. It also includes 512kB flash memory, 64kB of Ram, a Bluetooth wireless circuit (BLE), and various peripheral functions.

A detailed block diagram that shows the layout for the Rx23W SoC. Below the block diagram is a key to show the names of all the different components.

Figure 7 Renesas RX23W SoC Block diagram [9]

Finally, let’s look at the RX23W development board (Target Board) in figure 8. Here, we can see the design layout and detailed indicators for all of its components. Looking at Figure 9, we can also see a diagram for the current measurement header attachment & pattern cut points for the Target Board. One difference between the Target Board and the previously mentioned development board by Silicon Lab is the ability to measure power consumption. The Target board needs to connect to an external current consumption measurement circuit in order to perform the measurement.

A realistic image that shows an image of the Renesas Target Board for the RX23W module. It also identifies each component and lists its official name to the side.

Figure 8 Renesas Target Board for RX23W module [11]

A computer image of the Target Board for the RX23W module. It outlines and shows the current measurement header attachment and patter cut points circled in red.

Figure 9. Current Measurement Header Attachment & Pattern Cut Points for the Renesas Target Board for RX23W Module

Summary

To finish this article, I want to recap the main points covered today. Thank you for taking the time to read this installment of my web series and I hope you found it interesting.

In this article, we looked for Bluetooth microcontrollers that are radio-conformant, readily available, and suitable for data collection for edge AI systems. While researching potential microcontrollers, I came across several modules and development boards from Silicon Labs and Renesas.
After reviewing the products above and evaluating them with the criteria mentioned at the beginning of this article, I believe that the RX23W Group Target Board for the RX23W Module developed by Renesas is the most suitable product for data collection in Edge AI systems.
Similar to the RX23W, the BGM220P wireless Gecko Module Starter Kit by Silicon Labs is also suitable for data collection.