Smart Health Wristband Development with XMC4700

A prominent client in the health technology industry has engaged us to develop a unique type of wearable healthcare device that will continuously monitor key health and wellness data points and provide immediate feedback on a user's health in order to allow users to make informed choices about their health and well-being.

The client envisions a small wristband with various sensor technologies, low-energy hardware components, and cloud-connected software applications. The ultimate goal of the project is to provide a consistent user experience across all platforms, including mobile, web, and desktop.

The biggest challenge we faced was to develop an end-to-end solution, including printed circuit board (PCB) design, firmware development, product enclosure design, and building the cloud infrastructure, along with developing the software and ensuring integration with third-party solutions.

The ecosystem created for the wearable healthcare device incorporates multilayer PCBs (printed circuit boards) that are custom-designed and an event-driven cloud architecture. The ecosystem is built on Infineon Technologies' XMC4700, which utilises an ARM Cortex-M4 processor.

The primary objective was to develop a smart health and fitness wristband that could track vital signs and activity metrics with high accuracy and reliability. The project scope included:

• Complete hardware design and custom PCB layout
• Firmware and embedded system development for the Infineon microcontroller
• Ergonomic, durable wristband casing design and manufacturing
• Cloud infrastructure and backend development
• Mobile, web, and desktop application development
• REST APIs and SDKs for third-party integrations
• Over-the-Air (OTA) firmware updates for continuous device improvements

Our goal was to deliver a holistic solution where hardware, firmware, software, and cloud services worked seamlessly together.

Device Type: Wellness Device (Wearable Activity Monitor)

Main Objective: Continuous tracking of health and fitness metrics (real-time alerts & analytics) with combined applications.

Major Functions of this Device Include:

• Accurate health tracking of heart rate, blood oxygen levels, body temperature, and sleep patterns.
• Tracking daily activity by counting steps taken, Calories burnt while exercising and Distance travelled.
• Notifications, which include immediate notifications if any of the following occurs - Your heart rate exceeds normal limits, Blood oxygen level is very low and irregular sleep pattern(s).
• Cross-platform mobile (iOs, Android), web and desktop applications to use for monitoring, reporting and controlling the device.
• Cloud solution for secure storage, analytics and device management.
• Third Party Application Integration - APIs and SDKs for application developer partners and Health and Wellness focused organizations.
• Over-the-air (OTA) firmware updates (updates made automatically) to provide new features/functions or any issues related to the device.

Controller Used: Infineon XMC4700 series (ARM Cortex-M4 based)

Reasons for Selection:

• Low Power Consumption: The XMC4700 has a number of low power and sleep modes, allowing the monitoring device to last longer on batteries for continuous, 24/7 health monitoring.
• High Performance: The ARM Cortex-M4 core, which uses floating-point processing, can process multiple streams from sensors in real-time without any gaps in time between processing streams so that heart rate, SpO₂, and activity calculations are accurate.
• Security Built-in: Secure AES Encryption on-chip, secure storage of keys and hardware AES accelerators keep secure health and personal information secure while using cloud services.
• Rich Peripheral Set: The XMC4700 has built-in ADC's, timers, PWM's, I2C, SPI & UART & make it easy to connect a wide range of sensors to each other and to hide/data send through BLE/WiFi modules (connectivity).
• Scalability & Reliability: Designed for use in Industry, the XMC4700 will provide reliable service, regardless of temperature ranges and usage cycles.
• Ecosystem Support: All of the tools, documentation, sample applications, etc., available to you from the Infineon/XMC4700 ecosystem will help you complete all aspects of winning firmware development, testing, or validation faster than if you had no tools etc. to help.

Three main hurdles need to be overcome in developing a device that combines elements of consumer fitness tracking and medical monitoring into one usable "wearable" product:

• Signal Integrity: Capture microvolt signals from PPG (Heart Rate/SpO₂) and temperature sensors while dealing with noise in small and compact format.
• Power Budgeting: Maintain a 7+ day battery life while constantly sampling data in background mode.
• Data Security: Create end-to-end AES encrypted connection between the microcontroller unit (MCU) and the cloud to satisfy health data privacy standards.

The Core: Infineon XMC4700 Selection

The XMC4700 Series of Infineon was chosen over regular low power MCUs based on the industrial reliability of this family of processors and their architecture based attributes:

DSP Capabilities

The Cortex-M4 Floating Point Unit (FPU) provides the ability for real time processing of the Fast Fourier Transform (FFT) algorithm to remove movement artifacts from heart rate signals.

Peripheral Density

High-speed 12-bit ADC are used to accurately connect to analog sensors with no external converters required.

Memory Footprint

The controller has a maximum capacity of 2MB of Flash memory and 352KB of SRAM which meets the demand of running complex RTOS applications with multitasking capabilities and local data logging during times of loss of connectivity.

Hardware Implementation

Custom Multi-layer PCB

Four layers optimized for RF isolation (BLE/Wi-Fi) and shielding of analog signals.

Sensor Suite

Integrated MAX30102 (Heart Rate/Spo2), TMP117 (High accuracy temperature) and BMI160 (6-axis Accelerometer/Gyroscope).

Power Path

Designed with an LDO with ultra low quiescent current and a dedicated battery management IC (BMIC) that provides safety for Li-Po batteries.

Embedded System (Firmware)

Embedded System Firmware was developed using RTOS to improve the efficiency of multiple concurrent tasks. The following significant features were incorporated into the RTOS:

• Priority scheduling gives heart rates priority to be sampled during an interrupt request and above cloud synchronization tasks.
• An Over-the-Air Update is done with a dual bank of flash memory for "fail-safe" to allow the device to return to previous stable firmware in case of update failure.
• The XMC4700 uses dynamic power scaling so that it will enter deep sleep between periodic sensor sampling intervals. As a result, average current draw is measured in micro-amps.

End-to-End Cloud Integration

Communication protocol:

MQTT over TLS 1.2, allowing lightweight and secure bi-directional communication between the provider and the client

ServerBackend:

Serverless architecture based on AWS Lambda for scalable data processing.

Storage:

User profiles stored in relational databases, health data from wearables can be stored using NoSQL due to large amounts of data being generated quickly.

Selecting the Right Microcontroller:

Advanced algorithms require microcontrollers with sufficient processing resources (computational headroom), which many low-cost, low specification MCUs cannot provide.

Modular Firmware:

Communication protocol:

An RTOS helps develop modular firmware, making it much easier to integrate third-party SDKs and add future functionality.

Security Built-In:

The Infineon security microcontroller incorporates hardware-based encryption to establish user trust and meet regulatory requirements.