With the attention of modern people turning to health, a variety of devices for detecting vital signs at any time has been introduced into the market one after another, which can be used for detecting pulse, body temperature, electrocardiogram and personal motion state data. The market development space is amazing. This article will show you the features of the Vital Signs Monitoring (VSM) watch development module introduced by ADI (Analog Devices Inc.).
Flourishing VSM wearable devices
At present, there are many wearable devices that can detect vital signs on the market, such as smart bracelets and smart watches, as well as some products that specifically target movement function and health monitoring function. Some of these products can only be used for simple step counting, or added with pulse (heart rate) detection function, and some high-end products can also measure body temperature and electrocardiogram, which makes related products flourish in the market and attracts many manufacturers to invest in development.
In recent years, due to the epidemic of COVID-19, the adoption of wearable technology has been accelerated and its role in healthcare has been enhanced. People pay more attention to monitoring their health status, such as wearable fitness tracker, smart health watch, wearable ECG monitor, wearable sphygmomanometer, wearable biosensor, etc., all of which are quite common and popular wearable devices.
Complete development platform to speed up product development
To enable customers to accelerate the development of VSM wearable devices, ADI has introduced the development platform for EVAL-HCRWATCH4Z VSM watch, which is a modular development, demonstration and data collection platform for high-performance VSM applications based on ADI's analog front-end and sensor. This wearable, battery-powered device can provide continuous monitoring and on-demand spot-check measurements for photoplethysmography (PPG), electrodermal activity (EDA, based on bioimpedance), skin temperature, electrocardiography (ECG, based on biopotential), and motion/activity (based on 3-axis accelerometer). It allows multiple kinds of parameter data storage to be synchronized in internal memory, so that data retrieval, offline analysis and/or real-time monitoring can be performed on PC (Windows® operating system) or Android or iOS-based devices in the future.
This VSM watch is a modular development, demonstration and data collection platform with optimized electrical and mechanical design for the platform, carrying all the necessary circuitry to sense, condition, digitize, process, store and wirelessly transmit data related to real-time vital signs. The platform can minimize the risk of carrying out new electronic design and shorten the time to market of new final products, and can promote the evaluation of various ADI solutions and demonstration and solution of the challenges related to wearable devices in the wearable ecosystem powered by single battery, to allow developers to more focus on other value-added type tasks, such as algorithm development, and overall firmware for engineering, scientific research and validation.
The HCRWATCH4Z evaluation platform kit consists of VSM platform (the watch), charging cradle, USB-to-Micro-USB Type A cable and firmware debugging board. A USB cable can be used to charge the battery through the charging cradle, upgrade the platform firmware, and download the data stored in the internal flash memory for offline data analysis. In addition, for wireless transmission, VSM watch platform also has optional Bluetooth USB PC dongle (NRF52840) for wireless communication with PC.
Integrating high-quality devices to improve the VSM function
The HCRWATCH4Z evaluation platform can monitor various vital signs, such as pulse detection using photoplethysmography (PPG) technology. Using ADI's ADPD4100 as a complete multimodal sensor front end, it is operated to stimulating four LEDs on VSM watch and measure the return signal of up to eight separate current inputs. It has 12 time slots available, and can make 12 separate measurements per sampling period.
For motion and activity detection, ADI's ADXL362 is used, which is an ultra-low power, 3-axis, ± 2 g/± 4 g/± 8 g digital output high resolution (1 mg/LSB) accelerometer that senses motion state. Its power consumption is 1.8 μA at 100 samples per second (SPS) and 3.0 μA at 400 SPS, while its motion-activated wake-up mode requires only 270 nA.
For ECG detection, ADI's AD8233 is used, which is a 50 μA low noise single-lead analog output biopotential front end. The AD8233 can be connected to electrodes located on the top and bottom surfaces of the watch. The signal chain is configured like an ambulatory ECG device.
The HCRWATCH4Z evaluation platform can also detect bioimpedance measured using ADI's AD5940 impedance analog front end (AFE). Proper electrical contact between these two electrodes and skin is critical for accurate and reliable long-term measurement. These two electrodes are also used for ECG measurement, which temporarily shorts them together, so the impedance measurement is not valid when ECG measurement is ongoing.
This platform can also detect skin and ambient temperature. It is based on thermistor. The thermistor used for skin temperature measurement is thermally coupled to the bottom of the watch. The thermistor will be connected to one of the analog inputs of ADPD4100.
ADI has designed basic operation modes for VSM watches, and can select functions such as high-performance PPG, synchronous PGG with EDA, synchronous PPG with ECG spot check, high-performance ECG spot check and multi-wavelength PPG through the provided device configuration files, and will continue to develop other functional use cases in the future.
These operating modes are intended to demonstrate the different types of configurations that may exist for VSM watches, but are not specific to the end applications. VSM watches are highly configurable, allowing programming of configurations that are not supported by existing hardware, software, and firmware, and users can load these use cases as the starting point of a good foundation, so as to explore various measurement technologies of interest before modifying the platform for specific purposes.
Provide algorithms and use cases as well as rich online resources
In the evaluation of embedded algorithm, it includes the pedometer algorithm that obtains raw data from 3-axis accelerometer and outputs walking steps, and an automatic gain control that feeds digital output from ADPD4100 to this algorithm to ensure proper configuration of LED current and AFE gain and maximize the usefulness of optical signal. The default goal is to have 70% allowable range per LED (which can be determined independently). The gain control has not been optimized to achieve ideal performance and power consumption, but can be further improved according to the requirements of the end application to achieve longer battery life.
The algorithm can also use PPG/ADPD signals to measure heart rate while eliminating motion-based interference. It runs on single channel PPG/ADPD signals and 3-axis accelerometer data to generate heart rate. The algorithm is provided in the way of the pre-built Cortex-M4 library along with header file, aiming at processing 50Hz PPG and accelerometer data.
PPG signals collected by wearable devices are prone to noise sources and other artifacts, which will have a negative impact on sensor measurement accuracy. A Signal Quality Index (SQI) algorithm provides scores (indexes) for each time window/segment of PPG data to determine whether it has sufficiently quality for other vital signs extraction or clinical diagnosis algorithms to estimate heart rate. The SQI function supports PPG signal frequencies of 25-100Hz, and the SQI score is a floating-point value between 0 (poor signal quality) and 1 (excellent quality).
For ECG heart rate monitoring, the algorithm measures heart rate from ECG signal by detecting QRS peak of ECG signal. The algorithm is provided in the way of the pre-built Cortex-M4 library along with header file, and is designed to process ECG signals with ODR up to 200Hz.
To help customers speed up product development, Arrow and ADI offer a rich set of developer resources such as technical collateral and user documentation, all of which can be obtained online on Arrow' Github website, such as Github Repository Attached to VSM Watch Hardware and Software and VSM Watch Wikipedia Page, and you can also view more information about related devices, such as high precision, impedance and electrochemical front end - AD5940BCBZ, ultra-low power, 1.8 V, 3 mm × 3 mm, 2-channel capacitive converter - AD7156BCBZ, 50 μA, 2 mm × 1.7 mm WLCSP, low noise, heart rate monitor for wearable products - AD8233ACBZ-R7, advanced battery management PMIC - ADP5360ACBZ-1-R7 with ultra-low power fuel gauge, battery protection, buck and buck boost functions, micro-electromechanical (MEMS) accelerometer - ADXL362BCCZ with micro-power, 3-axis, ±2 g/±4 g/±8 g digital output, and multimodal sensor front end - ADPD4100.
Conclusion
Wearable devices supporting VSM have become the best technological products for modern people to pursue health, representing a rapidly developing new blue ocean market, which is worthy of active investment in related product development by manufacturers. ADI's HCRWATCH4Z evaluation platform has integrated many high-quality devices and provided excellent software and hardware product reference design, which is a springboard for manufacturers to develop related products and is worthy of in-depth understanding by interested manufacturers.
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