Analog Devices UG-1221 User manual

User Guide | EVAL-HCRWATCH4Z
UG-1221
Vital Signs Monitoring (VSM) Watch
PLEASE SEE THE LAST PAGE FOR AN IMPORTANT
WARNING AND LEGAL TERMS AND CONDITIONS. Rev. 0 | 1 of 33
FEATURES
►Vital signs monitoring platform
►Wearable battery-powered platform
►Real-time live data view
►Data storage to flash memory for offline analysis
►Easy configuration
DEVICES HOSTED IN THE VSM WATCH
►nRF52840
►ADP5360
►ADXL362
►ADPD4100
►AD8233
►AD5940
►AD7156
EVALUATION KIT CONTENTS
►VSM platform (the watch)
►Charging cradle
►USB Type A to micro USB cable
►Firmware debug board
SOFTWARE NEEDED
►VSM WaveTool
GENERAL DESCRIPTION
The vital signs monitoring (VSM) watch, EVAL-HCRWATCH4Z, is a
modular development, demonstration, and data collection platform
for high performance vital signs monitoring applications based on
Analog Devices, Inc., analog front ends (AFEs) and sensors.
The VSM watch is a wearable, battery-powered device that enables
the continuous monitoring and on-demand spot check measure-
ment of photoplethysmography (PPG), electrodermal activity (EDA,
bioimpedance-based), skin temperature, electrocardiography (ECG,
biopotential based), and motion/activity (based on a 3‑axis acceler-
ometer).
The VSM watch allows synchronized, multiparameter data storage
on internal memory for later data retrieval and offline analysis
and/or live monitoring on a PC (Windows® OS) or Android- or
iOS-based device.
PREPARING THE VSM WATCH
Before using the VSM watch, proper preparations must be made.
Ensure that the battery of the watch is charged and the VSM Wave-
Tool PC program is installed. See the Powering Up the System
for the First Time section for installation instructions. Upgrade the
watch firmware using the VSM WaveTool.
CONDITIONS REGARDING THE USE OF THIS
PRODUCT IN HEALTHCARE APPLICATIONS
This device design is being provided as-is without any express or
implied representations or warranties of any kind and the use of
this device shall impose no legal obligation on Analog Devices, Inc.,
and its subsidiaries, employees, directors, officers, servants, and
agents. In addition, it is understood and agreed to that the device
is not authorized for use in safety critical healthcare applications
(such as life support) in which malfunction or failure of a product
can be expected to result in personal injury or death. This device
must not be used for diagnostic purposes. It must not be used with
a defibrillator or other equipment that produces high voltages more
than the supply rails on the evaluation board.
This device is provided for evaluation and development purposes
only. It is not intended for use as, or as part of, a product. Any
use of the device in such applications is at your own risk and you
shall fully indemnify Analog Devices, its subsidiaries, employees,
directors, officers, servants and agents for all liability and expenses
arising from such unauthorized usage. You are solely responsible
for compliance with all legal and regulatory requirements connected
to such use.

User Guide EVAL-HCRWATCH4Z
TABLE OF CONTENTS
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Features................................................................ 1
Devices Hosted in the VSM Watch........................1
Evaluation Kit Contents......................................... 1
Software Needed...................................................1
General Description...............................................1
Preparing the VSM Watch..................................... 1
Conditions Regarding the Use of This Product
in Healthcare Applications................................... 1
Evaluation Platform Overview............................... 3
Evaluation Platform............................................... 6
Overview............................................................ 6
Powering Up the System for the First Time........6
Water Resistance............................................... 6
Software............................................................. 6
Bluetooth USB PC Dongle (nRF52840)............. 6
Buttons............................................................... 7
Display Indicators...............................................7
Vital Signs Monitored...........................................11
Photoplethysmography—ADPD4100............... 11
Motion and Activity–ADXL362.......................... 11
Electrocardiography–AD8233...........................11
Bioimpedance–AD5940....................................11
Skin and Ambient Temperature........................ 12
Use Cases........................................................... 13
Embedded Algorithms for Evaluation.................. 15
Pedometer........................................................15
Automatic Gain Control.................................... 15
Heart Rate Monitoring...................................... 15
Signal Quality Index......................................... 15
ECG Heart Rate Monitoring............................. 15
Battery Life and Memory Footprint...................... 16
Battery Life....................................................... 16
Memory Footprint ............................................ 16
Schematics and Layouts..................................... 17
FCC Compliance Statement................................28
Ordering Information............................................29
Bill of Materials.................................................29
Device Models..................................................33
REVISION HISTORY
12/2021—Revision 0: Initial Version

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EVALUATION PLATFORM OVERVIEW
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Figure 1. Overview of VSM Watch Platform
Figure 2. VSM Watch Expanded View
Figure 3. Connections and Buttons–Top of Watch

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EVALUATION PLATFORM OVERVIEW
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Figure 4. Connections and Buttons–Bottom of Watch
Figure 5. Connections and Buttons–Sides of Watch
Figure 6. Charging Cradle
Figure 7. Firmware Debug Board

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EVALUATION PLATFORM OVERVIEW
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Figure 8. Simplified Electrical Block Diagram

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EVALUATION PLATFORM
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OVERVIEW
The VSM watch is a modular development, demonstration, and
data collection platform for high performance vital signs monitoring
applications based on Analog Devices analog front ends and sen-
sors.
The platform optimized electrical and mechanical design hosts all
the required circuits to sense, condition, digitize, process, store,
and wirelessly transmit real-time, vital sign related data. This plat-
form does the following:
►Minimizes the risks associated with a new electronic design
►Minimizes the time to market for a new final product
►Facilitates the evaluation of a wide range of Analog Devices
solutions in a single battery-powered wearable ecosystem
►Highlights and addresses the challenges associated with a wear-
able device
►Allows the developer to focus on other added value tasks, such
as algorithm development, and the overall firmware for engineer-
ing and scientific research and validation
This platform is not intended to do the following:
►Act as the final product for a specific application.
►Demonstrate an application-specific optimized design. Trade-offs
were made to allow platform flexibility.
The evaluation platform kit contains the following items (see Figure
9:
►VSM platform (the watch)
►Charging cradle
►USB Type A to micro USB cable
►Firmware debug board
Figure 9. Evaluation Kit Contents
The USB cable is used for the following purposes:
►Recharge the battery via the charging cradle (connecting the
watch to a PC or wall adapter)
►Upgrade the platform firmware (using VSM Wavetool)
►Download data stored in the internal flash memory for offline
data analyses or other purposes
Use the watch only with the USB cable provided.
POWERING UP THE SYSTEM FOR THE FIRST
TIME
The VSM watch is shipped from the factory in an ultra low power
shipment mode. To exit this power mode, place the watch into the
charging cradle and connect the USB cable to provide power.
Before using the watch for the first time, fully charge the battery by
connecting the VSM watch to a PC or wall adapter using the USB
cable provided.
WATER RESISTANCE
The VSM watch is IP68 rated. Despite this rating, exercise caution
if showering, swimming, or doing any other activity with the VSM
watch that exposes it directly to moisture.
SOFTWARE
For information on the VSM watch software, refer to the VSM watch
software user guide included with the VSM WaveTool (available for
download on the Analog Devices website at www.analog.com).
BLUETOOTH USB PC DONGLE (NRF52840)
The VSM watch platform leverages an off-the-shelf Nordic Semi-
conductor Bluetooth® low energy (BLE) dongle for communicating
wirelessly with a PC (see Figure 10). The nRF52840 is available for
purchase separately through multiple online vendors.
Figure 10. BLE USB PC Dongle (nRF52840)

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EVALUATION PLATFORM
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BUTTONS
Two buttons are found on the side of the VSM watch. Table 1 to
Table 3 explain the uses of these buttons.
Table 1. Button Descriptions
Button Description
Navigation Short press to proceed to the next screen
Action Short press for OK
Table 2. Button Usage in Watch App
Button Combinations Button Actions Button Press Timings (sec)
Action Button Short Press Selects the current page action 0.05
Navigation Button Short Press Navigates to the next page 0.05
Action Button Long Press Returns to the previous page action 3
Navigation Button Long Press Calls a soft reset of the watch app 3
Action and Navigation Button Long Press Enters the bootloader 3
Navigation Button Long Press When Watch Is Powered Down Wakes up the watch 1
Table 3. Button Usage in Bootloader
Button Combinations Button Actions Button Press Timings (sec)
Action Button Short Press No action Not applicable
Navigation Button Short Press No action Not applicable
Action Button Long Press No action Not applicable
Navigation Button Long Press Enters watch app 7
Action and Navigation Button Long Press Enters watch app 7
Action Button Short Press No action Not applicable
DISPLAY INDICATORS
Figure 11. Starting Up
Figure 12. Restart from Any Page

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EVALUATION PLATFORM
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Figure 13. Firmware Upgrade
Figure 14. Main Page Interface
Figure 15. Heart Rate Page

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Figure 16. Waveform Page
Figure 17. Low Touch Page

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EVALUATION PLATFORM
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Figure 18. Setting Page
Figure 19. About Page

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VITAL SIGNS MONITORED
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To minimize the power line interference (50 Hz/60 Hz) and improve
the quality of the output signal, use the BLE USB PC dongle as
explained in the Bluetooth USB PC Dongle (nRF52840) section.
PHOTOPLETHYSMOGRAPHY—ADPD4100
The ADPD4100 operates as a complete multimodal sensor front
end, stimulating up to eight LEDs (four on the VSM watch) and
measuring the return signal on up to eight separate current inputs.
Twelve time slots are available, enabling 12 separate measure-
ments per sampling period.
The data output and functional configuration use an I2C interface on
the ADPD4101 or a serial port interface (SPI) on the ADPD4100.
The control circuitry includes flexible LED signaling and synchro-
nous detection. The devices use a 1.8 V analog core and 1.8 V/3.3
V compatible digital input/output (I/O).
Refer to the ADPD4100 product page and data sheet for further
details.
See Table 4 and Table 5 for details on the hardware implementa-
tion.
Table 4. Electrical Connections to the ADPD4100 Inputs
Input Pin Description
IN1 VEMD8080 Photodiode 1
IN2 VEMD8080 Photodiode 2
IN3 Temperature sensor
IN4 Temperature sensor
IN5 Bioimpedance/ECG
IN6 Bioimpedance/ECG
IN7 Bioimpedance/ECG
IN8 Bioimpedance/ECG
Table 5. Electrical Connections to the ADPD4100 LED Current Sinks
Current Sink Color Wavelength (nm) No. of LEDs
LED1A Green 530 1
LED2A Infrared 940 1
LED3A Red 660 1
LED4A Blue 470 1
For more details on how to configure the various slots of
the ADPD4100 and other configuration information, refer to the
ADPD4100 data sheet.
MOTION AND ACTIVITY–ADXL362
Motion is sensed by the ADXL362, an ultra low power, 3-axis, ±2
g/±4 g/±8 g digital output high resolution (1 mg/LSB) accelerometer.
The power consumption of the ADXL362 is 1.8 µA at 100 samples
per second (SPS) and 3.0 µA at 400 SPS, whereas its motion
activated wake-up mode only requires 270 nA.
A pedometer algorithm is embedded for evaluation that can be
enabled in the VSM WaveTool.
Refer to the ADXL362 data sheet for more details on various
configuration options available for this device.
ELECTROCARDIOGRAPHY–AD8233
The AD8233 is a 50 µA, 2.0 mm × 1.7 mm, wafer level chip
scale package (WLCSP), low noise, single lead, analog output,
biopotential front end.
Integrated ECG Electrodes
The AD8233 is connected to the electrodes hosted in the top and
bottom surfaces of the VSM watch. The two electrodes on the top
of the watch are connected to the IN− pin and RLD pin, whereas
the two electrodes on the bottom of the watch are shorted together
(temporarily while this measurement is active) and connected to the
IN+ input.
The quality of the contact of the bottom electrodes has a dramatic
effect on the output waveform. Dry, hairy skin poses a challenge
for this measurement until moisture accumulates between the skin
and the electrodes. Moisture accumulation typically happens a few
minutes after the user puts on the device. Accumulated moisture
decreases the contact impedance and, therefore, the quality of the
output waveform improves.
The configuration of this signal chain is similar to an ambulatory
ECG device (Holter monitor). See Table 6.
Table 6. Electrical Specifications of the ECG Signal Chain1
Specification Value (Typical) Unit
Passing Bandwidth 0.4 to 42 Hz
High-Pass Filter First order N/A
Low-Pass Filter Second order (quality factor = 0.671) N/A
AD8233 Gain 151 V/V
Analog-to-Digital
Converter (ADC)
Resolution
16 Bits
Noise (Referred to Input) 13 µV p-p
Sampling Rate 50 to 1000 SPS
1N/A means not applicable.
Refer to the AD8233 data sheet for more details on the device.
External ECG Cables
The charging cradle provides a secondary micro USB connection to
be used with external wired electrodes.
BIOIMPEDANCE–AD5940
Impedance is measured using the AD5940 impedance AFE. Proper
electrical contact between the two electrodes and the skin is critical
for accurate and reliable long-term measurement. Adequate tight-
ness of the watch strap helps achieve proper contact, and wearing
the watch beside, but not on top of, the ulnar styloid process (the

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VITAL SIGNS MONITORED
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protruding wrist bone) also helps ensure a reliable and high quality
measurement. See Table 7.
Note that the two electrodes are also used by the ECG meas-
urement, which temporarily shorts them together. Therefore, the
impedance measurement is not valid while the ECG measurement
is ongoing.
Table 7. Electrical Specifications of the AD5940
Specification Value (Typical) Unit
Conductivity Range 0.2 to 20 µS (3%)
Accuracy at 0.2 µs 3 %
Accuracy at 1 µs 0.8 %
Accuracy at 10 µs 0.1 %
Accuracy at 20 µs 3 %
Resolution at 1 µs 1 nS
Resolution at 10 µs 2 nS
Excitation Frequency 100 Hz
Sampling Rate 30 SPS
SKIN AND AMBIENT TEMPERATURE
The skin temperature measurement is based on a thermistor
(NTCG104EF104FTDSX). The thermistor used in the skin tempera-
ture measurement is thermally coupled to the bottom of the watch.
This thermistor is connected to one of the analog inputs of the
ADPD4100, and its performance is heavily dependent on the me-
chanical connection that is made to the body. This version of the
watch has poor heat conduction between the thermistor and watch
body that results in a larger inaccuracy in the temperature data than
the theoretical value of 0.2°C. To overcome this shortcoming, the
user can configure a temperature correction factor using the VSM
WaveTool, depending on the temperature deviation seen in their de-
vice. The procedure to configure the correction factor is explained
in the software user guide included with the VSM WaveTool.
See Table 8 for the electrical specifications of the signal chain that
measures skin temperature.
Table 8. Electrical Specifications of the Signal Chain That Measures Skin
Temperature
Specification Value (Typical)
Temperature Range −30°C to +50°C
Resolution at 25°C 0.1°C

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USE CASES
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The following basic modes of operation for the VSM watch are
selectable by the supplied device configuration files (future use
cases will be developed):
►High performance PPG
►Synchronized PGG with EDA
►Synchronized PPG with ECG spot check
►High performance ECG spot check
►Multiwavelength PPG
These modes of operation are intended to demonstrate the different
types of configurations that are possible with the VSM watch, but
they are not specific to an end application. The high configurability
of the VSM watch allows the possibility to program a configuration
that cannot be supported by the existing hardware, software, and
firmware. Users can load these use cases as a known good starting
point to explore measurements of interest before modifying the
platform for their specific purpose.
Refer to the software user guide for details on how to evaluate and
modify these use cases in the VSM WaveTool.
All use cases are designed to allow automatic logging to the
on-board NAND flash when the watch detects that it is being worn,
based on its capacitive sensor. The logging in progress indicator
on the watch display (as shown in Figure 20) is seen only when
this feature is used to indicate active logging and the percentage of
memory used.
See Table 9 through Table 13 for more information on the use
cases.
Figure 20. NAND Flash Logging Indicator with Percentage of Memory Used
Table 9. Use Cases1
Use Case PPG (SPS) Motion (SPS) Impedance (SPS) ECG (SPS) Temperature (SPS)
Shipment Mode Off Off Off Off Off
Hibernate Off Off Off Off Off
PPG–High Performance (1 LED) 500 50 N/A N/A 1
ECG–High Performance 50 50 N/A 1000 1
PPG and Impedance (1 LED) 100 50 30 N/A 1
PPG and ECG (1 LED) 100 50 N/A 250 1
PPG–All LEDs 100 50 N/A N/A 1
1N/A means not applicable.
Table 10. Default ADPD4100 Configuration for Each Use Case
Use Case Sampling Rate (SPS)
Transimpedance Amplifier
Gain Channel 1/Channel 2 Pulse Width Slot/Wavelength Number of Pulses
PPG–High Performance (1 LED) 500 50/50 2 F/530 64
ECG–High Performance 50 50/50 2 F/530 64
PPG and Impedance (1 LED) 100 50/50 2 F/530 64
PPG and ECG (1 LED) 100 50/50 2 F/530 64
PPG–All LEDs 100 50/50 2 F/530, G/660, H/850, I/470 64
Table 11. Default ADXL362 Configuration for Each Use Case
Use Case Sampling Rate (SPS) Measurement Range (g)
PPG–High Performance (1 LED) 50 8
ECG–High Performance 50 8
PPG and Impedance (1 LED) 50 8
PPG and ECG (1 LED) 50 8
PPG–All LEDs 50 8

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USE CASES
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Table 12. Default AD5940 Configuration for Each Use Case1
Use Case Sampling Rate (SPS)
PPG–High Performance (1 LED) N/A
ECG–High Performance 1000
PPG and Impedance (1 LED) 30
PPG and ECG (1 LED) 250
PPG–All LEDs N/A
1N/A means not applicable.
Table 13. Default AD8233 Configuration for Each Use Case1
Use Case AC or DC Coupling Fast Reset Mode Gain
PPG–High Performance (1 LED) N/A N/A N/A
ECG–High Performance DC coupling On 150
PPG and Impedance (1 LED) N/A N/A N/A
PPG and ECG (1 LED) DC coupling On 150
PPG–All LEDs N/A N/A N/A
1N/A means not applicable.

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EMBEDDED ALGORITHMS FOR EVALUATION
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Advanced algorithms with specific device configurations are de-
tailed in the Pedometer section through ECG Heart Rate Monitoring
section.
PEDOMETER
A pedometer algorithm takes raw data from the 3-axis accelerome-
ter and outputs the steps taken.
AUTOMATIC GAIN CONTROL
The digitized output of the ADPD4100 is fed to this algorithm to
ensure that the LED current and AFE gain is configured appropri-
ately, to maximize the usefulness of the optical signal. The default
target is 70% of the allowable range for each LED (independently
determined). Automatic gain control is not optimized to achieve an
ideal performance vs. power. Further improvements can be made
based on the requirements of the end application to improve battery
life.
HEART RATE MONITORING
The heart rate monitoring algorithm measures heart rate using a
PPG signal while removing the motion based interference. This al-
gorithm operates on a single channel PPG signal, together with the
3-axis accelerometer data to produce the heart rate. The algorithm
is provided as a prebuilt Arm® Cortex®-M4 library along with a
header file. The algorithm is designed to work with synchronized
PPG and accelerometer data at 50 Hz.
SIGNAL QUALITY INDEX
PPG signals collected via wearable devices are prone to noise
sources and other artifacts that negatively impact the measurement
accuracy of the sensor. The signal quality index (SQI) algorithm
gives a score (index) for each time window or segment of the PPG
data. This score determines if the PPG data is of a sufficiently
high quality to be useful for other vital sign extraction or clinical
diagnostic algorithms that estimate the heart rate. The SQI feature
is supported for PPG signal frequencies ranging from 25 Hz to 100
Hz. The SQI score is a floating-point value between 0 (poor signal
quality) and 1 (excellent quality). The VSM WaveTool has an option
to display the SQI in all use case views. The SQI can be calculated
on any of the green, red, infrared, or blue LEDs present on the
watch.
ECG HEART RATE MONITORING
The ECG heart rate monitoring algorithm measures heart rate from
the ECG signal by detecting the QRS peak of the ECG signal. The
algorithm is provided as a prebuilt Cortex-M4 library along with a
header file. The algorithm is designed to work with an ECG signal
with an output date rate up to 200 Hz.

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BATTERY LIFE AND MEMORY FOOTPRINT
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BATTERY LIFE
The battery life is determined by the type and number of sensors
enabled and the sampling rate configured. The battery life is also
dependent on other configuration details, such as the LED current
in the PPG measurements. See Table 14.
Table 14. System Battery Life for Several Use Cases
Use Case Memory Live BLE Battery Life (Hours)
Shipment Mode No No 30000+
Hibernate No No 1000+
PPG–High Performance Yes Yes 14
ECG–High Performance Yes Yes 40
PPG and Impedance Yes Yes 50
PPG and ECG Yes Yes 40
PPG–All LEDs Yes Yes 20
The VSM watch is powered by a rechargeable 200 mAh battery.
All the default use cases are designed to maximize the perform-
ance. By modifying various parameters of the AFEs, the user
can improve battery duration. For instance, in the ADPD4100, the
default gain in the automatic gain control algorithm is set to 25 kΩ,
so as to get best PPG performance with various skin tones. Setting
the gain to 100 k or 200 k and lowering the current value results in
significant improvement in battery duration for continuous usage.
MEMORY FOOTPRINT
The VSM watch hosts a 512 MB memory.
The actual capacity of the memory is determined by the type and
number of sensors enabled and the sampling rate configured. See
Table 15.
Table 15. Memory Capacity (in Hours) for Different Use Cases
Vital Signs Memory Capacity (Hours)
PPG–High Performance 18
ECG–High Performance 22
PPG and Impedance 63
PPG and ECG 43
PPG–All LEDs 23

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Figure 21. Microcontroller Connections

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Figure 22. Memory and Buttons
Figure 23. Level Shifter and Display Connections

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Figure 24. ECG Circuitry

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Figure 25. AD5940 Circuitry and Connection to Optical Board
Figure 26. PMIC Circuitry