Maxim Integrated MAX32664C User manual

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Measuring SpO2and Heart Rate
Using MAX32664C – A Quick Start Guide
UG6924; Rev 0; 6/19
Abstract
The MAX32664C is a variant of the MAX32664 sensor-hub family, which is specifically targeted
for measurement of SpO2and heart rate. Combined with the MAX86141 optical sensor and a 3-
axis accelerometer, it provides the sensor’s raw data, as well as calculated SpO2or heart-rate
data, to a host device through its I2C slave interface. This document provides step-by-step
instructions that enable a user to communicate with the MAX32664C and to calibrate, configure,
and receive measurement and monitoring data.

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Table of Contents
Introduction ...................................................................................................................................4
1 Architecture................................................................................................................................5
1.1 Communicating with MAX32664C.......................................................................................6
1.2 Accelerometer .....................................................................................................................7
2 Measuring SpO2on Wrist (WSpO2)..........................................................................................8
2.1 Initial Calibration Mode for Final Product ............................................................................8
2.2 Raw Data Collection Mode................................................................................................11
2.2.1 Raw Data Collection in Algorithm Mode .....................................................................11
2.2.2 Pure Raw Data Collection...........................................................................................13
2.3 Algorithm Mode .................................................................................................................15
2.3.1 Algorithm Settings and Configurations .......................................................................16
3 Measuring Heart-Rate on Wrist (WHRM) ................................................................................17
3.1 Setup .................................................................................................................................17
3.2 Raw Data Collection Mode................................................................................................17
3.2.1 Raw Data Collection in Algorithm Mode .....................................................................17
3.2.2 Pure Raw Data Collection...........................................................................................20
3.3 Algorithm Mode .................................................................................................................22
3.3.1 Algorithm Settings and Configurations .......................................................................23
Revision History ..........................................................................................................................24
List of Figures
Figure 1. Architecture diagram for health-sensing applications. ...................................................5

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List of Tables
Table 1. Read Status Byte Value..................................................................................................6
Table 2. Host-Side Accelerometer—Sending Data to MAX32664C .............................................7
Table 3. Host Commands—WSpO2in Calibration Mode .............................................................9
Table 4. Format of Received Samples—WSpO2in Calibration/Algorithm Mode .......................10
Table 5. Host Commands—WSpO2 Raw Data with Algorithm Mode.........................................11
Table 6. Host Commands—WSpO2Pure Raw Data..................................................................13
Table 7. Format of Received Samples—WSpO2in Pure Raw Mode.........................................14
Table 8. Host Commands—WSpO2Algorithm Mode.................................................................15
Table 9. Configurations and Settings—WSpO2..........................................................................16
Table 10. Host Commands—WHRM Raw Data with Algorithm Mode........................................18
Table 11. Format of Received Samples—WHRM in Algorithm Mode.........................................19
Table 12. Host Commands—WHRM Pure Raw Data.................................................................20
Table 13. Format of Received Samples—WHRM in Pure Raw Data Mode ...............................21
Table 14. Host Commands—WHRM Algorithm Mode................................................................22
Table 15. Configurations and Settings—WHRM.........................................................................23

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Introduction
The MAX32664C is a variant of the MAX32664 sensor-hub family that enables users to capture
raw data, as well as calculated SpO2and heart-rate data. The part is preprogrammed with the
firmware, drivers, and algorithm that are required to interface with the MAX86141 sensor device
through the SPI port. The I2C slave interface is dedicated to establishing communication with a
host microcontroller.
In order to properly capture and calculate the data, this solution requires an accelerometer. The
MAX32664C firmware includes the required drivers for the Kionix®KX122 accelerometer, which
is wired together with the MAX86141 to the same SPI port. Alternatively, a host-side
accelerometer can be used. In this case, the sampled accelerometer data is required to be
periodically reported to the MAX32664C by the host microcontroller using commands described
in this application note.
This document provides the instructions necessary to create a solution with the MAX32664C
based on the MAXREFDES102# reference design.
Kionix is a registered trademark of Kionix, Inc.

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1 Architecture
A typical health-sensing design includes a host microcontroller communicating with the
MAX32664C through the I2C bus. Two GPIO pins are needed to control the reset and the startup
in Application or Bootloader mode through the RSTN and multifunction I/O (MFIO) pins. An MFIO
pin is also used in Application mode to interrupt the host for I2C communication. The MAX32664C
interfaces to the MAX86141 optical sensor through the SPI bus.
An accelerometer is mandatory for heart-rate monitoring. A KX122 accelerometer can be
connected directly to the MAX32664C. Alternatively, an external 3-axis host-side accelerometer
can be used. In this case, the host needs to periodically provide accelerometer readings to sensor-
hub using the commands provided in this document. For more information, see the MAX32664
User Guide.
Figure 1. Architecture diagram for health-sensing applications.