Maxim Integrated MAX32664A Quick Start Manual

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Measuring Heart Rate and SpO

Using the MAX32664A – A Quick Start Guide

UG7087; Rev 0; 8/19

Abstract

The MAX32664A is a variant of the MAX32664 sensor-hub family, which is specifically targeted for the finger-based measurement of heart rate and SpO sensor and a 3-axis accelerometer, it provides a sensor’s raw data, as well as calculated heartrate and SpO step-by-step instructions that enable a user to communicate with the MAX32664A, and to calibrate, configure, and receive measurement and monitoring data.

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data to a host device through its I2C slave interface. This document provides

. Combined with the MAX30101 optical

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Table of Contents

Introduction ................................................................................................................................ 3

1 Architecture ............................................................................................................................. 4

1.1 Communicating with the MAX32664A ............................................................................... 5

1.2 Accelerometer .................................................................................................................. 6

2 Calibration of the SpO2 Algorithm ........................................................................................... 7

2.1 Calibration of SpO2 Coefficients for the Final Product ...................................................... 7

2.2 Algorithm Settings and Configurations .............................................................................. 8

3 Measuring Heart Rate and SpO2 on Finger ...........................................................................11

3.1 Raw Data Collection Mode ..............................................................................................11

3.2 Algorithm Mode: Heart Rate and SpO2 ...........................................................................13

Revision History ........................................................................................................................15

List of Figures

Figure 1. Architecture diagram for health-sensing applications. ................................................. 4

List of Tables

Table 1. Read Status Byte Value ............................................................................................... 5

Table 2. Host-Side Accelerometer—Sending Data to the MAX32664A ...................................... 6

Table 3. Configurations and Settings—HR/SpO

Table 4. Host Commands—SpO

Calibration ............................................................................. 9

Table 5. Format of Received Samples—SpO

Table 6. Host Commands—Raw Data Mode .............................................................................11

Table 7. Format of Received Samples—Raw Data Mode .........................................................12

Table 8. Host Commands—HR/SpO

Algorithm ........................................................................13

Table 9. Format of Received Samples—HR/SpO

........................................................................ 8

Calibration Mode ...............................................10

Algorithm ....................................................14

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Introduction

The MAX32664A is a variant of the MAX32664 sensor-hub family that enables users to capture raw data as well as calculated heart-rate and SpO is preprogrammed with the firmware, drivers, and algorithm that are required to interface with the

MAX30101 sensor device through an I

C master port. The I2C slave interface is dedicated to

establishing communication with a host microcontroller.

In order to properly capture and calculate the data, it is recommended that accelerometer data be provided to the MAX32664A. The MAX32664A firmware includes the required drivers for the

Kionix

KX122 accelerometer, which is wired together with the MAX30101 to the same I2C port. Alternatively, a host-side accelerometer can be used. In this case, the sampled accelerometer data must be periodically reported to the MAX32664A by the host microcontroller.

This document provides the instructions necessary to create a solution with the MAX32664A based on the MAXREFDES220# reference design.

data through finger contact. The MAX32664A

Kionix is a registered trademark of Kionix, Inc.

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1 Architecture

A typical health-sensing design includes a host microcontroller that communicates with the

MAX32664A through the I in Application or Bootloader mode through the RSTN and multifunction input/output (MFIO) pins. An MFIO pin is also used in Application mode to interrupt the host for I MAX32664A interfaces with the MAX30101 optical sensor through a second I

To enter Bootloader mode:

C bus. Two GPIO pins are needed to control the reset and the startup

C communication. The

C bus.

• Set the RSTN pin to low for 10ms.

• While RSTN is low, set the MFIO pin to low. (The MFIO pin should be set to low at least

1ms before the RSTN pin is set to high.)

• After the 10ms has elapsed, set the RSTN pin to high.

• After an additional 50ms has elapsed, the MAX32664 is in Bootloader mode.

To enter Application mode:

• Set the RSTN pin to low for 10ms.

• While RSTN is low, set the MFIO pin to high.

• After the 10ms has elapsed, set the RSTN pin to high. (The MFIO pin should be set to

high at least 1ms before the RSTN pin is set to high.)

• After an additional 50ms has elapsed, the MAX32664 is in Application mode and the

application performs its initialization of the application software.

• After approximately 1 second from when the RSTN pin was set to high, the application

completes the initialization and the device is ready to accept I

Figure 1 shows the top-level architecture.

Figure 1. Architecture diagram for health-sensing applications.

C commands.

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1.1 Communicating with the MAX32664A

STATUS

BYTE VALUE

0x00

The write transaction was successful.

0x01

Illegal Family Byte and/or Command Byte was used.

0x02

This function is not implemented.

0x03

Incorrect number of bytes sent for the requested Family Byte.

0x04

Illegal configuration value was attempted to be set.

0x05

Incorrect mode specified. (In bootloader: Device is busy. Try again.)

0x80

General error while receiving/flashing a page during the bootloader sequence.

0x81

Checksum error while decrypting/checking page data.

0x82

Authorization error.

0x83

Application not valid.

0xFE

Device is busy. Try again.

0xFF

Unknown error.

A host should use the I2C bus to communicate with the MAX32664A (slave) using a series of commands. A generic write command includes the following fields:

Slave_WriteAddress(1 byte)|Command_Family(1 byte)|Command_Index(1 byte)|Value(multiple bytes)

A generic response includes the following fields:

Slave_ReadAddress(1 byte)|Status(1 byte)|Value(multiple bytes)

Slave_WriteAddress and Slave_ReadAddress are set to 0xAA and 0xAB, respectively.

The read status byte is an indicator of success (0x00) or failure, as shown Table 1.

Table 1. Read Status Byte Value

DESCRIPTION

This document provides examples of commands for establishing communication with the MAX32664A. For a complete list of commands and instructions for the I

C interface, see the

MAX32664 User Guide.

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1.2 Accelerometer

MAX32664

(HEX)

AA 44 04 01 01

Enable the host accelerometer.

AB 00

Success

Success; 6 is the

samples in FIFO

The following should be executed periodically at 200ms:

Write data to the input FIFO of the

N = 20

Success; sensor hub not busy

For best results, it is recommended that accelerometer data be provided to the MAX32664A.

calculation requires a resting condition, and the algorithm uses accelerometer data to detect

SpO

excessive motion. In such a condition, computation is paused, and the user is informed with a motion flag.

A sensor hub accelerometer can be integrated through the I case, the required driver for KX122 is already included. The user only needs to follow the reference schematics to connect the accelerometer and enable it before starting the algorithm, as described later in this document.

Alternatively, a host-side accelerometer can be used. In order to use the host-side accelerometer:

1. The host should start the accelerometer just before enabling the algorithm to maximize the initial synchronization between the PPG and accelerometer samples. However, accelerometer samples collected prior to receiving the confirmation of the algorithm

enable I

C command should be discarded.

2. The host is required to use a 3-axis accelerometer at a 100Hz sampling rate. If a higher sampling rate is chosen, samples should be decimated to be synchronized with a 10ms PPG sampling time.

3. The host must queue five accelerometer samples and feed them at the same time to the MAX32664A using the commands shown in Table 2. The period of feeding samples should be 200ms. Because the sensor and the host accelerometer use different clock sources, exact synchronization between them is not possible.

C port of the MAX32664A. In this

Table 2. Host-Side Accelerometer—Sending Data to the MAX32664A

HOST COMMAND

(HEX)

AA 13 00 04

AA 14 00 [Sample 1 values] … [Sample N values]

AA 00 00 Read the sensor hub status. AB 00 00

Read the sensor sample size for the accelerometer (optional).

sensor hub. Each sample has three 2-byte integer values for X, Y, and Z in milli-g.

DESCRIPTION

RESPONSE

AB 00 06

AB 00 Success

DESCRIPTION

number of bytes per

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2 Calibration of the SpO2 Algorithm

2.1 Calibration of SpO2 Coefficients for the Final Product

Due to variations in the physical design and optical shield of the final product, a calibration procedure is required to be performed once in a controlled environment. This procedure is important to ensure the quality of the SpO standard lab with a reference SpO

device to determine three calibration coefficients: a, b, and c.

The details of the calibration procedure are described in the Guidelines for SpO2 Measurement Using the Maxim MAX32664 Sensor Hub application note.

Once three calibration coefficients are obtained, they need to be loaded to the MAX32664A every time prior to starting the algorithm. But first, they are required to be converted to a 32-bit integer format using the following:

calculation. This step is typically performed in a

• A

• B

• C

= round (105 x a)

int32

= round (105 x b)

int32

= round (105 x c)

int32

For example, the default measured calibration coefficients are:

• a = 1.5958422

• b = -34.659664

• c = 112.68987

They are sent to the MAX32664A in integer format after conversion:

• A

• B

• C

= round (105 x a) = 0x00026F60

int32

= round (105 x b) = 0xFFCB1D12

int32

= round (105 x c) = 0x00ABF37B

int32

The calibration coefficients may be stored in the host flash separately and loaded to the MAX32664A after every reset.

Table 4 shows the sequence of commands for the calibration process. Table 5 shows the format of received samples. Typically, R values are needed for the calibration process, as described in the Guidelines for SpO2 Measurement Using the Maxim MAX32664 Sensor Hub application note.

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2.2 Algorithm Settings and Configurations

FAMILY

BYTE

ALGORITHM

INDEX

CONFIGURATION

INDEX

DEFAULT

VALUE

SpO2 calibration coefficients*

A = 1.5958422

(0x00abf37b)

Table 3 shows the settings that are available for the heart rate (HR)/SpO2 algorithm. To update the algorithm settings, be sure to send the appropriate commands BEFORE enabling the algorithm, as shown in Table 8.

Table 3. Configurations and Settings—HR/SpO2

DESCRIPTION

0x50 for write

0x51 for read

0x02 0x0B

100,000 (12 bytes comprised of three 32-bit signed values)

(0x00026f60) B = -34.659664 (0xffcb1d12) C = 112.68987

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Table 4 shows the list of commands to start the SpO

HOST COMMAND

(HEX)

RESPONSE

(HEX)

Host initializes the MAX32664A in calibration mode and starts the algorithm using following commands:

1.1

AA 10 00 03

Set the output mode to sensor + algorithm

accelerometer, and algorithm data).

AB 00

1.2

AA 10 01 0F

Set the sensor hub interrupt threshold.

AB 00

1.3

AA 52 00 01

Enable the AGC.

AB 00

1.4

AA 44 04* 01 00 (if sensor

accelerometer is used)

Enable the accelerometer with the sensor

accelerometer.)

AB 00

1.5

AA 44 03* 01

Enable the AFE (e.g., the MAX30101).

AB 00

1.6

AA 52 02 02 (SpO2 calibration report)

Enable the HR/SpO2 algorithm. The format of the samples is shown in Table 5.

AB 00

1.7

Wait for 100ms before sending the next command. Any command to change sensor registers should appear AFTER enabling the algorithm or they will be overwritten.

READING SAMPLES

Host reads the samples upon receiving the MFIO interrupt from the MAX32664A. For SpO2 calibration, continue as needed to capture the R value. See Table 5.

2.1

AA 00 00

Read the sensor hub status byte:

If DataRdyInt is set, proceed to the next step.

AB 00 08

2.2

AA 12 00

Get the number of samples (nn) in the FIFO.

AB 00 nn

2.3

AA 12 01

Read the data stored in the FIFO; nn

format of the samples is shown in Table 5.

AB 00

nn_samples

Host ends the procedure:

3.1

AA 44 03* 00

Disable the AFE (e.g., the MAX30101).*

AB 00

3.2

AA 44 04* 00

Disable the accelerometer.* (Do not use this command if there is no accelerometer.)

AB 00

3.3

AA 52 02 00

Disable the algorithm.

AB 00

calibration.

Table 4. Host Commands—SpO2 Calibration

START ALGORITHM

hub accelerometer is used) AA 44 04* 01 01 (if Host

COMMAND DESCRIPTION

data (0x03) (streamed data will include PPG,

hub or host-side accelerometer.* (Do not use this command if there is no

Bit 0: Sensor comm error Bits 1 and 2: Reserved Bit 3: FIFO filled to threshold (DataRdyInt) Bit 4: Output FIFO overflow (FifoOutOvrInt) Bit 5: Input FIFO overflow (FifoInOverInt) Bit 6: Sensor hub busy (DevBusy) Bit 7: Reserved

samples (30 bytes each) will be read. The

STOP

*Provided indexes are example for sensors such as the MAX30101 AFE or KX122 accelerometer

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data_for_

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Table 5. Format of Received Samples—SpO2 Calibration Mode

# OF BYTES

(MSB FIRST)

LED1

IR counter

LED2

Red counter

LED3

N/A 9 LED4

N/A

Two's complement. LSB =

0.001g

Two's complement. LSB =

0.001g

Two's complement. LSB =

0.001g

Heart rate

10x heart-rate value

Heart rate confidence

Calculated confidence level in %

SpO2

10x SpO2 value

Algorithm current state:

3: Finger is detected

24 R 2

10x calculated R value

Algorithm current status:

-6: Finger excessive motion

Reserved

DATA SOURCE BYTE INDEX DATA ITEM

MAX30101 (12 Bytes)*

12 accelX 2

Accelerometer (6 Bytes)*

HR/SpO2 Algorithm (12 Bytes)**

14 accelY 2

16 accelZ 2

Algorithm state

Algorithm status

DESCRIPTION

0: No object is detected 1: Something is on sensor 2: Another object is detected

0: Success 1: Not ready

-1: Something is on sensor

-2: Device excessive motion

-3: No object

-4: Pressing too hard

-5: Object instead of finger

*If the output mode includes the sensor. **If the output mode includes the algorithm.

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3 Measuring Heart Rate and SpO2 on Finger

HOST COMMAND

(HEX)

RESPONSE

(HEX)

START ALGORITHM

Host initializes the MAX32664A:

1.1

AA 10 00 01

Set the output mode to sensor data (0x01,

accelerometer data).

AB 00

1.2

AA 10 01 0F

Set the sensor hub interrupt threshold.

AB 00

1.3

AA 44 04* 01 00 (if sensor

accelerator is used)

Enable the accelerometer with the sensor

accelerometer.)

AB 00

1.4

AA 44 03* 01

Enable the AFE (e.g., the MAX30101).

AB 00

1.5

AA 52 02 01

Enable the HR/SpO2 algorithm

AB 00

1.6

AA 52 00 00

Disable the AGC.

AB 00

1.7

Wait for 100ms before sending the next command. Any command to change the sensor registers should appear AFTER enabling the algorithm or they will be overwritten.

1.8

AA 40 03 0C [7F]

Set the MAX30101 LED1 (red) current to half

saturated.

AB 00

1.9

AA 40 03 0D [7F]

Set the MAX30101 LED2 (IR) current to half

saturated.

AB 00

READING SAMPLES

Host reads samples upon receiving the MFIO interrupt by the MAX32664A. For raw data, repeat as needed to collect PPG counters.

2.1

AA 00 00

Read the sensor hub status byte:

If DataRdyInt is set, proceed to the next step.

AB 00 08

2.2

AA 12 00

Get the number of samples (nn) in the FIFO.

AB 00 nn

2.3

AA 12 01

Read the data stored in the FIFO; nn

format of samples is shown in Table 7.

AB 00

nn_samples

3.1 Raw Data Collection Mode

For hardware testing purposes, the user may choose to start the MAX32664A to collect raw PPG samples. In this case, the host configures the MAX32664A to work in Raw Data mode (no algorithm report). Table 6 lists the set of commands that are needed to work in this mode. In Raw Data mode, only raw PPG samples and accelerometer data are included in the received samples.

The AGC must be turned off to collect raw PPG data, as shown in step 1.6 in Table 6. In this case, LED currents will not be adjusted automatically. Although the algorithm is running, it will not affect the PPG samples. If the reported PPG data is saturated, you can reduce the LED currents as shown. Note that updating MAX30101 registers should appear AFTER enabling the algorithm and the MAX30101, or they will be overwritten during initialization. By setting the output mode to sensor data in step 1.1, only the 12-byte PPG data of the MAX30101 and 6-byte accel data will be reported in received samples.

Table 6. Host Commands—Raw Data Mode

hub accelerator is used) AA 44 04* 01 01 (if host

COMMAND DESCRIPTION

streamed data will include only PPG and

hub or host-side accelerometer.* (Do not use this command if there is no

of full scale. Reduce [7F] if the signal is

of full scale. Reduce [7F] if signal is

samples (18 bytes each) will be read. The

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data_for_

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STOP

Host ends the procedure:

3.1

AA 44 03* 00

Disable the AFE (e.g., the MAX30101).*

AB 00

3.2

AA 44 04* 00

Disable the accelerometer.* (Do not use this command if there is no accelerometer.)

AB 00

3.2

AA 52 02 00

Disable the algorithm.

AB 00

# OF BYTES

(MSB FIRST)

LED1

IR counter

LED2

Red counter

LED3

N/A 9 LED4

N/A

Two's complement. LSB =

0.001g

Two's complement. LSB =

0.001g

Two's complement. LSB =

0.001g

*Provided indexes are example for sensors such as the MAX30101 AFE or KX122 accelerometer.

Table 7. Format of Received Samples—Raw Data Mode

DATA SOURCE BYTE INDEX DATA ITEM

MAX30101 (12 Bytes)*

12 accelX 2

Accelerometer (6 Bytes)*

*If the output mode includes the sensor.

14 accelY 2

16 accelZ 2

DESCRIPTION

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3.2 Algorithm Mode: Heart Rate and SpO2

HOST COMMAND

(HEX)

RESPONSE

(HEX)

Host initializes the MAX32664A:

1.1

AA 50 02 0B

00 AB F3 7B (example for C)

Set SpO2 calibration coefficients derived from the

AB 00

1.2

AA 10 00 03

Set output mode to sensor + algorithm data (0x03,

and algorithm data).

AB 00

1.3

AA 10 01 0F

Set sensor hub interrupt threshold.

AB 00

1.4

AA 52 00 01

Enable the AGC.

AB 00

1.5

AA 44 04* 01 00 (if sensor

accelerator is used)

Enable the accelerometer with the sensor hub or

accelerometer.)

AB 00

1.6

AA 44 03* 01

Enable the AFE (e.g., the MAX30101).

AB 00

1.7

AA 52 02 01 (normal algorithm report)

Enable the HR/SpO2 algorithm. The format of the samples is shown in Table 9.

AB 00

READING SAMPLES

Host reads the samples upon receiving the MFIO interrupt by the MAX32664A.

2.1

AA 00 00

Read the sensor hub status byte:

If DataRdyInt is set, proceed to next step.

AB 00 08

2.2

AA 12 00

Get the number of samples (nn) in the FIFO.

AB 00 nn

2.3

AA 12 01

Read the data stored in the FIFO; nn samples (24

shown in Table 9.

AB 00

nn_samples

STOP

Host ends the procedure:

3.1

AA 44 03* 00

Disable the AFE (e.g., the MAX30101).*

AB 00

3.2

AA 44 04* 00

Disable the accelerometer.* (Do not use this command if there is no accelerometer.)

AB 00

3.3

AA 52 02 00

Disable the algorithm.

AB 00

Table 8 shows the list of commands to start the HR/SpO2 algorithm.

Table 8. Host Commands—HR/SpO2 Algorithm

START ALGORITHM

00 02 6F 60 (example for A) FF CB 1D 12 (example for B)

hub accelerator is used) AA 44 04* 01 01 (if host

COMMAND DESCRIPTION

procedure in section 2.1. Provided example for: A = 1.5958422, B = -34.659664, C = 112.68987.

streamed data will include PPG, accelerometer,

host-side accelerometer.* (Do not use this command if there is no

bytes each) will be read. The format of samples is

*Provided indexes are example for sensors such as the MAX30101 AFE or KX122 accelerometer.

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data_for_

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Table 9. Format of Received Samples—HR/SpO2 Algorithm

# OF BYTES

(MSB FIRST)

LED1

IR counter

LED2

Red counter

LED3

N/A 9 LED4

N/A

Two's complement. LSB =

0.001g

Two's complement. LSB =

0.001g

Two's complement. LSB =

0.001g

Heart rate

10x heart-rate value

Heart rate confidence

Calculated confidence level in %

SpO2

10x SpO2 value

Algorithm current state:

3: Finger is detected

DATA SOURCE BYTE INDEX DATA ITEM

MAX30101 (12 Bytes)*

12 accelX 2

Accelerometer (6 Bytes)*

HR/SpO2 Algorithm (6 Bytes)**

*If the output mode includes the sensor. **If the output mode includes the algorithm.

14 accelY 2

16 accelZ 2

Algorithm state

DESCRIPTION

0: No object is detected 1: Something is on sensor 2: Another object is detected

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Revision History

REVISION

NUMBER

0 08/19 Initial release —

REVISION

DATE

DESCRIPTION

PAGES

CHANGED

©2019 by Maxim Integrated Products, Inc. All rights reserved. Information in this publication concerning the devices, applications, or technology described is intended to suggest possible uses and may be superseded. MAXIM INTEGRATED PRODUCTS, INC. DOES NOT ASSUME LIABILITY FOR OR PROVIDE A REPRESENTATION OF ACCURACY OF THE INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED IN THIS DOCUMENT. MAXIM ALSO DOES NOT ASSUME LIABILITY FOR INTELLECTUAL PROPERTY INFRINGEMENT RELATED IN ANY MANNER TO USE OF INFORMATION, DEVICES, OR TECHNOLOGY DESCRIBED HEREIN OR OTHERWISE. The information contained within this document has been verified according to the general principles of electrical and mechanical engineering or registered trademarks of Maxim Integrated Products, Inc. All other product or service names are the property of their respective owners.

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Maxim Integrated MAX32664A Quick Start Manual

Specifications and Main Features

Frequently Asked Questions

User Manual