موديول سنسور معدل ضربات القلب MAX30100 - أخضر

The MAX30100 pulse oximeter and heart rate sensor is an I2C-based low-power plug-and-play biometric sensor. It can be used by students, hobbyists, engineers, manufacturers, and game & mobile developers who want to incorporate live heart-rate data into their projects.

MAX30100 Module Hardware Overview

The module features the MAX30100 – a modern, integrated pulse oximeter and heart rate sensor IC, from Analog Devices. It combines two LEDs, a photodetector, optimized optics, and low-noise analog signal processing to detect pulse oximetry (SpO2) and heart rate (HR) signals.

On the right, the MAX30100 has two LEDs – a RED and an IR LED. And on the left is a very sensitive photodetector. The idea is that you shine a single LED at a time, detecting the amount of light shining back at the detector, and, based on the signature, you can measure blood oxygen level and heart rate.

Power Requirement

The MAX30100 chip requires two different supply voltages: 1.8V for the IC and 3.3V for the RED and IR LEDs. So the module comes with 3.3V and 1.8V regulators. This allows you to connect the module to any microcontroller with 5V, 3.3V, even 1.8V level I/O.

One of the most important features of the MAX30100 is its low power consumption: the MAX30100 consumes less than 600μA during measurement. Also it is possible to put the MAX30100 in standby mode, where it consumes only 0.7μA. This low power consumption allows implementation in battery powered devices such as handsets, wearables or smart watches.

On-Chip Temperature Sensor

The MAX30100 has an on-chip temperature sensor that can be used to compensate for the changes in the environment and to calibrate the measurements.

This is a reasonably precise temperature sensor that measures the ‘die temperature’ in the range of -40˚C to +85˚C with an accuracy of ±1˚C.

I2C Interface

The module uses a simple two-wire I2C interface for communication with the microcontroller. It has a fixed I2C address: 0xAEHEX (for write operation) and 0xAFHEX (for read operation).

FIFO Buffer

The MAX30100 embeds a FIFO buffer for storing data samples. The FIFO has a 16-sample memory bank, which means it can hold up to 16 SpO2 and heart rate samples. The FIFO buffer can offload the microcontroller from reading each new data sample from the sensor, thereby saving system power.

Interrupts

The MAX30100 can be programmed to generate an interrupt, allowing the host microcontroller to perform other tasks while the data is collected by the sensor. The interrupt can be enabled for 5 different sources:

• Power Ready : triggers on power-up or after a brownout condition.


• SpO2 Data Ready : triggers after every SpO2 data sample is collected.


• Heart Rate Data Ready : triggers after every heart rate data sample is collected.


• Temperature Ready : triggers when an internal die temperature conversion is finished.


• FIFO Almost Full : triggers when the FIFO becomes full and future data is about to lost.

The INT line is an open-drain, so it is pulled HIGH by the onboard resistor. When an interrupt occurs the INT pin goes LOW and stays LOW until the interrupt is cleared.

Technical Specifications

Here are the technical specifications:

You can find extensive information for the MAX30100 sensor from the datasheet.

How MAX30100 Pulse Oximeter and Heart Rate Sensor Works?

The MAX30100, or any optical pulse oximeter and heart-rate sensor for that matter, consists of a pair of high-intensity LEDs (RED and IR, both of different wavelengths) and a photodetector. The wavelengths of these LEDs are 660nm and 880nm, respectively.

The MAX30100 works by shining both lights onto the finger or earlobe (or essentially anywhere where the skin isn’t too thick, so both lights can easily penetrate the tissue) and measuring the amount of reflected light using a photodetector. This method of pulse detection through light is called Photoplethysmogram.

The working of MAX30100 can be divided into two parts: Heart Rate Measurement and Pulse Oximetry (measuring the oxygen level of the blood).

Heart Rate Measurement

The oxygenated hemoglobin (HbO2) in the arterial blood has the characteristic of absorbing IR light. The redder the blood (the higher the hemoglobin), the more IR light is absorbed. As the blood is pumped through the finger with each heartbeat, the amount of reflected light changes, creating a changing waveform at the output of the photodetector. As you continue to shine light and take photodetector readings, you quickly start to get a heart-beat (HR) pulse reading.

Pulse Oximetry

Pulse oximetry is based on the principle that the amount of RED and IR light absorbed varies depending on the amount of oxygen in your blood. The following graph is the absorption-spectrum of oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb).

As you can see from the graph, deoxygenated blood absorbs more RED light (660nm), while oxygenated blood absorbs more IR light (880nm). By measuring the ratio of IR and RED light received by the photodetector, the oxygen level (SpO2) in the blood is calculated.

MAX30100 Module Pinout

The MAX30100 module brings out the following connections.

VIN is the power pin. You can connect it to 3.3V or 5V output from your Arduino.

SCL is the I2C clock pin, connect to your Arduino’s I2C clock line.

SDA is the I2C data pin, connect to your Arduino’s I2C data line.

INT The MAX30100 can be programmed to generate an interrupt for each pulse. This line is open-drain, so it is pulled HIGH by the onboard resistor. When an interrupt occurs the INT pin goes LOW and stays LOW until the interrupt is cleared.

IRD The MAX30100 integrates an LED driver to drive LED pulses for SpO2 and HR measurements. Use this if you want to drive the IR LED yourself, otherwise leave it unconnected.

RD pin is similar to the IRD pin, but is used to drive the Red LED. If you don’t want to drive the red LED yourself, leave it unconnected.

GND is the ground.

MAX30100 Not Working – Problem and Solutions to Fix

There is no doubt that the MAX30100 module is cheap and very popular among hobbyists, but unfortunately the module (sold in the thousands) has a serious design problem. Well, let’s fix it.

The Problem

The MAX30100 chip requires two different supply voltages: 1.8V for the IC and 3.3V for the RED and IR LEDs. So the module comes with two linear voltage regulators – U1 and U2. The first generates 5V to 3.3V. The second regulator is connected to the output of the first and generates 1.8V.

Now take a closer look at the 4.7kΩ pull-up resistors (R1, R2 and R3) for the SCL, SDA and INT signal lines. They are connected to the 1.8V supply (highlighted with a thick red line)!

The two regulators U1, U2 and the trace that connects the 4.7kΩ pull-up resistors to the 1.8V supply are highlighted on the module as well.

If you connect such module to the Arduino’s 5V logic – it will not show up on the I2C bus because the logic level is too low (Arduino reports HIGH if the voltage exceeds 3.0V for 5V-boards and 2.0V for 3.3V-boards). Even with a 3.3V logic board, it will not work.

Don’t worry! We have two solutions to fix this problem.

Solution 1 (tested):

1. Cut the trace in the place of the red line. This will disconnect all 4.7kΩ pull-up resistors from the 1.8V supply voltage.


2. Now make a jumper as shown by the yellow line with a piece of wire or a solder blob. This will pull all the 4.7kΩ resistors up to 3.3V.

Here’s the board with and without the modifications:

After following these steps, connect the module to the Arduino UNO using the wiring diagram below:

The wiring is fairly easy. Simply connect the VIN pin to Arduino’s 3.3V and GND to ground. Connect the SCL pin to the I2C clock pin and the SDA pin to the I2C data pin on your Arduino. Finally connect the INT pin to digital pin 2.

Solution 2 (tested):

The second solution is to remove all 4.7kΩ pullup resistors from the board. We will use external pullup resistors on the SCL, SDA and INT signal lines later.

Here’s the board with and without the resistors removed:

After removing the resistors, connect the module to the Arduino UNO using the wiring diagram below:

The wiring is the same as the first one; you just need to add external 4.7kΩ pullup resistors on the SCL, SDA and INT signal lines.

Our Evaluation:

We have tested both solutions and they work great. So try one which is easier for you to implement.

Library Installation

There are several libraries available for the MAX30100 sensor. However in our example, we are using the one by OXullo Intersecans. This library exposes most of the features of the MAX30100 and offers simple and easy to use functions to calculate pulse rate and SpO2. You can download this library from within the Arduino IDE Library Manager.

To install the library navigate to the Sketch > Include Library > Manage Libraries… Wait for Library Manager to download libraries index and update list of installed libraries.

Filter your search by typing max30100. There should be a couple entries. Look for MAX30100lib Library by OXullo Intersecans. Click on the entry, and then select Install.

Example 1 – Measuring Heart-Rate (BPM) and Oxygen Saturation (SpO2)

This is where the fun really begins! In this example, we’ll measure heart rate (Beats Per Minute or BPM) and blood oxygen level (SpO2) of the person we’re monitoring.