Heart Rate Monitor via LoRaWAN

This project enables real-time heart rate monitoring using the Wireless Tracker connected to a MAX30102 pulse oximetry sensor. Data transmits via LoRaWAN to the SnapEmu platform for visualization.

Hardware Requirements

Component	Purpose
Heltec Wireless Tracker	Main controller + LoRa TX
HT-M7603 Indoor LoRa Gateway	LoRaWAN network gateway
MAX30102 Heart Rate Sensor	Pulse oximetry sensor
DuPont Wires	Connections

Wiring Diagram

The MAX30102 connects via I2C:

MAX30102 Pin	Tracker Pin	Description
VCC	3V3	Power (3.3V)
GND	GND	Ground
SDA	GPIO45	I2C Data
SCL	GPIO46	I2C Clock

Tip

GPIO45 and GPIO46 are recommended for I2C as they don’t conflict with built-in peripherals on the Wireless Tracker.

Software Setup

1. Configure LoRa Gateway

   Set up your HT-M7603 gateway with SnapEmu platform following the official Heltec documentation.

2. Register Device on SnapEmu

   Register your Wireless Tracker node following the SnapEmu device connection guide.

3. Install Libraries

   Required Arduino libraries:

   • Wire.h (built-in)
   • MAX30102_PulseOximeter.h
   • LoRaWan_APP.h (Heltec library)

4. Test Sensor Standalone

   Upload the test code to verify sensor operation before adding LoRaWAN.

5. Deploy Full Application

   Upload the complete LoRaWAN code with your OTAA credentials.

Code Examples

Sensor Test

#include <Wire.h>
#include "MAX30102_PulseOximeter.h"

#define REPORTING_PERIOD_MS 1000
PulseOximeter pox;
uint32_t tsLastReport = 0;

void onBeatDetected() {
    Serial.println("Beat detected!");
}

void setup() {
    Serial.begin(115200);
    Wire.begin(45, 46);  // SDA=GPIO45, SCL=GPIO46
    Serial.print("Initializing MAX30102..");
    delay(3000);

    if (!pox.begin()) {
        Serial.println("FAILED");
        for(;;);
    } else {
        Serial.println("SUCCESS");
    }

    pox.setIRLedCurrent(MAX30102_LED_CURR_7_6MA);
    pox.setOnBeatDetectedCallback(onBeatDetected);
}

void loop() {
    pox.update();

    if (millis() - tsLastReport > REPORTING_PERIOD_MS) {
        float heartRate = pox.getHeartRate();
        float spo2 = pox.getSpO2();

        Serial.print("HR: ");
        Serial.print(heartRate > 0 ? String(heartRate) : "N/A");
        Serial.print(" bpm / SpO2: ");
        Serial.print(spo2 > 0 ? String(spo2) : "N/A");
        Serial.println("%");

        tsLastReport = millis();
    }
}

LoRaWAN Code

#include <Wire.h>
#include "MAX30102_PulseOximeter.h"
#include "LoRaWan_APP.h"

#define REPORTING_PERIOD_MS 1000

// OTAA Parameters - Replace with your SnapEmu values
uint8_t devEui[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xA8 };
uint8_t appEui[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
uint8_t appKey[] = { 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88,
                     0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88 };

// LoRaWAN Configuration
uint16_t userChannelsMask[6] = { 0x00FF, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000 };
LoRaMacRegion_t loraWanRegion = ACTIVE_REGION;
DeviceClass_t loraWanClass = CLASS_A;
uint32_t appTxDutyCycle = 15000;  // 15 second transmit interval
bool overTheAirActivation = true;
bool loraWanAdr = true;
bool isTxConfirmed = true;
uint8_t appPort = 2;
uint8_t confirmedNbTrials = 4;

PulseOximeter pox;
uint32_t tsLastReport = 0;

static void prepareTxFrame(uint8_t port) {
    pox.update();
    float heartRate = pox.getHeartRate();
    float spo2 = pox.getSpO2();
    unsigned char *puc;

    appDataSize = 0;

    // Packet header
    appData[appDataSize++] = 0x04;
    appData[appDataSize++] = 0x00;
    appData[appDataSize++] = 0x0A;
    appData[appDataSize++] = 0x02;

    // Heart rate (4 bytes float)
    puc = (unsigned char *)(&heartRate);
    appData[appDataSize++] = puc[0];
    appData[appDataSize++] = puc[1];
    appData[appDataSize++] = puc[2];
    appData[appDataSize++] = puc[3];

    // Separator
    appData[appDataSize++] = 0x12;

    // SpO2 (4 bytes float)
    puc = (unsigned char *)(&spo2);
    appData[appDataSize++] = puc[0];
    appData[appDataSize++] = puc[1];
    appData[appDataSize++] = puc[2];
    appData[appDataSize++] = puc[3];

    Serial.printf("TX: HR=%.1f SpO2=%.1f\n", heartRate, spo2);
}

void onBeatDetected() {
    Serial.println("Beat!");
}

void setup() {
    Serial.begin(115200);
    Wire.begin(45, 46);
    Mcu.begin(HELTEC_BOARD, SLOW_CLK_TPYE);

    Serial.print("Initializing MAX30102..");
    delay(3000);

    if (!pox.begin()) {
        Serial.println("FAILED");
        for(;;);
    }
    Serial.println("SUCCESS");

    pox.setIRLedCurrent(MAX30102_LED_CURR_27_1MA);
    pox.setOnBeatDetectedCallback(onBeatDetected);

    LoRaWAN.init(loraWanClass, loraWanRegion);
    LoRaWAN.setDefaultDR(3);
}

void loop() {
    pox.update();

    // Local display
    if (millis() - tsLastReport > REPORTING_PERIOD_MS) {
        float heartRate = pox.getHeartRate();
        float spo2 = pox.getSpO2();

        Serial.printf("HR: %s bpm | SpO2: %s%%\n",
            heartRate > 0 ? String(heartRate).c_str() : "N/A",
            spo2 > 0 ? String(spo2).c_str() : "N/A");

        tsLastReport = millis();
    }

    // LoRaWAN state machine
    switch (deviceState) {
        case DEVICE_STATE_INIT:
        case DEVICE_STATE_JOIN:
            LoRaWAN.join();
            break;
        case DEVICE_STATE_SEND:
            prepareTxFrame(appPort);
            LoRaWAN.send();
            deviceState = DEVICE_STATE_CYCLE;
            break;
        case DEVICE_STATE_CYCLE:
            txDutyCycleTime = appTxDutyCycle +
                randr(-APP_TX_DUTYCYCLE_RND, APP_TX_DUTYCYCLE_RND);
            LoRaWAN.cycle(txDutyCycleTime);
            deviceState = DEVICE_STATE_SLEEP;
            break;
        case DEVICE_STATE_SLEEP:
            LoRaWAN.sleep(loraWanClass);
            break;
        default:
            deviceState = DEVICE_STATE_INIT;
            break;
    }
}

Decoder

// SnapEmu payload decoder
function Decoder(bytes, port) {
    var decoded = {};

    if (bytes.length >= 13) {
        // Extract heart rate (bytes 4-7)
        var hrBytes = new Uint8Array([bytes[4], bytes[5], bytes[6], bytes[7]]);
        var hrView = new DataView(hrBytes.buffer);
        decoded.heartRate = hrView.getFloat32(0, true);

        // Extract SpO2 (bytes 9-12)
        var spo2Bytes = new Uint8Array([bytes[9], bytes[10], bytes[11], bytes[12]]);
        var spo2View = new DataView(spo2Bytes.buffer);
        decoded.spo2 = spo2View.getFloat32(0, true);
    }

    return decoded;
}

Platform Features

SnapEmu provides:

• Real-time heart rate graph
• SpO2 level monitoring
• Historical data (up to 1 month)
• Mobile app + web interface

Troubleshooting

Issue	Solution
No heartbeat detected	Ensure finger is properly placed, adjust LED current
Erratic readings	Clean sensor, reduce movement, check power supply
LoRa join failed	Verify gateway connection, check OTAA credentials
Data not on platform	Check decoder function, verify port number matches

References

• SnapEmu Documentation
• Heltec Sensor Decoding Guide

Based on the project by ashley15 on Hackster.io.