Published September 17, 2026 © MIT

MicroECG - Low cost pocket ECG solution

MicroECG is a low-cost, WiFi-enabled, single-lead ECG monitor built with ESP8266 and AD8232. It streams real-time hea

IntermediateWork in progress28

Things used in this project

Hardware components

NodeMCU ESP8266 Breakout Board

SparkFun Electronics SparkFun Single Lead Heart Rate Monitor - AD8232

Battery 1200mAh Li-ion

Electrodes LA/RA (touch) + optional chest lead

3.3v LDO Voltage Regulator

TP4056 Battery Charging Module

Enclosure Box

Software apps and online services

Arduino IDE

Microsoft VS Code

Hand tools and fabrication machines

Soldering iron (generic)

Story

In today’s world, cardiovascular diseases (CVDs) are one of the leading causes of mortality, claiming millions of lives every year. Early detection and timely monitoring of heart health are crucial for managing these conditions effectively. However, in many rural and remote areas, access to advanced healthcare facilities is limited, leaving a significant portion of the population at risk of undiagnosed heart conditions. Imagine a scenario: A middle-aged farmer working in a rural area experiences occa- sional chest discomfort but dismisses it due to lack of access to medical facilities. One day, he suffers a major heart event because his condition went undetected for years. This is not just an isolated case but a recurring reality in underserved regions. What if there was a device that could have detected his heart condition earlier, allowing timely intervention? Electrocardiography (ECG) is an indispensable tool for diagnosing cardiac conditions by analyzing the heart’s electrical activity. However, conventional ECG systems often multi-lead, hospital-grade machines pose barriers in rural and low-resource settings due to high costs, bulkiness, and the requirement for trained personnel. Our project - Micro-ECG aims to eliminate these limitations by offering a fully portable, battery-powered, single-lead ECG system that uses: • A WiFi-based microcontroller (ESP8266) for communication. • A real-time, browser-based user interface via captive portal. • Hardware-level noise suppression using op-amps and RC filters. • Frontend ECG signal filtering using hand-crafted JavaScript code. Unlike Bluetooth-based systems or mobile apps, Micro-ECG works independently across devices, requiring only a browser to operate. With both on-device and external chest electrodes, it captures and visualizes cardiac signals accurately.

System Architecture

Normalised system architecture of an ECG device is simple

Flow graph of an Simple ECG Device

To cut costs, we avoided printer or display, that is usually used to show the ECG signal waveform, but as ESP8266(a great low cost microcontroller) also comes with WIFI, so instead we preferred to transfer the ECG data to your Smart Devices providing flexibility and more power for further processing the signal better than a small capacity MCU, When the future focus is actually AI analysis with large dataset of past recorded anomalies.

Prototype Overview

MicroECG Prototype Overview

User Manual - https://github.com/Raju-Adhikary/MicroECG/blob/master/User%20Manual/

Project Report - https://github.com/Raju-Adhikary/MicroECG/tree/master/Report/report2/

Demo

MicroECG - Parameters Detection Screen

MicroECG - Controls Screen

MicroECG - Recordings Screen

Screenshot, Demo - https://github.com/Raju-Adhikary/MicroECG/tree/master/images

3D Model and Videos - https://github.com/Raju-Adhikary/MicroECG/tree/master/3d%20Model%20and%20Videos

Enclosure Lebels - https://github.com/Raju-Adhikary/MicroECG/tree/master/Lebel

ESP8266 Arduino IDE code

#include <DNSServer.h>
#include <WebSocketsServer.h>
#include <ESP8266WebServer.h>
// #include <ESP8266mDNS.h>

const byte DNS_PORT = 53;
IPAddress apIP(172, 217, 28, 1);
DNSServer dnsServer;
ESP8266WebServer server(80);
WebSocketsServer webSocket = WebSocketsServer(81);


// ADC buffer and indexing variables
int *adcBuffer = nullptr;    // Dynamic buffer pointer
int sampleIndex = 0;
int sps = 10;                // Default saadcBuffermples per second
unsigned long previousMillis = 0;
const long sendInterval = 300;   // Time interval to send data (333ms)

unsigned long lastSampleTime = 0;  // Time of last sample
long sampleInterval = 1000 / sps;  // Interval between each sample based on SPS


String webServerIndexPage = "<!DOCTYPE html><html lang=\"en\"><head><meta charset=\"UTF-8\"><meta name=\"viewport\" content=\"width=device-width, initial-scale=1\"><title>Micro ECG</title><style>*{margin:0;padding:0;box-sizing:border-box;font-family:Arial,sans-serif}body{background:#f4f4f9;color:#333}button,input{padding:3px 9px;margin:5px;background-color:#f4f4f9;border:.1px solid #00f;box-shadow:2px 2px 2px gray}button:hover,input:hover{box-shadow:none}.pushButton[active]{background-color:#0f05}.container{max-width:1200px;margin:20px auto;padding:20px;background:#fff;border-radius:10px;box-shadow:0 4px 8px #0000001a}.header{text-align:center;padding:10px 0;border-bottom:2px solid #e0e0e0}.header h1{font-size:2rem;color:#007bff}.snap-container{width:100%;margin:auto}.canvas-container{margin-top:20px;text-align:center;position:sticky;top:0;pointer-events:none;background-color:#fff5}canvas,.snap-container img{border:1px solid #ddd;width:100%;height:100px}.tabs{display:flex;flex-wrap:wrap;gap:10px}.tabs button{margin:0;flex:1 1 auto}.tabs button[active]{box-shadow:none;border:none}.tab-contents>div:not([active]){display:none}.parameters{display:flex;flex-wrap:wrap;gap:20px;padding:20px 0}.parameter{flex:1 1 auto;background:#f9f9f9;padding:10px;border-radius:5px;box-shadow:0 2px 4px #0000001a;text-align:center;min-width:30%}.parameter span{font-size:1rem;color:#555;font-weight:700;white-space:nowrap}.controls,.settings,.flexbox{display:flex;flex-wrap:wrap;justify-content:center;align-items:center;gap:10px}.control,.flexbox div,.setting{flex:1 1 auto;text-align:center;padding:10px;box-shadow:0 2px 4px #0000001a}.ai-assistant{margin:20px 0;background:#e7f5ff;padding:15px;border-radius:8px;text-align:center;box-shadow:0 2px 4px #0000001a}.ai-assistant h2{font-size:1.5rem;color:#00f}.ai-assistant p{font-size:1rem;color:#444;margin-top:10px}.footer{text-align:center;margin-top:20px;font-size:.7rem;color:#333}.danger{color:red!important;border-color:red!important}@media (max-width: 668px){.parameters{flex-direction:column}.flexbox{width:100%}}</style></head><body><noscript>Please Enable JavaScript in your browser...!!</noscript><div class=container><div class=header><h1>Micro ECG â™¥(Alpha)</h1></div><div class=snap-container id=snap-container></div><div class=canvas-container><canvas id=ecgCanvas></canvas></div><div class=tabs><button data-id=parameters active>PARAMETERS</button> <button data-id=ai-assistant>AI</button> <button data-id=controls>CONTROLS</button> <button data-id=recordings>RECORDINGS</button> <button data-id=settings disabled>SETTINGS</button></div><div class=tab-contents><div class=parameters active><div class=parameter><span>Result: <span id=param-result>â€¢_Â°</span></span></div><div class=parameter><span>Heart Rate: <span id=param-hr>â€¢_Â° </span>bpm</span></div><div class=parameter><span>QRS Duration: <span id=param-qrs>â€¢_Â° </span>ms</span></div><div class=parameter><span>QT Interval: <span id=param-qt>â€¢_Â° </span>ms</span></div><div class=parameter><span>PR Interval: <span id=param-pr>â€¢_Â° </span>ms</span></div><div class=parameter><span>ST Interval: <span id=param-st>â€¢_Â° </span>ms</span></div></div><div class=ai-assistant><h2>AI Assistant</h2><p id=ai-output></p><button id=ai-assistBtn>âŸ³ Get Assistance</button></div><div class=controls><div class=control style=width:100%></div><div class='control pushButton'data-toggle=isHold><span>HOLD</span></div><div class='control pushButton'id=recordBtn><span>RECORD</span></div><div class=control onclick='data_plot=[]'><span>CLEAR</span></div><div class=control id=takeSnapBtn><span>SNAP</span></div><div class=control style=width:100%></div><div class=control><span>TIME/DIV</span><br>âˆ’ <input type=range class='multiturn minZero'data-default=50 max=100 min=0 oninput='scale.x=this.dataset.value/10'value=50> +</div><div class=control><span>VOLT/DIV</span><br>âˆ’ <input type=range class=multiturn data-default=120 max=100 min=0 oninput='scale.y=this.dataset.value/10'value=50> +</div><div class=control><span>POSITION VERTICAL</span><br>â–² <input type=range class=multiturn data-default=13 max=100 min=0 oninput='move.y=10*this.dataset.value'value=50> â–¼</div><div class=control><span>POSITION HORIZONTAL</span><br>â® <input type=range class='multiturn minZero'data-default=0 max=100 min=0 oninput='move.x=10*this.dataset.value'value=50> â</div><div class=control style=width:100%></div></div><div class='flexbox recordings'><div class=flexbox style=width:100%><label for=''>IMPORT(.json)</label><input type=file accept=.json id=recordingImport></div><div class=flexbox id=recordings><div class=flexbox><div class=pushButton>NO RECORD FOUND<br><sub>mm:hh dd-mm-yyyy</sub></div><div class=download>â¤“</div><div class=download>x</div></div></div></div></div><div class=footer><a href='/test' target='_blank'>Open in External Browser</a><p style=display:block;background-color:#eee><b>Disclaimer:</b> The project is not designed nor certified to diagnose any serious problem. We, the creators, developers, and distributors of this App/Website/device are not liable for any inaccuracies, misinterpretations, or adverse outcomes resulting from its use. Use of the App/Website/device is at your own risk and discretion.</div></div><script type=\"text/javascript\" charset=\"utf-8\">(()=>{document.head.appendChild(Object.assign(document.createElement(\"style\"),{innerHTML:\".notify-container {width: 100%; max-height: 230px; overflow: scroll; display: flex; flex-direction: column;align-items: center; position: fixed; top: 10px; left: 0; pointer-events: none;}.notify-container > div {max-width: 400px; margin: 10px; border-radius: 5px; text-align: center; padding: 10px 20px;background: #eef; color: #00f; position: relative; box-shadow: 0 2px 5px rgba(0, 0, 0, 0.2);transition: transform 0.5s; pointer-events: auto;}.notify-container > div:hover { transform: translateY(10%); }.notifyClose { position: absolute; right: 5px; bottom: 25%; font-weight: bold; cursor: pointer; }\"}));let e=document.body.appendChild(Object.assign(document.createElement(\"div\"),{className:\"notify-container\"}));document.notify=(t=\"\",a,n)=>{let 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Connection established!\",\"success\"),wSocket.send(300)},wSocket.onmessage=function(e){var t=new Uint16Array(e.data);let a=[];for(let n=0;n<t.length;n+=2){var r=t[n]|t[n+1]<<8;a.push(1.4*r+1600)}feedData(a,300)},wSocket.onerror=function(e){document.notify(\"WebSocket: Error \"+e,\"error\")},wSocket.onclose=function(){document.notify(\"WebSocket: Connection closed\",\"warning\")};var graphCanvas=document.getElementById(\"ecgCanvas\"),ctx=graphCanvas.getContext(\"2d\"),scale={x:5,y:12},move={x:0,y:130},isHold=!1,isRecording=!1,recording=[],ECGResult=[];function render(){ctx.clearRect(0,0,graphCanvas.width,graphCanvas.height);var e=(e=data_plot.slice(-graphCanvas.width*scale.x-move.x,-1-move.x)).map(e=>e/scale.y-move.y);ECGResult=ECGinterpreter(e,300),ctx.beginPath(),ctx.moveTo(...a(0,e[0]));for(var t=0;t<e.length;t++)ctx.lineTo(...a(t/scale.x,e[t]));function a(e,t){return[e,graphCanvas.height-t]}ctx.strokeStyle=\"red\",ctx.stroke(),requestAnimationFrame(render)}graphCanvas.width=graphCanvas.offsetParent.offsetWidth,addEventListener(\"resize\",()=>{graphCanvas.width=graphCanvas.offsetParent.offsetWidth}),\"serviceWorker\"in navigator&&navigator.serviceWorker.register(\"./sw.js\").catch(console.log),setTimeout(render,100),(()=>{let e=document.querySelectorAll(\".tabs>button\"),t=document.querySelectorAll(\".tab-contents>div\");e.forEach(a=>{a.addEventListener(\"click\",()=>{e.forEach(e=>e.removeAttribute(\"active\")),t.forEach(e=>e.removeAttribute(\"active\")),a.setAttribute(\"active\",\"\"),document.querySelector(\".\"+a.dataset.id).setAttribute(\"active\",\"\")})})})(),document.getElementById(\"takeSnapBtn\").addEventListener(\"click\",()=>{let e=document.createElement(\"img\");e.src=graphCanvas.toDataURL(\"image/png\"),e.addEventListener(\"click\",e.remove),document.getElementById(\"snap-container\").appendChild(e),prompt(\"Save SNAPSHOT As:\",t=>{dbManager.add(\"metadata\",{name:t||\"SNAPSHOT\",startTime:(new Date).toISOString(),snapURL:e.src,type:\"snapshot\"})})});const dbManager=new IDBManager({dbName:\"EcgRecordings\",dbVersion:1,onUpgrade(e,t,a,n){e.objectStoreNames.contains(\"metadata\")||e.createObjectStore(\"metadata\",{keyPath:\"id\",autoIncrement:!0}),e.objectStoreNames.contains(\"dataChunks\")||e.createObjectStore(\"dataChunks\",{keyPath:\"id\",autoIncrement:!0})}});var dbVariables={chunkNo:0,metadataID:null,prevChunkID:null};async function startRecording(e){dbVariables.metadataID=await dbManager.add(\"metadata\",{name:e||\"RECORD\",startTime:(new Date).toISOString(),endTime:null,dataChunkId:null,type:\"dataStream\"}),dbVariables.chunkNo=0,dbVariables.prevChunkID=null,isRecording=!0}async function logData(e){dbVariables.chunkNo++,e=await dbManager.add(\"dataChunks\",{data:e,chunkNo:dbVariables.chunkNo}),1==dbVariables.chunkNo?await dbManager.update(\"metadata\",dbVariables.metadataID,{dataChunkId:e}):await dbManager.update(\"dataChunks\",dbVariables.prevChunkID,{nextChunkId:e}),await dbManager.update(\"metadata\",dbVariables.metadataID,{totalChunks:dbVariables.chunkNo,endTime:(new Date).toISOString()}),dbVariables.prevChunkID=e}async function exportData(e){let t=await dbManager.get(\"metadata\",e),a=[],n=t.dataChunkId;for(;n;){var r=await dbManager.get(\"dataChunks\",n);if(!r)break;0<a.length?a[0].data.push(...r.data):a.push(r),n=r.nextChunkId||null}n&&(t.totalChunks=1,delete a[0].nextChunkId),e=new Blob([JSON.stringify({metadata:t,chunks:a})],{type:\"application/json\"});let i=Object.assign(document.createElement(\"a\"),{href:URL.createObjectURL(e),download:\"ECGREC-\"+t.name+t.startTime+\".json\"});i.click()}document.getElementById(\"recordBtn\").addEventListener(\"click\",e=>{let t=e.currentTarget;isRecording=!1,t.hasAttribute(\"active\")&&prompt(\"Save RECORDING As:\",startRecording,()=>t.removeAttribute(\"active\"))}),updateRecordingUI(),dbManager.addChangeEventListener(updateRecordingUI,\"metadata\");alert('If the page does not open in your browser, please open it in your browser.  172.217.28.1')</script></body></html> ";
String webServerSW = "const CACHE_NAME='offlineServe-v1.0.0';self.addEventListener('install',e=>{self.skipWaiting()}),self.addEventListener('activate',e=>{e.waitUntil(caches.keys().then(e=>Promise.all(e.map(e=>e!==CACHE_NAME?caches.delete(e):null))))}),self.addEventListener('fetch',n=>{n.respondWith(caches.match(n.request).then(e=>e||fetch(n.request).then(t=>caches.open(CACHE_NAME).then(e=>(e.put(n.request,t.clone()),t))).catch(()=>new Response('You are offline. Please check your connection.',{status:200,headers:{'Content-Type':'text/plain'}}))))});";

void webSocketEvent(uint8_t num, WStype_t type, uint8_t* payload, size_t length) {

    switch (type) {
        case WStype_DISCONNECTED:
        Serial.printf("[%u] Disconnected!\n", num);
        break;
        case WStype_CONNECTED:
        {
            IPAddress ip = webSocket.remoteIP(num);
            Serial.printf("[%u] Connected from %d.%d.%d.%d url: %s\n", num, ip[0], ip[1], ip[2], ip[3], payload);
        }
        break;
        case WStype_TEXT:
        Serial.printf("[%u] get Text: %s\n", num, payload);

        //int arrayLen = payload - 0;
        int newSps = atoi((const char*)payload);

        // Try to parse the samples per second (SPS) from the message
        if (newSps > 0 && newSps != sps) {
            // Adjust the number of samples per second if needed
            sps = newSps;

            // Reallocate the ADC buffer with the new size
            if (adcBuffer != nullptr) {
                free(adcBuffer); // Free old buffer
            }
            adcBuffer = (int *)malloc(sps * sizeof(int)); // Allocate new buffer

            // Update sampling interval based on SPS
            sampleInterval = 1000 / sps;

            Serial.print("New SPS: ");
            Serial.println(sps);
        }


        break;
    }
}

void handleNotFound() {
    server.sendHeader("Location", "/", true); //Redirect to our html web page
    server.send(301, "text/plane", "");
}


void setup() {
    Serial.begin(115200);

    // Serial.setDebugOutput(true);

    Serial.println();
    Serial.println();
    Serial.println();

    for (uint8_t t = 4; t > 0; t--) {
        Serial.printf("[SETUP] BOOT WAIT %d...\n", t);
        Serial.flush();
        delay(1000);
    }

    adcBuffer = (int *)malloc(sps * sizeof(int));

    WiFi.mode(WIFI_AP);
    WiFi.softAPConfig(apIP, apIP, IPAddress(255, 255, 255, 0));
    WiFi.softAP("Micro_ECG_RANMPGroupF");
    // start webSocket server
    webSocket.begin();
    webSocket.onEvent(webSocketEvent);

    // if (MDNS.begin("esp8266")) {
    //   Serial.println("MDNS responder started");
    // }
    dnsServer.start(DNS_PORT, "*", apIP);
    // handle index
    server.on("/", []() {
        server.send(200, "text/html", webServerIndexPage);
    });
    server.on("/sw.js", []() {
        server.send(200, "application/javascript", webServerSW);
    });

    server.on("/test", []() {
        server.sendHeader("Location", "https://github.io/", true);
        server.send(302, "text/plane", "Redirecting...");
    });

    server.onNotFound(handleNotFound);
    server.begin();
    
    // // Add service to MDNS
    // MDNS.addService("http", "tcp", 80);
    // MDNS.addService("ws", "tcp", 81);
    
}

unsigned long last_10sec = 0;
unsigned int counter = 0;

void loop() {
    unsigned long t = millis();
    webSocket.loop();
    dnsServer.processNextRequest();
    server.handleClient();

    // if ((t - last_10sec) > 10 * 1000) {
    //     counter++;
    //     bool ping = (counter % 2);
    //     int i = webSocket.connectedClients(ping);
    //     Serial.printf("%d Connected websocket clients ping: %d\n", i, ping);
    //     last_10sec = millis();
    // }

    // Check if it's time to sample ADC data based on SPS
    unsigned long currentMillis = millis();

    if (currentMillis - lastSampleTime >= sampleInterval) {
        // Read ADC and store it in buffer
        adcBuffer[sampleIndex] = analogRead(A0);
        sampleIndex++;
        // Reset buffer and send data every 333ms
        if (sampleIndex >= sps) {
            Serial.printf("147................................");
            sendSamplesThroughWebSocket(adcBuffer, sps);
            sampleIndex = 0; // Reset buffer index
        }

        lastSampleTime = currentMillis;
    }
    // //Send data every 333ms
    if (currentMillis - previousMillis >= sendInterval) {
        if (sampleIndex > 0) {
            sendSamplesThroughWebSocket(adcBuffer, sampleIndex);
            sampleIndex = 0; // Reset buffer index
        }
        previousMillis = currentMillis;
    }
}

// Function to send ADC samples via WebSocket
void sendSamplesThroughWebSocket(int *samples, int count) {
  // Create a buffer to hold raw data (binary format)
  uint8_t buffer[count * sizeof(int)];
  memcpy(buffer, samples, count * sizeof(int));  // Copy ADC samples to buffer

  // Send the buffer as a binary message over WebSocket
  webSocket.broadcastBIN(buffer, count * sizeof(int));
}