Arduino Nano ESP32 - Web Plotter

This tutorial instructs you on how to build a web-based plotter that resemble the Serial Plotter found in the Arduino IDE. This web-based plotter enables monitoring of real-time data from an Arduino Nano ESP32 using a web browser on either your smartphone or PC. The plotted data will be presented in a graph format, looks like what you typically observe in the Serial Plotter of the Arduino IDE.

Arduino Nano ESP32 web plotter

Hardware Preparation

1×Arduino Nano ESP32
1×USB Cable Type-C
1×(Recommended) Screw Terminal Adapter for Arduino Nano

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you. We appreciate your support.

How Web Plotter Works

  • The Arduino Nano ESP32 code creates both a web server and a WebSocket server.
  • When a user accesses the webpage hosted on the Arduino Nano ESP32 board via a web browser, the Arduino Nano ESP32's web server sends back the web content (HTML, CSS, JavaScript) to the browser.
  • The JavaScript code running in the web browser creates a graph resembling the Serial Plotter.
  • Upon clicking the connect button on the webpage, the JavaScript code initiates a WebSocket connection to the WebSocket server running on the Arduino Nano ESP32 board.
  • The Arduino Nano ESP32 sends data over the WebSocket connection to the web browser in a format similar to that used by the Serial Plotter (details provided in the next part).
  • The JavaScript code in the web browser receives the data and plots it on the graph.

The data format that Arduino Nano ESP32 sends to web plotter

To plot multiple variables, we need to separate variables from each other by “\t” or " " character. The last value MUST be terminated by “\r\n” characters.

In detail:

  • The first variable
plotter.broadcastTXT(data_1);
  • The middle variables
plotter.broadcastTXT("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. plotter.broadcastTXT(data_2); plotter.broadcastTXT("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. plotter.broadcastTXT(data_3);
  • The last variable
plotter.broadcastTXT("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. plotter.broadcastTXT(data_4); plotter.broadcastTXT("\r\n"); // The last value is terminated by a carriage return ('\r') and a newline ('\n') character.

For more detail, please refer to Arduino Nano ESP32 - Serial Plotter tutorial

Arduino Nano ESP32 Code - Web Plotter

The webpage's content (HTML, CSS, JavaScript) is stored separately in an index.h file. Therefore, in the Arduino IDE, we will have two code files:

  • An .ino file containing the Arduino Nano ESP32 code, which creates both a web server and a WebSocket server.
  • An .h file that houses the webpage's content.

Detailed Instructions

To get started with Arduino Nano ESP32, follow these steps:

  • If you are new to Arduino Nano ESP32, refer to the tutorial on how to set up the environment for Arduino Nano ESP32 in the Arduino IDE.
  • Connect the Arduino Nano ESP32 board to your PC via a USB cable
  • Open Arduino IDE on your PC.
  • Select the right Arduino Nano ESP32 board (e.g. Arduino Nano ESP32) and COM port.
  • Open the Library Manager by clicking on the Library Manager icon on the left navigation bar of Arduino IDE.
  • Search “ESPAsyncWebServer”, then find the ESPAsyncWebServer created by lacamera.
  • Click Install button to install ESPAsyncWebServer library.
Arduino Nano ESP32 ESPAsyncWebServer library
  • You will be asked to install the dependency. Click Install All button.
Arduino Nano ESP32 ESPAsyncWebServer dependencies library
  • Search “WebSockets”, then find the WebSockets created by Markus Sattler.
  • Click Install button to install WebSockets library.
Arduino Nano ESP32 WebSockets library
  • On Arduino IDE, create new sketch, Give it a name, for example, newbiely.com.ino
  • Copy the below code and open with Arduino IDE
/* * This Arduino Nano ESP32 code was developed by newbiely.com * * This Arduino Nano ESP32 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano-esp32/arduino-nano-esp32-web-plotter */ #include <WiFi.h> #include <ESPAsyncWebServer.h> #include <WebSocketsServer.h> #include "index.h" // contains HTML, JavaScript and CSS const char* ssid = "YOUR_WIFI_SSID"; // REPLACE IT WITH YOUR OWN NETWORK CREDENTIALS const char* password = "YOUR_WIFI_PASSWORD"; // REPLACE IT WITH YOUR OWN NETWORK CREDENTIALS AsyncWebServer server(80); WebSocketsServer plotter = WebSocketsServer(81); // WebSocket server on port 81 int last_update = 0; void setup() { Serial.begin(9600); delay(1000); // Connect to Wi-Fi WiFi.begin(ssid, password); while (WiFi.status() != WL_CONNECTED) { delay(1000); Serial.println("Connecting to WiFi..."); } Serial.println("Connected to WiFi"); // Initialize WebSocket server plotter.begin(); // Serve a basic HTML page with JavaScript to create the WebSocket connection server.on("/", HTTP_GET, [](AsyncWebServerRequest* request) { Serial.println("Web Server: received a web page request"); String html = HTML_CONTENT; // Use the HTML content from the index.h file request->send(200, "text/html", html); }); server.begin(); Serial.print("Arduino Nano ESP32 Web Server's IP address: "); Serial.println(WiFi.localIP()); } void loop() { plotter.loop(); if (millis() - last_update > 500) { last_update = millis(); String data_1 = String(random(0, 100)); String data_2 = String(random(0, 100)); String data_3 = String(random(0, 100)); String data_4 = String(random(0, 100)); // TO SERIAL PLOTTER Serial.print(data_1); Serial.print("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. Serial.print(data_2); Serial.print("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. Serial.print(data_3); Serial.print("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. Serial.println(data_4); // The last value is terminated by a carriage return ('\r') and a newline ('\n') character. // TO WEB PLOTTER plotter.broadcastTXT(data_1); plotter.broadcastTXT("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. plotter.broadcastTXT(data_2); plotter.broadcastTXT("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. plotter.broadcastTXT(data_3); plotter.broadcastTXT("\t"); // A tab character ('\t') or a space (' ') is printed between the two values. plotter.broadcastTXT(data_4); plotter.broadcastTXT("\r\n"); // The last value is terminated by a carriage return ('\r') and a newline ('\n') character. } }
  • Modify the WiFi information (SSID and password) in the code to match your own network credentials.
  • Create the index.h file On Arduino IDE by:
    • Either click on the button just below the serial monitor icon and choose New Tab, or use Ctrl+Shift+N keys.
    Arduino IDE 2 adds file
    • Give the file's name index.h and click OK button
    Arduino IDE 2 adds file index.h
    • Copy the below code and paste it to the index.h.
    /* * This Arduino Nano ESP32 code was developed by newbiely.com * * This Arduino Nano ESP32 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano-esp32/arduino-nano-esp32-web-plotter */ const char *HTML_CONTENT = R"=====( <!DOCTYPE html> <html> <head> <title>Arduino Nano ESP32 - Web Plotter</title> <meta name="viewport" content="width=device-width, initial-scale=0.7"> <style> body {text-align: center; height: 750px; } h1 {font-weight: bold; font-size: 20pt; padding-bottom: 5px; color: navy; } h2 {font-weight: bold; font-size: 15pt; padding-bottom: 5px; } button {font-weight: bold; font-size: 15pt; } #footer {width: 100%; margin: 0px; padding: 0px 0px 10px 0px; bottom: 0px; } .sub-footer {margin: 0 auto; position: relative; width:400px; } .sub-footer a {position: absolute; font-size: 10pt; top: 3px; } </style> <script> var COLOR_BACKGROUND = "#FFFFFF"; var COLOR_TEXT = "#000000"; var COLOR_BOUND = "#000000"; var COLOR_GRIDLINE = "#F0F0F0"; var COLOR_LINE = ["#0000FF", "#FF0000", "#009900", "#FF9900", "#CC00CC", "#666666", "#00CCFF", "#000000"]; var LEGEND_WIDTH = 10; var X_TITLE_HEIGHT = 40; var Y_TITLE_WIDTH = 40; var X_VALUE_HEIGHT = 40; var Y_VALUE_WIDTH = 50; var PLOTTER_PADDING_TOP = 30; var PLOTTER_PADDING_RIGHT = 30; var X_GRIDLINE_NUM = 5; var Y_GRIDLINE_NUM = 4; var WSP_WIDTH = 400; var WSP_HEIGHT = 200; var MAX_SAMPLE = 50; // in sample var X_MIN = 0; var X_MAX = MAX_SAMPLE; var Y_MIN = -5; var Y_MAX = 5; var X_TITLE = "X"; var Y_TITLE = "Y"; var plotter_width; var plotter_height; var plotter_pivot_x; var plotter_pivot_y; var sample_count = 0; var buffer = ""; var data = []; var webSocket; var canvas; var ctx; function init(){ canvas = document.getElementById("graph"); canvas.style.backgroundColor = COLOR_BACKGROUND; ctx = canvas.getContext("2d"); canvas_resize(); setInterval(update_plotter, 1000 / 60); } function connect_to_esp32(){ if(webSocket == null){ webSocket = new WebSocket("ws://" + window.location.host + ":81"); document.getElementById("ws_state").innerHTML = "CONNECTING"; webSocket.onopen = ws_onopen; webSocket.onclose = ws_onclose; webSocket.onmessage = ws_onmessage; webSocket.binaryType = "arraybuffer"; } else webSocket.close(); } function ws_onopen(){ document.getElementById("ws_state").innerHTML = "<span style='color: blue'>CONNECTED</span>"; document.getElementById("btn_connect").innerHTML = "Disconnect"; } function ws_onclose(){ document.getElementById("ws_state").innerHTML = "<span style='color: gray'>CLOSED</span>"; document.getElementById("btn_connect").innerHTML = "Connect"; webSocket.onopen = null; webSocket.onclose = null; webSocket.onmessage = null; webSocket = null; } function ws_onmessage(e_msg){ e_msg = e_msg || window.event; // MessageEvent console.log(e_msg.data); buffer += e_msg.data; buffer = buffer.replace(/\r\n/g, "\n"); buffer = buffer.replace(/\r/g, "\n"); while(buffer.indexOf("\n") == 0) buffer = buffer.substr(1); if(buffer.indexOf("\n") <= 0) return; var pos = buffer.lastIndexOf("\n"); var str = buffer.substr(0, pos); var new_sample_arr = str.split("\n"); buffer = buffer.substr(pos + 1); for(var si = 0; si < new_sample_arr.length; si++) { var str = new_sample_arr[si]; var arr = []; if(str.indexOf("\t") > 0) arr = str.split("\t"); else arr = str.split(" "); for(var i = 0; i < arr.length; i++){ var value = parseFloat(arr[i]); if(isNaN(value)) continue; if(i >= data.length) { var new_line = [value]; data.push(new_line); // new line } else data[i].push(value); } sample_count++; } for(var line = 0; line < data.length; line++){ while(data[line].length > MAX_SAMPLE) data[line].splice(0, 1); } auto_scale(); } function map(x, in_min, in_max, out_min, out_max){ return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min; } function get_random_color(){ var letters = '0123456789ABCDEF'; var _color = '#'; for (var i = 0; i < 6; i++) _color += letters[Math.floor(Math.random() * 16)]; return _color; } function update_plotter(){ if(sample_count <= MAX_SAMPLE) X_MAX = sample_count; else X_MAX = 50; ctx.clearRect(0, 0, WSP_WIDTH, WSP_HEIGHT); ctx.save(); ctx.translate(plotter_pivot_x, plotter_pivot_y); ctx.font = "bold 20px Arial"; ctx.textBaseline = "middle"; ctx.textAlign = "center"; ctx.fillStyle = COLOR_TEXT; // draw X axis title if(X_TITLE != "") ctx.fillText(X_TITLE, plotter_width / 2, X_VALUE_HEIGHT + X_TITLE_HEIGHT / 2); // draw Y axis title if(Y_TITLE != ""){ ctx.rotate(-90 * Math.PI / 180); ctx.fillText(Y_TITLE, plotter_height / 2, -Y_VALUE_WIDTH - Y_TITLE_WIDTH / 2); ctx.rotate(90 * Math.PI / 180); } ctx.font = "16px Arial"; ctx.textAlign = "right"; ctx.strokeStyle = COLOR_BOUND; for(var i = 0; i <= Y_GRIDLINE_NUM; i++){ var y_gridline_px = -map(i, 0, Y_GRIDLINE_NUM, 0, plotter_height); y_gridline_px = Math.round(y_gridline_px) + 0.5; ctx.beginPath(); ctx.moveTo(0, y_gridline_px); ctx.lineTo(plotter_width, y_gridline_px); ctx.stroke(); ctx.strokeStyle = COLOR_BOUND; ctx.beginPath(); ctx.moveTo(-7 , y_gridline_px); ctx.lineTo(4, y_gridline_px); ctx.stroke(); var y_gridline_value = map(i, 0, Y_GRIDLINE_NUM, Y_MIN, Y_MAX); y_gridline_value = y_gridline_value.toFixed(1); ctx.fillText(y_gridline_value + "", -15, y_gridline_px); ctx.strokeStyle = COLOR_GRIDLINE; } ctx.strokeStyle = COLOR_BOUND; ctx.textAlign = "center"; ctx.beginPath(); ctx.moveTo(0.5, y_gridline_px - 7); ctx.lineTo(0.5, y_gridline_px + 4); ctx.stroke(); for(var i = 0; i <= X_GRIDLINE_NUM; i++){ var x_gridline_px = map(i, 0, X_GRIDLINE_NUM, 0, plotter_width); x_gridline_px = Math.round(x_gridline_px) + 0.5; ctx.beginPath(); ctx.moveTo(x_gridline_px, 0); ctx.lineTo(x_gridline_px, -plotter_height); ctx.stroke(); ctx.strokeStyle = COLOR_BOUND; ctx.beginPath(); ctx.moveTo(x_gridline_px, 7); ctx.lineTo(x_gridline_px, -4); ctx.stroke(); var x_gridline_value; if(sample_count <= MAX_SAMPLE) x_gridline_value = map(i, 0, X_GRIDLINE_NUM, X_MIN, X_MAX); else x_gridline_value = map(i, 0, X_GRIDLINE_NUM, sample_count - MAX_SAMPLE, sample_count);; ctx.fillText(x_gridline_value.toString(), x_gridline_px, X_VALUE_HEIGHT / 2 + 5); ctx.strokeStyle = COLOR_GRIDLINE; } var line_num = data.length; for(var line = 0; line < line_num; line++){ // draw graph var sample_num = data[line].length; if(sample_num >= 2){ var y_value = data[line][0]; var x_px = 0; var y_px = -map(y_value, Y_MIN, Y_MAX, 0, plotter_height); if(line == COLOR_LINE.length) COLOR_LINE.push(get_random_color()); ctx.strokeStyle = COLOR_LINE[line]; ctx.beginPath(); ctx.moveTo(x_px, y_px); for(var i = 0; i < sample_num; i++){ y_value = data[line][i]; x_px = map(i, X_MIN, X_MAX -1, 0, plotter_width); y_px = -map(y_value, Y_MIN, Y_MAX, 0, plotter_height); ctx.lineTo(x_px, y_px); } ctx.stroke(); } // draw legend var x = plotter_width - (line_num - line) * LEGEND_WIDTH - (line_num - line - 1) * LEGEND_WIDTH / 2; var y = -plotter_height - PLOTTER_PADDING_TOP / 2 - LEGEND_WIDTH / 2; ctx.fillStyle = COLOR_LINE[line]; ctx.beginPath(); ctx.rect(x, y, LEGEND_WIDTH, LEGEND_WIDTH); ctx.fill(); } ctx.restore(); } function canvas_resize(){ canvas.width = 0; // to avoid wrong screen size canvas.height = 0; document.getElementById('footer').style.position = "fixed"; var width = window.innerWidth - 20; var height = window.innerHeight - 20; WSP_WIDTH = width; WSP_HEIGHT = height - document.getElementById('header').offsetHeight - document.getElementById('footer').offsetHeight; canvas.width = WSP_WIDTH; canvas.height = WSP_HEIGHT; ctx.font = "16px Arial"; var y_min_text_size = ctx.measureText(Y_MIN.toFixed(1) + "").width; var y_max_text_size = ctx.measureText(Y_MAX.toFixed(1) + "").width; Y_VALUE_WIDTH = Math.round(Math.max(y_min_text_size, y_max_text_size)) + 15; plotter_width = WSP_WIDTH - Y_VALUE_WIDTH - PLOTTER_PADDING_RIGHT; plotter_height = WSP_HEIGHT - X_VALUE_HEIGHT - PLOTTER_PADDING_TOP; plotter_pivot_x = Y_VALUE_WIDTH; plotter_pivot_y = WSP_HEIGHT - X_VALUE_HEIGHT; if(X_TITLE != "") { plotter_height -= X_TITLE_HEIGHT; plotter_pivot_y -= X_TITLE_HEIGHT; } if(Y_TITLE != "") { plotter_width -= Y_TITLE_WIDTH; plotter_pivot_x += Y_TITLE_WIDTH; } ctx.lineWidth = 1; } function auto_scale(){ if(data.length >= 1){ var max_arr = []; var min_arr = []; for(var i = 0; i < data.length; i++){ if(data[i].length >= 1){ var max = Math.max.apply(null, data[i]); var min = Math.min.apply(null, data[i]); max_arr.push(max); min_arr.push(min); } } var max = Math.max.apply(null, max_arr); var min = Math.min.apply(null, min_arr); var MIN_DELTA = 10.0; if((max - min) < MIN_DELTA){ var mid = (max + min) / 2; max = mid + MIN_DELTA / 2; min = mid - MIN_DELTA / 2; } var range = max - min; var exp; if (range == 0.0) exp = 0; else exp = Math.floor(Math.log10(range / 4)); var scale = Math.pow(10, exp); var raw_step = (range / 4) / scale; var step; potential_steps =[1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0]; for (var i = 0; i < potential_steps.length; i++) { if (potential_steps[i] < raw_step) continue; step = potential_steps[i] * scale; Y_MIN = step * Math.floor(min / step); Y_MAX = Y_MIN + step * (4); if (Y_MAX >= max) break; } var count = 5 - Math.floor((Y_MAX - max) / step); Y_MAX = Y_MIN + step * (count - 1); ctx.font = "16px Arial"; var y_min_text_size = ctx.measureText(Y_MIN.toFixed(1) + "").width; var y_max_text_size = ctx.measureText(Y_MAX.toFixed(1) + "").width; Y_VALUE_WIDTH = Math.round(Math.max(y_min_text_size, y_max_text_size)) + 15; plotter_width = WSP_WIDTH - Y_VALUE_WIDTH - PLOTTER_PADDING_RIGHT; plotter_pivot_x = Y_VALUE_WIDTH; } } window.onload = init; </script> </head> <body onresize="canvas_resize()"> <h1 id="header">Arduino Nano ESP32 - Web Plotter</h1> <canvas id="graph"></canvas> <br> <div id="footer"> <div class="sub-footer"> <h2>WebSocket <span id="ws_state"><span style="color: gray">CLOSED</span></span></h2> </div> <button id="btn_connect" type="button" onclick="connect_to_esp32();">Connect</button> </div> </body> </html> )=====";
    • Now you have the code in two files: newbiely.com.ino and index.h
    • Click Upload button on Arduino IDE to upload code to Arduino Nano ESP32.
    • Open the Serial Monitor
    • Check out the result on Serial Monitor.
    COM6
    Send
    Connecting to WiFi... Connected to WiFi Arduino Nano ESP32 Web Server's IP address IP address: 192.168.0.6
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    Newline  
    • Take note of the IP address displayed, and enter this address into the address bar of a web browser on your smartphone or PC.
    • You will see the webpage it as below:
    Arduino Nano ESP32 plotter web browser
    • Click the CONNECT button to connect the webpage to Arduino Nano ESP32 via WebSocket.
    • You will see the plotter plots data as the below image.
    Arduino Nano ESP32 web graph
    • You can open the Serial Plotter on Arduino IDE to compare with the Web Plotter on the web browser.

    ※ NOTE THAT:

    • If you modify the HTML content in the index.h file and do not make any changes to the newbiely.com.ino file, when you compile and upload the code to the Arduino Nano ESP32 using the Arduino IDE, the IDE will not update the HTML content.
    • To force the Arduino IDE to update the HTML content in this scenario, you need to make a change in the newbiely.com.ino file. For example, you can add an empty line or include a comment.

    Line-by-line Code Explanation

    The above Arduino Nano ESP32 code contains line-by-line explanation. Please read the comments in the code!

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