ESP32 as Web Server controlling two relays and one LCD display via I2C bus

In this example we will use the Espressif ESP32 working as Web server with WiFi connection, that host a web page witch allows to control on-off state of two relays. This can be util for to drive high voltage loads connected to 110VAC or 220VAC, such as motors, electrovalves, contactors, etc.

For the compete code, follow the link to GitHub

  ESP32 Web server
  Includes an lcd H44780 conected via I2C bus. The IP addres obtained via 
  DHCP protocol is printed in the display. 
  The dispay even shows the status of each of two relays conected
  and handled by the HTML code.
  This sketch it is based on the Rui Santos original Web server example 
  and was modified by me in Ramos Mejía, ARGENTINA, August 2020.
  - Osvaldo Cantone
    Relé1 GPIO.15
    Relé2 GPIO.2
    SDA GPIO.21
    SCL GPIO.22

#include <Arduino.h>
#include <WiFi.h>
#include <LiquidCrystal_PCF8574.h>
#include <Wire.h>

LiquidCrystal_PCF8574 lcd(0x27); // set the LCD address to 0x27 for a 16 chars and 2 line display

// Replace the X's with your network credentials
const char* ssid = "XXXXXXXXXXXXX";
const char* password = "XXXXXXXXXXXXX";

// Set web server port number to 80
WiFiServer server(80);

// Variable to store the HTTP request
String header;

// Auxiliar variables to store the current output state
String relay1State = "off";
String relay2State = "off";

// Assign output variables to GPIO pins
//const int output26 = 26;
//const int output27 = 27;
const int Relay1 = 15;
const int Relay2 = 2;

// Current time
unsigned long currentTime = millis();
// Previous time
unsigned long previousTime = 0; 
// Define timeout time in milliseconds (example: 2000ms = 2s)
const long timeoutTime = 2000;
int show = -1;

void setup() {

  int error;

  // Initialize the output variables as outputs
  pinMode(Relay1, OUTPUT);
  pinMode(Relay2, OUTPUT);
  // Set outputs to LOW
  digitalWrite(Relay1, LOW);
  digitalWrite(Relay2, LOW);

  //Initializing the display
  error = Wire.endTransmission();
  Serial.print("Error: ");

  if (error == 0) {
    Serial.println(": LCD found.");
    show = 0;
    lcd.begin(16, 2); // initialize the lcd
 } else {
    Serial.println(": LCD not found.");
  } // if
    lcd.setCursor(0, 0);
//  lcd.print("0123456789ABCDEF");
    lcd.print(" ESP32 WebSerer ");

  // Connect to Wi-Fi network with SSID and password
  Serial.print("Connecting to ");
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
  // Print local IP address and start web server
  Serial.println("WiFi connected.");
  Serial.println("IP address: ");

    lcd.setCursor(0, 1);
    lcd.setCursor(0, 0);
    lcd.print("ESP32 ");
    lcd.setCursor(0, 1);
    lcd.print("R1: ON   R2: ON ");


void loop(){
  WiFiClient client = server.available();   // Listen for incoming clients

  if (client) {                             // If a new client connects,
    currentTime = millis();
    previousTime = currentTime;
    Serial.println("New Client.");          // print a message out in the serial port
    String currentLine = "";                // make a String to hold incoming data from the client
    while (client.connected() && currentTime - previousTime <= timeoutTime) {  // loop while the client's connected
      currentTime = millis();
      if (client.available()) {             // if there's bytes to read from the client,
        char c =;             // read a byte, then
        Serial.write(c);                    // print it out the serial monitor
        header += c;
        if (c == '\n') {                    // if the byte is a newline character
          // if the current line is blank, you got two newline characters in a row.
          // that's the end of the client HTTP request, so send a response:
          if (currentLine.length() == 0) {
            // HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
            // and a content-type so the client knows what's coming, then a blank line:
            client.println("HTTP/1.1 200 OK");
            client.println("Connection: close");

            // turns the GPIOs on and off
            if (header.indexOf("GET /26/on") >= 0) {
              Serial.println("GPIO 26 on");
              relay1State = "on";
              digitalWrite(Relay1, HIGH);
                lcd.setCursor(4, 1);

            } else if (header.indexOf("GET /26/off") >= 0) {
              Serial.println("GPIO 26 off");
              relay1State = "off";
              digitalWrite(Relay1, LOW);
                lcd.setCursor(4, 1);
                lcd.print("ON ");

            } else if (header.indexOf("GET /27/on") >= 0) {
              Serial.println("GPIO 27 on");
              relay2State = "on";
              digitalWrite(Relay2, HIGH);
                lcd.setCursor(13, 1);
            } else if (header.indexOf("GET /27/off") >= 0) {
              Serial.println("GPIO 27 off");
              relay2State = "off";
              digitalWrite(Relay2, LOW);
                lcd.setCursor(13, 1);
                lcd.print("ON ");

            // Display the HTML web page
            client.println("<!DOCTYPE html><html>");
            client.println("<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">");
            client.println("<link rel=\"icon\" href=\"data:,\">");
                        // CSS to style the on/off buttons 
            // Feel free to change the background-color and font-size attributes to fit your preferences
            client.println("<style>html { font-family: Helvetica; display: inline-block; margin: 0px auto; text-align: center;}");
            client.println(".button { background-color: #4CAF50; border: none; color: white; padding: 16px 40px;");
            client.println("text-decoration: none; font-size: 30px; margin: 2px; cursor: pointer;}");
            client.println(".button2 {background-color: #555555;}</style></head>");

            // Web Page Heading
            client.println("<body><h1>ESP32 Web Server</h1>");
            client.println("<p>Adapted by Osvaldo Cantone <a href=></a> </p>");

            // Display current state, and ON/OFF buttons for GPIO 26  
            client.println("<p>Relay 1 (GPIO 15) - State: " + relay1State + "</p>");
            // If the output26State is off, it displays the ON button       
            if (relay1State=="off") {
              client.println("<p><a href=\"/26/on\"><button class=\"button\">ON</button></a></p>");
            } else {
              client.println("<p><a href=\"/26/off\"><button class=\"button button2\">OFF</button></a></p>");

            // Display current state, and ON/OFF buttons for GPIO 27  
            client.println("<p>Relay 2 (GPIO 2) - State: " + relay2State + "</p>");
            // If the output27State is off, it displays the ON button       
            if (relay2State=="off") {
              client.println("<p><a href=\"/27/on\"><button class=\"button\">ON</button></a></p>");
            } else {
              client.println("<p><a href=\"/27/off\"><button class=\"button button2\">OFF</button></a></p>");

            // The HTTP response ends with another blank line
            // Break out of the while loop
          } else { // if you got a newline, then clear currentLine
            currentLine = "";
        } else if (c != '\r') {  // if you got anything else but a carriage return character,
          currentLine += c;      // add it to the end of the currentLine
    // Clear the header variable
    header = "";
    // Close the connection
    Serial.println("Client disconnected.");