Problem with NodeMCU connected to relay to turn on/off a lamp

I’ve a NodeMCU connected to a relay. My project was to turn on/off the lamps in my room using the NodeMCU as an HTTP server with buttons.

The thing is, when I turn on the lamps, they last around 10 minutes on and then they go off. It’s like the NodeMCU restarts, since I cannot connect to its local IP address for a while after this happens.

Is there something I’m missing?

Here’s the code:

#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>

/*Put your SSID & Password*/
const char* ssid = "Dr. No";  // Enter SSID here
const char* password = "martini007";  //Enter Password here

ESP8266WebServer server(80);

uint8_t LED1pin = 2;
bool LED1status = LOW;

uint8_t LED2pin = 16;
bool LED2status = LOW;

int relayInput = 13;

void setup() {
  pinMode(relayInput, OUTPUT);
  pinMode(LED1pin, OUTPUT);
  pinMode(LED2pin, OUTPUT);

  Serial.println("Connecting to ");

  //connect to your local wi-fi network
  WiFi.begin(ssid, password);

  //check wi-fi is connected to wi-fi network
  while (WiFi.status() != WL_CONNECTED) {
  Serial.println("WiFi connected..!");
  Serial.print("Got IP: ");  Serial.println(WiFi.localIP());

  server.on("/", handle_OnConnect);
  server.on("/encendidas", handle_on);
  server.on("/apagadas", handle_off);

  Serial.println("HTTP server started");
void loop() {
  digitalWrite(LED2pin, LOW);
  digitalWrite(LED1pin, LOW);

void handle_OnConnect() {
  Serial.println("GPIO7 Status: OFF | GPIO6 Status: OFF");
  server.send(200, "text/html", SendHTML(LED1status,LED2status)); 

void handle_on() {
  digitalWrite(relayInput, HIGH);
  Serial.println("GPIO7 Status: ON");
  server.send(200, "text/html", SendHTML(true,LED2status)); 

void handle_off() {
  LED1status = LOW;
  digitalWrite(relayInput, LOW);
  Serial.println("GPIO7 Status: OFF");
  server.send(200, "text/html", SendHTML(false,LED2status)); 

void handle_NotFound(){
  server.send(404, "text/plain", "Not found");

String SendHTML(uint8_t led1stat,uint8_t led2stat){
  String ptr = "<!DOCTYPE html> <html>\n";
  ptr +="<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0, user-scalable=no\">\n";
  ptr +="<title>UCI 0.1</title>\n";
  ptr +="<style>html { font-family: Arial; display: inline-block; margin: 10px auto; text-align: center;}\n";
  ptr +="body{margin-top: 200px;} h1 {color: #444444;margin: 50px auto 30px;} h3 {color: #444444;margin-bottom: 50px;}\n";
  ptr +=".button {display: block;width: 80px;background-color: #FF0000;border: none;color: white;padding: 13px 30px;text-decoration: none;font-size: 25px;margin: 0px auto 35px;cursor: pointer;border-radius: 4px;}\n";
  ptr +=".button-on {background-color: #1abc9c;}\n";
  ptr +=".button-on:active {background-color: #16a085;}\n";
  ptr +=".button-off {background-color: #34495e;}\n";
  ptr +=".button-off:active {background-color: #2c3e50;}\n";
  ptr +="p {font-size: 14px;color: #888;margin-bottom: 10px;}\n";
  ptr +="</style>\n";
  ptr +="</head>\n";
  ptr +="<body>\n";
  ptr +="<h1>UCI</h1>\n";
    ptr +="<h3>Unidad de control de iluminacion 0.1</h3>\n";
  {ptr +="<p>Luces alcoba: ENCENDIDAS</p><a class=\"button button-off\" href=\"/apagadas\">OFF</a>\n";}
  {ptr +="<p>Luces alcoba: APAGADAS</p><a class=\"button button-on\" href=\"/encendidas\">ON</a>\n";}

  ptr +="</body>\n";
  ptr +="</html>\n";
  return ptr;

The cables are connected to the NodeMCU GND and D7 input (GPIO13)

"Is there something I'm missing?"

post your code (over here)

“Is there something I’m missing?”

post your code (over here)

Sorry! Done

What powers the NodeMCU?

The SSR's input is an LED and resistor in series.
It may prove easier to troubleshoot with just an LED and resistor (or with "D0" onboard).

What powers the NodeMCU?

An USB cable connected to an 110v adapter

I don't know much about HTML'ing.
Wondering if this is a case for the implementation of

A project I was working on had a very long millis-based rest and the NodeMCU "reset" after a few minutes for lack of that.
[The watchdog timer trips otherwise.]

A project I was working on had a very long millis-based rest and the NodeMCU “reset” after a few minutes for lack of that.
[The watchdog timer trips otherwise.]

I’m very new in this, sorry, I don’t understand most of what you say :frowning:

“Is there something I’m missing?”

You can disconnect the relay and just control the LED to see if the relay is an issue. You can also try just hard coding the html and use client.println to send the individual html lines like bottom. Recursive String building like you use below might also cause memory problems. At a minimum I would use something like String ptr = “”; to clear the assembled String after using it or before assembling a new one.

  String ptr = "<!DOCTYPE html> <html>\n";
  ptr +="<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0, user-scalable=no\">\n";
  ptr +="<title>UCI 0.1</title>\n";
  Rui Santos
  Complete project details at  

// Load Wi-Fi library
#include <ESP8266WiFi.h>

// Replace with your network credentials
const char* ssid     = "ARRIS-D1FA";
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 output5State = "off";
String output4State = "off";

// Assign output variables to GPIO pins
const int output5 = 5;
const int output4 = 4;

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

void setup() {
  // Initialize the output variables as outputs
  pinMode(output5, OUTPUT);
  pinMode(output4, OUTPUT);
  // Set outputs to LOW
  digitalWrite(output5, LOW);
  digitalWrite(output4, LOW);

  // 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: ");

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

  if (client) {                             // If a new client connects,
    Serial.println("New Client.");          // print a message out in the serial port
    String currentLine = "";                // make a String to hold incoming data from the client
    currentTime = millis();
    previousTime = currentTime;
    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 /5/on") >= 0) {
              Serial.println("GPIO 5 on");
              output5State = "on";
              digitalWrite(output5, HIGH);
            } else if (header.indexOf("GET /5/off") >= 0) {
              Serial.println("GPIO 5 off");
              output5State = "off";
              digitalWrite(output5, LOW);
            } else if (header.indexOf("GET /4/on") >= 0) {
              Serial.println("GPIO 4 on");
              output4State = "on";
              digitalWrite(output4, HIGH);
            } else if (header.indexOf("GET /4/off") >= 0) {
              Serial.println("GPIO 4 off");
              output4State = "off";
              digitalWrite(output4, LOW);
            // 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: #195B6A; border: none; color: white; padding: 16px 40px;");
            client.println("text-decoration: none; font-size: 30px; margin: 2px; cursor: pointer;}");
            client.println(".button2 {background-color: #77878A;}</style></head>");
            // Web Page Heading
            client.println("<body><h1>ESP8266 Web Server</h1>");
            // Display current state, and ON/OFF buttons for GPIO 5  
            client.println("<p>GPIO 5 - State " + output5State + "</p>");
            // If the output5State is off, it displays the ON button       
            if (output5State=="off") {
              client.println("<p><a href=\"/5/on\"><button class=\"button\">ON</button></a></p>");
            } else {
              client.println("<p><a href=\"/5/off\"><button class=\"button button2\">OFF</button></a></p>");
            // Display current state, and ON/OFF buttons for GPIO 4  
            client.println("<p>GPIO 4 - State " + output4State + "</p>");
            // If the output4State is off, it displays the ON button       
            if (output4State=="off") {
              client.println("<p><a href=\"/4/on\"><button class=\"button\">ON</button></a></p>");
            } else {
              client.println("<p><a href=\"/4/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.");

I see (capital) Strings in there!

May be it is due to the power.
Are you driving the relay directly with the ESP 32?

That sounds like a reset indeed. So why don't you check for the error message? That's the beauty of the ESP8266, it basically never crashes silently, it'll always give a stack trace on the default Serial output. So connect it to your laptop/computer and see what you get in the Serial monitor!

Then when you have your message, copy/paste it in the ESP exception decoder extension for the Arduino IDE, and it'll tell you what's going on.

Feel free to post both the complete decoded stack trace with your program here. Just remember to use code tags.