🎯 Build Your Own Timer Plug (Mobile Charger Auto Cut-Off) Using ESP32 (Hotspot Mode)

📅 By Dinesh D | Tech DIY Projects | Nov 2025

🚀 Introduction
Want a simple plug that automatically cuts power to your mobile charger after a set time — and that works without any router or internet? In this project I built a Wi-Fi hotspot timer plug using an ESP32 and a 5V relay module. The ESP32 creates its own Wi-Fi network. Open the web page it serves, set the HH:MM:SS timer, and the relay will turn the charger ON and then auto cut-off when time finishes.

This post gives the full program, pin configuration, wiring, step-by-step usage, and what photos/video clips to include in your Blogspot post.

🧠 Project Concept

ESP32 runs in Access Point (hotspot) mode.
A simple web UI served by the ESP32 lets the user set a timer.
When the timer starts, ESP32 energizes the relay → charger receives power.
When timer expires or user presses Stop, ESP32 de-energizes the relay → power cut-off.

This is perfect for charging control, lamp timers, and other small AC loads (observe safety limits of your relay).

🧰 Components Used

Component	Quantity
ESP32 Dev Board (any DevKit)	1
5V Relay Module (with opto isolation recommended)	1
AC Plug & Socket (mains rated)	1 set
USB Cable (to power ESP32)	1
Jumper Wires	several
Small project box / enclosure	optional

Tools: screwdriver, wire stripper, multimeter, hot glue / tape, soldering iron (optional)

🔌 Pin Configuration & Connections

ESP32 → Relay (DC control side)

relay VCC → 5V (ESP32 5V or external 5V)
relay GND → GND (ESP32 GND)
relay IN → GPIO 5 (ESP32 control pin)

Relay → AC (mains side) — Important: mains wiring must be done safely

Live (hot) wire from mains → COM on relay
NO (Normally Open) → Live to charger input
Neutral wire → Direct to charger neutral (do not switch neutral)
Earth (if present) → Earth to charger earth

Notes:

Use relay rated for your mains voltage & current (e.g., 250VAC @ 10A or higher).
If your relay module uses 5V coil, power it from ESP32 5V pin or separate 5V supply (common GND).
For safety, place AC wiring inside an insulated enclosure and keep low-voltage wiring separate.

📟 ESP32 Code (Hotspot Mode + Timer + Auto Cut-Off)
Copy this into Arduino IDE, select your ESP32 board and upload.

#include <WiFi.h>
#include <WebServer.h>

// Hotspot credentials (change if you want)
const char* ssid = "Charger_AP";
const char* password = "12345678";

WebServer server(80);

const int relayPin = 5;  // GPIO5 -> Relay IN
unsigned long timerDuration = 0;  // milliseconds
unsigned long startTime = 0;
bool isCharging = false;

// Simple HTML UI
String webPage = R"rawliteral(
<!DOCTYPE html><html>
<head>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Timer Plug - Auto Cut Off</title>
  <style>
    body { font-family: Arial, sans-serif; text-align:center; padding:24px; }
    h2 { color:#1a4d8f; }
    .time { font-size:18px; margin:6px; width:80px; padding:8px; border-radius:6px; border:1px solid #ccc; }
    button { padding:12px 20px; margin:10px; border:none; color:#fff; border-radius:6px; background:#1a4d8f; cursor:pointer; }
    .stop { background:#d9534f; }
  </style>
</head>
<body>
  <h2>⏱️ Mobile Charger Auto Cut-Off</h2>
  <form action="/start">
    <input class="time" type="number" name="hours" placeholder="HH" min="0" max="24">
    <input class="time" type="number" name="minutes" placeholder="MM" min="0" max="59">
    <input class="time" type="number" name="seconds" placeholder="SS" min="0" max="59"><br>
    <button type="submit">Start Charging</button>
  </form>
  <form action="/stop">
    <button class="stop" type="submit">Stop Charging</button>
  </form>
  <p>Connect your phone to WiFi: <b>Charger_AP</b> (pwd: 12345678)<br>Open: <b>192.168.4.1</b></p>
</body>
</html>
)rawliteral";

void setup() {
  Serial.begin(115200);
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, HIGH); // Ensure relay is OFF initially (HIGH = OFF for many modules)

  // Start hotspot
  WiFi.softAP(ssid, password);
  Serial.println("Access Point started");
  Serial.print("IP: "); Serial.println(WiFi.softAPIP());

  // Routes
  server.on("/", []() {
    server.send(200, "text/html", webPage);
  });

  server.on("/start", []() {
    int h = server.hasArg("hours") ? server.arg("hours").toInt() : 0;
    int m = server.hasArg("minutes") ? server.arg("minutes").toInt() : 0;
    int s = server.hasArg("seconds") ? server.arg("seconds").toInt() : 0;

    timerDuration = ((unsigned long)h * 3600UL + (unsigned long)m * 60UL + (unsigned long)s) * 1000UL;
    startTime = millis();
    digitalWrite(relayPin, LOW); // Turn relay ON (LOW for many modules)
    isCharging = true;

    Serial.printf("Started: %dh %dm %ds -> %lu ms\n", h, m, s, timerDuration);
    server.send(200, "text/html", "<h2>Charging Started</h2><a href='/'>Back</a>");
  });

  server.on("/stop", []() {
    digitalWrite(relayPin, HIGH); // Turn relay OFF
    isCharging = false;
    Serial.println("Stopped manually");
    server.send(200, "text/html", "<h2>Charging Stopped</h2><a href='/'>Back</a>");
  });

  server.begin();
}

void loop() {
  server.handleClient();

  if (isCharging) {
    unsigned long elapsed = millis() - startTime;
    if (elapsed >= timerDuration) {
      digitalWrite(relayPin, HIGH); // Auto cut-off
      isCharging = false;
      Serial.println("Timer complete - Relay OFF");
    }
  }
}

🛡️ Safety Warnings

Work carefully with mains voltage. If you are not confident with AC wiring, get help from a qualified electrician.
Use a relay rated for the load (voltage & current).
Insulate all exposed mains connections; use a proper enclosure.
Keep low-voltage electronics (ESP32) isolated from mains wiring.

🧪 How to Test (Step-by-step)

Upload code to ESP32 using Arduino IDE.
Power ESP32 with USB (from phone charger or power bank).
On your phone: connect to WiFi Charger_AP (password: 12345678).
Open browser → go to http://192.168.4.1.
Enter a short timer (eg. 00:00:10) and press Start Charging.
Verify: relay clicks and charger supplies phone. After 10s the relay should click OFF.

🎉 Final Result
✅ Simple hotspot-based timer plug that works without internet
✅ Web UI to set time & manual stop button
✅ Auto cut-off protects charger/battery
✅ Easy to adapt for lamps, fans, and other small appliances

❤️ Want More?
If you want, I can also:

provide a Blogspot HTML-ready post (with image placeholders),
add a live countdown on the web UI,
supply a simple circuit diagram image for download.

Contact / Questions: reply here and I’ll help you finish the blog post or improve features.

D Trend

Sunday, 16 November 2025