Smart Weather Station + Auto Ventilation System using Arduino (Wokwi Simulation)

▶ Open Wokwi

🧠 MakeMindz

Overview Parts Setup Wiring Code Logic Test Quiz More ▶ Wokwi

🚀 MakeMindz Summer Course · Module 3

Smart Weather Station
+ Auto Ventilation

A complete Arduino project — DHT22 sensor, servo vent, LCD display, and alarm system — simulated 100% in your browser using Wokwi. No hardware, no cost, no waiting.

🎓 Beginner Friendly ⏱️ ~45 minutes 🖥️ Browser Simulation 🤖 Arduino UNO 🌡️ DHT22 Sensor ⚙️ Servo Motor

▶ Start Simulation on Wokwi 📖 Read Tutorial

🖥️ Simulation Platform: Wokwi — Free, Online, No Installation Required

Build and run this entire circuit in your browser. Paste the diagram.json and code, then simulate instantly.

🔗 wokwi.com →

00

What You'll Build & Learn

Module Overview

The Smart Weather Station with Auto Ventilation is a real-time environmental monitoring system that automatically controls a servo vent based on temperature and humidity. You'll learn sensor reading, servo control, LCD display, alarm systems, and threshold-based automation — all inside Wokwi.

🌡️

Sensor Reading

Read temp & humidity from DHT22 in real-time

⚙️

Servo Control

Auto open/close vent based on temperature

📟

LCD Display

Show live weather data on 16×2 I²C screen

🔔

Alarm System

Blink red LED + buzz at critical temperature

🧠

IoT Logic

Threshold-based decision making with millis()

🖥️

Wokwi Sim

Test & debug the full circuit — free, online

01

Components Used

Step 1

All components exist as virtual parts in Wokwi — no shopping, no soldering. Here's what each part does:

01

Arduino UNOThe brain — runs your code and controls everything.

02

DHT22 SensorMeasures temperature (−40° to 80°C) and humidity.

03

LCD 1602 (I²C)16×2 character display — only 2 data wires via I²C.

04

Servo Motor (SG90)Rotates 0°–170° to simulate a vent flap.

05

Green LEDLights up when temperature is cool (below 28°C).

06

Yellow LEDLights up in warm zone (28°C–35°C).

07

Red LEDBlinks rapidly at danger level (35°C+).

08

220Ω Resistors ×3Protect LEDs from too much current — always required!

09

BuzzerSounds a 1200 Hz alarm every 800ms during critical heat.

10

Push ButtonCycles between 3 LCD screens using debounce logic.

02

How to Set Up the Wokwi Simulation

Step 2 · Most Important

💡

Wokwi is a FREE online Arduino simulator. Run this project at wokwi.com — no account needed to start, no software to install.

1

🌐 Open Wokwi in Your Browser

Go to wokwi.com in any modern browser (Chrome, Firefox, Edge).

• Click "New Project" on the homepage
• Select "Arduino UNO" from the board list
• You'll see a blank canvas with Arduino UNO already placed

💡

Create a free Wokwi account to save your project and share it with your teacher using a link!

2

📋 Paste diagram.json — The Fastest Setup Method

 

Wokwi simulation — complete weather station circuit with all components wired

Instead of adding components one by one, paste the complete circuit as a diagram.json file to set up all parts AND wires automatically.

• Click the "diagram.json" tab (next to sketch.ino)
• Select all existing text and delete it
• Copy and paste the complete diagram.json below
• Press Ctrl+S to save — the circuit appears automatically ✅

⚠️

Copy the COMPLETE JSON — it starts with { and ends with }. Don't miss any part!

diagram.json — Paste into Wokwi

{
  "version": 1,
  "author": "Smart Weather Station",
  "editor": "wokwi",
  "parts": [
    { "type": "wokwi-arduino-uno",  "id": "uno",  "top": 200, "left": 180, "attrs": {} },
    { "type": "wokwi-dht22",         "id": "dht1", "top": 0,    "left": 0,   "attrs": { "temperature": "-34.9" } },
    { "type": "wokwi-lcd1602",       "id": "lcd1", "top": -147, "left": 390, "attrs": { "pins": "i2c" } },
    { "type": "wokwi-servo",         "id": "sv1",  "top": 0,    "left": 450, "attrs": { "horn": "cross" } },
    { "type": "wokwi-led",           "id": "ledG", "top": 420, "left": 80,  "attrs": { "color": "green"  } },
    { "type": "wokwi-led",           "id": "ledY", "top": 420, "left": 130, "attrs": { "color": "yellow" } },
    { "type": "wokwi-led",           "id": "ledR", "top": 420, "left": 180, "attrs": { "color": "red"    } },
    { "type": "wokwi-resistor",      "id": "rG",   "top": 460, "left": 80,  "attrs": { "value": "220" } },
    { "type": "wokwi-resistor",      "id": "rY",   "top": 460, "left": 130, "attrs": { "value": "220" } },
    { "type": "wokwi-resistor",      "id": "rR",   "top": 460, "left": 180, "attrs": { "value": "220" } },
    { "type": "wokwi-buzzer",        "id": "bz1",  "top": 420, "left": 280, "attrs": {} },
    { "type": "wokwi-pushbutton",    "id": "btn1", "top": 420, "left": 370, "attrs": { "color": "blue" } }
  ],
  "connections": [
    [ "dht1:VCC",  "uno:3.3V",   "red",    [] ],
    [ "dht1:SDA",  "uno:7",      "green",  [] ],
    [ "dht1:GND",  "uno:GND.1", "black",  [] ],
    [ "lcd1:VCC",  "uno:5V",     "red",    [] ],
    [ "lcd1:GND",  "uno:GND.2", "black",  [] ],
    [ "lcd1:SDA",  "uno:A4",     "blue",   [] ],
    [ "lcd1:SCL",  "uno:A5",     "yellow", [] ],
    [ "sv1:PWM",   "uno:9",      "orange", [] ],
    [ "sv1:V+",    "uno:5V",     "red",    [] ],
    [ "sv1:GND",   "uno:GND.3", "black",  [] ],
    [ "ledG:A",    "rG:1",       "green",  [] ],
    [ "rG:2",      "uno:2",      "green",  [] ],
    [ "ledG:C",    "uno:GND.4", "black",  [] ],
    [ "ledY:A",    "rY:1",       "yellow", [] ],
    [ "rY:2",      "uno:3",      "yellow", [] ],
    [ "ledY:C",    "uno:GND.5", "black",  [] ],
    [ "ledR:A",    "rR:1",       "red",    [] ],
    [ "rR:2",      "uno:4",      "red",    [] ],
    [ "ledR:C",    "uno:GND.6", "black",  [] ],
    [ "bz1:1",     "uno:5",      "purple", [] ],
    [ "bz1:2",     "uno:GND.7", "black",  [] ],
    [ "btn1:1.l", "uno:6",      "blue",   [] ],
    [ "btn1:2.l", "uno:GND.8", "black",  [] ]
  ],
  "dependencies": {}
}

3

📚 Install Libraries (One Click in Wokwi)

Create a file called libraries.txt in Wokwi (click the "+" icon next to the file tabs) and paste these three lines:

libraries.txt

DHT sensor library
LiquidCrystal I2C
Servo

💡

Wokwi auto-downloads these libraries when you start the simulation. No manual installation needed!

03

Circuit Wiring Reference

Step 3

If you used diagram.json above, wiring is already done! This table is your reference if wiring manually.

Component	Pin	Arduino	Wire
DHT22	VCC	3.3V	Red
DHT22	SDA (Data)	Pin 7	Green
DHT22	GND	GND	Black
LCD 1602	VCC	5V	Red
LCD 1602	SDA	A4	Blue
LCD 1602	SCL	A5	Yellow
Servo Motor	PWM Signal	Pin 9	Orange
Servo Motor	V+ Power	5V	Red
LED Green → 220Ω	Anode (+)	Pin 2	Green
LED Yellow → 220Ω	Anode (+)	Pin 3	Yellow
LED Red → 220Ω	Anode (+)	Pin 4	Red
Buzzer	Positive (+)	Pin 5	Purple
Push Button	Pin 1.l	Pin 6	Blue

💡

All LED cathodes (−) and GND pins connect to any GND on the Arduino. Use INPUT_PULLUP for the button — no external resistor needed!

04

The Arduino Code — Full & Explained

Step 4

Click the sketch.ino tab in Wokwi, delete existing code, and paste the full sketch below.

① Libraries & Pin Definitions

sketch.ino — Part 1/4

// ============================================================
//  SMART WEATHER STATION + AUTO VENTILATION
//  Arduino UNO | Wokwi Simulation | MakeMindz Summer Course
// ============================================================

#include <DHT.h>               // Temperature & humidity sensor library
#include <Wire.h>              // I2C communication (for LCD)
#include <LiquidCrystal_I2C.h>  // LCD display control
#include <Servo.h>             // Servo motor control

// ── Pin definitions ──────────────────────────
#define DHT_PIN     7    // DHT22 data wire
#define DHT_TYPE    DHT22
#define SERVO_PIN   9    // Servo PWM signal (~pin)
#define LED_GREEN   2    // Green status LED
#define LED_YELLOW  3    // Yellow status LED
#define LED_RED     4    // Red alarm LED
#define BUZZER_PIN  5    // Buzzer
#define BTN_PIN     6    // Push button for LCD screens

// ── Library objects ──────────────────────────
DHT              dht(DHT_PIN, DHT_TYPE);
LiquidCrystal_I2C lcd(0x27, 16, 2);   // LCD at I2C address 0x27
Servo            ventServo;

// ── State variables ──────────────────────────
float tempC     = 0, humidity = 0, heatIndex = 0;
int   ventAngle = 0, screen = 0;
bool  alarmOn   = false, blinkState = false, prevBtn = HIGH;
unsigned long lastRead = 0, lastBlink = 0, lastBuzz = 0, dbBtn = 0;

② The setup() Function — Runs Once on Boot

sketch.ino — Part 2/4

void setup() {
  dht.begin();
  lcd.init();
  lcd.backlight();

  ventServo.attach(SERVO_PIN);
  ventServo.write(0);          // Start with vent fully CLOSED

  pinMode(LED_GREEN,  OUTPUT);
  pinMode(LED_YELLOW, OUTPUT);
  pinMode(LED_RED,    OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(BTN_PIN, INPUT_PULLUP); // Uses internal pull-up resistor

  // Splash screen for 1.8 seconds
  lcd.setCursor(2, 0); lcd.print("WeatherStation");
  lcd.setCursor(3, 1); lcd.print("Auto Vent v1");
  delay(1800);
  lcd.clear();

  // Boot LED test — light each LED one by one
  digitalWrite(LED_GREEN,  HIGH); delay(200);
  digitalWrite(LED_YELLOW, HIGH); delay(200);
  digitalWrite(LED_RED,    HIGH); delay(200);
  digitalWrite(LED_GREEN,  LOW);
  digitalWrite(LED_YELLOW, LOW);
  digitalWrite(LED_RED,    LOW);
}

③ The loop() Function — Heart of the System

sketch.ino — Part 3/4

void loop() {
  unsigned long now = millis();

  // ── Read sensor every 2 seconds (non-blocking) ──
  if (now - lastRead >= 2000) {
    lastRead = now;
    float t = dht.readTemperature();
    float h = dht.readHumidity();

    if (!isnan(t) && !isnan(h)) {
      tempC = t; humidity = h;
      heatIndex = dht.computeHeatIndex(t, h, false);
    }

    // ── Smooth servo movement (5° per step) ──
    int targetAngle = tempToVent(tempC);
    if (ventAngle < targetAngle)      ventAngle = min(ventAngle + 5, targetAngle);
    else if (ventAngle > targetAngle)  ventAngle = max(ventAngle - 5, targetAngle);
    ventServo.write(ventAngle);

    // ── Update LEDs ──
    if (tempC < 28) {
      digitalWrite(LED_GREEN, HIGH); digitalWrite(LED_YELLOW, LOW); digitalWrite(LED_RED, LOW);
      alarmOn = false;
    } else if (tempC < 35) {
      digitalWrite(LED_GREEN, LOW); digitalWrite(LED_YELLOW, HIGH); digitalWrite(LED_RED, LOW);
      alarmOn = false;
    } else {
      digitalWrite(LED_GREEN, LOW); digitalWrite(LED_YELLOW, LOW);
      alarmOn = true;
    }

    // ── Refresh LCD ──
    lcd.clear();
    switch (screen) {
      case 0: showScreenTemp();    break;
      case 1: showScreenHeatIdx(); break;
      case 2: showScreenVent();    break;
    }
  }

  // ── Blink red LED every 300ms when alarm ──
  if (alarmOn && now - lastBlink >= 300) {
    lastBlink = now; blinkState = !blinkState;
    digitalWrite(LED_RED, blinkState ? HIGH : LOW);
  }

  // ── Sound buzzer every 800ms when alarm ──
  if (alarmOn && now - lastBuzz >= 800) {
    lastBuzz = now;
    tone(BUZZER_PIN, 1200, 120);   // 1200Hz for 120ms
  }

  // ── Button: cycle LCD screens with debounce ──
  bool btn = digitalRead(BTN_PIN);
  if (prevBtn == HIGH && btn == LOW && now - dbBtn > 200) {
    screen = (screen + 1) % 3;   // Cycle: 0 → 1 → 2 → 0
    dbBtn = now; lcd.clear();
  }
  prevBtn = btn;
  delay(20);
}

④ Helper Functions — Vent Control + LCD Screens

sketch.ino — Part 4/4

// Maps temperature to vent angle using proportional control
int tempToVent(float t) {
  if (t < 25.0)  return 0;                                            // Cool → CLOSED
  if (t < 30.0)  return map(t*10, 250, 300, 0,  60);  // Warm → partial
  if (t < 38.0)  return map(t*10, 300, 380, 60, 160); // Hot  → wide open
  return 170;                                                           // Critical → FULLY open
}

// Screen 0: Temperature + Humidity bar
void showScreenTemp() {
  lcd.setCursor(0, 0); lcd.print("Temp: "); lcd.print(tempC, 1); lcd.print("\xDFC");
  lcd.setCursor(0, 1); lcd.print("Hum: ");  lcd.print((int)humidity); lcd.print("%");
}

// Screen 1: Heat Index + comfort level
void showScreenHeatIdx() {
  lcd.setCursor(0, 0); lcd.print("Heat Index:");
  lcd.setCursor(0, 1);
  if      (heatIndex < 27) lcd.print("Comfort  ");
  else if (heatIndex < 32) lcd.print("Caution  ");
  else if (heatIndex < 41) lcd.print("Warning! ");
  else                     lcd.print("DANGER!! ");
  lcd.print(heatIndex, 1); lcd.print("\xDFC");
}

// Screen 2: Vent status + progress bar
void showScreenVent() {
  int pct = map(ventAngle, 0, 170, 0, 100);
  lcd.setCursor(0, 0); lcd.print("Vent: "); lcd.print(pct); lcd.print("%   ");
  lcd.setCursor(0, 1); lcd.print("[");
  for (int i = 0; i < 12; i++) lcd.print(i < pct/9 ? "#" : "-");
  lcd.print("]");
}

05

How the Automation Logic Works

Key Concept

This project uses threshold-based decision making — the same logic used in real IoT and smart building systems.

Below 25°C

Cool Zone

🟢 Vent Closed (0°)

Green LED on. Temperature is comfortable — no ventilation needed.

25°C – 30°C

Warm Zone

🟡 Partial Open (0–60°)

Yellow LED. Vent gradually opens as temperature rises.

30°C – 38°C

Hot Zone

🟠 Wide Open (60–160°)

Vent opens wide to push hot air out quickly.

Above 38°C

🚨 Critical

🔴 Full Open + Alarm

Red LED blinks (300ms) + buzzer every 800ms at 1200Hz.

🔑 Why Use millis() Instead of delay()?

This is one of the most important concepts in Arduino programming:

• delay(2000) — FREEZES the entire program for 2 seconds. Button presses are missed. LEDs can't blink. Servo can't respond.
• millis() — The program keeps running and simply CHECKS if 2 seconds have passed. Everything works in parallel!

💡

This is called Non-Blocking Code — it's how professional Arduino programs are written. Always prefer millis() over delay() when multiple things need to happen simultaneously!

06

Run & Test Your Simulation

The Fun Part!

▶

Press the Green Play Button

In Wokwi, click the big green ▶ Play button. You should see:

• LCD shows "WeatherStation / Auto Vent v1" for 1.8 seconds
• All 3 LEDs flash one by one (boot test)
• LCD switches to live temperature and humidity

⚠️

If you see a compile error, check that your libraries.txt file exists with the exact library names from Step 3.

🌡️

Change the Temperature Slider

Click the DHT22 sensor in the simulation — a popup shows temperature and humidity sliders. Try:

• Set to 20°C → Green LED lights, servo stays at 0° (closed)
• Set to 28°C → Yellow LED lights, servo starts opening
• Set to 36°C → Red LED blinks fast, buzzer sounds, servo fully open!
• Drag back to 20°C → Watch the servo smoothly close back down

💡

The servo moves smoothly (5° per step) rather than jumping instantly — that's the smoothing code in loop() working!

🔘

Click the Blue Button to Cycle Screens

Click the blue push button in the simulation to switch between 3 LCD displays:

• Screen 0: Temperature + Humidity percentage
• Screen 1: Heat Index + comfort level (Comfort / Caution / Warning / DANGER)
• Screen 2: Vent open percentage + progress bar

FREE SIMULATION

Open the Full Simulation on Wokwi

Run this entire project in your browser — no sign-up required to view. Click "Copy and Tinker" to make your own editable version.

Open Wokwi Simulation

08

Knowledge Check Quiz

Test Yourself!

Answer these 5 questions to check your understanding before the next module.

1 What does the DHT22 sensor measure?

Distance and proximity Temperature and humidity Light intensity and colour Voltage and current

2 Why do we use millis() instead of delay() in the main loop?

delay() uses more memory than millis() millis() is a newer, faster command delay() freezes the whole program, so buttons and LED blinking stop working They do exactly the same thing

3 Which Arduino pin controls the servo motor?

Pin 7 Pin A4 Pin 5 Pin 9

4 What happens when temperature exceeds 38°C?

The green LED turns on and the vent closes The yellow LED turns on and nothing else changes The red LED blinks, buzzer sounds, and vent opens fully to 170° The Arduino restarts automatically

5 Why are 220Ω resistors connected in series with each LED?

To make them brighter by amplifying the signal To limit current and protect the LEDs from burning out To slow down the blinking speed They are optional and make no difference

09

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