IoT Engineering Course using ESP32 with 12 Real-World Projects

📦Smart Home Automation System

Circuit Diagram & Complete GPIO Planning

🎯 Objective of This Lesson

Students will learn:

How to plan GPIO pins properly
How to distribute power safely
How to connect multiple sensors correctly
How to avoid common ESP32 mistakes
How to design a stable Smart Home hardware setup

🧩 Components Used

ESP32
DHT11 Temperature Sensor
Ultrasonic Sensor (HC-SR04)
MQ3 Gas Sensor
Servo Motor (Door Lock)
2-Channel Relay Module (AC + Pump)
External 5V Power Supply

🧠 STEP 1 – GPIO Planning (Very Important)

We must avoid:

Boot pins
ADC conflicts
Input-only confusion
Power overload

📌 Final GPIO Planning Table

Device	ESP32 Pin	Type
DHT11	GPIO 4	Digital Input
Ultrasonic TRIG	GPIO 5	Digital Output
Ultrasonic ECHO	GPIO 18	Digital Input
MQ3 (Analog)	GPIO 34	Analog Input
Servo (Door Lock)	GPIO 13	PWM Output
AC Relay	GPIO 26	Digital Output
Pump Relay	GPIO 27	Digital Output

🧠 Why These Pins?

✅ GPIO 34

Input only
Perfect for analog (MQ3)

✅ GPIO 13

PWM supported
Safe for servo

✅ GPIO 26 & 27

Stable digital output
Good for relay modules

✅ GPIO 4, 5, 18

Safe general-purpose pins
No boot conflict

⚡ STEP 2 – Power Planning (Critical Section)

This project has multiple 5V devices.

🔋 Power Requirements

Device	Voltage	Notes
ESP32	5V (USB)	Internal 3.3V logic
DHT11	3.3V or 5V	Safe
Ultrasonic	5V	Needs stable supply
MQ3	5V	Heater element inside
Servo	5V	High current device
Relay	5V	Coil current

🚨 IMPORTANT RULE

❌ Do NOT power everything from ESP32 5V pin.

Servo + Relay + MQ3 together draw high current.

✅ Recommended Power Setup

Use:

👉 External 5V 2A Adapter

Power distribution:

5V Adapter
↓
Breadboard Power Rail
↓
Servo
Relay Module
MQ3
Ultrasonic

ESP32 powered separately via USB.

⚠ Connect ALL GNDs together.

Common ground is mandatory.

🧠 STEP 3 – Individual Component Wiring

🔹 1️⃣ DHT11 Connection

DHT11 Pin	ESP32
VCC	3.3V
GND	GND
DATA	GPIO 4

🔹 2️⃣ Ultrasonic Sensor

Ultrasonic	ESP32
VCC	5V
GND	GND
TRIG	GPIO 5
ECHO	GPIO 18

⚠ Optional: Use voltage divider for ECHO (safer).

🔹 3️⃣ MQ3 Gas Sensor

MQ3	ESP32
VCC	5V
GND	GND
AO	GPIO 34

🔹 4️⃣ Servo Motor (Door Lock)

Servo	ESP32
Red	External 5V
Brown	GND
Orange	GPIO 13

🔹 5️⃣ Relay Module

Relay	ESP32
VCC	5V
GND	GND
IN1	GPIO 26 (AC)
IN2	GPIO 27 (Pump)

🧠 STEP 4 – Circuit Layout Strategy

When placing on breadboard:

1️⃣ Keep power rails clean
2️⃣ Separate high-current devices
3️⃣ Avoid loose jumper wires
4️⃣ Keep servo wires short
5️⃣ Mount ultrasonic properly

🔒 STEP 5 – Safety Considerations

⚠ Never connect real AC directly during testing.
Use bulb for simulation.

⚠ Keep gas testing controlled.
⚠ Ensure pump dry-run protection.
⚠ Check relay isolation.

🧠 STEP 6 – Block Diagram (Conceptual)

DHT11 → 
Ultrasonic → 
MQ3 →         ESP32 → Relay (AC)
PIR →                 Relay (Pump)
Servo →
                         ↓
                     Blynk Cloud

🎯 Common Mistakes to Avoid

Using GPIO 0, 2, 15 incorrectly
Forgetting common ground
Powering servo from ESP32 5V
Using delay() in final code
Not testing individually

🎓 Learning Outcomes

After this lesson, students will:

Understand GPIO planning
Learn safe power distribution
Design multi-device circuits
Avoid hardware failures
Think like embedded engineers