📘Home Security System

🎯 Objective of This Lesson

Students will learn:

• What is motion detection

• What is a PIR sensor

• How PIR detects human movement

• Internal working principle

• Types of PIR sensors

• Applications in real world

🔍 What is Motion Detection?

Motion detection means:

Detecting movement of a person or object in a specific area.

In home security systems, motion detection is used to:

• Detect intruders

• Trigger alarms

• Turn ON lights automatically

• Send security alerts

🌡 What is PIR Sensor?

PIR stands for:

Passive Infrared Sensor

It is called passive because:

• It does NOT emit energy

• It only detects infrared radiation from objects

Every human body emits infrared radiation (heat).

PIR sensor detects change in infrared levels.

🧠 Working Principle of PIR Sensor

The PIR sensor works based on:

👉 Infrared radiation detection

Step-by-step working:

1️⃣ Human body emits infrared radiation
2️⃣ PIR sensor detects heat energy
3️⃣ When a person moves, infrared level changes
4️⃣ Sensor detects this change
5️⃣ Output pin becomes HIGH
6️⃣ ESP32 reads motion detected

Important:

PIR detects motion, not presence.
If a person stands still → sometimes no detection.

🔬 Internal Structure of PIR Sensor

Inside PIR module:

• Pyroelectric sensor element

• Fresnel lens (white dome)

• Amplifier circuit

• Comparator circuit

• Output stage

🔹 Pyroelectric Sensor

This is the core sensing element.

It detects change in infrared radiation.

When IR radiation changes → small voltage is generated.

🔹 Fresnel Lens

The white dome cover:

• Focuses infrared signals

• Increases detection range

• Divides detection area into zones

📡 How PIR Detects Movement

The sensor has two sensing slots.

When a person moves:

• First slot detects heat

• Then second slot detects heat

• This difference creates signal

• Motion is detected

No movement → no change → no output.

🔌 PIR Sensor Pin Description

Most common PIR module (HC-SR501 type) has 3 pins:

Output:

LOW → No motion
HIGH → Motion detected

⚙ Adjustable Settings on PIR

Most PIR modules have two potentiometers:

1️⃣ Sensitivity Adjustment

• Adjust detection range

2️⃣ Time Delay Adjustment

• Adjust how long output stays HIGH

There is also a trigger mode jumper:

• H mode (Retriggerable)

• L mode (Non-Retriggerable)

📏 PIR Detection Range

Typical values:

• Range: 5 to 7 meters

• Angle: 110° to 120°

Depends on module and adjustment.

🔋 Power Requirements

• Operating Voltage: 5V

• Output Signal: 3.3V – 5V compatible

• Safe for ESP32 digital input

🏠 Real-World Applications

PIR sensors are used in:

• Home security systems

• Automatic lights

• Motion cameras

• Smart door alarms

• Energy saving systems

• Smart classrooms

⚠ Important Limitations

Students must understand:

• Cannot detect through walls

• Sensitive to temperature changes

• Can be triggered by pets

• Needs warm-up time (30–60 seconds)

⏳ Warm-Up Time

After power ON:

• Wait 30–60 seconds

• Sensor stabilizes

• During this time output may fluctuate

🎓 Learning Outcomes

After this lesson, students understand:

• What is infrared radiation

• What is passive sensor

• How PIR detects motion

• Difference between motion & presence

• Practical security sensor basics