Motion Detected: ESP32 with PIR Sensor (HC-SR501)

🧠 What is a PIR Sensor?

PIR = Passive Infrared Sensor

• A PIR sensor detects motion by measuring changes in infrared radiation.

• Every warm object (like humans and animals) emits infrared (IR) radiation.

• PIR sensors don’t emit anything; they only detect IR changes. That’s why they are called passive.

🧪 How Does It Work?

• The PIR sensor has two slots made of pyroelectric sensors.

• When a human or animal moves in front of the sensor, one slot sees more IR radiation than the other.

• This sudden change causes a voltage difference and the sensor outputs HIGH (3.3V or 5V) for a short time.

So in short:
👉 No motion → LOW output
👉 Motion detected → HIGH output

🧰 Components Required

📟 PIR Sensor Pin Description (HC-SR501)

There are two knobs on the sensor:

1. Time Delay – Adjust how long output stays HIGH after motion.

2. Sensitivity – Adjust how far motion can be detected (typically up to 6 meters).

🔌 Circuit Diagram – Connect PIR Sensor to ESP32

If you’re using an LED for indication, connect:

• LED anode (+) → GPIO 2 (or any other GPIO)

• LED cathode (–) → 220Ω resistor → GND

  🔍 How to Test?

  1. Upload the code to ESP32.

  2. Open Serial Monitor at 115200 baud rate.

  3. Move your hand in front of the PIR sensor — you'll see Motion Detected!

  4. Stay still — you'll see No Motion.

  5. LED should turn ON/OFF according to motion.

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  💡 Real-World Project Ideas

  Project Idea	Description
  🔐 Security Alarm	Trigger buzzer or send message when motion detected
  💡 Smart Lighting	Turn on lights only when someone is in the room
  🧠 IoT Notification	Use WiFi to send alerts to mobile or Telegram bot
  🛌 Sleep Monitor	Turn off fan/light if no motion detected for 1 hour
  🐶 Pet Detector	Know when your pet enters a room

   

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  ❓ FAQs

  Q1: Can PIR detect behind walls?
  ➡️ No, PIR only detects line-of-sight IR radiation. It cannot see through walls or glass.

  Q2: Can PIR detect small objects?
  ➡️ It depends on heat and movement. It’s good at detecting humans and large animals.

  Q3: Is PIR sensor affected by sunlight or heat?
  ➡️ Yes, strong sunlight or high ambient temperature can affect sensitivity.

HOW TO OPERATE