HCSR501 PIR Motion Sensor (Passive Infrared Sensor)

👁️‍🗨️ HC-SR501 PIR Motion Sensor
Human Motion Detection • Low Power • Smart Automation
The HC-SR501 PIR Motion Sensor Module is a widely used Passive Infrared (PIR) sensor designed to detect motion from humans or animals by sensing changes in infrared radiation. It is commonly used in security systems, automatic lighting, robotics, and IoT projects.
The module includes a pyroelectric infrared sensor and Fresnel lens that helps detect movement within its detection range.
📊 Infographic Overview
🔹 Basic Specifications
Feature
Details
🔌 Operating Voltage
5V – 20V DC
⚡ Operating Current
~50 µA (very low power)
📡 Output Type
Digital (High/Low)
📏 Detection Range
3 – 7 meters
📐 Detection Angle
~120°
⏱ Delay Time
Adjustable (3s – 5 min)
🌡 Operating Temperature
-15°C to +70°C
🧩 Main Components (Based on the Image)
The module typically contains:
🔹 Fresnel Lens Dome – focuses infrared signals
🔹 PIR Sensor Element – detects infrared radiation changes
🔹 BISS0001 Controller IC – signal processing chip
🔹 Sensitivity Adjustment Potentiometer
🔹 Delay Time Adjustment Potentiometer
🔹 Voltage regulator & capacitors
🔌 Pin Configuration
Pin
Function
VCC
Power supply (5–20V)
OUT
Digital output signal
GND
Ground
⚙️ Working Principle
The PIR sensor detects infrared radiation emitted by warm objects like humans.
Step-by-Step Operation
1️⃣ The Fresnel lens focuses infrared radiation onto the sensor.
2️⃣ The PIR element detects changes in heat energy.
3️⃣ When a human or animal moves, IR levels change.
4️⃣ The controller IC processes the signal.
5️⃣ The module outputs HIGH signal when motion is detected.
📐 Sensor Layout (Simplified)
HC-SR501 PIR Motion Sensor

┌────────────────────┐
│ Fresnel Lens │
│ (Motion Detection)│
└────────────────────┘
│
┌────────────────────┐
│ PIR Sensor Chip │
│ Signal Processor │
└────────────────────┘

Adjustments
┌───────────────┐
│ Sensitivity │
│ Delay Time │
└───────────────┘

Pins
┌─────┬─────┬─────┐
│VCC │OUT │GND │
└─────┴─────┴─────┘
🎛 Adjustable Settings
The HC-SR501 has two adjustable potentiometers:
🔧 Sensitivity Adjustment
Controls motion detection distance
⏱ Delay Time Adjustment
Controls how long the output stays HIGH after motion detection
🤖 Common Applications
🏠 Home security systems
💡 Automatic lighting systems
🚪 Smart door automation
🤖 Robotics motion detection
📷 Security camera triggering
🌐 IoT smart home devices
🔌 Compatible Microcontrollers
The PIR sensor can easily connect to popular development boards:
Arduino Uno
ESP32
Arduino Nano
Raspberry Pi
💡 Advantages
✅ Very low power consumption
✅ Wide detection angle (~120°)
✅ Adjustable sensitivity and delay
✅ Easy digital output interface
✅ Ideal for motion detection systems
⚠️ Limitations
❌ Cannot detect stationary objects
❌ Sensitive to temperature changes
❌ False triggers possible from pets or heat sources
🔧 Example Project Idea
💡 Automatic Motion-Activated Light
Components
PIR Motion Sensor (HC-SR501)
Arduino Uno
Relay module
LED light or bulb
Working
✔ Sensor detects human motion
✔ Microcontroller activates relay
✔ Light turns ON automatically
✔ Light turns OFF after delay