PIR motion sensor HC-SR501

The HC-SR501 PIR (Passive Infrared) Motion Sensor is one of the most popular and widely used motion detection modules in electronics. It works by detecting the infrared radiation naturally emitted by warm bodies — such as humans and animals — within its field of view. When a person or object moves across the sensor's detection zone, the change in IR levels triggers the sensor to output a HIGH digital signal, which can be read by any microcontroller or used to drive an external device directly.

At the heart of the module is a pyroelectric infrared sensor paired with a white Fresnel lens that focuses incoming IR onto the sensing element and widens the detection area to a roughly 120° cone, with a maximum range of about 7 meters. The module includes two adjustment potentiometers: one to set the sensitivity / detection distance, and another to set the delay time — how long the output stays HIGH after motion is detected (adjustable from approximately 0.3 seconds up to ~18 seconds, or longer on some variants).

A handy trigger mode jumper lets you choose between two behaviors: non-repeatable (L) mode, where the output goes high once and then returns low after the delay, and repeatable (H) mode (the default), where the output stays high as long as motion continues to be detected and only resets after the last movement plus the delay time.

The module operates on a wide input voltage range of 5V to 20V DC thanks to its on-board voltage regulator, while drawing an extremely low standby current of around 65µA, making it ideal for battery-powered and energy-saving projects. Its 3.3V logic-level output is directly compatible with Arduino, ESP8266/ESP32, Raspberry Pi, STM32, PIC, and other common boards.

Compact at just 32 × 24mm with convenient mounting holes, the HC-SR501 is perfect for DIY security alarms, automatic lighting, occupancy detection, and home automation.

Important note: After power-on, the sensor needs about 30–60 seconds to stabilize and calibrate to its environment. During this warm-up period it may produce a few false triggers. Mount it away from direct heat sources, moving air, and direct sunlight for best results.

Pin Configuration

The module has 3 pins:

• VCC: Power input (5V–20V DC, typically 5V)
• OUT: Digital output signal (3.3V HIGH when motion detected, 0V LOW when idle)
• GND: Ground

Specifications

• Module: HC-SR501 PIR Motion Sensor
• Operating Voltage: DC 5V – 20V
• Static (Standby) Current: ~65 µA
• Output Level: HIGH = 3.3V · LOW = 0V
• Trigger Modes: L = non-repeatable · H = repeatable (default)
• Delay Time: Adjustable, ~0.3 sec to ~18 sec
• Block (Lockout) Time: ~0.2 seconds
• Detection Angle: < 120° cone
• Detection Range: up to ~7 meters (adjustable)
• Lens Diameter: 23mm (default Fresnel lens)
• PCB Dimensions: approx. 32 × 24mm
• Mounting Hole Spacing: 28mm
• Mounting Hole Diameter: 2mm
• Operating Temperature: −15°C to +70°C
• Adjustments: Sensitivity (distance) + Delay time (two potentiometers)
• Sensing Type: Passive Infrared (pyroelectric)

How It Works

When a warm body enters the detection range, the sensor output goes HIGH. When the body leaves the range, the output automatically returns LOW after the set delay time. This automatic induction makes it ideal for triggering lights, alarms, cameras, or microcontroller actions without any manual input.

Applications

• Security and intruder alarm systems
• Automatic lighting (turn lights on when motion is detected)
• Home automation and smart home projects
• Energy-saving / occupancy-based controls
• Automatic door triggers
• Motion-activated cameras and surveillance
• Visitor / customer detection for shops
• Automatic fans, displays, and signage
• Robotics — obstacle / presence detection
• Pet and wildlife monitoring
• Arduino, ESP32, and Raspberry Pi learning projects
• Battery-powered IoT sensors