How HC-SR501 PIR Sensor Works & Interface It With Arduino

The PIR sensor detects motion by sensing changes in infrared radiation, which is emitted by all warm-blooded animals, including humans. When someone or something moves within the sensor’s range, the PIR sensor triggers a response, making it ideal for applications where detecting motion is crucial. You’ll find PIR sensors in a wide array of modern devices, such as security systems, automatic light switches, garage door openers, and countless other applications designed to respond to motion or presence.

What makes the HC-SR501 stand out is its ease of use, affordability, and adjustable features, such as sensitivity and delay time. These settings allow you to tailor the sensor’s performance to your specific needs, whether you’re monitoring a small area or a large space. It’s also compact and compatible with microcontrollers like Arduino and Raspberry Pi, making it an excellent choice for hobbyists and professionals alike.

How does a PIR sensor work?

All objects, including the human body, emit heat energy in the form of infrared radiation when their temperature is above absolute zero (0 Kelvin / -273.15 °C). This heat radiation increases as the temperature of the object rises, making hotter objects emit more infrared radiation. However, this radiation is not detectable by the human eye, as it is emitted in the infrared spectrum, which lies just beyond the visible light range. PIR (Passive Infrared) sensors are designed to detect this infrared radiation, specifically the thermal energy emitted by living beings or warm objects in their surroundings.

The ability of a PIR sensor to detect this radiation relies on the principle that all objects emit infrared energy, with warmer bodies emitting more of it. PIR sensors are often used in applications such as motion detection, security systems, and energy-efficient lighting because they can sense the presence of people or animals based on the changes in infrared radiation in their environment. These sensors use specialized components that can detect minute variations in infrared radiation, triggering an alarm or action when a moving body enters their field of view.