HC-SR501 PIR Motion Sensor

The HC-SR501 PIR Motion Sensor is one of the most popular motion detection modules for Arduino, Raspberry Pi, ESP8266/ESP32 and general embedded electronics projects. PIR stands for Passive Infrared: the sensor does not transmit energy; instead, it detects changes in infrared radiation caused by a warm body moving across its field of view. A white Fresnel lens focuses infrared energy onto the pyroelectric sensing element, while the onboard control IC and supporting components process the signal and provide a clean digital output. This module is useful wherever automatic human presence detection is required. It can be used to switch lights, trigger a buzzer, wake a microcontroller, activate a camera, count people passing through a doorway, or add occupancy sensing to smart home prototypes. The wide 4.5V to 20V DC input range makes it convenient for 5V Arduino systems, 12V automation panels and battery-powered experiments. The OUT pin goes HIGH when motion is detected and returns LOW after the adjustable hold time. Most HC-SR501 boards include two onboard potentiometers: one for detection distance and one for output delay time. A jumper position is commonly provided for trigger mode selection: repeatable trigger mode keeps the output active while motion continues, while non-repeatable mode gives a single timed pulse. Pin connection is simple: VCC, OUT and GND. For microcontroller use, connect VCC to a suitable supply, GND to common ground and OUT to a digital input pin. Package includes one HC-SR501 PIR Motion Sensor Module with Fresnel lens fitted. Because this is a generic HC-SR501 module, minor PCB colour, component layout or adjustment range differences may be present depending on production batch.