How does an HC-SR501 PIR Sensor Work & How to Interface it with ESP32?

This project centers around the HC-SR501 PIR (Passive Infrared) motion sensor module and an ESP32 development board, working together to detect human or animal movement in an environment. The PIR sensor features a pyroelectric element beneath a multi-faceted Fresnel lens, which divides the detection zone into zones that focus ambient infrared radiation emitted by warm bodies. When a person moves across these zones, the sensor detects a sudden change in the infrared energy levels. This shift generates a small electrical voltage change, which the module's onboard controller processes to trigger its digital output pin. Using jumper wires on a breadboard, the digital output pin of the HC-SR501 is connected to a designated digital input pin on the ESP32. Through the Arduino IDE software, the ESP32 is programmed to continuously monitor this input pin. When the PIR sensor detects motion, its output goes HIGH, and the ESP32 reads this state change. In response, the ESP32 executes its programmed logic to drive an LED connected to one of its general-purpose input/output (GPIO) pins, turning the LED on to visually indicate that motion has been successfully sensed.