Tutorials
PIR Sensor with ESP32

PIR Sensor with ESP32

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Introduction

This tutorial shows you how to interface an ESP32 development board with a PIR (Passive Infrared) motion sensor to detect movement within its field of view. You’ll learn to wire the components and write firmware that reads the sensor’s digital output. By the end, you’ll be able to build simple presence-sensing projects—security alarms, automatic lights, or data-loggers—that react to motion.

Learning Objectives

  • Understand how a PIR motion sensor detects infrared changes
  • Install ESP32 board support in the Arduino IDE (or PlatformIO)
  • Wire the PIR sensor to the ESP32 safely
  • Write, upload, and debug Arduino-style code that reads a digital input

Background Information

A PIR motion sensor, such as the HC-SR501 module, contains a pyroelectric element that generates a tiny voltage when it “sees” a change in infrared radiation. When the element’s output crosses a threshold, an onboard comparator drives the OUT pin HIGH for a user-adjustable period.

  • Why use a PIR? Low cost, low power, simple digital interface.
  • Alternatives: Ultrasonic HC-SR04 (sonar-based, reflects sound), RCWL-0516 microwave radar.

Pros & Cons:

  • Pros: No moving parts, wide detection range (~3–7 m), adjustable sensitivity/delay.
  • Cons: Blind to stationary heat sources, long warm-up time (~60 s), susceptible to rapid temperature shifts.

Getting Started

Required Downloads and Installations

  1. Arduino IDE (Windows/macOS/Linux):
  2. ESP32 Board Support for Arduino IDE:

Required Components

Component NameQuanitity
ESP32 Dev Board1
PIR Motion Sensor Module (HC-SR501)1
Breadboard (Optional)1
Female-to-Male Jumper Wires3
Male-to-Male Jumper Wires (Optional)3
USB-C (or USB-A) to USB-C Cable1

Required Tools and Equipment

  • Computer (Windows/macOS/Linux)
  • USB cable compatible with your ESP32

Part 1: Wiring the PIR Motion Sensor

Introduction

In this section, you’ll learn how to power the PIR sensor and connect its output pin to the ESP32’s GPIO, ensuring correct logic-level compatibility.

Objective

  • Power the PIR at the correct voltage
  • Connect the signal pin to an ESP32 digital input
  • Verify wiring with a simple continuity or voltage test

Background Information

PIR modules typically run on 5 V, but the HC-SR501 will also work at 3.3 V.

Components

  • 1 × ESP32 Dev Board
  • 1 × HC-SR501 PIR Sensor
  • 3 × Female to Male jumper wires (VCC, GND, OUT)
  • 1 x Breadboard (Optional)
  • 3 x Male to Male jumper wires (Optional)

Instructional

Refer to your sensors specifications to determine which pin is VCC, GND, and OUT.

  • Power
    • Connect PIR VCC → ESP32 3V3
    • Connect PIR GND → ESP32 GND
  • Signal
    • Connect PIR OUT → ESP32 GPIO 36 (or any free digital pin)

Example

Wiring the Sensor to the ESP32 DevBoard I used a breadboard but the wires from the PIR sensor can also be directly connected to the DevBoard.

Part 2: Writing the Code Step by Step

Introduction

Now that your hardware is correctly wired, this section walks you through creating, compiling, and uploading an Arduino-style sketch to the ESP32. We’ll explain each line of code in detail so that you understand how to configure the PIR input, read its digital state, and drive an LED (or other output) in response to motion.

Objective

  • Understand the Arduino interface.
  • Declare and initialize pin constants and I/O modes
  • Implement the 60 s warm-up delay for the PIR module
  • Continuously read the PIR’s digital output
  • Drive an LED (optional) or simply print status to Serial

Background Information

This section focuses on coding in the Arduino IDE. The language is very similar to C or C++. If you have any background knowledge in those languages, you will recognize the code and its formatting. If you don’t have experience in C/C++, don’t worry, I’ll will be breaking down the code into very manageable chunks.

Components

  • 1 × ESP32 Dev Board (already wired)
  • 1 × Computer with Arduino IDE

Instructional

Step 1 – Create a New Sketch and Declare Pins

  1. Open a New Sketch:

    • File → New.

  2. At the Top of the Sketch, Enter the Pin Definitions:

    const int pirPin = 36;     // Connect PIR OUT → GPIO 36
const int ledPin = 17;     // (Optional) Connect an LED → GPIO 17
int motionState    = LOW;  // To track motion

Step 2 – Write setup() to Configure I/O and Warm Up the PIR

  1. Initialize Serial (for Debugging):

    void setup() {
Serial.begin(115200);
    • This opens a Serial connection at 115200 baud so we can print “Motion detected!” or “No motion.” to the Serial Monitor.

  2. Set pinMode for pirPin and ledPin:

    pinMode(pirPin, INPUT_PULLDOWN);
pinMode(ledPin, OUTPUT);
digitalWrite(ledPin, LOW);
    • INPUT_PULLDOWN ensures GPIO 14 sits at 0 V when PIR OUT is off.
    • We set the LED pin to OUTPUT and drive it LOW initially (LED off).

  3. Warm Up the PIR (60 Seconds):

    delay(60000);  // Wait 60 s for the PIR to stabilize before reading
    • Why 60s? Most HC-SR501 modules need about a minute to let the comparator’s reference settle. During this time, the output can remain HIGH or oscillate. Only after ~60 s will the PIR accurately hold LOW when there is no motion.

  4. The complete setup() now looks like:

    void setup() {
   Serial.begin(115200);
   pinMode(pirPin, INPUT_PULLDOWN);
   pinMode(ledPin, OUTPUT);
   digitalWrite(ledPin, LOW);
   delay(60000);    // PIR warm-up (≈60 s)
}

Step 3 – Write loop() to Read Motion and Drive LED

  1. Read PIR Output:

    motionState = digitalRead(pirPin);
    • pirPin is configured as a digital input (INPUT_PULLDOWN in setup()), so this returns HIGH (1) when motion is detected, or LOW (0) when there is no motion.

  2. If Motion Is Detected:

    if (motionState == HIGH) {
   Serial.println("Motion detected!");
   digitalWrite(ledPin, HIGH);
}
    • When motionState is HIGH, the code:
      • Prints “Motion detected!” to the Serial Monitor.
      • Drives ledPin to HIGH, which turns the LED on.

  3. If No Motion:

    else {
   Serial.println("No motion.");
   digitalWrite(ledPin, LOW);
}
    • When motionState is LOW, the code:
      • Prints “No motion.” to the Serial Monitor.
      • Drives ledPin to LOW, which turns the LED off.

  4. Pause Before Next Read:

    delay(500);
    • Waits for 500 ms before repeating.

  5. The complete loop() now looks like:

    void loop() {
motionState = digitalRead(pirPin);
if (motionState == HIGH) {
   Serial.println("Motion detected!");
   digitalWrite(ledPin, HIGH);
} else {
   Serial.println("No motion.");
   digitalWrite(ledPin, LOW);
}
delay(500);
}

Example

https://github.com/user-attachments/assets/bcda9a3e-026e-4b88-883c-91de892a472b

Serial Monitor Output

Analysis

The loop function continuously polls the PIR sensor and drives an LED based on its digital output. First, digitalRead(pirPin) samples the PIR’s output pin (which is held LOW by an internal pull‐down when idle) to detect whether motion has been sensed. When the sensor output goes HIGH, the code prints “Motion detected!” to the Serial Monitor and sets ledPin HIGH to turn on the LED. Conversely, when the output is LOW, it prints “No motion.” and turns the LED off. By adding delay(500) between readings, we ensure that any motion lasting at least half a second is caught reliably. This approach highlights core concepts—digital input reading, conditional branching, and digital output driving—while the Serial prints offer real‐time feedback for debugging.

Additional Resources

Useful links

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