HC-SR501 PIR Motion Sensor with ESP32 DOIT Kit v1

Introduction

The HC-SR501 PIR (Passive Infrared) sensor is used to detect motion by sensing infrared radiation from objects, mainly humans and animals. It’s widely used in security systems, automatic lights, and smart IoT projects.

Key features:

• Detection range: 3–7 meters (adjustable).
• Output: HIGH (1) when motion is detected, LOW (0) when no motion.
• Adjustable sensitivity and delay time using onboard trimmers.
• Low power consumption, easy to interface with ESP32.

In this tutorial, we’ll connect the HC-SR501 PIR sensor to ESP32 (GPIO 18), read motion detection signals, and display results in the Serial Monitor.

Components Required

• ESP32 DOIT DevKit v1
• HC-SR501 PIR Motion Sensor
• Breadboard and jumper wires
• USB cable

ESP32 & HC-SR501 Pin Connections

HC-SR501 Pin	ESP32 DOIT Kit v1 Pin
VCC	3.3V (or 5V, depending on module)
GND	GND
OUT	GPIO 18

Arduino Code

// HC-SR501 PIR Motion Sensor with ESP32
// OUT pin connected to GPIO 18

int pirPin = 18;   // PIR sensor OUT pin
int pirState = LOW; // Store PIR state

void setup() {
  Serial.begin(115200);
  pinMode(pirPin, INPUT); // Set PIR as input
}

void loop() {
  int sensorValue = digitalRead(pirPin);

  if (sensorValue == HIGH && pirState == LOW) {
    Serial.println("Motion Detected!");
    pirState = HIGH;
  }
  else if (sensorValue == LOW && pirState == HIGH) {
    Serial.println("No Motion");
    pirState = LOW;
  }

  delay(100); // Small delay for stability
}

Step-by-Step Code Explanation

Define PIR pin & state

int pirPin = 18;
int pirState = LOW;

PIR output pin connected to GPIO 18, initial state set to LOW.

Setup Function

pinMode(pirPin, INPUT);

Configures GPIO 18 as input.

Loop Function

int sensorValue = digitalRead(pirPin);

Reads PIR sensor output:

• HIGH → Motion detected
• LOW → No motion

State Change Detection

• Only prints message when sensor value changes.
• Avoids spamming Serial Monitor.

Real-Life Applications of PIR with ESP32

• 🏠 Home Security Systems → Detect intruders.
• 💡 Automatic Lighting → Turn on lights when someone enters a room.
• 🤖 Robotics → Detect human presence.
• 🏢 Energy Saving Systems → Switch off unused devices in offices.
• 🚪 Smart Doors → Open/close doors automatically.

Troubleshooting

Problem	Cause	Solution
Always HIGH	Warm-up time	Wait 30–60 seconds after powering
No detection	Wrong wiring	Check OUT → GPIO 18, VCC, GND
Too sensitive	Sensitivity too high	Adjust potentiometer on sensor
Delay too long	Time delay set high	Adjust delay trimmer clockwise/counterclockwise