HC-SR501 PIR Motion Sensor

Overview

The HC-SR501 is a passive infrared (PIR) motion sensor module that detects changes in infrared radiation — which is how it "sees" warm bodies moving in its field of view. It's the classic, low-cost motion detector used in hobby alarms, automatic lighting, security systems, occupancy sensors, and scare-the-cat projects. When motion is detected, it drives its output pin HIGH for a user-configurable duration.

The module includes two onboard potentiometers — one for sensitivity (detection distance, roughly 3–7 meters) and one for time delay (how long the output stays HIGH after a trigger, from about 3 seconds up to 5 minutes). A jumper on the side selects the trigger mode: repeatable (H) extends the timer on each new detection, while non-repeatable (L) resets only after the delay expires.

This manual covers specifications, the pinout, wiring for Arduino, ESP32, Raspberry Pi, and the Pico, a working code example per platform, and FAQs about warm-up time, tuning the pots, and false-trigger mitigation.

At a Glance

Voltage

5V - 20V

Output

Digital HIGH / LOW

Detection Range

Up to ~7 m

Field of View

~110°

Trigger Mode

Repeat / Non-Repeat

Pins

3 (VCC, Echo, GND)

Specifications

Parameter	Value
Sensor Type	Passive infrared (PIR)
Operating Voltage	5V - 20V (regulator onboard)
Output Voltage	3.3V HIGH / 0V LOW
Detection Range	3 - 7 meters (adjustable)
Detection Angle	~110° cone
Time Delay (Ton)	~3 s to ~5 min (adjustable)
Blocking Time (Toff)	~2.5 s (fixed)
Trigger Modes	H (repeatable) / L (non-repeatable)
Warm-up Time	~30 - 60 seconds
Current Draw	< 65 mA
Pin Count	3 (VCC, OUT/Echo, GND)

Pinout Diagram

Wiring Guide

Arduino Wiring

Power the PIR sensor from the Arduino's 5V rail. The output swings 0V / 3.3V, which the Arduino reads as LOW / HIGH on any digital pin.

Module Pin	Arduino Pin
VCC	5V
Echo (OUT)	D2 (any digital pin)
GND	GND

Tip: Let the sensor warm up for 30–60 seconds after powering on before trusting the output — PIR sensors self-calibrate during this window.

ESP32 Wiring

Power from the ESP32's VIN/5V pin (USB-powered). The 3.3V output from the module is ideal for ESP32 logic levels.

Module Pin	ESP32 Pin
VCC	5V (VIN)
Echo (OUT)	GPIO 4 (any GPIO)
GND	GND

Info: The ESP32 can deep-sleep and wake up on the PIR's rising edge — a great way to build a battery-powered motion alarm.

Raspberry Pi Wiring

The Pi's 5V rail can power the module directly. The 3.3V output is safe for any Pi GPIO input pin.

Module Pin	Raspberry Pi Pin
VCC	5V (Pin 2)
Echo (OUT)	GPIO 17 (Pin 11)
GND	GND (Pin 6)

Warning: Do not connect the PIR output to a 5V input-only device — the output is 3.3V, and some 5V logic may not register it as HIGH.

Raspberry Pi Pico Wiring

Power from the Pico's VBUS or VSYS (5V USB) and read the output on any GP pin.

Module Pin	Pico Pin
VCC	VBUS (Pin 40, 5V)
Echo (OUT)	GP15 (Pin 20)
GND	GND (Pin 38)

Code Examples

Arduino

pir_motion.ino

// HC-SR501 PIR Motion Sensor - basic motion detection

const int pirPin = 2;
const int ledPin = 13;

void setup() {
  Serial.begin(9600);
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  Serial.println("PIR warming up... wait 30-60 seconds.");
  delay(30000);
  Serial.println("Ready.");
}

void loop() {
  int state = digitalRead(pirPin);
  if (state == HIGH) {
    digitalWrite(ledPin, HIGH);
    Serial.println("Motion detected!");
  } else {
    digitalWrite(ledPin, LOW);
  }
  delay(100);
}

ESP32

pir_esp32.ino

// HC-SR501 PIR on ESP32 - interrupt-driven motion detection

const int pirPin = 4;
volatile bool motion = false;

void IRAM_ATTR onMotion() {
  motion = true;
}

void setup() {
  Serial.begin(115200);
  pinMode(pirPin, INPUT);
  attachInterrupt(digitalPinToInterrupt(pirPin), onMotion, RISING);
  Serial.println("PIR ready (warming up...).");
  delay(30000);
}

void loop() {
  if (motion) {
    motion = false;
    Serial.println("Motion detected!");
  }
  delay(50);
}

Raspberry Pi

pir_motion.py

# HC-SR501 PIR Motion Sensor on Raspberry Pi
# Install: pip install gpiozero

from gpiozero import MotionSensor
from signal import pause

pir = MotionSensor(17)

print("PIR warming up...")
pir.wait_for_no_motion()
print("Ready. Waiting for motion.")

pir.when_motion    = lambda: print("Motion detected!")
pir.when_no_motion = lambda: print("All clear.")

pause()

Raspberry Pi Pico (MicroPython)

pir_pico.py

# HC-SR501 PIR on Raspberry Pi Pico

from machine import Pin
import time

pir = Pin(15, Pin.IN)
led = Pin(25, Pin.OUT)  # onboard LED

print("Warming up PIR sensor...")
time.sleep(30)
print("Ready.")

while True:
    if pir.value() == 1:
        led.on()
        print("Motion detected!")
    else:
        led.off()
    time.sleep_ms(100)

Frequently Asked Questions

Why does the sensor trigger randomly when I first power it on?

PIR sensors need 30–60 seconds of warm-up to calibrate against the ambient IR background. Ignore readings during this window. Also keep it away from moving heat sources (sunlight through leaves, HVAC vents).

What's the difference between the H and L jumper positions?

H (repeatable): each motion detection during the Ton period restarts the timer — the output stays HIGH as long as motion continues. L (non-repeatable): the output goes LOW after Ton regardless of further motion, then there's a short blocking period before it can re-trigger. H is the most common choice.

How do I tune the sensitivity and time delay pots?

Looking at the board with the two potentiometers facing you: the left pot is typically sensitivity (CW = farther range) and the right pot is time delay (CW = longer Ton). Tune in small increments and test between adjustments.

Can I power it from 3.3V?

No — the onboard regulator needs at least 4.5V to work. The module has a minimum supply of 5V. If you need 3.3V-only operation, look at the AM312 mini PIR instead.

Output is stuck HIGH — what's wrong?

Either the warm-up period hasn't completed, the time-delay pot is set very high (up to 5 minutes), or something warm keeps moving in the sensor's field (e.g. a fan blowing warm air, a pet, or direct sunlight). Cover the sensor to verify it eventually drops LOW.

Can I use this sensor outdoors?

Not reliably. Temperature swings, wind, and direct sunlight cause false triggers, and the module isn't weatherproof. Use it indoors, or enclose it in a weatherproof housing with a window that passes IR (e.g., HDPE).

Documentation